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Jogi SP, Peng Q, Jafari R, Otazo R, Wu C. Novel spin-lock time sampling strategies for improved reproducibility in quantitative T1ρ mapping. NMR IN BIOMEDICINE 2024:e5244. [PMID: 39152756 DOI: 10.1002/nbm.5244] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2024] [Revised: 07/12/2024] [Accepted: 08/05/2024] [Indexed: 08/19/2024]
Abstract
This study aimed to optimize the sampling of spin-lock times (TSLs) in quantitative T1ρ mapping for improved reproducibility. Two new TSL sampling schemes were proposed: (i) reproducibility-guided random sampling (RRS) and (ii) reproducibility-guided optimal sampling (ROS). They were compared to the existing linear sampling (LS) and precision-guided sampling (PS) schemes for T1ρ reproducibility through numerical simulations, phantom experiments, and volunteer studies. Each study evaluated the four sampling schemes with three commonly used T1ρ preparations based on composite and balanced spin-locking. Additionally, the phantom and volunteer studies investigated the impact of B0 and B1 field inhomogeneities on T1ρ reproducibility, respectively. The reproducibility was assessed using the coefficient of variation (CoV) by repeating the T1ρ measurements eight times for phantom experiments and five times for volunteer studies. Numerical simulations resulted in lower mean CoVs for the proposed RRS (1.74%) and ROS (0.68%) compared to LS (2.93%) and PS (3.68%). In the phantom study, the mean CoVs were also lower for RRS (2.7%) and ROS (2.6%) compared to LS (4.1%) and PS (3.1%). Furthermore, the mean CoVs of the proposed RRS and ROS were statistically lower (P < 0.001) compared to existing LS and PS schemes at a B1 offset of 20%. In the volunteer study, consistently lower mean CoVs were observed in bilateral thigh muscles for RRS (9.3%) and ROS (9.2%) compared to LS (10.9%) and PS (10.2%), and the difference was more prominent at B0 offsets higher than 50 Hz. The proposed sampling schemes improve the reproducibility of quantitative T1ρ mapping by optimizing the selection of TSLs. This improvement is especially beneficial for longitudinal studies that track and monitor disease progression and treatment response.
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Affiliation(s)
- Sandeep Panwar Jogi
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Qi Peng
- Department of Radiology, Albert Einstein College of Medicine and Montefiore Medical Center, Bronx, New York, USA
| | - Ramin Jafari
- Philips Healthcare, MR Clinical Science, Cambridge, Massachusetts, USA
| | - Ricardo Otazo
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York, USA
- Department of Radiology, Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | - Can Wu
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York, USA
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2
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Gram M, Christa M, Gutjahr FT, Albertova P, Williams T, Jakob PM, Bauer WR, Nordbeck P. Quantification of the rotating frame relaxation time T 2ρ: Comparison of balanced spin-lock and continuous-wave Malcolm-Levitt preparations. NMR IN BIOMEDICINE 2024:e5199. [PMID: 38924172 DOI: 10.1002/nbm.5199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Revised: 04/09/2024] [Accepted: 05/12/2024] [Indexed: 06/28/2024]
Abstract
For the quantification of rotating frame relaxation times, the T2ρ relaxation pathway plays an essential role. Nevertheless, T2ρ imaging has been studied only to a small extent compared with T1ρ, and preparation techniques for T2ρ have so far been adapted from T1ρ methods. In this work, two different preparation concepts are compared specifically for the use of T2ρ mapping. The first approach involves transferring the balanced spin-locking (B-SL) concept of T1ρ imaging. The second and newly proposed approach is a continuous-wave Malcolm-Levitt (CW-MLEV) pulse train with zero echo times and was motivated from T2 preparation strategies. The modules are tested in Bloch simulations for their intrinsic sensitivity to field inhomogeneities and validated in phantom experiments. In addition, myocardial T2ρ mapping was performed in mice as an exemplary application. Our results demonstrate that the CW-MLEV approach provides superior robustness and thus suggest that established methods of T1ρ imaging are not best suited for T2ρ experiments. In the presence of field inhomogeneities, the simulations indicated an increased banding compensation by a factor of 4.1 compared with B-SL. Quantification of left ventricular T2ρ time in mice yielded more consistent results, and values in the range of 59.2-61.1 ms (R2 = 0.986-0.992) were observed at 7 T.
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Affiliation(s)
- Maximilian Gram
- Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
- Experimental Physics 5, University of Würzburg, Würzburg, Germany
| | - Martin Christa
- Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
- Comprehensive Heart Failure Center (CHFC), University Hospital Würzburg, Würzburg, Germany
| | | | - Petra Albertova
- Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
- Experimental Physics 5, University of Würzburg, Würzburg, Germany
| | - Tatjana Williams
- Department of Cardiovascular Genetics, Comprehensive Heart Failure Center (CHFC), University Hospital Würzburg, Würzburg, Germany
| | | | - Wolfgang Rudolf Bauer
- Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
- Comprehensive Heart Failure Center (CHFC), University Hospital Würzburg, Würzburg, Germany
| | - Peter Nordbeck
- Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
- Comprehensive Heart Failure Center (CHFC), University Hospital Würzburg, Würzburg, Germany
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3
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Zu Z, Adelnia F, Harkins K, Wang F, Ostenson J, Gore JC. Correction of errors in estimates of T 1ρ at low spin-lock amplitudes in the presence of B 0 and B 1 inhomogeneities. NMR IN BIOMEDICINE 2023; 36:e4951. [PMID: 37070215 PMCID: PMC10619883 DOI: 10.1002/nbm.4951] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2022] [Revised: 04/11/2023] [Accepted: 04/12/2023] [Indexed: 05/06/2023]
Abstract
Relaxation rates R1ρ in the rotating frame measured by spin-lock methods at very low locking amplitudes (≤ 100 Hz) are sensitive to the effects of water diffusion in intrinsic gradients and may provide information on tissue microvasculature, but accurate estimates are challenging in the presence of B0 and B1 inhomogeneities. Although composite pulse preparations have been developed to compensate for nonuniform fields, the transverse magnetization comprises different components and the spin-lock signals measured do not decay exponentially as a function of locking interval at low locking amplitudes. For example, during a typical preparation sequence, some of the magnetization in the transverse plane is nutated to the Z-axis and later tipped back, and so does not experience R1ρ relaxation. As a result, if the spin-lock signals are fit to a monoexponential decay with locking interval, there are residual errors in quantitative estimates of relaxation rates R1ρ and their dispersion with weak locking fields. We developed an approximate theoretical analysis to model the behaviors of the different components of the magnetization, which provides a means to correct these errors. The performance of this correction approach was evaluated both through numerical simulations and on human brain images at 3 T, and compared with a previous correction method using matrix multiplication. Our correction approach has better performance than the previous method at low locking amplitudes. Through careful shimming, the correction approach can be applied in studies using low spin-lock amplitudes to assess the contribution of diffusion to R1ρ dispersion and to derive estimates of microvascular sizes and spacings. The results of imaging eight healthy subjects suggest that R1ρ dispersion in human brain at low locking fields arises from diffusion among inhomogeneities that generate intrinsic gradients on a scale of capillaries (~7.4 ± 0.5 μm).
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Affiliation(s)
- Zhongliang Zu
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Fatemeh Adelnia
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Kevin Harkins
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Department of Biomedical Engineering, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Feng Wang
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Jason Ostenson
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - John C. Gore
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Deparment of Physics and Astronomy, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Department of Biomedical Engineering, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee, USA
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Pala S, Hänninen NE, Nykänen O, Liimatainen T, Nissi MJ. New methods for robust continuous wave T 1ρ relaxation preparation. NMR IN BIOMEDICINE 2023; 36:e4834. [PMID: 36115012 PMCID: PMC10078184 DOI: 10.1002/nbm.4834] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Revised: 09/08/2022] [Accepted: 09/12/2022] [Indexed: 06/15/2023]
Abstract
Measurement of the longitudinal relaxation time in the rotating frame of reference (T1ρ ) is sensitive to the fidelity of the main imaging magnetic field (B0 ) and that of the RF pulse (B1 ). The purpose of this study was to introduce methods for producing continuous wave (CW) T1ρ contrast with improved robustness against field inhomogeneities and to compare the sensitivities of several existing and the novel T1ρ contrast generation methods with the B0 and B1 field inhomogeneities. Four hard-pulse and four adiabatic CW-T1ρ magnetization preparations were investigated. Bloch simulations and experimental measurements at different spin-lock amplitudes under ideal and non-ideal conditions, as well as theoretical analysis of the hard-pulse preparations, were conducted to assess the sensitivity of the methods to field inhomogeneities, at low (ω1 << ΔB0 ) and high (ω1 >> ΔB0 ) spin-locking field strengths. In simulations, previously reported single-refocus and new triple-refocus hard-pulse and double-refocus adiabatic preparation schemes were found to be the most robust. The mean normalized absolute deviation between the experimentally measured relaxation times under ideal and non-ideal conditions was found to be smallest for the refocused preparation schemes and broadly in agreement with the sensitivities observed in simulations. Experimentally, all refocused preparations performed better than those that were non-refocused. The findings promote the use of the previously reported hard-pulse single-refocus ΔB0 and B1 insensitive T1ρ as a robust method with minimal RF energy deposition. The double-refocus adiabatic B1 insensitive rotation-4 CW-T1ρ preparation offers further improved insensitivity to field variations, but because of the extra RF deposition, may be preferred for ex vivo applications.
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Affiliation(s)
- Swetha Pala
- Department of Applied PhysicsUniversity of Eastern FinlandKuopioFinland
| | - Nina E. Hänninen
- Department of Applied PhysicsUniversity of Eastern FinlandKuopioFinland
- Research Unit of Medical Imaging, Physics and TechnologyUniversity of OuluOuluFinland
| | - Olli Nykänen
- Department of Applied PhysicsUniversity of Eastern FinlandKuopioFinland
- Research Unit of Medical Imaging, Physics and TechnologyUniversity of OuluOuluFinland
| | - Timo Liimatainen
- Research Unit of Medical Imaging, Physics and TechnologyUniversity of OuluOuluFinland
- Department of RadiologyOulu University HospitalOuluFinland
| | - Mikko J. Nissi
- Department of Applied PhysicsUniversity of Eastern FinlandKuopioFinland
- Research Unit of Medical Imaging, Physics and TechnologyUniversity of OuluOuluFinland
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Stenroos P, Pirttimäki T, Paasonen J, Paasonen E, Salo RA, Koivisto H, Natunen T, Mäkinen P, Kuulasmaa T, Hiltunen M, Tanila H, Gröhn O. Isoflurane affects brain functional connectivity in rats 1 month after exposure. Neuroimage 2021; 234:117987. [PMID: 33762218 DOI: 10.1016/j.neuroimage.2021.117987] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Revised: 02/16/2021] [Accepted: 03/16/2021] [Indexed: 10/21/2022] Open
Abstract
Isoflurane, the most commonly used preclinical anesthetic, induces brain plasticity and long-term cellular and molecular changes leading to behavioral and/or cognitive consequences. These changes are most likely associated with network-level changes in brain function. To elucidate the mechanisms underlying long-term effects of isoflurane, we investigated the influence of a single isoflurane exposure on functional connectivity, brain electrical activity, and gene expression. Male Wistar rats (n = 22) were exposed to 1.8% isoflurane for 3 h. Control rats (n = 22) spent 3 h in the same room without exposure to anesthesia. After 1 month, functional connectivity was evaluated with resting-state functional magnetic resonance imaging (fMRI; n = 6 + 6) and local field potential measurements (n = 6 + 6) in anesthetized animals. A whole genome expression analysis (n = 10+10) was also conducted with mRNA-sequencing from cortical and hippocampal tissue samples. Isoflurane treatment strengthened thalamo-cortical and hippocampal-cortical functional connectivity. Cortical low-frequency fMRI power was also significantly increased in response to the isoflurane treatment. The local field potential results indicating strengthened hippocampal-cortical alpha and beta coherence were in good agreement with the fMRI findings. Furthermore, altered expression was found in 20 cortical genes, several of which are involved in neuronal signal transmission, but no gene expression changes were noted in the hippocampus. Isoflurane induced prolonged changes in thalamo-cortical and hippocampal-cortical function and expression of genes contributing to signal transmission in the cortex. Further studies are required to investigate whether these changes are associated with the postoperative behavioral and cognitive symptoms commonly observed in patients and animals.
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Affiliation(s)
- Petteri Stenroos
- A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland, P.O. Box 1627, FI,-70211 Kuopio, Finland
| | - Tiina Pirttimäki
- A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland, P.O. Box 1627, FI,-70211 Kuopio, Finland
| | - Jaakko Paasonen
- A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland, P.O. Box 1627, FI,-70211 Kuopio, Finland
| | - Ekaterina Paasonen
- A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland, P.O. Box 1627, FI,-70211 Kuopio, Finland
| | - Raimo A Salo
- A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland, P.O. Box 1627, FI,-70211 Kuopio, Finland
| | - Hennariikka Koivisto
- A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland, P.O. Box 1627, FI,-70211 Kuopio, Finland
| | - Teemu Natunen
- Institute of Biomedicine, University of Eastern Finland, P.O. Box 1627, FI,-70211 Kuopio, Finland
| | - Petra Mäkinen
- Institute of Biomedicine, University of Eastern Finland, P.O. Box 1627, FI,-70211 Kuopio, Finland
| | - Teemu Kuulasmaa
- Institute of Biomedicine, University of Eastern Finland, P.O. Box 1627, FI,-70211 Kuopio, Finland
| | - Mikko Hiltunen
- Institute of Biomedicine, University of Eastern Finland, P.O. Box 1627, FI,-70211 Kuopio, Finland
| | - Heikki Tanila
- A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland, P.O. Box 1627, FI,-70211 Kuopio, Finland
| | - Olli Gröhn
- A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland, P.O. Box 1627, FI,-70211 Kuopio, Finland
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6
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Johnson CP, Thedens DR, Kruger SJ, Magnotta VA. Three-Dimensional GRE T 1ρ mapping of the brain using tailored variable flip-angle scheduling. Magn Reson Med 2020; 84:1235-1249. [PMID: 32052489 DOI: 10.1002/mrm.28198] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Revised: 01/07/2020] [Accepted: 01/13/2020] [Indexed: 12/26/2022]
Abstract
PURPOSE To introduce a new approach called tailored variable flip-angle (VFA) scheduling for SNR-efficient 3D T1ρ mapping of the brain using a magnetization-prepared gradient-echo sequence. METHODS Simulations were used to assess the relative SNR efficiency, quantitative accuracy, and spatial blurring of tailored VFA scheduling for T1ρ mapping of brain tissue compared with magnetization-prepared angle-modulated partitioned k-space spoiled gradient-echo snapshots (MAPSS), a state-of-the-art technique for accurate 3D gradient-echo T1ρ mapping. Simulations were also used to calculate optimal imaging parameters for tailored VFA scheduling versus MAPSS, without and with nulling of CSF. Four participants were imaged at 3T MRI to demonstrate the feasibility of tailored VFA scheduling for T1ρ mapping of the brain. Using MAPSS as a reference standard, in vivo data were used to validate the relative SNR efficiency and quantitative accuracy of the new approach. RESULTS Tailored VFA scheduling can provide a 2-fold to 4-fold gain in the SNR of the resulting T1ρ map as compared with MAPSS when using identical sequence parameters while limiting T1ρ quantification errors to 2% or less. In vivo whole-brain 3D T1ρ maps acquired with tailored VFA scheduling had superior SNR efficiency than is achievable with MAPSS, and the SNR efficiency improved with a greater number of views per segment. CONCLUSIONS Tailored VFA scheduling is an SNR-efficient GRE technique for 3D T1ρ mapping of the brain that provides increased flexibility in choice of imaging parameters compared with MAPSS, which may benefit a variety of applications.
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Affiliation(s)
- Casey P Johnson
- Veterinary Clinical Sciences Department, University of Minnesota, Saint Paul, MN, USA.,Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA
| | | | | | - Vincent A Magnotta
- Department of Radiology, University of Iowa, Iowa City, IA, USA.,Department of Psychiatry, University of Iowa, Iowa City, IA, USA.,Department of Biomedical Engineering, University of Iowa, Iowa City, IA, USA
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7
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Zhu Y, Liu Y, Ying L, Liu X, Zheng H, Liang D. Bio-SCOPE: fast biexponential T 1ρ mapping of the brain using signal-compensated low-rank plus sparse matrix decomposition. Magn Reson Med 2019; 83:2092-2106. [PMID: 31762102 DOI: 10.1002/mrm.28067] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Revised: 09/28/2019] [Accepted: 10/14/2019] [Indexed: 12/15/2022]
Abstract
PURPOSE To develop and evaluate a fast imaging method based on signal-compensated low-rank plus sparse matrix decomposition to accelerate data acquisition for biexponential brain T1ρ mapping (Bio-SCOPE). METHODS Two novel strategies were proposed to improve reconstruction performance. A variable-rate undersampling scheme was used with a varied acceleration factor for each k-space along the spin-lock time direction, and a modified nonlinear thresholding scheme combined with a feature descriptor was used for Bio-SCOPE reconstruction. In vivo brain T1ρ mappings were acquired from 4 volunteers. The fully sampled k-space data acquired from 3 volunteers were retrospectively undersampled by net acceleration rates (R) of 4.6 and 6.1. Reference values were obtained from the fully sampled data. The agreement between the accelerated T1ρ measurements and reference values was assessed with Bland-Altman analyses. Prospectively undersampled data with R = 4.6 and R = 6.1 were acquired from 1 volunteer. RESULTS T1ρ -weighted images were successfully reconstructed using Bio-SCOPE for R = 4.6 and 6.1 with signal-to-noise ratio variations <1 dB and normalized root mean square errors <4%. Accelerated and reference T1ρ measurements were in good agreement for R = 4.6 (T1ρ s : 18.6651 ± 1.7786 ms; T1ρ l : 88.9603 ± 1.7331 ms) and R = 6.1 (T1ρ s : 17.8403 ± 3.3302 ms; T1ρ l : 88.0275 ± 4.9606 ms) in the Bland-Altman analyses. T1ρ parameter maps from prospectively undersampled data also show reasonable image quality using the Bio-SCOPE method. CONCLUSION Bio-SCOPE achieves a high net acceleration rate for biexponential T1ρ mapping and improves reconstruction quality by using a variable-rate undersampling data acquisition scheme and a modified soft-thresholding algorithm in image reconstruction.
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Affiliation(s)
- Yanjie Zhu
- Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
| | - Yuanyuan Liu
- Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China.,University of Chinese Academy of Sciences, Beijing, China.,Shenzhen College of Advanced Technology, University of Chinese Academy of Sciences, Shenzhen, China
| | - Leslie Ying
- Department of Biomedical Engineering and Department of Electrical Engineering, University at Buffalo, The State University of New York, Buffalo, New York
| | - Xin Liu
- Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
| | - Hairong Zheng
- Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
| | - Dong Liang
- Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
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8
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Chen W, Karampinos DC. Chemical-shift encoding-based water-fat separation with multifrequency fat spectrum modeling in spin-lock MRI. Magn Reson Med 2019; 83:1608-1624. [PMID: 31592557 DOI: 10.1002/mrm.28026] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Revised: 08/18/2019] [Accepted: 09/09/2019] [Indexed: 01/19/2023]
Abstract
PURPOSE Chemical exchange saturation transfer is used commonly to generate MRI contrast based on the chemical exchange effect. The spin-lock techniques can also be used to probe the chemical exchange and other molecular motion processes in tissues. The presence of fat can cause errors in spin-lock MRI. Signals from fat are typically suppressed based on spectral selectivity or T1 nulling approaches in spin-lock imaging. However, these methods cannot be used to suppress fat signals from multiple fat peaks. To address this problem, we report chemical-shift encoding-based water-fat separation approaches with multifrequency fat spectrum modeling. METHODS Both the conventional spin-lock and the adiabatic continuous-wave constant-amplitude spin lock (ACCSL) with multi-echo acquisitions are investigated for chemical-shift encoding-based water-fat separation in spin-lock imaging. A comparison is made of reconstructions based on 3 models: a single-peak fat spectrum model, a standard precalibrated proton density 6-peak fat spectrum model, and the self-calibrated relaxation-dependent 3-peak fat spectrum model. Comparisons were performed using Bloch simulations, phantom, and in vivo experiments at 3 T. RESULTS Conventional spin-lock acquisitions cannot be used for reliable water-fat separation with a multipeak fat spectrum model. Water-fat separation based on ACCSL acquisitions achieves superior performance compared with the use of conventional spin-lock acquisitions. The best result is achieved from ACCSL acquisition with self-calibrated relaxation-dependent multipeak fat spectrum modeling. CONCLUSION The ACCSL acquisition can be used for chemical-shift encoding-based water-fat separation with multipeak fat spectrum modeling. This approach has the potential to improve quantitative analysis using spin-lock MRI for assessing the biochemical properties of tissues.
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Affiliation(s)
- Weitian Chen
- Department of Imaging and Interventional Radiology, the Chinese University of Hong Kong, Shatin, Hong Kong SAR, China
| | - Dimitrios C Karampinos
- Department of Diagnostic and Interventional Radiology, Technical University of Munich, Munich, Germany
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9
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Jiang B, Chen W. On-resonance and off-resonance continuous wave constant amplitude spin-lock and T 1ρ quantification in the presence of B 1 and B 0 inhomogeneities. NMR IN BIOMEDICINE 2018; 31:e3928. [PMID: 29693744 DOI: 10.1002/nbm.3928] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Revised: 02/06/2018] [Accepted: 03/06/2018] [Indexed: 06/08/2023]
Abstract
Spin-lock MRI is a valuable diagnostic imaging technology, as it can be used to probe the macromolecule environment of tissues. Quantitative T1ρ imaging is one application of spin-lock MRI that is reported to be promising for a number of clinical applications. Spin-lock is often performed with a continuous RF wave at a constant RF amplitude either on resonance or off resonance. However, both on- and off-resonance spin-lock approaches are susceptible to B1 and B0 inhomogeneities, which results in image artifacts and quantification errors. In this work, we report a continuous wave constant amplitude spin-lock approach that can achieve negligible image artifacts in the presence of B1 and B0 inhomogeneities for both on- and off-resonance spin-lock. Under the adiabatic condition, by setting the maximum B1 amplitude of the adiabatic pulses equal to the B1 amplitude of spin-lock RF pulse, the spins are ensured to align along the effective field throughout the spin-lock process. We show that this results in simultaneous compensation of B1 and B0 inhomogeneities for both on- and off-resonance spin-lock. The relaxation effect during the entire adiabatic half passage (AHP) and reverse AHP, and the stationary solution of the Bloch-McConnell equation present at off-resonance frequency offset, are considered in the revised relaxation model. We demonstrate that these factors create a direct current component to the conventional relaxation model. In contrast to the previously reported dual-acquisition method, the revised relaxation model just requires one acquisition to perform quantification. The simulation, phantom, and in vivo experiments demonstrate that the proposed approach achieves superior image quality compared with the existing methods, and the revised relaxation model can perform T1ρ quantification with one acquisition instead of two.
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Affiliation(s)
- Baiyan Jiang
- Department of Imaging and Interventional Radiology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong SAR, China
| | - Weitian Chen
- Department of Imaging and Interventional Radiology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong SAR, China
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10
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Jin T, Mehrens H, Wang P, Kim SG. Chemical exchange-sensitive spin-lock MRI of glucose analog 3-O-methyl-d-glucose in normal and ischemic brain. J Cereb Blood Flow Metab 2018; 38:869-880. [PMID: 28485194 PMCID: PMC5987935 DOI: 10.1177/0271678x17707419] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Glucose transport is important for understanding brain glucose metabolism. We studied glucose transport with a presumably non-toxic and non-metabolizable glucose analog, 3-O-methyl-d-glucose, using a chemical exchange-sensitive spin-lock MRI technique at 9.4 Tesla. 3-O-methyl-d-glucose showed comparable chemical exchange properties with d-glucose and 2-deoxy-d-glucose in phantoms, and higher and lower chemical exchange-sensitive spin-lock sensitivity than Glc and 2-deoxy-d-glucose in in vivo experiments, respectively. The changes of the spin-lattice relaxation rate in the rotating frame (Δ R1ρ) in normal rat brain peaked at ∼15 min after the intravenous injection of 1 g/kg 3-O-methyl-d-glucose and almost maintained a plateau for >1 h. Doses up to 4 g/kg 3-O-methyl-d-glucose were linearly correlated with Δ R1ρ. In rats with focal ischemic stroke, chemical exchange-sensitive spin-lock with 3-O-methyl-d-glucose injection at 1 h after stroke onset showed reduced Δ R1ρ in the ischemic core but higher Δ R1ρ in the peri-core region compared to normal tissue, which progressed into the ischemic core at 3 h after stroke onset. This suggests that the hyper-chemical exchange-sensitive spin-lock region observed at 1 h is the ischemic penumbra at-risk of infarct. In summary, 3-O-methyl-d-glucose-chemical exchange-sensitive spin-lock can be a sensitive MRI technique to probe the glucose transport in normal and ischemic brains.
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Affiliation(s)
- Tao Jin
- 1 NeuroImaging Laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, PA, USA.,2 Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Hunter Mehrens
- 1 NeuroImaging Laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Ping Wang
- 1 NeuroImaging Laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Seong-Gi Kim
- 3 Center for Neuroscience Imaging Research, Institute for Basic Science (IBS), Suwon, Korea.,4 Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea
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Tan Y, Xu J, Chen R, Chen B, Xu J, Ren D, Chan Q, Mei Y, Wu Y, Xu Y. Use of T 1 relaxation time in rotating frame (T 1 ρ) and apparent diffusion coefficient to estimate cerebral stroke evolution. J Magn Reson Imaging 2018; 48:1247-1254. [PMID: 29446510 DOI: 10.1002/jmri.25971] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Accepted: 01/26/2018] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND The major factor for the appropriate treatment strategies for ischemia patients is its onset timing. PURPOSE/HYPOTHESIS To study to evaluate the diagnostic accuracy of T1 relaxation time in a rotating frame (T1 ρ) and apparent diffusion coefficient (ADC) from MRI to estimate ischemia stages. STUDY TYPE Prospective. POPULATION/SUBJECTS/PHANTOM/SPECIMEN/ANIMAL MODEL In all, 73 patients (49 males, aged 29-78 years and 24 females, aged 22-94 years) with ischemia were prospectively imaged with T1 ρ and diffusion MRI during the postischemic period. FIELD STRENGTH/SEQUENCE 3T/T1 ρ and diffusion-weighted imaging (DWI). ASSESSMENT Ischemic parenchyma included tissue with elevated signal areas on DWI and correlative hypointense areas on ADC maps. STATISTICAL TESTS The sensitivity of variables to ischemia time was quantified by analyzing the respective correlations of these values with onset time. RESULTS ΔT1 ρ (ipsilateral-contralateral differences in T1 ρ) (R2 = 0.956) and T1 ρipsi (ipsilateral ischemia T1 ρ values) (R2 = 0.941) were elevated in all ischemic lesions; these values increased linearly as a function of time, unlike ΔADC (ipsilateral-contralateral differences in ADC) (R2 = -0.410) and ADCipsi (ipsilateral ischemia ADC values) (R2 = 0.550). ΔT1 ρ and T1 ρipsi were significantly different between all stages (P < 0.01), except the acute and hyperacute stages (P = 0.589 for ΔT1 ρ, P = 0.290 for T1 ρipsi , respectively), but ΔADC and ADCipsi only between the late subacute and early subacute stages (P < 0.01) and the late subacute and chronic stages (P < 0.01). DATA CONCLUSION These data suggest that T1 ρ can provide estimates for the ischemic time in patients. T1 ρ has the potential to outperform diffusion for single-timepoint examination because the T1 ρ change during strokes is positive and linear. If patients with suspected stroke are scanned by MRI within the appropriate timeframe, T1 ρ may provide tools for evaluating stroke onset, potentially aiding in treatment strategies. LEVEL OF EVIDENCE 4 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:1247-1254.
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Affiliation(s)
- Yuefa Tan
- Department of Medical Imaging Center, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Jun Xu
- Department of Hematology, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Ruiying Chen
- Department of Medical Imaging Center, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Bin Chen
- Department of Medical Imaging Center, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Juan Xu
- Department of Medical Imaging Center, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Daokun Ren
- Department of Medical Imaging Center, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | | | | | - Yuankui Wu
- Department of Medical Imaging Center, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Yikai Xu
- Department of Medical Imaging Center, Nanfang Hospital, Southern Medical University, Guangzhou, China
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12
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Mangia S, Svatkova A, Mascali D, Nissi MJ, Burton PC, Bednarik P, Auerbach EJ, Giove F, Eberly LE, Howell MJ, Nestrasil I, Tuite PJ, Michaeli S. Multi-modal Brain MRI in Subjects with PD and iRBD. Front Neurosci 2017; 11:709. [PMID: 29311789 PMCID: PMC5742124 DOI: 10.3389/fnins.2017.00709] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Accepted: 12/04/2017] [Indexed: 01/09/2023] Open
Abstract
Idiopathic rapid eye movement sleep behavior disorder (iRBD) is a condition that often evolves into Parkinson's disease (PD). Therefore, by monitoring iRBD it is possible to track the neurodegeneration of individuals who may progress to PD. Here we aimed at piloting the characterization of brain tissue properties in mid-brain subcortical regions of 10 healthy subjects, 8 iRBD, and 9 early-diagnosed PD. We used a battery of magnetic resonance imaging (MRI) contrasts at 3 T, including adiabatic and non-adiabatic rotating frame techniques developed by our group, along with diffusion tensor imaging (DTI) and resting-state fMRI. Adiabatic T1ρ and T2ρ, and non-adiabatic RAFF4 (Relaxation Along a Fictitious Field in the rotating frame of rank 4) were found to have lower coefficient of variations and higher sensitivity to detect group differences as compared to DTI parameters such as fractional anisotropy and mean diffusivity. Significantly longer T1ρ were observed in the amygdala of PD subjects vs. controls, along with a trend of lower functional connectivity as measured by regional homogeneity, thereby supporting the notion that amygdalar dysfunction occurs in PD. Significant abnormalities in reward networks occurred in iRBD subjects, who manifested lower network strength of the accumbens. In agreement with previous studies, significantly longer T1ρ occurred in the substantia nigra compacta of PD vs. controls, indicative of neuronal degeneration, while regional homogeneity was lower in the substantia nigra reticulata. Finally, other trend-level findings were observed, i.e., lower RAFF4 and T2ρ in the midbrain of iRBD subjects vs. controls, possibly indicating changes in non-motor features as opposed to motor function in the iRBD group. We conclude that rotating frame relaxation methods along with functional connectivity measures are valuable to characterize iRBD and PD subjects, and with proper validation in larger cohorts may provide pathological signatures of iRBD and PD.
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Affiliation(s)
- Silvia Mangia
- Department of Radiology, Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN, United States
| | - Alena Svatkova
- Department of Pediatrics, University of Minnesota, Minneapolis, MN, United States.,Central European Institute of Technology (CEITEC), Masaryk University, Brno, Czechia
| | - Daniele Mascali
- MARBILab, Centro Fermi - Museo Storico Della Fisica e Centro di Studi e Ricerche Enrico Fermi, Rome, Italy
| | - Mikko J Nissi
- Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
| | - Philip C Burton
- Department of Radiology, Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN, United States
| | - Petr Bednarik
- Department of Radiology, Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN, United States.,Central European Institute of Technology (CEITEC), Masaryk University, Brno, Czechia
| | - Edward J Auerbach
- Department of Radiology, Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN, United States
| | - Federico Giove
- MARBILab, Centro Fermi - Museo Storico Della Fisica e Centro di Studi e Ricerche Enrico Fermi, Rome, Italy.,Fondazione Santa Lucia IRCCS, Rome, Italy
| | - Lynn E Eberly
- Division of Biostatistics, University of Minnesota, Minneapolis, MN, United States
| | - Michael J Howell
- Department of Neurology, University of Minnesota, Minneapolis, MN, United States
| | - Igor Nestrasil
- Department of Pediatrics, University of Minnesota, Minneapolis, MN, United States
| | - Paul J Tuite
- Department of Neurology, University of Minnesota, Minneapolis, MN, United States
| | - Shalom Michaeli
- Department of Radiology, Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN, United States
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13
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Okuaki T, Takayama Y, Nishie A, Ogino T, Obara M, Honda H, Miyati T, Van Cauteren M. T 1ρ mapping improvement using stretched-type adiabatic locking pulses for assessment of human liver function at 3 T. Magn Reson Imaging 2017; 40:17-23. [DOI: 10.1016/j.mri.2017.03.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Revised: 02/17/2017] [Accepted: 03/25/2017] [Indexed: 11/13/2022]
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14
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Dong H, Hwang SM, Wendland M, You L, Clarke J, Inglis B. Ultralow-field and spin-locking relaxation dispersion in postmortem pig brain. Magn Reson Med 2017; 78:2342-2351. [PMID: 28164366 DOI: 10.1002/mrm.26621] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2016] [Revised: 11/28/2016] [Accepted: 01/02/2017] [Indexed: 11/08/2022]
Abstract
PURPOSE To investigate tissue-specific differences, a quantitative comparison was made between relaxation dispersion in postmortem pig brain measured at ultralow fields (ULF) and spin locking at 7 tesla (T). The goal was to determine whether ULF-MRI has potential advantages for in vivo human brain imaging. METHODS Separate specimens of gray matter and white matter were investigated using an ULF-MRI system with superconducting quantum interference device (SQUID) signal detection to measure T1ULF at fields from 58.7 to 235.0 μT and using a commercial MRI scanner to measure T1ρ7T at spin-locking fields from 5.0 to 235.0 μT. RESULTS At matched field strengths, T1ρ7T is 50 to 100% longer than T1ULF. Furthermore, dispersion in T1ULF is close to linear between 58.7 and 235 µT, whereas dispersion in T1ρ7T is highly nonlinear over the same range. A subtle elbow in the T1ULF dispersion at approximately 140 µT is tentatively attributed to the local dipolar field of macromolecules. It is suggested that different relaxation mechanisms dominate each method and that ULF-MRI has a fundamentally different sensitivity to the macromolecular structure of neural tissue. CONCLUSIONS Ultralow-field MRI may offer distinct, quantitative advantages for human brain imaging, while simultaneously avoiding the severe heating limitation imposed on high-field spin locking. Magn Reson Med 78:2342-2351, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Hui Dong
- Department of Physics, University of California, Berkeley, California, USA.,State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences (CAS), Shanghai, China.,CAS Center for ExcelleNce in Superconducting Electronics (CENSE), Shanghai, China
| | - Seong-Min Hwang
- Department of Physics, University of California, Berkeley, California, USA.,Center for Biosignals, Korea Research Institute of Standards and Science, Daejeon, Republic of Korea
| | - Michael Wendland
- Berkeley Preclinical Imaging Core (BPIC) Facility, University of California, Berkeley, California, USA
| | - Lixing You
- Department of Physics, University of California, Berkeley, California, USA.,State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences (CAS), Shanghai, China.,CAS Center for ExcelleNce in Superconducting Electronics (CENSE), Shanghai, China
| | - John Clarke
- Department of Physics, University of California, Berkeley, California, USA
| | - Ben Inglis
- Henry H. Wheeler, Jr. Brain Imaging Center (BIC), University of California, Berkeley, California, USA
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15
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Chen W. Artifacts correction for T1rho imaging with constant amplitude spin-lock. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 274:13-23. [PMID: 27842257 DOI: 10.1016/j.jmr.2016.11.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2016] [Revised: 10/16/2016] [Accepted: 11/04/2016] [Indexed: 06/06/2023]
Abstract
T1rho imaging with constant amplitude spin-lock is prone to artifacts in the presence of B1 RF and B0 field inhomogeneity. Despite significant technological progress, improvements on the robustness of constant amplitude spin-lock are necessary in order to use it for routine clinical practice. This work proposes methods to simultaneously correct for B1 RF and B0 field inhomogeneity in constant amplitude spin-lock. By setting the maximum B1 amplitude of the excitation adiabatic pulses equal to the expected constant amplitude spin-lock frequency, the spins become aligned along the effective field throughout the spin-lock process. This results in T1rho-weighted images free of artifacts, despite the spatial variation of the effective field caused by B1 RF and B0 field inhomogeneity. When the pulse is long, the relaxation effect during the adiabatic half passage may result in a non-negligible error in the mono-exponential relaxation model. A two-acquisition approach is presented to solve this issue. Simulation, phantom, and in-vivo scans demonstrate the proposed methods achieve superior image quality compared to existing methods, and that the two-acquisition method is effective in resolving the relaxation effect during the adiabatic half passage.
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Affiliation(s)
- Weitian Chen
- Department of Imaging and Interventional Radiology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong Special Administrative Region.
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16
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Rautiainen J, Nieminen MT, Salo EN, Kokkonen HT, Mangia S, Michaeli S, Gröhn O, Jurvelin JS, Töyräs J, Nissi MJ. Effect of collagen cross-linking on quantitative MRI parameters of articular cartilage. Osteoarthritis Cartilage 2016; 24:1656-64. [PMID: 27143363 DOI: 10.1016/j.joca.2016.04.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2015] [Revised: 03/31/2016] [Accepted: 04/23/2016] [Indexed: 02/02/2023]
Abstract
OBJECTIVE To investigate the sensitivity of quantitative magnetic resonance imaging (MRI) parameters to increase of collagen cross-linking in articular cartilage, a factor possibly contributing to the aging-related development of osteoarthritis (OA). The issue has not been widely studied although collagen cross-links may significantly affect the evaluation of cartilage imaging outcome. DESIGN Osteochondral samples (n = 14) were prepared from seven bovine patellae. To induce cross-linking, seven samples were incubated in threose while the other seven served as non-treated controls. The specimens were scanned at 9.4 T for T1, T1Gd (dGEMRIC), T2, adiabatic and continuous wave (CW) T1ρ, adiabatic T2ρ and T1sat relaxation times. Specimens from adjacent tissue were identically treated and used for reference to determine biomechanical properties, collagen, proteoglycan and cross-link contents, fixed charge density (FCD), collagen fibril anisotropy and water concentration of cartilage. RESULTS In the threose-treated sample group, cross-links (pentosidine, lysyl pyridinoline (LP)), FCD and equilibrium modulus were significantly (P < 0.05) higher as compared to the non-treated group. Threose treatment resulted in significantly greater T1Gd relaxation time constant (+26%, P < 0.05), although proteoglycan content was not altered. Adiabatic and CW-T1ρ were also significantly increased (+16%, +28%, P < 0.05) while pre-contrast T1 was significantly decreased (-10%, P < 0.05) in the threose group. T2, T2ρ and T1sat did not change significantly. CONCLUSION Threose treatment induced collagen cross-linking and changes in the properties of articular cartilage, which were detected by T1, T1Gd and T1ρ relaxation time constants. Cross-linking should be considered especially when interpreting the outcome of contrast-enhanced MRI in aging populations.
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Affiliation(s)
- J Rautiainen
- Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Research Unit of Medical Imaging, Physics and Technology, Faculty of Medicine, University of Oulu, Oulu, Finland; Medical Research Center Oulu, University of Oulu, Oulu, Finland.
| | - M T Nieminen
- Research Unit of Medical Imaging, Physics and Technology, Faculty of Medicine, University of Oulu, Oulu, Finland; Medical Research Center Oulu, University of Oulu, Oulu, Finland; Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland.
| | - E-N Salo
- Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland.
| | - H T Kokkonen
- Diagnostic Imaging Center, Kuopio University Hospital, Kuopio, Finland.
| | - S Mangia
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA.
| | - S Michaeli
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA.
| | - O Gröhn
- Department of Neurobiology, A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland.
| | - J S Jurvelin
- Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Diagnostic Imaging Center, Kuopio University Hospital, Kuopio, Finland.
| | - J Töyräs
- Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Diagnostic Imaging Center, Kuopio University Hospital, Kuopio, Finland.
| | - M J Nissi
- Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Research Unit of Medical Imaging, Physics and Technology, Faculty of Medicine, University of Oulu, Oulu, Finland; Medical Research Center Oulu, University of Oulu, Oulu, Finland; Diagnostic Imaging Center, Kuopio University Hospital, Kuopio, Finland.
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17
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Nissi MJ MJ, Salo EN, Tiitu V, Liimatainen T, Michaeli S, Mangia S, Ellermann J, Nieminen MT. Multi-parametric MRI characterization of enzymatically degraded articular cartilage. J Orthop Res 2016; 34:1111-20. [PMID: 26662555 PMCID: PMC4903086 DOI: 10.1002/jor.23127] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Accepted: 12/08/2015] [Indexed: 02/04/2023]
Abstract
Several laboratory and rotating frame quantitative MRI parameters were evaluated and compared for detection of changes in articular cartilage following selective enzymatic digestion. Bovine osteochondral specimens were subjected to 44 h incubation in control medium or in collagenase or chondroitinase ABC to induce superficial collagen or proteoglycan (glycosaminoglycan) alterations. The samples were scanned at 9.4 T for T1 , T1 Gd (dGEMRIC), T2 , adiabatic T1 ρ , adiabatic T2 ρ , continuous-wave T1 ρ , TRAFF2 , and T1 sat relaxation times and for magnetization transfer ratio (MTR). For reference, glycosaminoglycan content, collagen fibril orientation and biomechanical properties were determined. Changes primarily in the superficial cartilage were noted after enzymatic degradation. Most of the studied parameters were sensitive to the destruction of collagen network, whereas glycosaminoglycan depletion was detected only by native T1 and T1 Gd relaxation time constants throughout the tissue and by MTR superficially. T1 , adiabatic T1 ρ , adiabatic T2 ρ , continuous-wave T1 ρ , and T1 sat correlated significantly with the biomechanical properties while T1 Gd correlated with glycosaminoglycan staining. The findings indicated that most of the studied MRI parameters were sensitive to both glycosaminoglycan content and collagen network integrity, with changes due to enzymatic treatment detected primarily in the superficial tissue. Strong correlation of T1 , adiabatic T1ρ , adiabatic T2 ρ , continuous-wave T1 ρ , and T1 sat with the altered biomechanical properties, reflects that these parameters were sensitive to critical functional properties of cartilage. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1111-1120, 2016.
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Affiliation(s)
- Mikko J. Nissi MJ
- Department of Applied Physics, University of Eastern Finland, Kuopio, Finland,Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland,Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland,CMRR, Department of Radiology, University of Minnesota, Minneapolis, MN, USA,Diagnostic Imaging Center, Kuopio University Hospital, Kuopio, Finland,Corresponding author: Mikko J. Nissi, Department of Applied Physics, University of Eastern Finland, POB 1627, FI-70211 Kuopio, Finland, Telephone number: +358-50-5955517, Fax number: +358-17-162585
| | - Elli-Noora Salo
- Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland,Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland
| | - Virpi Tiitu
- Institute of Biomedicine, Anatomy, University of Eastern Finland, Kuopio, Finland
| | - Timo Liimatainen
- Diagnostic Imaging Center, Kuopio University Hospital, Kuopio, Finland,Department of Biotechnology and Molecular Medicine, A. I. Virtanen Institute, University of Eastern Finland, Kuopio, Finland
| | - Shalom Michaeli
- CMRR, Department of Radiology, University of Minnesota, Minneapolis, MN, USA
| | - Silvia Mangia
- CMRR, Department of Radiology, University of Minnesota, Minneapolis, MN, USA
| | - Jutta Ellermann
- CMRR, Department of Radiology, University of Minnesota, Minneapolis, MN, USA
| | - Miika T. Nieminen
- Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland,Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland,Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland
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18
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Gilani IA, Sepponen R. Quantitative rotating frame relaxometry methods in MRI. NMR IN BIOMEDICINE 2016; 29:841-861. [PMID: 27100142 DOI: 10.1002/nbm.3518] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2013] [Revised: 01/21/2016] [Accepted: 02/18/2016] [Indexed: 06/05/2023]
Abstract
Macromolecular degeneration and biochemical changes in tissue can be quantified using rotating frame relaxometry in MRI. It has been shown in several studies that the rotating frame longitudinal relaxation rate constant (R1ρ ) and the rotating frame transverse relaxation rate constant (R2ρ ) are sensitive biomarkers of phenomena at the cellular level. In this comprehensive review, existing MRI methods for probing the biophysical mechanisms that affect the rotating frame relaxation rates of the tissue (i.e. R1ρ and R2ρ ) are presented. Long acquisition times and high radiofrequency (RF) energy deposition into tissue during the process of spin-locking in rotating frame relaxometry are the major barriers to the establishment of these relaxation contrasts at high magnetic fields. Therefore, clinical applications of R1ρ and R2ρ MRI using on- or off-resonance RF excitation methods remain challenging. Accordingly, this review describes the theoretical and experimental approaches to the design of hard RF pulse cluster- and adiabatic RF pulse-based excitation schemes for accurate and precise measurements of R1ρ and R2ρ . The merits and drawbacks of different MRI acquisition strategies for quantitative relaxation rate measurement in the rotating frame regime are reviewed. In addition, this review summarizes current clinical applications of rotating frame MRI sequences. Copyright © 2016 John Wiley & Sons, Ltd.
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Affiliation(s)
- Irtiza Ali Gilani
- Brain Research Unit, Department of Neuroscience and Biomedical Engineering, Aalto University, Aalto, Finland
- Advanced Magnetic Imaging Center, Aalto University, Aalto, Finland
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey
| | - Raimo Sepponen
- Department of Electronics, School of Electrical Engineering, Aalto University, Aalto, Finland
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19
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Casula V, Autio J, Nissi MJ, Auerbach EJ, Ellermann J, Lammentausta E, Nieminen MT. Validation and optimization of adiabatic T 1ρ and T 2ρ for quantitative imaging of articular cartilage at 3 T. Magn Reson Med 2016; 77:1265-1275. [PMID: 26946182 DOI: 10.1002/mrm.26183] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2015] [Revised: 02/02/2016] [Accepted: 02/06/2016] [Indexed: 12/22/2022]
Abstract
PURPOSE The aim of the present work was to validate and optimize adiabatic T1ρ and T2ρ mapping for in vivo measurements of articular cartilage at 3 Tesla (T). METHODS Phantom and in vivo experiments were systematically performed on a 3T clinical system to evaluate the sequences using hyperbolic secant HS1 and HS4 pulses. R1ρ and R2ρ relaxation rates were studied as a function of agarose and chondroitin sulfate concentration and pulse duration. Optimal in vivo protocol was determined by imaging the articular cartilage of two volunteers and varying the sequence parameters, and successively applied in eight additional subjects. Reproducibility was assessed in phantoms and in vivo. RESULTS Relaxation rates depended on agarose and chondroitin sulfate concentration. The sequences were able to generate relaxation time maps with pulse lengths of 8 and 6 ms for HS1 and HS4, respectively. In vivo findings were in good agreement with the phantoms. The implemented adiabatic T1ρ and T2ρ sequences demonstrated regional variation in relaxation time maps of femorotibial cartilage. Reproducibility in phantoms and in vivo was good to excellent for both adiabatic T1ρ and T2ρ . CONCLUSIONS The findings indicate that sequences are suitable for quantitative in vivo assessment of articular cartilage at 3 T. Magn Reson Med 77:1265-1275, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Victor Casula
- Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland.,Medical Research Center, University of Oulu and Oulu University Hospital, Oulu, Finland
| | - Joonas Autio
- Center for Life Science and Technologies, RIKEN, Kobe, Japan
| | - Mikko J Nissi
- Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland.,Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN.,Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.,Diagnostic Imaging Center, Kuopio University Hospital, Kuopio, Finland
| | - Edward J Auerbach
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Jutta Ellermann
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | | | - Miika T Nieminen
- Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland.,Medical Research Center, University of Oulu and Oulu University Hospital, Oulu, Finland.,Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland
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20
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Wáng YXJ, Zhang Q, Li X, Chen W, Ahuja A, Yuan J. T1ρ magnetic resonance: basic physics principles and applications in knee and intervertebral disc imaging. Quant Imaging Med Surg 2015; 5:858-85. [PMID: 26807369 PMCID: PMC4700236 DOI: 10.3978/j.issn.2223-4292.2015.12.06] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Accepted: 12/06/2015] [Indexed: 12/15/2022]
Abstract
T1ρ relaxation time provides a new contrast mechanism that differs from T1- and T2-weighted contrast, and is useful to study low-frequency motional processes and chemical exchange in biological tissues. T1ρ imaging can be performed in the forms of T1ρ-weighted image, T1ρ mapping and T1ρ dispersion. T1ρ imaging, particularly at low spin-lock frequency, is sensitive to B0 and B1 inhomogeneity. Various composite spin-lock pulses have been proposed to alleviate the influence of field inhomogeneity so as to reduce the banding-like spin-lock artifacts. T1ρ imaging could be specific absorption rate (SAR) intensive and time consuming. Efforts to address these issues and speed-up data acquisition are being explored to facilitate wider clinical applications. This paper reviews the T1ρ imaging's basic physic principles, as well as its application for cartilage imaging and intervertebral disc imaging. Compared to more established T2 relaxation time, it has been shown that T1ρ provides more sensitive detection of proteoglycan (PG) loss at early stages of cartilage degeneration. T1ρ has also been shown to provide more sensitive evaluation of annulus fibrosis (AF) degeneration of the discs.
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21
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Zhao F, Yuan J, Lu G, Zhang LH, Chen ZY, Wáng YXJ. T1ρ relaxation time in brain regions increases with ageing: an experimental MRI observation in rats. Br J Radiol 2015; 89:20140704. [PMID: 26529226 DOI: 10.1259/bjr.20140704] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
OBJECTIVE T1ρ variation is associated with neurodegenerative diseases. This study aims to observe T1ρ relaxation time changes in rat brains associated with normal ageing in Sprague-Dawley (SD) rats, Wistar Kyoto (WKY) rats and spontaneously hypertension rats (SHRs). METHODS 18 male SD rats, 11 male WKY rats and 11 male SHRs were used. T1ρ measurement was performed at 3-T MR with a spin-lock frequency of 500 Hz. SD rats were scanned at the ages of 5, 8, 10 and 15 months. SHRs and WKY rats were scanned at the ages of 6, 9 and 12 months. RESULTS For SD rats, T1ρ at the thalamus, hippocampus and frontal cortices increased significantly from 5 to 15 months (p < 0.05). For the WKY rats and SHRs, the T1ρ values in the thalamus, hippocampus and frontal cortices also increased significantly from 6 to 12 months (p < 0.05). Furthermore, T1ρ in the thalamus, hippocampus and frontal cortices of SHRs were consistently higher than those of WKY rats at the ages of 6, 9 and 12 months (p < 0.05). The percentage regional T1ρ differences between WKY rats and SHRs did not change during ageing. CONCLUSION An increase in T1ρ was associated with age-related changes of the rat brain. ADVANCES IN KNOWLEDGE An age-related and hypertension-related T1ρ increase in rat brain regions was observed in the thalamus, hippocampus and frontal cortical regions of the rat brain.
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Affiliation(s)
- Feng Zhao
- 1 Department of Imaging and Interventional Radiology, Faculty of Medicine, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong
| | - Jing Yuan
- 1 Department of Imaging and Interventional Radiology, Faculty of Medicine, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong.,2 Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, Happy Valley, Hong Kong
| | - Gang Lu
- 3 Division of Neurosurgery, Faculty of Medicine, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong
| | - Li H Zhang
- 4 School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, Hong Kong
| | - Zhi Y Chen
- 5 Laboratory of Ultrasound Molecular Imaging, The Third Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - Yì-Xiáng J Wáng
- 1 Department of Imaging and Interventional Radiology, Faculty of Medicine, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong
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22
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Abstract
The spin-lattice relaxation time constant in rotating frame (T1rho) is useful for assessment of the properties of macromolecular environment inside tissue. Quantification of T1rho is found promising in various clinical applications. However, T1rho imaging is prone to image artifacts and quantification errors, which remains one of the greatest challenges to adopt this technique in routine clinical practice. The conventional continuous wave spin-lock is susceptible to B1 radiofrequency (RF) and B0 field inhomogeneity, which appears as banding artifacts in acquired images. A number of methods have been reported to modify T1rho prep RF pulse cluster to mitigate this effect. Adiabatic RF pulse can also be used for spin-lock with insensitivity to both B1 RF and B0 field inhomogeneity. Another source of quantification error in T1rho imaging is signal evolution during imaging data acquisition. Care is needed to affirm such error does not take place when specific pulse sequence is used for imaging data acquisition. Another source of T1rho quantification error is insufficient signal-to-noise ratio (SNR), which is common among various quantitative imaging approaches. Measurement of T1rho within an ROI can mitigate this issue, but at the cost of reduced resolution. Noise-corrected methods are reported to address this issue in pixel-wise quantification. For certain tissue type, T1rho quantification can be confounded by magic angle effect and the presence of multiple tissue components. Review of these confounding factors from inherent tissue properties is not included in this article.
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Affiliation(s)
- Weitian Chen
- Department of Imaging and Interventional Radiology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, China
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Pishko GL, Muldoon LL, Pagel MA, Schwartz DL, Neuwelt EA. Vascular endothelial growth factor blockade alters magnetic resonance imaging biomarkers of vascular function and decreases barrier permeability in a rat model of lung cancer brain metastasis. Fluids Barriers CNS 2015; 12:5. [PMID: 25879723 PMCID: PMC4429592 DOI: 10.1186/2045-8118-12-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Accepted: 01/27/2015] [Indexed: 12/27/2022] Open
Abstract
Background Blockade of vascular endothelial growth factor (VEGF) to promote vascular normalization and inhibit angiogenesis has been proposed for the treatment of brain metastases; however, vascular normalization has not been well-characterized in this disease. We investigated the effect of treatment with bevacizumab anti-VEGF antibody on magnetic resonance imaging (MRI) biomarkers of brain tumor vascular characteristics in comparison to small molecule delivery in a rat model of human lung cancer brain metastasis. Methods Athymic rats with A549 human lung adenocarcinoma intracerebral xenografts underwent MRI at 11.75 T before and one day after treatment with bevacizumab (n = 8) or saline control (n = 8) to evaluate tumor volume, free water content (edema), blood volume and vascular permeability (Ktrans). One day later, permeability to 14C-aminoisobutyric acid (AIB) was measured in tumor and brain to assess the penetration of a small drug-like molecule. Results In saline control animals, tumor volume, edema and permeability increased over the two day assessment period. Compared to controls, bevacizumab treatment slowed the rate of tumor growth (P = 0.003) and blocked the increase in edema (P = 0.033), but did not alter tumor blood volume. Bevacizumab also significantly reduced Ktrans (P = 0.033) and AIB passive permeability in tumor (P = 0.04), but not to peritumoral tissue or normal brain. Post-treatment Ktrans correlated with AIB levels in the bevacizumab-treated rats but not in the saline controls. Conclusions The correlation of an MRI biomarker for decreased vascular permeability with decreased AIB concentration in tumor after antiangiogenic treatment suggests that bevacizumab partially restored the normal low permeability characteristics of the blood–brain barrier in a model of human lung cancer brain metastasis.
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25
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Adiabatic rotating frame relaxation of MRI reveals early cartilage degeneration in a rabbit model of anterior cruciate ligament transection. Osteoarthritis Cartilage 2014; 22:1444-52. [PMID: 25278055 DOI: 10.1016/j.joca.2014.04.023] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Revised: 03/21/2014] [Accepted: 04/23/2014] [Indexed: 02/02/2023]
Abstract
OBJECTIVE To investigate the sensitivity of seven quantitative magnetic resonance imaging (MRI) parameters (adiabatic T1ρ, adiabatic T2ρ, continuous wave (CW) T1ρ, relaxation along a fictitious field (RAFF), T2 measured with adiabatic double echo (DE) and Carr-Purcell-Meiboom-Gill (CPMG) sequence, and T1 during off-resonance saturation [magnetization transfer (MT)]) to detect early osteoarthritic changes in a rabbit model of anterior cruciate ligament transection (ACLT). METHODS ACLT was unilaterally induced in the knees of New Zealand White rabbits (n = 8) while contralateral joints served as controls. Femoral condyles of the joints were harvested 4 weeks post-ACLT. MRI was performed at 9.4 T. For reference, quantitative histology, Mankin grading and biomechanical measurements were conducted. RESULTS Reference methods demonstrated early, superficial cartilage degeneration in the ACLT group, including significant loss of proteoglycans in both medial and lateral compartments, increased collagen fibril anisotropy in the lateral condyle and decreased biomechanical properties at both medial and lateral compartments. CW-T1ρ was prolonged in the lateral compartment of ACLT joints while adiabatic T1ρ and T2ρ detected degenerative changes in tissue in both lateral and medial condyles (P < 0.05). DE-T2 was significantly (P < 0.05) elevated only in the lateral compartment while CPMG-T2, MT or RAFF did not show a statistically significant difference between the groups. CONCLUSIONS Adiabatic T1ρ and T2ρ relaxation times detected most sensitively early degenerative changes in cartilage 4 weeks post-ACLT in a rabbit model.
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26
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Rautiainen J, Nissi MJ, Salo EN, Tiitu V, Finnilä MAJ, Aho OM, Saarakkala S, Lehenkari P, Ellermann J, Nieminen MT. Multiparametric MRI assessment of human articular cartilage degeneration: Correlation with quantitative histology and mechanical properties. Magn Reson Med 2014; 74:249-259. [PMID: 25104181 DOI: 10.1002/mrm.25401] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Revised: 06/23/2014] [Accepted: 07/17/2014] [Indexed: 12/15/2022]
Abstract
PURPOSE To evaluate the sensitivity of quantitative MRI techniques (T1 , T1,Gd , T2 , continous wave (CW) T1ρ dispersion, adiabatic T1ρ , adiabatic T2ρ , RAFF and inversion-prepared magnetization transfer (MT)) for assessment of human articular cartilage with varying degrees of natural degeneration. METHODS Osteochondral samples (n = 14) were obtained from the tibial plateaus of patients undergoing total knee replacement. MRI of the specimens was performed at 9.4T and the relaxation time maps were evaluated in the cartilage zones. For reference, quantitative histology, OARSI grading and biomechanical measurements were performed and correlated with MRI findings. RESULTS All MRI parameters, except T1,Gd , showed statistically significant differences in tangential and full-thickness regions of interest (ROIs) between early and advanced osteoarthritis (OA) groups, as classified by OARSI grading. CW-T1ρ showed significant dispersion in all ROIs and featured classical laminar structure of cartilage with spin-lock powers below 1000 Hz. Adiabatic T1ρ , T2ρ , CW-T1ρ, MT, and RAFF correlated strongly with OARSI grade and biomechanical parameters. CONCLUSION MRI parameters were able to differentiate between early and advanced OA. Furthermore, rotating frame methods, namely adiabatic T1ρ , adiabatic T2ρ , CW-T1ρ , and RAFF, as well as MT experiment correlated strongly with biomechanical parameters and OARSI grade, suggesting high sensitivity of the parameters for cartilage degeneration. Magn Reson Med 74:249-259, 2015. © 2014 Wiley Periodicals, Inc.
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Affiliation(s)
- Jari Rautiainen
- Department of Diagnostic Radiology, University of Oulu, Oulu, Finland.,Medical Research Center Oulu, University of Oulu, Oulu, Finland.,Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
| | - Mikko J Nissi
- Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.,Center for Magnetic Resonance Research, Departments of Radiology and Orthopaedic Surgery, University of Minnesota, Minneapolis, Minnesota, USA
| | - Elli-Noora Salo
- Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland
| | - Virpi Tiitu
- Institute of Biomedicine, Anatomy, University of Eastern Finland, Kuopio, Finland
| | | | - Olli-Matti Aho
- Department of Anatomy and Cell Biology, University of Oulu, Oulu, Finland
| | - Simo Saarakkala
- Medical Research Center Oulu, University of Oulu, Oulu, Finland.,Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland.,Department of Medical Technology, University of Oulu, Oulu, Finland
| | - Petri Lehenkari
- Department of Anatomy and Cell Biology, University of Oulu, Oulu, Finland
| | - Jutta Ellermann
- Center for Magnetic Resonance Research, Departments of Radiology and Orthopaedic Surgery, University of Minnesota, Minneapolis, Minnesota, USA
| | - Miika T Nieminen
- Department of Diagnostic Radiology, University of Oulu, Oulu, Finland.,Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland
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27
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Kauppinen RA. Multiparametric magnetic resonance imaging of acute experimental brain ischaemia. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2014; 80:12-25. [PMID: 24924265 DOI: 10.1016/j.pnmrs.2014.05.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Revised: 05/07/2014] [Accepted: 05/07/2014] [Indexed: 06/03/2023]
Abstract
Ischaemia is a condition in which blood flow either drops to zero or proceeds at severely decreased levels that cannot supply sufficient oxidizable substrates to maintain energy metabolism in vivo. Brain, a highly oxidative organ, is particularly susceptible to ischaemia. Ischaemia leads to loss of consciousness in seconds and, if prolonged, permanent tissue damage is inevitable. Ischaemia primarily results in a collapse of cerebral energy state, followed by a series of subtle changes in anaerobic metabolism, ion and water homeostasis that eventually initiate destructive internal and external processes in brain tissue. (31)P and (1)H NMR spectroscopy were initially used to evaluate anaerobic metabolism in brain. However, since the early 1990s (1)H Magnetic Resonance Imaging (MRI), exploiting the nuclear magnetism of tissue water, has become the key method for assessment of ischaemic brain tissue. This article summarises multi-parametric (1)H MRI work that has exploited diffusion, relaxation and magnetisation transfer as 'contrasts' to image ischaemic brain in preclinical models for the first few hours, with a view to assessing evolution of ischaemia and tissue viability in a non-invasive manner.
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Affiliation(s)
- Risto A Kauppinen
- School of Experimental Psychology and Clinical Research and Imaging Centre, University of Bristol, 12a Priory Road, Bristol BS8 1TU, UK.
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28
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Andronesi OC, Bhat H, Reuter M, Mukherjee S, Caravan P, Rosen BR. Whole brain mapping of water pools and molecular dynamics with rotating frame MR relaxation using gradient modulated low-power adiabatic pulses. Neuroimage 2013; 89:92-109. [PMID: 24345390 DOI: 10.1016/j.neuroimage.2013.12.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2013] [Revised: 11/27/2013] [Accepted: 12/07/2013] [Indexed: 10/25/2022] Open
Abstract
Nuclear magnetic resonance (NMR) relaxation in the rotating frame is sensitive to molecular dynamics on the time scale of water molecules interacting with macromolecules or supramolecular complexes, such as proteins, myelin and cell membranes. Hence, longitudinal (T1ρ) and transverse (T2ρ) relaxation in the rotating frame may have a great potential to probe the macromolecular fraction of tissues. This stimulated a large interest in using this MR contrast to image brain under healthy and disease conditions. However, experimental challenges related to the use of intense radiofrequency irradiation have limited the widespread use of T1ρ and T2ρ imaging. Here, we present methodological development to acquire 3D high-resolution or 2D (multi-)slice selective T1ρ and T2ρ maps of the entire human brain within short acquisition times. These improvements are based on a class of gradient modulated adiabatic pulses that reduce the power deposition, provide slice selection, and mitigate artifacts resulting from inhomogeneities of B1 and B0 magnetic fields. Based on an analytical model of the T1ρ and T2ρ relaxation we compute the maps of macromolecular bound water fraction, correlation and exchange time constants as quantitative biomarkers informative of tissue macromolecular content. Results obtained from simulations, phantoms and five healthy subjects are included.
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Affiliation(s)
- Ovidiu C Andronesi
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
| | - Himanshu Bhat
- Siemens Medical Solutions USA Inc, Charlestown, MA 02129, USA
| | - Martin Reuter
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
| | - Shreya Mukherjee
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
| | - Peter Caravan
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
| | - Bruce R Rosen
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
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29
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Mangia S, Carpenter AF, Tyan AE, Eberly LE, Garwood M, Michaeli S. Magnetization transfer and adiabatic T1ρ MRI reveal abnormalities in normal-appearing white matter of subjects with multiple sclerosis. Mult Scler 2013; 20:1066-73. [PMID: 24336350 DOI: 10.1177/1352458513515084] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Accepted: 11/04/2013] [Indexed: 01/07/2023]
Abstract
BACKGROUND Diffuse abnormalities are known to occur within the brain tissue of multiple sclerosis (MS) patients that is "normal appearing" on T1-weighted and T2-weighted magnetic resonance images. OBJECTIVES With the goal of exploring the sensitivity of novel MRI parameters to detect such abnormalities, we implemented an inversion-prepared magnetization transfer (MT) protocol and adiabatic T1ρ and T2ρ rotating frame relaxation methods. METHODS Nine relapsing-remitting MS patients and seven healthy controls were recruited. Relaxation parameters were measured in a single slice just above the lateral ventricles and approximately parallel to the AC-PC line. RESULTS The MT ratio of regions encompassing the normal-appearing white matter (NAWM) was different in MS patients as compared with controls (p = 0.043); however, the T1 measured during off-resonance irradiation (T1sat) was substantially more sensitive than the MT ratio for detecting differences between groups (p = 0.0006). Adiabatic T1ρ was significantly prolonged in the NAWM of MS patents as compared to controls (by 6%, p = 0.026), while no differences were found among groups for T2ρ. No differences among groups were observed in the cortical gray matter for any relaxation parameter. CONCLUSIONS The results suggest degenerative processes occurring in the NAWM of MS, likely not accompanied by significant abnormalities in iron content.
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Affiliation(s)
- Silvia Mangia
- Center for Magnetic Resonance Research (CMRR), Department of Radiology, University of Minnesota, USA
| | - Adam F Carpenter
- Department of Neurology, University of Minnesota, USA Brain Sciences Center, VA Medical Center, USA
| | - Andy E Tyan
- Department of Neurology, University of Minnesota, USA
| | - Lynn E Eberly
- Division of Biostatistics, School of Public Health, University of Minnesota, USA
| | - Michael Garwood
- Center for Magnetic Resonance Research (CMRR), Department of Radiology, University of Minnesota, USA
| | - Shalom Michaeli
- Center for Magnetic Resonance Research (CMRR), Department of Radiology, University of Minnesota, USA
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30
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Murase K. A theoretical and numerical consideration of the longitudinal and transverse relaxations in the rotating frame. Magn Reson Imaging 2013; 31:1544-58. [PMID: 23993793 DOI: 10.1016/j.mri.2013.07.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2013] [Revised: 06/29/2013] [Accepted: 07/02/2013] [Indexed: 11/17/2022]
Abstract
We previously derived a simple equation for solving time-dependent Bloch equations by a matrix operation. The purpose of this study was to present a theoretical and numerical consideration of the longitudinal (R1ρ=1/T1ρ) and transverse relaxation rates in the rotating frame (R2ρ=1/T2ρ), based on this method. First, we derived an equation describing the time evolution of the magnetization vector (M(t)) by expanding the matrix exponential into the eigenvalues and the corresponding eigenvectors using diagonalization. Second, we obtained the longitudinal magnetization vector in the rotating frame (M1ρ(t)) by taking the inner product of M(t) and the eigenvector with the smallest eigenvalue in modulus, and then we obtained the transverse magnetization vector in the rotating frame (M2ρ(t)) by subtracting M1ρ(t) from M(t). For comparison, we also computed the spin-locked magnetization vector. We derived the exact solutions for R1ρ and R2ρ from the eigenvalues, and compared them with those obtained numerically from M1ρ(t) and M2ρ(t), respectively. There was excellent agreement between them. From the exact solutions for R1ρ and R2ρ, R2ρ was found to be given by R2ρ=(2R2+R1)/2-R1ρ/2, where R1 and R2 denote the conventional longitudinal and transverse relaxation rates, respectively. We also derived M1ρ(t) and M2ρ(t) for bulk water protons, in which the effect of chemical exchange was taken into account using a 2-pool chemical exchange model, and we compared the R1ρ and R2ρ values obtained from the eigenvalues and those obtained numerically from M1ρ(t) and M2ρ(t). There was also excellent agreement between them. In conclusion, this study will be useful for better understanding of the longitudinal and transverse relaxations in the rotating frame and for analyzing the contrast mechanisms in T1ρ- and T2ρ-weighted MRI.
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Affiliation(s)
- Kenya Murase
- Department of Medical Physics and Engineering, Division of Medical Technology and Science, Faculty of Health Science, Graduate School of Medicine, Osaka University, 1-7 Yamadaoka, Suita, Osaka 565-0871, Japan.
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31
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Ellermann J, Ling W, Nissi MJ, Arendt E, Carlson CS, Garwood M, Michaeli S, Mangia S. MRI rotating frame relaxation measurements for articular cartilage assessment. Magn Reson Imaging 2013; 31:1537-43. [PMID: 23993794 DOI: 10.1016/j.mri.2013.06.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Revised: 06/03/2013] [Accepted: 06/08/2013] [Indexed: 12/20/2022]
Abstract
In the present work we introduced two MRI rotating frame relaxation methods, namely adiabatic T1ρ and Relaxation Along a Fictitious Field (RAFF), along with an inversion-prepared Magnetization Transfer (MT) protocol for assessment of articular cartilage. Given the inherent sensitivity of rotating frame relaxation methods to slow molecular motions that are relevant in cartilage, we hypothesized that adiabatic T1ρ and RAFF would have higher sensitivity to articular cartilage degradation as compared to laboratory frame T2 and MT. To test this hypothesis, a proteoglycan depletion model was used. Relaxation time measurements were performed at 0 and 48h in 10 bovine patellar specimens, 5 of which were treated with trypsin and 5 untreated controls were stored under identical conditions in isotonic saline for 48h. Relaxation times measured at 48h were longer than those measured at 0h in both groups. The changes in T2 and MT relaxation times after 48h were approximately 3 times larger in the trypsin treated specimens as compared to the untreated group, whereas increases of adiabatic T1ρ and RAFF were 4 to 5 fold larger. Overall, these findings demonstrate a higher sensitivity of adiabatic T1ρ and RAFF to the trypsin-induced changes in bovine patellar cartilage as compared to the commonly used T2 and MT. Since adiabatic T1ρ and RAFF are advantageous for human applications as compared to standard continuous-wave T1ρ methods, adiabatic T1ρ and RAFF are promising tools for assessing cartilage degradation in clinical settings.
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Affiliation(s)
- Jutta Ellermann
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, USA.
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Jokivarsi KT, Liimatainen T, Kauppinen RA, Gröhn OHJ, Närväinen J. Relaxation along a fictitious field (RAFF) and Z-spectroscopy using alternating-phase irradiation (ZAPI) in permanent focal cerebral ischemia in rat. PLoS One 2013; 8:e69157. [PMID: 23874898 PMCID: PMC3714241 DOI: 10.1371/journal.pone.0069157] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Accepted: 06/11/2013] [Indexed: 11/18/2022] Open
Abstract
Cerebral ischemia alters the molecular dynamics and content of water in brain tissue, which is reflected in NMR relaxation, diffusion and magnetization transfer (MT) parameters. In this study, the behavior of two new MRI contrasts, Relaxation Along a Fictitious Field (RAFF) and Z-spectroscopy using Alternating-Phase Irradiation (ZAPI), were quantified together with conventional relaxation parameters (T1, T2 and T1ρ) and MT ratios in acute cerebral ischemia in rat. The right middle cerebral artery was permanently occluded and quantitative MRI data was acquired sequentially for the above parameters for up to 6 hours. The following conclusions were drawn: 1) Time-dependent changes in RAFF and T1ρ relaxation are not coupled to those in MT. 2) RAFF relaxation evolves more like transverse, rather than longitudinal relaxation. 3) MT measured with ZAPI is less sensitive to ischemia than conventional MT. 4) ZAPI data suggest alterations in the T2 distribution of macromolecules in acute cerebral ischemia. It was shown that both RAFF and ZAPI provide complementary MRI information from acute ischemic brain tissue. The presented multiparametric MRI data may aid in the assessment of brain tissue status early in ischemic stroke.
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Affiliation(s)
- Kimmo T Jokivarsi
- Department of Neurobiology, A.I. Virtanen Institute, University of Eastern Finland, Kuopio, Finland
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Jin T, Kim SG. Characterization of non-hemodynamic functional signal measured by spin-lock fMRI. Neuroimage 2013; 78:385-95. [PMID: 23618601 DOI: 10.1016/j.neuroimage.2013.04.045] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2012] [Revised: 04/03/2013] [Accepted: 04/12/2013] [Indexed: 01/29/2023] Open
Abstract
Current functional MRI techniques measure hemodynamic changes induced by neural activity. Alternative measurement of signals originated from tissue is desirable and may be achieved using T1ρ, the spin-lattice relaxation time in the rotating-frame, which is measured by spin-lock MRI. Functional T1ρ changes in the brain can have contributions from vascular dilation, tissue acidosis, and potentially other contributions. When the blood contributions were suppressed with a contrast agent at 9.4 T, a small tissue-originated T1ρ change was consistently observed at the middle cortical layers of cat visual cortex during visual stimulation, which had different dynamic characteristics compared to hemodynamic fMRI such as a faster response and no post-stimulus undershoot. Functional tissue T1ρ is highly dependent on the magnetic field strength and experimental parameters such as the power of the spin-locking pulse. With a 500Hz spin-locking pulse, the tissue T1ρ without the blood contribution increased during visual stimulation, but decreased during acidosis-inducing hypercapnia and global ischemia, indicating different signal origins. Phantom studies suggest that it may have contribution from concentration decrease in metabolites. Even though the sensitivity is much weaker than BOLD and its exact interpretation needs further investigation, our results show that non-hemodynamic functional signal can be consistently observed by spin-lock fMRI.
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Affiliation(s)
- Tao Jin
- Neuroimaging Laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, PA 15203, USA.
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Zong X, Wang P, Kim SG, Jin T. Sensitivity and source of amine-proton exchange and amide-proton transfer magnetic resonance imaging in cerebral ischemia. Magn Reson Med 2013; 71:118-32. [PMID: 23401310 DOI: 10.1002/mrm.24639] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Revised: 12/19/2012] [Accepted: 12/19/2012] [Indexed: 12/25/2022]
Abstract
PURPOSE Amide-proton transfer (APT) and amine-water proton exchange (APEX) MRI can be viable to map pH-decreasing ischemic regions. However, their exact contributions are unclear. METHODS We measured APEX- and APT-weighted magnetization transfer ratio asymmetry (denoted as APEXw and APTw), apparent diffusion coefficient, T2 , and T1 images and localized proton spectra in rats with permanent middle cerebral artery occlusion at 9.4 T. Phantoms and theoretical studies were also performed. RESULTS Within 1-h postocclusion, APEXw and APTw maps showed hyperintensity (3.1% of M0 ) and hypointensity (-1.8%), respectively, in regions with decreased apparent diffusion coefficient. Ischemia increased lactate and gamma aminobutyric acid concentrations, but decreased glutamate and taurine concentrations. Over time, the APEXw contrast decreased with glutamate, taurine, and creatine, whereas the APTw contrast and lactate level were similar. Phantom and theoretical studies suggest that the source of APEXw signal is mainly from proteins at normal pH, whereas at decreased pH, gamma aminobutyric acid and glutamate contributions increase, inducing the positive APEXw contrast in ischemic regions. The APTw contrast is sensitive to lactate concentration and pH, but contaminated from contributions of the faster APEX processes. CONCLUSION Positive APEXw contrast is more sensitive to ischemia than negative APTw contrast. They may provide complementary tissue metabolic information.
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Affiliation(s)
- Xiaopeng Zong
- Neuroimaging Laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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Liimatainen T, Sierra A, Hanson T, Sorce DJ, Ylä-Herttuala S, Garwood M, Michaeli S, Gröhn O. Glioma cell density in a rat gene therapy model gauged by water relaxation rate along a fictitious magnetic field. Magn Reson Med 2011; 67:269-77. [PMID: 21721037 DOI: 10.1002/mrm.22997] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2011] [Revised: 03/24/2011] [Accepted: 04/18/2011] [Indexed: 11/09/2022]
Abstract
Longitudinal and transverse rotating-frame relaxation time constants, T(1) (ρ) and T(2) (ρ) , have previously been successfully applied to detect gene therapy responses and acute stroke in animal models. Those experiments were performed with continuous-wave irradiation or with frequency-modulated pulses operating in an adiabatic regime. The technique called Relaxation Along a Fictitious Field (RAFF) is a recent extension of frequency-modulated rotating-frame relaxation methods. In RAFF, spin locking takes place along a fictitious magnetic field, and the decay rate is a function of both T(1ρ) and T(2ρ) processes. In this work, the time constant characterizing water relaxation with RAFF (T(RAFF) ) was evaluated for its utility as a marker of response to gene therapy in a rat glioma model. To investigate the sensitivity to early treatment response, we measured several rotating-frame and free-precession relaxation time constants and the water apparent diffusion coefficients, and these were compared with histological cell counts in 8 days of treated and control groups of animals. T(RAFF) was the only parameter exhibiting significant association with cell density in three different tumor regions (border, intermediate, and core tissues). These results indicate that T(RAFF) may provide a marker to identify tumors responding to treatment.
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Affiliation(s)
- Timo Liimatainen
- Department of Biotechnology and Molecular Medicine A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland.
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36
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Witschey WRT, Pilla JJ, Ferrari G, Koomalsingh K, Haris M, Hinmon R, Zsido G, Gorman JH, Gorman RC, Reddy R. Rotating frame spin lattice relaxation in a swine model of chronic, left ventricular myocardial infarction. Magn Reson Med 2011; 64:1453-60. [PMID: 20677236 DOI: 10.1002/mrm.22543] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
T1ρ relaxation times were quantified in a swine model of chronic, left ventricular myocardial infarction. It was found that there were low frequency relaxation mechanisms that suppress endogenous contrast at low spin-lock amplitudes and in T2-weighted images. A moderate amplitude spin-locking pulse could overcome these relaxation mechanisms. Relaxation dispersion data were measured over a range of RF field amplitudes, and a model was formulated to include dipole-dipole relaxation modulated by molecular rotation and an apparent exchange mechanism. These techniques may find some use in the clinic for the observation of chronic, left ventricular cardiac remodeling.
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Affiliation(s)
- Walter R T Witschey
- Department of Radiology, Medical Physics, University Hospital Freiburg, Freiburg im Breisgau, Germany.
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Andronesi OC, Mintzopoulos D, Righi V, Psychogios N, Kesarwani M, He J, Yasuhara S, Dai G, Rahme LG, Tzika AA. Combined off-resonance imaging and T2 relaxation in the rotating frame for positive contrast MR imaging of infection in a murine burn model. J Magn Reson Imaging 2011; 32:1172-83. [PMID: 21031524 DOI: 10.1002/jmri.22349] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
PURPOSE To develop novel magnetic resonance (MR) imaging methods to monitor accumulation of macrophages in inflammation and infection. Positive-contrast MR imaging provides an alternative to negative-contrast MRI, exploiting the chemical shift induced by ultra-small superparamagnetic iron-oxide (USPIO) nanoparticles to nearby water molecules. We introduce a novel combination of off-resonance (ORI) positive-contrast MRI and T(2ρ) relaxation in the rotating frame (ORI-T(2ρ)) for positive-contrast MR imaging of USPIO. MATERIALS AND METHODS We tested ORI-T(2ρ) in phantoms and imaged in vivo the accumulation of USPIO-labeled macrophages at the infection site in a mouse model of burn trauma and infection with Pseudomonas aeruginosa (PA). PA infection is clinically important. The USPIO nanoparticles were injected directly in the animals in solution, and macrophage labeling occurred in vivo in the animal model. RESULTS We observed a significant difference between ORI-T(2ρ) and ORI, which leads us to suggest that ORI-T(2ρ) is more sensitive in detecting USPIO signal. To this end, the ORI-T(2ρ) positive contrast method may prove to be of higher utility in future research. CONCLUSION Our results may have direct implications in the longitudinal monitoring of infection, and open perspectives for testing novel anti-infective compounds.
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Affiliation(s)
- Ovidiu C Andronesi
- Department of Surgery, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, USA
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Jokivarsi KT, Hiltunen Y, Gröhn H, Tuunanen P, Gröhn OHJ, Kauppinen RA. Estimation of the onset time of cerebral ischemia using T1rho and T2 MRI in rats. Stroke 2010; 41:2335-40. [PMID: 20814006 DOI: 10.1161/strokeaha.110.587394] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND AND PURPOSE Time of ischemia onset is the most critical factor for patient selection for available drug treatment strategies. The purpose of this study was to evaluate the abilities of the absolute longitudinal rotating frame (T(1ρ)) and transverse (T(2)) MR relaxation times to estimate the onset time of ischemia in rats. METHODS Permanent middle cerebral artery occlusion in rats was used to induce focal cerebral ischemia and animals were imaged with multiparametric MRI at several time points up to 7 hours postischemia. Ischemic parenchyma was defined as tissue with apparent diffusion coefficient of water <70% from that in the contralateral nonischemic brain. RESULTS The difference in the absolute T(1ρ) and T(2) between ischemic and contralateral nonischemic striatum increased linearly within the first 6 hours of middle cerebral artery occlusion. The slopes for T(1ρ) and T(2) fits for both tissue types were similar; however, the time offsets were significantly longer for both MR parameters in the cortex than in the striatum. CONCLUSIONS T(1ρ) and T(2) MRI provide estimates for the onset time of cerebral ischemia requiring regional calibration curves from ischemic brain. Assuming that patients with suspected ischemic stroke are scanned by MRI within this timeframe, these MRI techniques may constitute unbiased tools for stroke onset time evaluation potentially aiding the decision-making for drug treatment strategies.
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Tesiram YA. Implementation equations for HS n RF pulses. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 204:333-9. [PMID: 20227899 PMCID: PMC2929662 DOI: 10.1016/j.jmr.2010.02.022] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2010] [Revised: 02/22/2010] [Accepted: 02/23/2010] [Indexed: 05/06/2023]
Abstract
Implementation equations for the family of stretched hyperbolic secant (HS(n)) pulses are derived in the linear adiabatic range for inversion of spins. These master equations provide convenience relations for relating the peak amplitude RF(max) of the pulse to the frequency sweep (bwdth) range of the pulse and its duration T(p). The bandwidth of the pulse can also be related to the effective coverage (bw(eff)) of the pulse to a defined or chosen spectral region. The choice of pulse determined by the use of these derived expressions guarantees uniform inversion to a prescribed efficiency across the selected spectral region. The performance of HS(n) pulses in determining the cut-off region between spectral regions was also examined. It is found that beyond a unique T(p)bwdth product no additional gain may be obtained by extending pulse durations for a chosen bwdth of pulse. An example of practical implementation of the inversion pulses is presented for adiabatic decoupling using HS(7) and HS(8) pulses. It is shown that despite added B(1) inhomogeneity in the form of additional amplifier power to 400% from optimal, these pulses can still yield reproducible decoupled spectra.
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Affiliation(s)
- Yasvir A Tesiram
- Oklahoma Medical Research Foundation, 825 NE 13th St, OKC, OK 73104, USA.
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Jokivarsi KT, Hiltunen Y, Tuunanen PI, Kauppinen RA, Gröhn OHJ. Correlating tissue outcome with quantitative multiparametric MRI of acute cerebral ischemia in rats. J Cereb Blood Flow Metab 2010; 30:415-27. [PMID: 19904287 PMCID: PMC2949115 DOI: 10.1038/jcbfm.2009.236] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Predicting tissue outcome remains a challenge for stroke magnetic resonance imaging (MRI). In this study, we have acquired multiparametric MRI data sets (including absolute T(1), T(2), diffusion, T(1rho) using continuous wave and adiabatic pulse approaches, cerebral blood flow (CBF), and amide proton transfer ratio (APTR) images) during and after 65 mins of middle cerebral artery occlusion (MCAo) in rats. The MRI scans were repeated 24 h after MCAo, when the animals were killed for quantitative histology. Magnetic resonance imaging parameters acquired at three acute time points were correlated with regionally matching cell count at 24 h. The results emphasize differences in the temporal profile of individual MRI contrasts during MCAo and especially during early reperfusion, and suggest that complementary information from CBF and tissue damage can be obtained with appropriate MRI contrasts. The data show that by using three to four MRI parameters, sensitive to both hemodynamic changes and different aspects of parenchymal changes, the fate of the tissue can be predicted with increased correlation compared with single-parameter techniques. Combined multiparametric MRI data and multiparametric analysis may provide an excellent tool for preclinical testing of new treatments and also has the potential to facilitate decision-making in the management of acute stroke patients.
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Affiliation(s)
- Kimmo T Jokivarsi
- Department of Neurobiology, AI Virtanen Institute for Molecular Sciences, University of Kuopio, Kuopio, Finland
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Mangia S, Liimatainen T, Garwood M, Michaeli S. Rotating frame relaxation during adiabatic pulses vs. conventional spin lock: simulations and experimental results at 4 T. Magn Reson Imaging 2009; 27:1074-87. [PMID: 19559559 DOI: 10.1016/j.mri.2009.05.023] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2008] [Revised: 05/15/2009] [Accepted: 05/19/2009] [Indexed: 01/10/2023]
Abstract
Spin relaxation taking place during radiofrequency (RF) irradiation can be assessed by measuring the longitudinal and transverse rotating frame relaxation rate constants (R(1rho) and R(2rho)). These relaxation parameters can be altered by utilizing different settings of the RF irradiation, thus providing a useful tool to generate contrast in MRI. In this work, we investigate the dependencies of R(1rho) and R(2rho) due to dipolar interactions and anisochronous exchange (i.e., exchange between spins with different chemical shift deltaomega not equal0) on the properties of conventional spin-lock and adiabatic pulses, with particular emphasis on the latter ones which were not fully described previously. The results of simulations based on relaxation theory provide a foundation for formulating practical considerations for in vivo applications of rotating frame relaxation methods. Rotating frame relaxation measurements obtained from phantoms and from the human brain at 4 T are presented to confirm the theoretical predictions.
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Affiliation(s)
- Silvia Mangia
- Department of Radiology, Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, 55455, USA.
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