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Kim K, Narsinh K, Ozhinsky E. Technical advances in motion-robust MR thermometry. Magn Reson Med 2024; 92:15-27. [PMID: 38501903 PMCID: PMC11132643 DOI: 10.1002/mrm.30057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2023] [Revised: 01/25/2024] [Accepted: 01/27/2024] [Indexed: 03/20/2024]
Abstract
Proton resonance frequency shift (PRFS) MR thermometry is the most common method used in clinical thermal treatments because of its fast acquisition and high sensitivity to temperature. However, motion is the biggest obstacle in PRFS MR thermometry for monitoring thermal treatment in moving organs. This challenge arises because of the introduction of phase errors into the PRFS calculation through multiple methods, such as image misregistration, susceptibility changes in the magnetic field, and intraframe motion during MRI acquisition. Various approaches for motion correction have been developed for real-time, motion-robust, and volumetric MR thermometry. However, current technologies have inherent trade-offs among volume coverage, processing time, and temperature accuracy. These tradeoffs should be considered and chosen according to the thermal treatment application. In hyperthermia treatment, precise temperature measurements are of increased importance rather than the requirement for exceedingly high temporal resolution. In contrast, ablation procedures require robust temporal resolution to accurately capture a rapid temperature rise. This paper presents a comprehensive review of current cutting-edge MRI techniques for motion-robust MR thermometry, and recommends which techniques are better suited for each thermal treatment. We expect that this study will help discern the selection of motion-robust MR thermometry strategies and inspire the development of motion-robust volumetric MR thermometry for practical use in clinics.
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Affiliation(s)
- Kisoo Kim
- Department of Radiology & Biomedical Imaging, University of California, San Francisco, California, USA
| | - Kazim Narsinh
- Department of Radiology & Biomedical Imaging, University of California, San Francisco, California, USA
| | - Eugene Ozhinsky
- Department of Radiology & Biomedical Imaging, University of California, San Francisco, California, USA
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2
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Scotti AM, Damen F, Gao J, Li W, Liew CW, Cai Z, Zhang Z, Cai K. Phase-independent thermometry by Z-spectrum MR imaging. Magn Reson Med 2022; 87:1731-1741. [PMID: 34752646 PMCID: PMC10029969 DOI: 10.1002/mrm.29072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Revised: 09/30/2021] [Accepted: 10/17/2021] [Indexed: 01/05/2023]
Abstract
PURPOSE Z-spectrum imaging, defined as the consecutive collection of images after saturating over a range of frequency offsets, has been recently proposed as a method to measure the fat-water fraction by the simultaneous detection of fat and water resonances. By incorporating a binomial pulse irradiated at each offset before the readout, the spectral selectivity of the sequence can be further amplified, making it possible to monitor the subtle proton resonance frequency shift that follows a change in temperature. METHODS We tested the hypothesis in aqueous and cream phantoms and in healthy mice, all under thermal challenge. The binomial module consisted of 2 sinc-shaped pulses of opposite phase separated by a delay. Such a delay served to spread out off-resonance spins, with the resulting excitation profile being a periodic function of the delay and the chemical shift. RESULTS During heating experiments, the water resonance shifted downfield, and by fitting the curve to a sine function it was possible to quantify the change in temperature. Results from Z-spectrum imaging correlated linearly with data from conventional MRI techniques like T1 mapping and phase differences from spoiled GRE. CONCLUSION Because the measurement is performed solely on magnitude images, the technique is independent of phase artifacts and is therefore applicable in mixed tissues (e.g., fat). We showed that Z-spectrum imaging can deliver reliable temperature change measurement in both muscular and fatty tissues.
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Affiliation(s)
- Alessandro M. Scotti
- Department of Radiology, University of Illinois at Chicago, Chicago, Illinois, USA
- Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Frederick Damen
- Department of Radiology, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Jin Gao
- Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois, USA
- Research Resources Center, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Weiguo Li
- Department of Radiology, University of Illinois at Chicago, Chicago, Illinois, USA
- Research Resources Center, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Chong Wee Liew
- Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Zimeng Cai
- School of Medical Engineering, Southern Medical University, Guangzhou, China
- Guangdong Provincial Key Laboratory of Image Processing, Southern Medical University, Guangzhou, China
| | - Zhuoli Zhang
- Department of Radiology, Northwestern University, Evanston, Illinois, USA
| | - Kejia Cai
- Department of Radiology, University of Illinois at Chicago, Chicago, Illinois, USA
- Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois, USA
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3
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Tarasek M, Akin O, Roberts J, Foo T, Yeo D. Heat Modulation of Intrinsic MR Contrasts for Tumor Characterization. Cancers (Basel) 2022; 14:cancers14020405. [PMID: 35053567 PMCID: PMC8773677 DOI: 10.3390/cancers14020405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 12/31/2021] [Accepted: 01/12/2022] [Indexed: 12/10/2022] Open
Abstract
(1) Background: The longitudinal relaxation time (T1), transverse relaxation time (T2), water proton chemical shift (CS), and apparent diffusion coefficient (ADC) are MR quantities that change with temperature. In this work, we investigate heat-induced intrinsic MR contrast types to add salient information to conventional MR imaging to improve tumor characterization. (2) Methods: Imaging tests were performed in vivo using different rat tumor models. The rats were cooled/heated to steady-state temperatures from 26–36 °C and quantitative measurements of T1, T2, and ADC were obtained. Temperature maps were measured using the proton resonance frequency shift (PRFS) method during the heating and cooling cycles. (3) Results: All tissue samples show repeatable relaxation parameter measurement over a range of 26–36 °C. Most notably, we observed a more than 3.3% change in T1/°C in breast adenocarcinoma tumors compared to a 1% change in benign breast fibroadenoma lesions. In addition, we note distinct values of T2/°C change for rat prostate carcinoma cells compared to benign tissue. (4) Conclusion: These findings suggest the possibility of improving MR imaging visualization and characterization of tissue with heat-induced contrast types. Specifically, these results suggest that the temporal thermal responses of heat-sensitive MR imaging contrast mechanisms in different tissue types contain information for improved (i) characterization of tumor/tissue boundaries for diagnostic and therapy purposes, and (ii) characterization of salient behavior of tissues, e.g., malignant versus benign tumors.
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Affiliation(s)
- Matthew Tarasek
- GE Global Research, Niskayuna, NY 12309, USA; (J.R.); (T.F.); (D.Y.)
- Correspondence:
| | - Oguz Akin
- Memorial Sloan-Kettering Cancer Center, Department of Radiology, New York, NY 10065, USA;
| | - Jeannette Roberts
- GE Global Research, Niskayuna, NY 12309, USA; (J.R.); (T.F.); (D.Y.)
| | - Thomas Foo
- GE Global Research, Niskayuna, NY 12309, USA; (J.R.); (T.F.); (D.Y.)
| | - Desmond Yeo
- GE Global Research, Niskayuna, NY 12309, USA; (J.R.); (T.F.); (D.Y.)
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4
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Tarasek M, Shu Y, Kang D, Tao S, Gray E, Huston J, Hua Y, Yeo D, Bernstein M, Foo T. Average SAR prediction, validation, and evaluation for a compact MR scanner head-sized RF coil. Magn Reson Imaging 2022; 85:168-176. [PMID: 34666159 PMCID: PMC8631045 DOI: 10.1016/j.mri.2021.10.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Revised: 09/01/2021] [Accepted: 10/12/2021] [Indexed: 01/03/2023]
Abstract
A recently developed compact 3 T (C3T) MRI scanner with high performance gradients [1, 2] has a dedicated radiofrequency (RF) transmit coil that exposes only the head, neck and a small portion of the upper body region during head-first scanning. Due to the unique coil geometry and patient positioning, the established SAR model used for a conventional whole-body scanner cannot be directly translated to the C3T. Here a specific absorption rate (SAR) estimation and validation framework was developed and used to implement a dedicated and accurate SAR prediction model for the C3T. Two different SAR prediction models for the C3T were defined and evaluated: one based on an anatomically derived exposed mass, and one using a fixed anatomical position located caudally to the RF coil to determine the exposed mass. After coil modeling and virtual human body simulation, the designed SAR prediction model was implemented on the C3T and verified with calorimetry and in vivo scan power monitoring. The fixed-demarcation exposed mass model was selected as appropriate exposed mass region to accurately estimate the SAR deposition in the patient on the C3T.
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Affiliation(s)
| | - Y. Shu
- Mayo Clinic, Department of Radiology, Rochester MN U.S
| | - D. Kang
- Mayo Clinic, Department of Radiology, Rochester MN U.S
| | - S. Tao
- Mayo Clinic, Department of Radiology, Jacksonville, FL U.S
| | - E. Gray
- Mayo Clinic, Department of Radiology, Rochester MN U.S
| | - J Huston
- Mayo Clinic, Department of Radiology, Rochester MN U.S
| | - Y Hua
- GE Global Research, Niskayuna NY U.S
| | | | | | - T.K. Foo
- GE Global Research, Niskayuna NY U.S
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5
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Campwala Z, Szewczyk B, Maietta T, Trowbridge R, Tarasek M, Bhushan C, Fiveland E, Ghoshal G, Heffter T, Gandomi K, Carvalho PA, Nycz C, Jeannotte E, Staudt M, Nalwalk J, Hellman A, Zhao Z, Burdette EC, Fischer G, Yeo D, Pilitsis JG. Predicting ablation zones with multislice volumetric 2-D magnetic resonance thermal imaging. Int J Hyperthermia 2021; 38:907-915. [PMID: 34148489 PMCID: PMC9284994 DOI: 10.1080/02656736.2021.1936215] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022] Open
Abstract
BACKGROUND High-intensity focused ultrasound (HIFU) serves as a noninvasive stereotactic system for the ablation of brain metastases; however, treatments are limited to simple geometries and energy delivery is limited by the high acoustic attenuation of the calvarium. Minimally-invasive magnetic resonance-guided robotically-assisted (MRgRA) needle-based therapeutic ultrasound (NBTU) using multislice volumetric 2-D magnetic resonance thermal imaging (MRTI) overcomes these limitations and has potential to produce less collateral tissue damage than current methods. OBJECTIVE To correlate multislice volumetric 2-D MRTI volumes with histologically confirmed regions of tissue damage in MRgRA NBTU. METHODS Seven swine underwent a total of 8 frontal MRgRA NBTU lesions. MRTI ablation volumes were compared to histologic tissue damage on brain sections stained with 2,3,5-triphenyltetrazolium chloride (TTC). Bland-Altman analyses and correlation trends were used to compare MRTI and TTC ablation volumes. RESULTS Data from the initial and third swine's ablations were excluded due to sub-optimal tissue staining. For the remaining ablations (n = 6), the limits of agreement between the MRTI and histologic volumes ranged from -0.149 cm3 to 0.252 cm3 with a mean difference of 0.052 ± 0.042 cm3 (11.1%). There was a high correlation between the MRTI and histology volumes (r2 = 0.831) with a strong linear relationship (r = 0.868). CONCLUSION We used a volumetric MRTI technique to accurately track thermal changes during MRgRA NBTU in preparation for human trials. Improved volumetric coverage with MRTI enhanced our delivery of therapy and has far-reaching implications for focused ultrasound in the broader clinical setting.
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Affiliation(s)
- Zahabiya Campwala
- Department of Neuroscience and Experimental Therapeutics, Albany Medical Center, Albany, NY, USA
| | - Benjamin Szewczyk
- Department of Neurosurgery, Albany Medical Center, Albany, NY, USA.,Robotics Engineering Department, Worcester Polytechnic Institute, Worcester, MA, USA
| | - Teresa Maietta
- Department of Neuroscience and Experimental Therapeutics, Albany Medical Center, Albany, NY, USA
| | - Rachel Trowbridge
- Department of Neuroscience and Experimental Therapeutics, Albany Medical Center, Albany, NY, USA
| | | | | | | | | | | | - Katie Gandomi
- Robotics Engineering Department, Worcester Polytechnic Institute, Worcester, MA, USA
| | | | - Christopher Nycz
- Robotics Engineering Department, Worcester Polytechnic Institute, Worcester, MA, USA
| | - Erin Jeannotte
- Animal Resources Facility, Albany Medical Center, Albany, NY, USA
| | - Michael Staudt
- Department of Neurosurgery, Albany Medical Center, Albany, NY, USA
| | - Julia Nalwalk
- Department of Neuroscience and Experimental Therapeutics, Albany Medical Center, Albany, NY, USA
| | - Abigail Hellman
- Department of Neuroscience and Experimental Therapeutics, Albany Medical Center, Albany, NY, USA
| | - Zhanyue Zhao
- Robotics Engineering Department, Worcester Polytechnic Institute, Worcester, MA, USA
| | | | - Gregory Fischer
- Robotics Engineering Department, Worcester Polytechnic Institute, Worcester, MA, USA
| | - Desmond Yeo
- GE Global Research Center, Niskayuna, NY, USA
| | - Julie G Pilitsis
- Department of Neuroscience and Experimental Therapeutics, Albany Medical Center, Albany, NY, USA.,Department of Neurosurgery, Albany Medical Center, Albany, NY, USA
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Gandomi KY, Carvalho PAWG, Tarasek M, Fiveland EW, Bhushan C, Williams E, Neubauer P, Zhao Z, Pilitsis J, Yeo D, Nycz CJ, Burdette E, Fischer GS. Modeling of Interstitial Ultrasound Ablation for Continuous Applicator Rotation With MR Validation. IEEE Trans Biomed Eng 2021; 68:1838-1846. [PMID: 32924937 PMCID: PMC8189669 DOI: 10.1109/tbme.2020.3023849] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The primary objective of cancer intervention is the selective removal of malignant cells while conserving surrounding healthy tissues. However, the accessibility, size and shape of the cancer can make achieving appropriate margins a challenge. One minimally invasive treatment option for these clinical cases is interstitial needle based therapeutic ultrasound (NBTU). In this work, we develop a finite element model (FEM) capable of simulating continuous rotation of a directional NBTU applicator. The developed model was used to simulate the thermal deposition for different rotation trajectories. The actual thermal deposition patterns for the simulated trajectories were then evaluated using magnetic resonance thermal imaging (MRTI) in a porcine skin gelatin phantom. An MRI-compatible robot was used to control the rotation motion profile of the physical NBTU applicator to match the simulated trajectory. The model showed agreement when compared to experimental measurements with Pearson correlation coefficients greater than 0.839 when comparing temperature fields within an area of 12.6 mm radius from the ultrasound applicator. The average temperature error along a 6.3 mm radius profile from the applicator was 1.27 °C. The model was able to compute 1 s of thermal deposition by the applicator in 0.2 s on average with a 0.1 mm spatial resolution and 0.5 s time steps. The developed simulation demonstrates performance suitable for real-time control which may enable robotically-actuated closed-loop conformal tumor ablation.
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7
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Wu M, Mulder HT, Baron P, Coello E, Menzel MI, van Rhoon GC, Haase A. Correction of motion-induced susceptibility artifacts and B 0 drift during proton resonance frequency shift-based MR thermometry in the pelvis with background field removal methods. Magn Reson Med 2020; 84:2495-2511. [PMID: 32367530 PMCID: PMC7402020 DOI: 10.1002/mrm.28302] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Revised: 04/06/2020] [Accepted: 04/07/2020] [Indexed: 12/12/2022]
Abstract
Purpose The linear change of the water proton resonance frequency shift (PRFS) with temperature is used to monitor temperature change based on the temporal difference of image phase. Here, the effect of motion‐induced susceptibility artifacts on the phase difference was studied in the context of mild radio frequency hyperthermia in the pelvis. Methods First, the respiratory‐induced field variations were disentangled from digestive gas motion in the pelvis. The projection onto dipole fields (PDF) as well as the Laplacian boundary value (LBV) algorithm were applied on the phase difference data to eliminate motion‐induced susceptibility artifacts. Both background field removal (BFR) algorithms were studied using simulations of susceptibility artifacts, a phantom heating experiment, and volunteer and patient heating data. Results Respiratory‐induced field variations were negligible in the presence of the filled water bolus. Even though LBV and PDF showed comparable results for most data, LBV seemed more robust in our data sets. Some data sets suggested that PDF tends to overestimate the background field, thus removing phase attributed to temperature. The BFR methods even corrected for susceptibility variations induced by a subvoxel displacement of the phantom. The method yielded successful artifact correction in 2 out of 4 patient treatment data sets during the entire treatment duration of mild RF heating of cervical cancer. The heating pattern corresponded well with temperature probe data. Conclusion The application of background field removal methods in PRFS‐based MR thermometry has great potential in various heating applications and body regions to reduce motion‐induced susceptibility artifacts that originate outside the region of interest, while conserving temperature‐induced PRFS. In addition, BFR automatically removes up to a first‐order spatial B0 drift.
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Affiliation(s)
- Mingming Wu
- Munich School of Bioengineering, TUM Department of Physics, Technical University of Munich, Garching, Germany
| | | | - Paul Baron
- Erasmus MC Cancer Institute, Rotterdam, the Netherlands
| | - Eduardo Coello
- Munich School of Bioengineering, TUM Department of Physics, Technical University of Munich, Garching, Germany.,GE Healthcare, Munich, Germany
| | | | | | - Axel Haase
- Munich School of Bioengineering, TUM Department of Physics, Technical University of Munich, Garching, Germany
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8
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Ferrer CJ, Bartels LW, van der Velden TA, Grüll H, Heijman E, Moonen CTW, Bos C. Field drift correction of proton resonance frequency shift temperature mapping with multichannel fast alternating nonselective free induction decay readouts. Magn Reson Med 2020; 83:962-973. [PMID: 31544289 PMCID: PMC6899537 DOI: 10.1002/mrm.27985] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 08/14/2019] [Accepted: 08/15/2019] [Indexed: 01/07/2023]
Abstract
PURPOSE To demonstrate that proton resonance frequency shift MR thermometry (PRFS-MRT) acquisition with nonselective free induction decay (FID), combined with coil sensitivity profiles, allows spatially resolved B0 drift-corrected thermometry. METHODS Phantom experiments were performed at 1.5T and 3T. Acquisition of PRFS-MRT and FID were performed during MR-guided high-intensity focused ultrasound heating. The phase of the FIDs was used to estimate the change in angular frequency δωdrift per coil element. Two correction methods were investigated: (1) using the average δωdrift over all coil elements (0th-order) and (2) using coil sensitivity profiles for spatially resolved correction. Optical probes were used for independent temperature verification. In-vivo feasibility of the methods was evaluated in the leg of 1 healthy volunteer at 1.5T. RESULTS In 30 minutes, B0 drift led to an apparent temperature change of up to -18°C and -98°C at 1.5T and 3T, respectively. In the sonicated area, both corrections had a median error of 0.19°C at 1.5T and -0.54°C at 3T. At 1.5T, the measured median error with respect to the optical probe was -1.28°C with the 0th-order correction and improved to 0.43°C with the spatially resolved correction. In vivo, without correction the spatiotemporal median of the apparent temperature was at -4.3°C and interquartile range (IQR) of 9.31°C. The 0th-order correction had a median of 0.75°C and IQR of 0.96°C. The spatially resolved method had the lowest median at 0.33°C and IQR of 0.80°C. CONCLUSION FID phase information from individual receive coil elements allows spatially resolved B0 drift correction in PRFS-based MRT.
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Affiliation(s)
- Cyril J. Ferrer
- Imaging DivisionUniversity Medical Center UtrechtUtrechtNetherlands
| | | | | | - Holger Grüll
- Faculty of Medicine and University Hospital of CologneDepartment of Diagnostic and Interventional RadiologyUniversity of CologneCologneGermany
| | - Edwin Heijman
- Faculty of Medicine and University Hospital of CologneDepartment of Diagnostic and Interventional RadiologyUniversity of CologneCologneGermany
- Oncology SolutionsPhilips ResearchAachenGermany
| | | | - Clemens Bos
- Imaging DivisionUniversity Medical Center UtrechtUtrechtNetherlands
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Kim K, Breton E, Gangi A, Vappou J. Simultaneous fat-referenced proton resonance frequency shift thermometry and MR elastography for the monitoring of thermal ablations. Magn Reson Med 2019; 84:339-347. [PMID: 31823418 DOI: 10.1002/mrm.28130] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 11/21/2019] [Accepted: 11/24/2019] [Indexed: 12/18/2022]
Abstract
PURPOSE Simultaneous fat-referenced proton resonance frequency shift (FRPRFS) thermometry combined with MR elastography (MRE) is proposed, to continuously monitor thermal ablations for all types of soft tissues, including fat-containing tissues. Fat-referenced proton resonance frequency shift thermometry makes it possible to measure temperature even in the water fraction of fat-containing tissues while enabling local field-drift correction. Magnetic resonance elastography allows measuring the mechanical properties of tissues that are related to tissue structural damage. METHODS A gradient-echo MR sequence framework was proposed that combines the need for multiple TE acquisitions for the water-fat separation of FRPRFS, and the need for multiple MRE phase offsets for elastogram reconstructions. Feasibility was first assessed in a fat-containing gelatin phantom undergoing moderate heating by a hot water circulation system. Subsequently, high intensity focused ultrasound heating was conducted in porcine muscle tissue ex vivo (N = 4; 2 samples, 2 locations/sample). RESULTS Both FRPRFS temperature maps and elastograms were updated every 4.1 seconds. In the gelatin phantom, FRPRFS was in good agreement with optical fiber thermometry (average difference 1.2 ± 1°C). In ex vivo high-intensity focused ultrasound experiments on muscle tissue, the shear modulus was found to decrease significantly by 34.3% ± 7.7% (experiment 1, sample 1), 17.9% ± 10.0% (experiment 2, sample 1), 55.1% ± 8.7% (experiment 3, sample 2), and 34.7% ± 8.4% (experiment 4, sample 2) as a result of temperature increase (ΔT = 22.5°C ± 4.2°C, 14.0°C ± 2.8°C, 14.7°C ± 3.7°C, and 14.5°C ± 3.0°C, respectively). CONCLUSION This study demonstrated the feasibility of monitoring thermal ablations with FRPRFS thermometry together with MRE, even in fat-containing tissues. The acquisition time is similar to non-FRPRFS thermometry combined with MRE.
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Affiliation(s)
- Kisoo Kim
- ICube - UMR7357, Université de Strasbourg, CNRS, Strasbourg, France
| | - Elodie Breton
- ICube - UMR7357, Université de Strasbourg, CNRS, Strasbourg, France
| | - Afshin Gangi
- ICube - UMR7357, Université de Strasbourg, CNRS, Strasbourg, France.,Department of Interventional Imaging, Hôpitaux Universitaires de Strasbourg, Strasbourg, France
| | - Jonathan Vappou
- ICube - UMR7357, Université de Strasbourg, CNRS, Strasbourg, France
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10
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Odéen H, Parker DL. Magnetic resonance thermometry and its biological applications - Physical principles and practical considerations. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2019; 110:34-61. [PMID: 30803693 PMCID: PMC6662927 DOI: 10.1016/j.pnmrs.2019.01.003] [Citation(s) in RCA: 70] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Accepted: 01/23/2019] [Indexed: 05/25/2023]
Abstract
Most parameters that influence the magnetic resonance imaging (MRI) signal experience a temperature dependence. The fact that MRI can be used for non-invasive measurements of temperature and temperature change deep inside the human body has been known for over 30 years. Today, MR temperature imaging is widely used to monitor and evaluate thermal therapies such as radio frequency, microwave, laser, and focused ultrasound therapy. In this paper we cover the physical principles underlying the biological applications of MR temperature imaging and discuss practical considerations and remaining challenges. For biological tissue, the MR signal of interest comes mostly from hydrogen protons of water molecules but also from protons in, e.g., adipose tissue and various metabolites. Most of the discussed methods, such as those using the proton resonance frequency (PRF) shift, T1, T2, and diffusion only measure temperature change, but measurements of absolute temperatures are also possible using spectroscopic imaging methods (taking advantage of various metabolite signals as internal references) or various types of contrast agents. Currently, the PRF method is the most used clinically due to good sensitivity, excellent linearity with temperature, and because it is largely independent of tissue type. Because the PRF method does not work in adipose tissues, T1- and T2-based methods have recently gained interest for monitoring temperature change in areas with high fat content such as the breast and abdomen. Absolute temperature measurement methods using spectroscopic imaging and contrast agents often offer too low spatial and temporal resolution for accurate monitoring of ablative thermal procedures, but have shown great promise in monitoring the slower and usually less spatially localized temperature change observed during hyperthermia procedures. Much of the current research effort for ablative procedures is aimed at providing faster measurements, larger field-of-view coverage, simultaneous monitoring in aqueous and adipose tissues, and more motion-insensitive acquisitions for better precision measurements in organs such as the heart, liver, and kidneys. For hyperthermia applications, larger coverage, motion insensitivity, and simultaneous aqueous and adipose monitoring are also important, but great effort is also aimed at solving the problem of long-term field drift which gets interpreted as temperature change when using the PRF method.
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Affiliation(s)
- Henrik Odéen
- University of Utah, Utah Center for Advanced Imaging Research, Department of Radiology and Imaging Sciences, 729 Arapeen Drive, Salt Lake City, UT 84108-1217, USA.
| | - Dennis L Parker
- University of Utah, Utah Center for Advanced Imaging Research, Department of Radiology and Imaging Sciences, 729 Arapeen Drive, Salt Lake City, UT 84108-1217, USA.
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11
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Cheng C, Zou C, Wan Q, Qiao Y, Pan M, Tie C, Liang D, Zheng H, Liu X. Dual-step iterative temperature estimation method for accurate and precise fat-referenced PRFS temperature imaging. Magn Reson Med 2018; 81:1322-1334. [PMID: 30230595 DOI: 10.1002/mrm.27396] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2018] [Revised: 05/15/2018] [Accepted: 05/19/2018] [Indexed: 12/24/2022]
Abstract
PURPOSE The aim of this study was to propose dual-step iterative temperature estimation (DITE) of a fat-referenced proton resonance frequency shift (PRFS) method to improve both the accuracy and precision of temperature estimations in fat-containing tissues. METHODS A fat-water signal model with multiple fat peaks was used to simultaneously estimate the temperature, fat/water intensity and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mtext>T</mml:mtext> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> <mml:mrow><mml:mrow/> <mml:mo>∗</mml:mo></mml:mrow> </mml:msubsup> </mml:math> , and field offset. In DITE, model fitting was implemented with alternating 2-step minimizations. The estimated temperature map was smoothed between the 2-step minimizations, which is considered to be the most important step for improving the temperature precision. The performance of DITE was evaluated with a Monte Carlo simulation, fat/water phantoms, and ex vivo brown adipose tissue experiments and then compared with the performance of previous fat-referenced proton resonance frequency shift methods. RESULTS In fat/water phantom experiment with a smooth temperature profile, the temperatures estimated by DITE are consistent with the thermometer results and present a better accuracy and precision than those of previous fat-referenced proton resonance frequency shift methods. In the brown adipose tissue heating experiment, the average mean error, SD, and RMS error were -0.08ºC, 0.46ºC, and 0.56ºC, respectively, over all of the measurements within the region of interest. CONCLUSION Our proposed DITE method improves both the accuracy and precision of temperature measurements in tissues with fat fractions between 20% and 80% under smooth distribution of the temperature profile and represents a simple fat-referenced thermometry method.
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Affiliation(s)
- Chuanli Cheng
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China.,Shenzhen College of Advanced Technology, University of Chinese Academy of Sciences, Shenzhen, China
| | - Chao Zou
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China.,Shenzhen College of Advanced Technology, University of Chinese Academy of Sciences, Shenzhen, China
| | - Qian Wan
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China.,Shenzhen College of Advanced Technology, University of Chinese Academy of Sciences, Shenzhen, China
| | - Yangzi Qiao
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
| | - Min Pan
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China.,Shenzhen Hospital of Guangzhou University of Chinese Medicine, Shenzhen, China
| | - Changjun Tie
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
| | - Dong Liang
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
| | - Hairong Zheng
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China.,Chongqing Collaborative Innovation Center for Minimally Invasive and Noninvasive Medicine, Chongqing, China
| | - Xin Liu
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China.,Chongqing Collaborative Innovation Center for Minimally Invasive and Noninvasive Medicine, Chongqing, China
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12
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Abstract
The unique ability of magnetic resonance imaging to measure temperature noninvasively, in vivo, makes it an attractive tool for monitoring interventional procedures, such as radiofrequency or microwave ablation in real-time. The most frequently used approach for magnetic resonance-based temperature measurement is proton resonance frequency (PRF) thermometry. Although it has many advantages, including tissue-independence and real-time capability, the main drawback is its motion sensitivity. This is likely the reason PRF thermometry in moving organs, such as the liver, is not commonly used in the clinical arena. In recent years, however, several developments suggest that motion-corrected thermometry in the liver is achievable. The present article summarizes the diverse attempts to correct thermometry in the liver. Therefore, the physical principle of PRF is introduced, with additional references for necrosis zone estimation and how to deal with fat phase modulation, and main magnetic field drifts. The primary categories of motion correction are presented, including general methods for motion compensation and library-based approaches, and referenceless thermometry and hybrid methods. Practical validation of the described methods in larger patient groups will be necessary to establish accurate motion-corrected thermometry in the clinical arena, with the goal of complete liver tumor ablation.
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13
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Hofstetter LW, Yeo DTB, Dixon WT, Marinelli L, Foo TK. Referenced MR thermometry using three-echo phase-based fat water separation method. Magn Reson Imaging 2018; 49:86-93. [PMID: 29409819 DOI: 10.1016/j.mri.2018.01.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Revised: 01/25/2018] [Accepted: 01/27/2018] [Indexed: 12/24/2022]
Abstract
A three-point image reconstruction method for internally referenced MR thermometry was developed. The technique exploits the fact that temperature-induced changes in the water resonance frequency are small relative to the chemical shift difference between water and fat signals. This property enabled the use of small angle approximations to derive an analytic phase-based fat-water separation method for MR thermometry. Ethylene glycol and cream cool-down experiments were performed to validate measurement technique. Over a cool-down temperature range of 20 °C, maximum deviation between probe and MR measurement (averaged over 1.3 cm3 region surrounding probe) was 0.6 °C and 1.1 °C for ethylene glycol and cream samples, respectively.
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Affiliation(s)
| | | | - W Thomas Dixon
- Department of Radiology, Emory University, Atlanta, GA, USA.
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14
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Zhang L, McCallister A, Koshlap KM, Branca RT. Correlation distance dependence of the resonance frequency of intermolecular zero quantum coherences and its implication for MR thermometry. Magn Reson Med 2017; 79:1429-1438. [PMID: 28656726 DOI: 10.1002/mrm.26801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Revised: 05/04/2017] [Accepted: 05/27/2017] [Indexed: 12/27/2022]
Abstract
PURPOSE Because the resonance frequency of water-fat intermolecular zero-quantum coherences (iZQCs) reflects the water-fat frequency separation at the microscopic scale, these frequencies have been proposed and used as a mean to obtain more accurate temperature information. The purpose of this work was to investigate the dependence of the water-fat iZQC resonance frequency on sample microstructure and on the specific choice of the correlation distance. METHODS The effect of water-fat susceptibility gradients on the water-methylene iZQC resonance frequency was first computed and then measured for different water-fat emulsions and for a mixture of porcine muscle and fat. Similar measurements were also performed for mixed heteronuclear spin systems. RESULTS A strong dependence of the iZQC resonance frequency on the sample microstructure and on the specific choice of the correlation distance was found for spin systems like water and fat that do not mix, but not for spin systems that mix at the molecular level. CONCLUSIONS Because water and fat spins do not mix at the molecular level, the water-fat iZQC resonance frequency and its temperature coefficient are not only affected by sample microstructure but also by the specific choice of the correlation distance. Magn Reson Med 79:1429-1438, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Le Zhang
- Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.,Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Andrew McCallister
- Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.,Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Karl M Koshlap
- Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Rosa Tamara Branca
- Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.,Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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15
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Zhang L, Burant A, McCallister A, Zhao V, Koshlap KM, Degan S, Antonacci M, Branca RT. Accurate MR thermometry by hyperpolarized 129 Xe. Magn Reson Med 2016; 78:1070-1079. [PMID: 27759913 DOI: 10.1002/mrm.26506] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Revised: 09/14/2016] [Accepted: 09/19/2016] [Indexed: 12/31/2022]
Abstract
PURPOSE To investigate the temperature dependence of the resonance frequency of lipid-dissolved xenon (LDX) and to assess the accuracy of LDX-based MR thermometry. METHODS The chemical shift temperature dependence of water protons, methylene protons, and LDX was measured from samples containing tissues with varying fat contents using a high-resolution NMR spectrometer. LDX results were then used to acquire relative and absolute temperature maps in vivo and the results were compared with PRF-based MR thermometry. RESULTS The temperature dependence of proton resonance frequency (PRF) is strongly affected by the specific distribution of water and fat. A redistribution of water and fat compartments can reduce the apparent temperature dependence of the water chemical shift from -0.01 ppm/°C to -0.006 ppm, whereas the LDX chemical shift shows a consistent temperature dependence of -0.21 ppm/°C. The use of the methylene protons resonance frequency as internal reference improves the accuracy of LDX-based MR thermometry, but degrades that of PRF-based MR thermometry, as microscopic susceptibility gradients affected lipid and water spins differently. CONCLUSION The LDX resonance frequency, with its higher temperature dependence, provides more accurate and precise temperature measurements, both in vitro and in vivo. More importantly, the resonance frequency of nearby methylene protons can be used to extract absolute temperature information. Magn Reson Med 78:1070-1079, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Le Zhang
- Department of Applied Physical Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.,Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Alex Burant
- Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.,Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Andrew McCallister
- Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.,Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Victor Zhao
- Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Karl M Koshlap
- Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Simone Degan
- Center for Molecular and Biomolecular Imaging, Department of Radiology and Dermatology, Duke University, Durham, North Carolina, USA
| | - Michael Antonacci
- Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.,Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Rosa Tamara Branca
- Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.,Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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16
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Poorman ME, Chaplin VL, Wilkens K, Dockery MD, Giorgio TD, Grissom WA, Caskey CF. Open-source, small-animal magnetic resonance-guided focused ultrasound system. J Ther Ultrasound 2016; 4:22. [PMID: 27597889 PMCID: PMC5011339 DOI: 10.1186/s40349-016-0066-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Accepted: 08/16/2016] [Indexed: 01/16/2023] Open
Abstract
BACKGROUND MR-guided focused ultrasound or high-intensity focused ultrasound (MRgFUS/MRgHIFU) is a non-invasive therapeutic modality with many potential applications in areas such as cancer therapy, drug delivery, and blood-brain barrier opening. However, the large financial costs involved in developing preclinical MRgFUS systems represent a barrier to research groups interested in developing new techniques and applications. We aim to mitigate these challenges by detailing a validated, open-source preclinical MRgFUS system capable of delivering thermal and mechanical FUS in a quantifiable and repeatable manner under real-time MRI guidance. METHODS A hardware and software package was developed that includes closed-loop feedback controlled thermometry code and CAD drawings for a therapy table designed for a preclinical MRI scanner. For thermal treatments, the modular software uses a proportional integral derivative controller to maintain a precise focal temperature rise in the target given input from MR phase images obtained concurrently. The software computes the required voltage output and transmits it to a FUS transducer that is embedded in the delivery table within the magnet bore. The delivery table holds the FUS transducer, a small animal and its monitoring equipment, and a transmit/receive RF coil. The transducer is coupled to the animal via a water bath and is translatable in two dimensions from outside the magnet. The transducer is driven by a waveform generator and amplifier controlled by real-time software in Matlab. MR acoustic radiation force imaging is also implemented to confirm the position of the focus for mechanical and thermal treatments. RESULTS The system was validated in tissue-mimicking phantoms and in vivo during murine tumor hyperthermia treatments. Sonications were successfully controlled over a range of temperatures and thermal doses for up to 20 min with minimal temperature overshoot. MR thermometry was validated with an optical temperature probe, and focus visualization was achieved with acoustic radiation force imaging. CONCLUSIONS We developed an MRgFUS platform for small-animal treatments that robustly delivers accurate, precise, and controllable sonications over extended time periods. This system is an open source and could increase the availability of low-cost small-animal systems to interdisciplinary researchers seeking to develop new MRgFUS applications and technology.
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Affiliation(s)
- Megan E. Poorman
- Department of Biomedical Engineering, Vanderbilt University, PMB 351631 2301 Vanderbilt Place, Nashville, 37235 TN USA
| | - Vandiver L. Chaplin
- Department of Biomedical Engineering, Vanderbilt University, PMB 351631 2301 Vanderbilt Place, Nashville, 37235 TN USA
- Chemical and Physical Biology Program, Vanderbilt University, 1161 21st Avenue South, Nashville, 37232 TN USA
| | - Ken Wilkens
- Institute of Imaging Science, Vanderbilt University, 1161 21st Avenue South, Nashville, 37232 TN USA
| | - Mary D. Dockery
- Department of Biomedical Engineering, Vanderbilt University, PMB 351631 2301 Vanderbilt Place, Nashville, 37235 TN USA
| | - Todd D. Giorgio
- Department of Biomedical Engineering, Vanderbilt University, PMB 351631 2301 Vanderbilt Place, Nashville, 37235 TN USA
| | - William A. Grissom
- Department of Biomedical Engineering, Vanderbilt University, PMB 351631 2301 Vanderbilt Place, Nashville, 37235 TN USA
- Institute of Imaging Science, Vanderbilt University, 1161 21st Avenue South, Nashville, 37232 TN USA
| | - Charles F. Caskey
- Institute of Imaging Science, Vanderbilt University, 1161 21st Avenue South, Nashville, 37232 TN USA
- Department of Radiology, Vanderbilt University, 1161 21st Avenue South, Nashville, 37232 TN USA
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17
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Lam MK, de Greef M, Bouwman JG, Moonen CTW, Viergever MA, Bartels LW. Multi-gradient echo MR thermometry for monitoring of the near-field area during MR-guided high intensity focused ultrasound heating. Phys Med Biol 2015; 60:7729-45. [DOI: 10.1088/0031-9155/60/19/7729] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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18
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Baron P, Deckers R, Bouwman JG, Bakker CJG, de Greef M, Viergever MA, Moonen CTW, Bartels LW. Influence of water and fat heterogeneity on fat-referenced MR thermometry. Magn Reson Med 2015; 75:1187-97. [PMID: 25940426 DOI: 10.1002/mrm.25727] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 03/19/2015] [Accepted: 03/20/2015] [Indexed: 12/25/2022]
Abstract
PURPOSE To investigate the effect of the aqueous and fatty tissue magnetic susceptibility distribution on absolute and relative temperature measurements as obtained directly from the water/fat (w/f) frequency difference. METHODS Absolute thermometry was investigated using spherical phantoms filled with pork and margarine, which were scanned in three orthogonal orientations. To evaluate relative fat referencing, multigradient echo scans were acquired before and after heating pork tissue via high-intensity focused ultrasound (HIFU). Simulations were performed to estimate the errors that can be expected in human breast tissue. RESULTS The sphere experiment showed susceptibility-related errors of 8.4 °C and 0.2 °C for pork and margarine, respectively. For relative fat referencing measurements, fat showed pronounced phase changes of opposite polarity to aqueous tissue. The apparent mean temperature for a numerical breast model assumed to be 37 °C was 47.2 ± 21.6 °C. Simulations of relative fat referencing for a HIFU sonication (ΔT = 29.7 °C) yielded a maximum temperature error of 6.6 °C compared with 2.5 °C without fat referencing. CONCLUSION Variations in the observed frequency difference between water and fat are largely due to variations in the w/f spatial distribution. This effect may lead to considerable errors in absolute MR thermometry. Additionally, fat referencing may exacerbate rather than correct for proton resonance frequency shift-temperature measurement errors.
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Affiliation(s)
- Paul Baron
- Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands
| | - Roel Deckers
- Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands
| | - Job G Bouwman
- Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands
| | - Chris J G Bakker
- Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands
| | - Martijn de Greef
- Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands
| | - Max A Viergever
- Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands
| | - Chrit T W Moonen
- Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands
| | - Lambertus W Bartels
- Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands
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19
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Tarasek MR, Pellicer R, Hofstetter LW, Numan WCM, Bakker JF, Kotek G, Togni P, Verhaart RF, Fiveland EW, Houston GC, van Rhoon GC, Paulides MM, Yeo DTB. Validation of MR thermometry: method for temperature probe sensor registration accuracy in head and neck phantoms. Int J Hyperthermia 2015; 30:142-9. [PMID: 24571177 DOI: 10.3109/02656736.2014.887794] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
PURPOSE Magnetic resonance thermometry (MRT) is an attractive means to non-invasively monitor in vivo temperature during head and neck hyperthermia treatments because it can provide multi-dimensional temperature information with high spatial resolution over large regions of interest. However, validation of MRT measurements in a head and neck clinical set-up is crucial to ensure the temperature maps are accurate. Here we demonstrate a unique approach for temperature probe sensor localisation in head and neck hyperthermia test phantoms. METHODS We characterise the proton resonance frequency shift temperature coefficient and validate MRT measurements in an oil-gel phantom by applying a combination of MR imaging and 3D spline fitting for accurate probe localisation. We also investigate how uncertainties in both the probe localisation and the proton resonance frequency shift (PRFS) thermal coefficient affect the registration of fibre-optic reference temperature probe and MRT readings. RESULTS The method provides a two-fold advantage of sensor localisation and PRFS thermal coefficient calibration. We provide experimental data for two distinct head and neck phantoms showing the significance of this method as it mitigates temperature probe localisation errors and thereby increases accuracy of MRT validation results. CONCLUSIONS The techniques presented here may be used to simplify calibration experiments that use an interstitial heating device, or any heating method that provides rapid and spatially localised heat distributions. Overall, the experimental verification of the data registration and PRFS thermal coefficient calibration technique provides a useful benchmarking method to maximise MRT accuracy in any similar context.
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Affiliation(s)
- Matthew R Tarasek
- GE Global Research, Diagnostics and Biomedical Technologies, One Research Circle , Niskayuna, New York , USA
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20
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Baron P, Deckers R, de Greef M, Merckel LG, Bakker CJG, Bouwman JG, Bleys RLAW, van den Bosch MAAJ, Bartels LW. Correction of proton resonance frequency shift MR-thermometry errors caused by heat-induced magnetic susceptibility changes during high intensity focused ultrasound ablations in tissues containing fat. Magn Reson Med 2013; 72:1580-9. [PMID: 24347129 DOI: 10.1002/mrm.25063] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2013] [Revised: 11/07/2013] [Accepted: 11/08/2013] [Indexed: 11/10/2022]
Abstract
PURPOSE In this study, we aim to demonstrate the sensitivity of proton resonance frequency shift (PRFS) -based thermometry to heat-induced magnetic susceptibility changes and to present and evaluate a model-based correction procedure. THEORY AND METHODS To demonstrate the expected temperature effect, field disturbances during high intensity focused ultrasound sonications were monitored in breast fat samples with a three-dimensional (3D) gradient echo sequence. To evaluate the correction procedure, the interface of tissue-mimicking ethylene glycol gel and fat was sonicated. During sonication, the temperature was monitored with a 2D dual flip angle multi-echo gradient echo sequence, allowing for PRFS-based relative and referenced temperature measurements in the gel and T1 -based temperature measurements in fat. The PRFS-based measurement in the gel was corrected by minimizing the discrepancy between the observed 2D temperature profile and the profile predicted by a 3D thermal model. RESULTS The HIFU sonications of breast fat resulted in a magnetic field disturbance which completely disappeared after cooling. For the correction method, the 5th to 95th percentile interval of the PRFS-thermometry error in the gel decreased from 3.8°C before correction to 2.0-2.3°C after correction. CONCLUSION This study has shown the effects of magnetic susceptibility changes induced by heating of breast fatty tissue samples. The resultant errors can be reduced by the use of a model-based correction procedure.
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Affiliation(s)
- Paul Baron
- Image Sciences Institute, University Medical Center Utrecht, Utrecht, The Netherlands
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21
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Hernando D, Sharma SD, Kramer H, Reeder SB. On the confounding effect of temperature on chemical shift-encoded fat quantification. Magn Reson Med 2013; 72:464-70. [PMID: 24123362 DOI: 10.1002/mrm.24951] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Revised: 08/10/2013] [Accepted: 08/21/2013] [Indexed: 12/12/2022]
Abstract
PURPOSE To characterize the confounding effect of temperature on chemical shift-encoded (CSE) fat quantification. METHODS The proton resonance frequency of water, unlike triglycerides, depends on temperature. This leads to a temperature dependence of the spectral models of fat (relative to water) that are commonly used by CSE-MRI methods. Simulation analysis was performed for 1.5 Tesla CSE fat-water signals at various temperatures and echo time combinations. Oil-water phantoms were constructed and scanned at temperatures between 0 and 40°C using spectroscopy and CSE imaging at three echo time combinations. An explanted human liver, rejected for transplantation due to steatosis, was scanned using spectroscopy and CSE imaging. Fat-water reconstructions were performed using four different techniques: magnitude and complex fitting, with standard or temperature-corrected signal modeling. RESULTS In all experiments, magnitude fitting with standard signal modeling resulted in large fat quantification errors. Errors were largest for echo time combinations near TEinit ≈ 1.3 ms, ΔTE ≈ 2.2 ms. Errors in fat quantification caused by temperature-related frequency shifts were smaller with complex fitting, and were avoided using a temperature-corrected signal model. CONCLUSION Temperature is a confounding factor for fat quantification. If not accounted for, it can result in large errors in fat quantifications in phantom and ex vivo acquisitions.
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Affiliation(s)
- Diego Hernando
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA
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22
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Lin JS, Hwang KP, Jackson EF, Hazle JD, Stafford RJ, Taylor BA. Multiparametric fat-water separation method for fast chemical-shift imaging guidance of thermal therapies. Med Phys 2013; 40:103302. [PMID: 24089932 DOI: 10.1118/1.4819815] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
PURPOSE A k-means-based classification algorithm is investigated to assess suitability for rapidly separating and classifying fat/water spectral peaks from a fast chemical shift imaging technique for magnetic resonance temperature imaging. Algorithm testing is performed in simulated mathematical phantoms and agar gel phantoms containing mixed fat/water regions. METHODS Proton resonance frequencies (PRFs), apparent spin-spin relaxation (T2*) times, and T1-weighted (T1-W) amplitude values were calculated for each voxel using a single-peak autoregressive moving average (ARMA) signal model. These parameters were then used as criteria for k-means sorting, with the results used to determine PRF ranges of each chemical species cluster for further classification. To detect the presence of secondary chemical species, spectral parameters were recalculated when needed using a two-peak ARMA signal model during the subsequent classification steps. Mathematical phantom simulations involved the modulation of signal-to-noise ratios (SNR), maximum PRF shift (MPS) values, analysis window sizes, and frequency expansion factor sizes in order to characterize the algorithm performance across a variety of conditions. In agar, images were collected on a 1.5T clinical MR scanner using acquisition parameters close to simulation, and algorithm performance was assessed by comparing classification results to manually segmented maps of the fat/water regions. RESULTS Performance was characterized quantitatively using the Dice Similarity Coefficient (DSC), sensitivity, and specificity. The simulated mathematical phantom experiments demonstrated good fat/water separation depending on conditions, specifically high SNR, moderate MPS value, small analysis window size, and low but nonzero frequency expansion factor size. Physical phantom results demonstrated good identification for both water (0.997 ± 0.001, 0.999 ± 0.001, and 0.986 ± 0.001 for DSC, sensitivity, and specificity, respectively) and fat (0.763 ± 0.006, 0.980 ± 0.004, and 0.941 ± 0.002 for DSC, sensitivity, and specificity, respectively). Temperature uncertainties, based on PRF uncertainties from a 5 × 5-voxel ROI, were 0.342 and 0.351°C for pure and mixed fat/water regions, respectively. Algorithm speed was tested using 25 × 25-voxel and whole image ROIs containing both fat and water, resulting in average processing times per acquisition of 2.00 ± 0.07 s and 146 ± 1 s, respectively, using uncompiled MATLAB scripts running on a shared CPU server with eight Intel Xeon(TM) E5640 quad-core processors (2.66 GHz, 12 MB cache) and 12 GB RAM. CONCLUSIONS Results from both the mathematical and physical phantom suggest the k-means-based classification algorithm could be useful for rapid, dynamic imaging in an ROI for thermal interventions. Successful separation of fat/water information would aid in reducing errors from the nontemperature sensitive fat PRF, as well as potentially facilitate using fat as an internal reference for PRF shift thermometry when appropriate. Additionally, the T1-W or R2* signals may be used for monitoring temperature in surrounding adipose tissue.
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Affiliation(s)
- Jonathan S Lin
- Department of Bioengineering, Rice University, 6100 Main Street, Houston, Texas 77005 and Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030
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23
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Streicher MN, Schäfer A, Ivanov D, Müller DK, Amadon A, Reimer E, Huber L, Dhital B, Rivera D, Kögler C, Trampel R, Pampel A, Turner R. Fast accurate MR thermometry using phase referenced asymmetric spin-echo EPI at high field. Magn Reson Med 2013; 71:524-33. [DOI: 10.1002/mrm.24681] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Markus N. Streicher
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
| | - Andreas Schäfer
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
| | - Dimo Ivanov
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
| | - Dirk K. Müller
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
| | - Alexis Amadon
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
| | - Enrico Reimer
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
| | - Laurentius Huber
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
| | - Bibek Dhital
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
| | - Debra Rivera
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
| | - Carsten Kögler
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
| | - Robert Trampel
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
| | - André Pampel
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
| | - Robert Turner
- Max Planck Institute for Human Cognitive and Brain Sciences; Stephanstr. Leipzig Germany
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24
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Hofstetter LW, Yeo DTB, Dixon WT, Kempf JG, Davis CE, Foo TK. Fat-referenced MR thermometry in the breast and prostate using IDEAL. J Magn Reson Imaging 2012; 36:722-32. [PMID: 22581513 DOI: 10.1002/jmri.23692] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Accepted: 04/02/2012] [Indexed: 11/05/2022] Open
Abstract
PURPOSE To demonstrate a three-echo fat-referenced MR thermometry technique that estimates and corrects for time-varying phase disturbances in heterogeneous tissues. MATERIALS AND METHODS Fat protons do not exhibit a temperature-dependent frequency shift. Fat-referenced thermometry methods exploit this insensitivity and use the signal from fat to measure and correct for magnetic field disturbances. In this study, we present a fat-referenced method that uses interpolation of the fat signal to correct for phase disturbances in fat free regions. Phantom and ex vivo tissue cool-down experiments were performed to evaluate the accuracy of this method in the absence of motion. Non-heated in vivo imaging of the breast and prostate was performed to demonstrate measurement robustness in the presence of systemic and motion-induced field disturbances. Measurement accuracy of the method was compared to conventional proton resonance frequency shift MR thermometry. RESULTS In the ex vivo porcine tissue experiment, maximum measurement error of the fat-referenced method was reduced 42% from 3.3 to 1.9°C when compared to conventional MR thermometry. In the breasts, measurement errors were reduced by up to 70% from 6.4 to 1.9°C. CONCLUSION Ex vivo and in vivo results show that the proposed method reduces measurement errors in the heterogeneous tissue experiments when compared to conventional MR thermometry.
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Madore B, Panych LP, Mei CS, Yuan J, Chu R. Multipathway sequences for MR thermometry. Magn Reson Med 2011; 66:658-68. [PMID: 21394774 DOI: 10.1002/mrm.22844] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2010] [Revised: 12/17/2010] [Accepted: 12/20/2010] [Indexed: 12/31/2022]
Abstract
MR-based thermometry is a valuable adjunct to thermal ablation therapies as it helps to determine when lethal doses are reached at the target and whether surrounding tissues are safe from damage. When the targeted lesion is mobile, MR data can further be used for motion-tracking purposes. The present work introduces pulse sequence modifications that enable significant improvements in terms of both temperature-to-noise-ratio properties and target-tracking abilities. Instead of sampling a single magnetization pathway as in typical MR thermometry sequences, the pulse-sequence design introduced here involves sampling at least one additional pathway. Image reconstruction changes associated with the proposed sampling scheme are also described. The method was implemented on two commonly used MR thermometry sequences: the gradient-echo and the interleaved echo-planar imaging sequences. Data from the extra pathway enabled temperature-to-noise-ratio improvements by up to 35%, without increasing scan time. Potentially of greater significance is that the sampled pathways featured very different contrast for blood vessels, facilitating their detection and use as internal landmarks for tracking purposes. Through improved temperature-to-noise-ratio and lesion-tracking abilities, the proposed pulse-sequence design may facilitate the use of MR-monitored thermal ablations as an effective treatment option even in mobile organs such as the liver and kidneys.
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Affiliation(s)
- Bruno Madore
- Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
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Landman BA, Huang AJ, Gifford A, Vikram DS, Lim IAL, Farrell JAD, Bogovic JA, Hua J, Chen M, Jarso S, Smith SA, Joel S, Mori S, Pekar JJ, Barker PB, Prince JL, van Zijl PCM. Multi-parametric neuroimaging reproducibility: a 3-T resource study. Neuroimage 2010; 54:2854-66. [PMID: 21094686 DOI: 10.1016/j.neuroimage.2010.11.047] [Citation(s) in RCA: 196] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2010] [Revised: 11/11/2010] [Accepted: 11/12/2010] [Indexed: 11/25/2022] Open
Abstract
Modern MRI image processing methods have yielded quantitative, morphometric, functional, and structural assessments of the human brain. These analyses typically exploit carefully optimized protocols for specific imaging targets. Algorithm investigators have several excellent public data resources to use to test, develop, and optimize their methods. Recently, there has been an increasing focus on combining MRI protocols in multi-parametric studies. Notably, these have included innovative approaches for fusing connectivity inferences with functional and/or anatomical characterizations. Yet, validation of the reproducibility of these interesting and novel methods has been severely hampered by the limited availability of appropriate multi-parametric data. We present an imaging protocol optimized to include state-of-the-art assessment of brain function, structure, micro-architecture, and quantitative parameters within a clinically feasible 60-min protocol on a 3-T MRI scanner. We present scan-rescan reproducibility of these imaging contrasts based on 21 healthy volunteers (11 M/10 F, 22-61 years old). The cortical gray matter, cortical white matter, ventricular cerebrospinal fluid, thalamus, putamen, caudate, cerebellar gray matter, cerebellar white matter, and brainstem were identified with mean volume-wise reproducibility of 3.5%. We tabulate the mean intensity, variability, and reproducibility of each contrast in a region of interest approach, which is essential for prospective study planning and retrospective power analysis considerations. Anatomy was highly consistent on structural acquisition (~1-5% variability), while variation on diffusion and several other quantitative scans was higher (~<10%). Some sequences are particularly variable in specific structures (ASL exhibited variation of 28% in the cerebral white matter) or in thin structures (quantitative T2 varied by up to 73% in the caudate) due, in large part, to variability in automated ROI placement. The richness of the joint distribution of intensities across imaging methods can be best assessed within the context of a particular analysis approach as opposed to a summary table. As such, all imaging data and analysis routines have been made publicly and freely available. This effort provides the neuroimaging community with a resource for optimization of algorithms that exploit the diversity of modern MRI modalities. Additionally, it establishes a baseline for continuing development and optimization of multi-parametric imaging protocols.
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Affiliation(s)
- Bennett A Landman
- Department of Electrical Engineering, Vanderbilt University, Nashville, TN 37235-1679, USA.
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Soher BJ, Wyatt C, Reeder SB, MacFall JR. Noninvasive temperature mapping with MRI using chemical shift water-fat separation. Magn Reson Med 2010; 63:1238-46. [PMID: 20432295 DOI: 10.1002/mrm.22310] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Tissues containing both water and lipids, e.g., breast, confound standard MR proton reference frequency-shift methods for mapping temperatures due to the lack of temperature-induced frequency shift in lipid protons. Generalized Dixon chemical shift-based water-fat separation methods, such as GE's iterative decomposition of water and fat with echo asymmetry and least-squares estimation method, can result in complex water and fat images. Once separated, the phase change over time of the water signal can be used to map temperature. Phase change of the lipid signal can be used to correct for non-temperature-dependent phase changes, such as amplitude of static field drift. In this work, an image acquisition and postprocessing method, called water and fat thermal MRI, is demonstrated in phantoms containing 30:70, 50:50, and 70:30 water-to-fat by volume. Noninvasive heating was applied in an Off1-On-Off2 pattern over 50 min, using a miniannular phased radiofrequency array. Temperature changes were referenced to the first image acquisition. Four fiber optic temperature probes were placed inside the phantoms for temperature comparison. Region of interest (ROI) temperature values colocated with the probes showed excellent agreement (global mean +/- standard deviation: -0.09 +/- 0.34 degrees C) despite significant amplitude of static field drift during the experiments.
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Affiliation(s)
- Brian J Soher
- Department of Radiology, Duke University, Durham, North Carolina 27710, USA.
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Pan X, Li C, Ying K, Weng D, Qin W, Li K. Model-based PRFS thermometry using fat as the internal reference and the extended Prony algorithm for model fitting. Magn Reson Imaging 2010; 28:418-26. [DOI: 10.1016/j.mri.2009.11.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2009] [Revised: 08/05/2009] [Accepted: 11/25/2009] [Indexed: 10/19/2022]
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Li C, Pan X, Ying K, Zhang Q, An J, Weng D, Qin W, Li K. An internal reference model-based PRF temperature mapping method with Cramer-Rao lower bound noise performance analysis. Magn Reson Med 2010; 62:1251-60. [PMID: 19780176 DOI: 10.1002/mrm.22121] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The conventional phase difference method for MR thermometry suffers from disturbances caused by the presence of lipid protons, motion-induced error, and field drift. A signal model is presented with multi-echo gradient echo (GRE) sequence using a fat signal as an internal reference to overcome these problems. The internal reference signal model is fit to the water and fat signals by the extended Prony algorithm and the Levenberg-Marquardt algorithm to estimate the chemical shifts between water and fat which contain temperature information. A noise analysis of the signal model was conducted using the Cramer-Rao lower bound to evaluate the noise performance of various algorithms, the effects of imaging parameters, and the influence of the water:fat signal ratio in a sample on the temperature estimate. Comparison of the calculated temperature map and thermocouple temperature measurements shows that the maximum temperature estimation error is 0.614 degrees C, with a standard deviation of 0.06 degrees C, confirming the feasibility of this model-based temperature mapping method. The influence of sample water:fat signal ratio on the accuracy of the temperature estimate is evaluated in a water-fat mixed phantom experiment with an optimal ratio of approximately 0.66:1.
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Affiliation(s)
- Cheng Li
- Engineering Physics, Tsinghua University, Beijing, People's Republic of China
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30
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Rempp H, Martirosian P, Boss A, Clasen S, Kickhefel A, Kraiger M, Schraml C, Claussen C, Pereira P, Schick F. MR temperature monitoring applying the proton resonance frequency method in liver and kidney at 0.2 and 1.5 T: segment-specific attainable precision and breathing influence. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2008; 21:333-43. [DOI: 10.1007/s10334-008-0139-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2008] [Revised: 07/18/2008] [Accepted: 08/07/2008] [Indexed: 12/13/2022]
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Abstract
Minimally invasive thermal therapy as local treatment of benign and malignant diseases has received increasing interest in recent years. Safety and efficacy of the treatment require accurate temperature measurement throughout the thermal procedure. Noninvasive temperature monitoring is feasible with magnetic resonance (MR) imaging based on temperature-sensitive MR parameters such as the proton resonance frequency (PRF), the diffusion coefficient (D), T1 and T2 relaxation times, magnetization transfer, the proton density, as well as temperature-sensitive contrast agents. In this article the principles of temperature measurements with these methods are reviewed and their usefulness for monitoring in vivo procedures is discussed. Whereas most measurements give a temperature change relative to a baseline condition, temperature-sensitive contrast agents and spectroscopic imaging can provide absolute temperature measurements. The excellent linearity and temperature dependence of the PRF and its near independence of tissue type have made PRF-based phase mapping methods the preferred choice for many in vivo applications. Accelerated MRI imaging techniques for real-time monitoring with the PRF method are discussed. Special attention is paid to acquisition and reconstruction methods for reducing temperature measurement artifacts introduced by tissue motion, which is often unavoidable during in vivo applications.
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Affiliation(s)
- Viola Rieke
- Department of Radiology, Stanford University, Stanford, CA 94305-5488, USA.
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Taylor BA, Hwang KP, Elliott AM, Shetty A, Hazle JD, Stafford RJ. Dynamic chemical shift imaging for image-guided thermal therapy: analysis of feasibility and potential. Med Phys 2008; 35:793-803. [PMID: 18383702 DOI: 10.1118/1.2831915] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
A fast chemical shift imaging (CSI) technique based on a multiple gradient-recalled acquisition using a small number of echoes with intentional aliasing of the reference lipid peak is studied to determine its feasibility for temperature monitoring. Simulations were implemented to find parameters where the lipid and water peaks can be measured using a Fourier-based peak fitting approach as well as using an innovative autoregressive moving average technique. A phantom consisting of 50% mayonnaise/50% lemon juice was calibrated to temperature and compared to literature values. A porcine kidney was treated ex vivo with an external laser and imaged with the CSI technique with comparisons to temperature readings from a fluoroptic monitoring system and complex phase difference (CPD) calculations. To demonstrate the technique in vivo, a Balb/c mouse with a CT26 xenograft in the subcutaneous lower back was treated using gold-coated, silica-core nanoshells heated with an 808 nm interstitial laser. Compared to standard CPD techniques using a two-dimensional fast spoiled gradient recalled echo, this technique maintains spatiotemporal resolution, has high signal-to-noise ratio and accuracy over a wide range of T2* tissue values, can separate water and lipid signals, and additionally can use the lipid peak, when present, as an internal reference.
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Affiliation(s)
- Brian A Taylor
- Department of Imaging Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA
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