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Scholey J, Nano T, Singhrao K, Mohammad O, Singer L, Larson PEZ, Descovich M. Linac- and CyberKnife-based MRI-only treatment planning of prostate SBRT using an optimized synthetic CT calibration curve. J Appl Clin Med Phys 2024:e14411. [PMID: 38837851 DOI: 10.1002/acm2.14411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Revised: 02/29/2024] [Accepted: 05/07/2024] [Indexed: 06/07/2024] Open
Abstract
PURPOSE CT Hounsfield Units (HUs) are converted to electron density using a calibration curve obtained from physical measurements of an electron density phantom. HU values assigned to an MRI-derived synthetic computed tomography (sCT) may present a different relationship with electron density compared to CT HU. Correct assignment of sCT HU values is critical for accurate dose calculation and delivery. The goals of this work were to develop a sCT calibration curve using patient data acquired on a clinically commissioned CT scanner and assess for CyberKnife- and volumetric modulated arc therapy (VMAT)-based MR-only treatment planning of prostate SBRT. METHODS Same-day CT and MRI simulation in the treatment position were performed on 10 patients treated with SBRT to the prostate. Dixon in-phase and out-of-phase MRIs were acquired on a 3T scanner using a 3D T1-weighted gradient-echo sequence to generate sCTs using a commercial sCT algorithm. CT and sCT datasets were co-registered and HU values compared using mean absolute error (MAE). An optimized HU-to-density calibration curve was created based on average HU values across an institutional patient database for each of the four sCT tissue types. Clinical CyberKnife and VMAT treatment plans were generated on each patient CT and recomputed onto corresponding sCTs. Dose distributions computed using CT and sCT were compared using gamma criteria and dose-volume-histograms. RESULTS For the optimized calibration curve, HU values were -96, 37, 204, and 1170 and relative electron densities were 0.95, 1.04, 1.1, and 1.7 for adipose, soft tissue, inner bone, and outer bone, respectively. The proposed sCT protocol produced total MAE of 94 ± 20HU. Gamma values mean ± std (min-max) were 98.9% ± 0.9% (97.1%-100%) and 97.7% ± 1.3% (95.3%-99.3%) for VMAT and CyberKnife plans, respectively. CONCLUSION MRI-derived sCT using the proposed approach shows excellent dosimetric agreement with conventional CT simulation, demonstrating the feasibility of MRI-derived sCT for prostate SBRT treatment planning.
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Affiliation(s)
- Jessica Scholey
- Department of Radiation Oncology, University of California San Francisco, San Francisco, California, USA
| | - Tomi Nano
- Department of Radiation Oncology, University of California San Francisco, San Francisco, California, USA
| | - Kamal Singhrao
- Department of Radiation Oncology, University of California San Francisco, San Francisco, California, USA
| | - Osama Mohammad
- Department of Radiation Oncology, University of California San Francisco, San Francisco, California, USA
| | - Lisa Singer
- Department of Radiation Oncology, University of California San Francisco, San Francisco, California, USA
| | - Peder Eric Zufall Larson
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, USA
| | - Martina Descovich
- Department of Radiation Oncology, University of California San Francisco, San Francisco, California, USA
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Baran E, Birczyński A, Dorożyński P, Kulinowski P. Spatially resolved polymer mobilization revisited - Three-dimensional, UltraShort Echo Time (3D UTE) magnetic resonance imaging of sodium alginate matrix tablets. J Colloid Interface Sci 2023; 649:626-634. [PMID: 37364462 DOI: 10.1016/j.jcis.2023.06.139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Revised: 05/24/2023] [Accepted: 06/19/2023] [Indexed: 06/28/2023]
Abstract
HYPOTHESIS Three-dimensional 1H UltraShort Echo Time magnetic resonance imaging (1H 3D UTE MRI) of the matrix tablet made of hydrophilic polymer hydrated in heavy water (D2O) will allow investigation of the hydration-induced spatiotemporal evolution of the material originally included in the matrix tablet during manufacturing (i.e., polymer chains and bound water). EXPERIMENTS The oblong-shaped sodium alginate matrix tablets were used to verify the hypothesis. The matrix was measured before and during hydration in D2O for up to 2 h using the 1H 3D UTE MRI. Five echo times (first at 20 μs) were used, resulting in five three-dimensional images (one image for each echo time). In chosen cross-sections, two parametric images, i.e., amplitude and T2* relaxation time maps, were calculated using "pixel-by-pixel" mono-exponential fitting. FINDINGS The regions of the alginate matrix with T2* shorter than 600 μs were analyzed before (air-dry matrix) and during hydration (parametric, spatiotemporal analysis). During the study, only hydrogen nuclei (protons) pre-existing in the air-dry sample (polymer and bound water) were monitored because the hydration medium (D2O) was not visible. As a result, it was found that morphological changes in regions having T2* shorter than 300 μs were the effect of fast initial water ingress into the core of the matrix and subsequent polymer mobilization (early hydration providing additional 5% w/w hydration medium content relating to air-dry matrix). In particular, evolving layers in T2* maps were detected, and a fracture network was formed shortly after the matrix immersion in D2O. The current study presented a coherent picture of polymer mobilization accompanied by local polymer density decrease. We concluded, that the T2* mapping using 3D UTE MRI can effectively be applied as a polymer mobilization marker.
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Affiliation(s)
- Ewelina Baran
- Institute of Technology, The Pedagogical University of Kraków, Podchorążych 2, 30-084 Kraków, Poland.
| | - Artur Birczyński
- Institute of Technology, The Pedagogical University of Kraków, Podchorążych 2, 30-084 Kraków, Poland.
| | - Przemysław Dorożyński
- Department of Drug Technology and Pharmaceutical Biotechnology, Medical University of Warsaw, Banacha 1, 02-097 Warszawa, Poland.
| | - Piotr Kulinowski
- Institute of Technology, The Pedagogical University of Kraków, Podchorążych 2, 30-084 Kraków, Poland.
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Motovilova E, Ching T, Vincent J, Shin J, Tan ET, Taracila V, Robb F, Hashimoto M, Sneag DB, Winkler SA. Dual-Channel Stretchable, Self-Tuning, Liquid Metal Coils and Their Fabrication Techniques. SENSORS (BASEL, SWITZERLAND) 2023; 23:7588. [PMID: 37688046 PMCID: PMC10490642 DOI: 10.3390/s23177588] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Revised: 08/28/2023] [Accepted: 08/29/2023] [Indexed: 09/10/2023]
Abstract
Flexible and stretchable radiofrequency coils for magnetic resonance imaging represent an emerging and rapidly growing field. The main advantage of such coil designs is their conformal nature, enabling a closer anatomical fit, patient comfort, and freedom of movement. Previously, we demonstrated a proof-of-concept single element stretchable coil design with a self-tuning smart geometry. In this work, we evaluate the feasibility of scaling this coil concept to a multi-element coil array and the associated engineering and manufacturing challenges. To this goal, we study a dual-channel coil array using full-wave simulations, bench testing, in vitro, and in vivo imaging in a 3 T scanner. We use three fabrication techniques to manufacture dual-channel receive coil arrays: (1) single-layer casting, (2) double-layer casting, and (3) direct-ink-writing. All fabricated arrays perform equally well on the bench and produce similar sensitivity maps. The direct-ink-writing method is found to be the most advantageous fabrication technique for fabrication speed, accuracy, repeatability, and total coil array thickness (0.6 mm). Bench tests show excellent frequency stability of 128 ± 0.6 MHz (0% to 30% stretch). Compared to a commercial knee coil array, the stretchable coil array is more conformal to anatomy and provides 50% improved signal-to-noise ratio in the region of interest.
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Affiliation(s)
- Elizaveta Motovilova
- Department of Radiology, Weill Cornell Medicine, New York, NY 10065, USA
- Department of Radiology and Imaging, Hospital for Special Surgery, New York, NY 10021, USA
| | - Terry Ching
- Pillar of Engineering Product Development, Singapore University of Technology and Design, Singapore 487372, Singapore
- Digital Manufacturing and Design (DManD) Centre, Singapore University of Technology and Design, Singapore 487372, Singapore
- Department of Biomedical Engineering, National University of Singapore, Singapore 117583, Singapore
| | | | - James Shin
- Department of Radiology, Weill Cornell Medicine, New York, NY 10065, USA
| | - Ek Tsoon Tan
- Department of Radiology and Imaging, Hospital for Special Surgery, New York, NY 10021, USA
| | | | | | - Michinao Hashimoto
- Pillar of Engineering Product Development, Singapore University of Technology and Design, Singapore 487372, Singapore
- Digital Manufacturing and Design (DManD) Centre, Singapore University of Technology and Design, Singapore 487372, Singapore
| | - Darryl B. Sneag
- Department of Radiology and Imaging, Hospital for Special Surgery, New York, NY 10021, USA
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Motovilova E, Aronowitz E, Vincent J, Shin J, Tan ET, Robb F, Taracila V, Sneag DB, Dyke JP, Winkler SA. Silicone-based materials with tailored MR relaxation characteristics for use in reduced coil visibility and in tissue-mimicking phantom design. Med Phys 2023. [PMID: 36737839 DOI: 10.1002/mp.16255] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Revised: 12/24/2022] [Accepted: 01/15/2023] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND The development of materials with tailored signal intensity in MR imaging is critically important both for the reduction of signal from non-tissue hardware, as well as for the construction of tissue-mimicking phantoms. Silicone-based phantoms are becoming more popular due to their structural stability, stretchability, longer shelf life, and ease of handling, as well as for their application in dynamic imaging of physiology in motion. Moreover, silicone can be also used for the design of stretchable receive radio-frequency (RF) coils. PURPOSE Fabrication of materials with tailored signal intensity for MRI requires knowledge of precise T1 and T2 relaxation times of the materials used. In order to increase the range of possible relaxation times, silicone materials can be doped with gadolinium (Gd). In this work, we aim to systematically evaluate relaxation properties of Gd-doped silicone material at a broad range of Gd concentrations and at three clinically relevant magnetic field strengths (1.5 T, 3 T, and 7 T). We apply the findings for rendering silicone substrates of stretchable receive RF coils less visible in MRI. Moreover, we demonstrate early stage proof-of-concept applicability in tissue-mimicking phantom development. MATERIALS AND METHODS Ten samples of pure and Gd-doped Ecoflex silicone polymer samples were prepared with various Gd volume ratios ranging from 1:5000 to 1:10, and studied using 1.5 T and 3 T clinical and 7 T preclinical scanners. T1 and T2 relaxation times of each sample were derived by fitting the data to Bloch signal intensity equations. A receive coil made from Gd-doped Ecoflex silicone polymer was fabricated and evaluated in vitro at 3 T. RESULTS With the addition of a Gd-based contrast agent, it is possible to significantly change T2 relaxation times of Ecoflex silicone polymer (from 213 ms to 20 ms at 1.5 T; from 135 ms to 17 ms at 3 T; and from 111.4 ms to 17.2 ms at 7 T). T1 relaxation time is less affected by the introduction of the contrast agent (changes from 608 ms to 579 ms; from 802.5 ms to 713 ms at 3 T; from 1276 ms to 979 ms at 7 T). First results also indicate that liver, pancreas, and white matter tissues can potentially be closely mimicked using this phantom preparation technique. Gd-doping reduces the appearance of the silicone-based coil substrate during the MR scan by up to 81%. CONCLUSIONS Gd-based contrast agents can be effectively used to create Ecoflex silicone polymer-based phantoms with tailored T2 relaxation properties. The relative low cost, ease of preparation, stretchability, mechanical stability, and long shelf life of Ecoflex silicone polymer all make it a good candidate for "MR invisible" coil development and bears promise for tissue-mimicking phantom development applicability.
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Affiliation(s)
- Elizaveta Motovilova
- Department of Radiology, Weill Cornell Medicine, New York, New York, USA.,Department of Radiology, Hospital for Special Surgery, New York, New York, USA
| | - Eric Aronowitz
- Department of Radiology, Weill Cornell Medicine, New York, New York, USA
| | | | - James Shin
- Department of Radiology, Weill Cornell Medicine, New York, New York, USA
| | - Ek Tsoon Tan
- Department of Radiology, Hospital for Special Surgery, New York, New York, USA
| | | | | | - Darryl B Sneag
- Department of Radiology, Hospital for Special Surgery, New York, New York, USA
| | - Jonathan P Dyke
- Department of Radiology, Weill Cornell Medicine, New York, New York, USA
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Scholey JE, Rajagopal A, Vasquez EG, Sudhyadhom A, Larson PEZ. Generation of synthetic megavoltage CT for MRI-only radiotherapy treatment planning using a 3D deep convolutional neural network. Med Phys 2022; 49:6622-6634. [PMID: 35870154 PMCID: PMC9588542 DOI: 10.1002/mp.15876] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Revised: 06/10/2022] [Accepted: 07/01/2022] [Indexed: 11/07/2022] Open
Abstract
BACKGROUND Megavoltage computed tomography (MVCT) has been implemented on many radiotherapy treatment machines for on-board anatomical visualization, localization, and adaptive dose calculation. Implementing an MR-only workflow by synthesizing MVCT from magnetic resonance imaging (MRI) would offer numerous advantages for treatment planning and online adaptation. PURPOSE In this work, we sought to synthesize MVCT (sMVCT) datasets from MRI using deep learning to demonstrate the feasibility of MRI-MVCT only treatment planning. METHODS MVCTs and T1-weighted MRIs for 120 patients treated for head-and-neck cancer were retrospectively acquired and co-registered. A deep neural network based on a fully-convolutional 3D U-Net architecture was implemented to map MRI intensity to MVCT HU. Input to the model were volumetric patches generated from paired MRI and MVCT datasets. The U-Net was initialized with random parameters and trained on a mean absolute error (MAE) objective function. Model accuracy was evaluated on 18 withheld test exams. sMVCTs were compared to respective MVCTs. Intensity-modulated volumetric radiotherapy (IMRT) plans were generated on MVCTs of four different disease sites and compared to plans calculated onto corresponding sMVCTs using the gamma metric and dose-volume-histograms (DVHs). RESULTS MAE values between sMVCT and MVCT datasets were 93.3 ± 27.5, 78.2 ± 27.5, and 138.0 ± 43.4 HU for whole body, soft tissue, and bone volumes, respectively. Overall, there was good agreement between sMVCT and MVCT, with bone and air posing the greatest challenges. The retrospective dataset introduced additional deviations due to sinus filling or tumor growth/shrinkage between scans, differences in external contours due to variability in patient positioning, or when immobilization devices were absent from diagnostic MRIs. Dose distributions of IMRT plans evaluated for four test cases showed close agreement between sMVCT and MVCT images when evaluated using DVHs and gamma dose metrics, which averaged to 98.9 ± 1.0% and 96.8 ± 2.6% analyzed at 3%/3 mm and 2%/2 mm, respectively. CONCLUSIONS MVCT datasets can be generated from T1-weighted MRI using a 3D deep convolutional neural network with dose calculation on a sample sMVCT in close agreement with the MVCT. These results demonstrate the feasibility of using MRI-derived sMVCT in an MR-only treatment planning workflow.
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Affiliation(s)
- Jessica E Scholey
- Department of Radiation Oncology, The University of California, San Francisco; San Francisco, CA 94158 USA
| | - Abhejit Rajagopal
- Department of Radiology and Biomedical Imaging, The University of California, San Francisco; San Francisco, CA 94158 USA
| | - Elena Grace Vasquez
- Department of Physics, The University of California, Berkeley; Berkeley, CA 94720 USA
| | - Atchar Sudhyadhom
- Department of Radiation Oncology, Brigham & Women’s Hospital/Dana-Farber Cancer Institute/Harvard Medical School, Boston, MA; 02115 USA
| | - Peder Eric Zufall Larson
- Department of Radiology and Biomedical Imaging, The University of California, San Francisco; San Francisco, CA 94158 USA
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Kaza E, Lee CY, King MT, Dyer MA, Cormack RA, Buzurovic I. First pointwise encoding time reduction with radial acquisition (PETRA) implementation for catheter detection in interstitial high-dose-rate (HDR) brachytherapy. Brachytherapy 2022; 21:501-510. [PMID: 35337748 DOI: 10.1016/j.brachy.2022.01.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2021] [Revised: 12/15/2021] [Accepted: 01/15/2022] [Indexed: 11/02/2022]
Abstract
PURPOSE A pointwise encoding time reduction with radial acquisition (PETRA) sequence was optimized to detect empty catheters in interstitial (HDR) brachytherapy with clinically acceptable spatial accuracy for the first time. Image quality and catheter detectability were assessed in phantoms, and the feasibility of PETRA's clinical implementation was assessed on a gynecological cancer patient. METHODS AND RESULTS Empty catheters embedded in a gelatin phantom displayed positive signal on PETRA and more accurate cross-sections than on clinically employed T2-weighted sequences, differing by 0.4 mm on average from their nominal 2 mm diameter. PETRA presented minimal susceptibility differences and a symmetric metal artifact, contrary to the clinical sequences. The PETRA-CT catheter tip position differences assessed by a treatment planning system (TPS) were < 1 mm. PETRA also detected an interstitial template with empty catheters penetrating a poultry phantom and fused very well with CT. Interstitial catheter positional difference between PETRA and CT images was < 1 mm on average, increasing with distance from isocenter. All interstitial catheters and the employed interstitial template were detected on PETRA images of an endometrial adenocarcinoma patient. Empty needles were traceable using a TPS, with higher spatial resolution and more favorable contrast than on T2-weighted images used for contouring. A treatment plan could be produced by combining information from PETRA for catheter detection and from T2-weighted images for tumor and organs delineation. CONCLUSIONS PETRA detected successfully and accurately interstitial catheters in phantoms. Its first clinical implementation shows a potential for MR-only treatment planning in interstitial HDR brachytherapy.
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Affiliation(s)
- Evangelia Kaza
- Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA.
| | - Casey Y Lee
- Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA
| | - Martin T King
- Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA
| | - Michael A Dyer
- Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA
| | - Robert A Cormack
- Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA
| | - Ivan Buzurovic
- Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA
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Agergaard AS, Malmgaard-Clausen NM, Svensson RB, Nybing JD, Boesen M, Kjaer M, Magnusson SP, Hansen P. UTE T2* mapping of tendinopathic patellar tendons: an MRI reproducibility study. Acta Radiol 2021; 62:215-224. [PMID: 32340475 DOI: 10.1177/0284185120918807] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND There is currently a lack of imaging modalities that can be used as a sensitive measure in tendinopathy. Recent findings suggest the applicability of ultra-short echo time (UTE) magnetic resonance imaging (MRI) T2* mapping in tendons, but the reproducibility remains unknown. PURPOSE To evaluate test-retest reproducibility of UTE MRI T2* mapping of tendinopathic patellar tendons and to evaluate the intra- and inter-observer reproducibility of the measurement. MATERIAL AND METHODS Fifteen patients with chronic patellar tendinopathy were evaluated with UTE MRI twice in a 3.0-T scanner on the same day. Manual segmentation of the patellar tendon was performed by two blinded investigators and automated T2*map reconstruction was performed in custom-made software. RESULTS There was a significant and numerically small difference in test-retest T2* values (T2*meandiff = 0.06 ± 0.07 ms ≈ 3.7%; P = 0.006) with an ICC = 0.91 (95% confidence interval [CI] 0.58-0.98; typical error of 3.0%). The intra- and inter-observer reproducibility showed no significant bias (P = 0.493 and P = 0.052), and generally substantial reproducibility was demonstrated for T2* (intra-observer ICC = 0.99; 95% CI 0.98-1.00 and inter-observer ICC = 0.99; 95% CI 0.96-1.00, and typical error 1.3% and 1.3%, respectively). CONCLUSION These data demonstrate a small bias between repeated measurements for UTE T2*, but with a very low associated mean difference (3.7%) between the two tests. The high ICC values and low typical error % demonstrate reproducibility of repeated T2*-mapping sessions. Further, the method showed substantial intra- and inter-observer reproducibility for T2* values proving feasibility for use of UTE T2* mapping in research and clinical practice.
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Affiliation(s)
- Anne-Sofie Agergaard
- Institute of Sports Medicine Copenhagen, Department of Orthopedic Surgery, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark
- Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
- Department of Physical and Occupational Therapy, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark
| | - Nikolaj M Malmgaard-Clausen
- Institute of Sports Medicine Copenhagen, Department of Orthopedic Surgery, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark
- Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Rene B Svensson
- Institute of Sports Medicine Copenhagen, Department of Orthopedic Surgery, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark
- Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Janus D Nybing
- Department of Radiology, Copenhagen University Hospital, Bispebjerg and Frederiksberg, Copenhagen, Denmark
| | - Mikael Boesen
- Department of Radiology, Copenhagen University Hospital, Bispebjerg and Frederiksberg, Copenhagen, Denmark
- Parker Institute, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark
| | - Michael Kjaer
- Institute of Sports Medicine Copenhagen, Department of Orthopedic Surgery, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark
- Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
| | - S. Peter Magnusson
- Institute of Sports Medicine Copenhagen, Department of Orthopedic Surgery, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark
- Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Philip Hansen
- Department of Radiology, Copenhagen University Hospital, Bispebjerg and Frederiksberg, Copenhagen, Denmark
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Scholey JE, Chandramohan D, Naren T, Liu W, Larson PEZ, Sudhyadhom A. Technical Note: A methodology for improved accuracy in stopping power estimation using MRI and CT. Med Phys 2020; 48:342-353. [PMID: 33107997 DOI: 10.1002/mp.14555] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 09/21/2020] [Accepted: 10/19/2020] [Indexed: 01/13/2023] Open
Abstract
PURPOSE Proton therapy is becoming an increasingly popular cancer treatment modality due to the proton's physical advantage in that it deposits the majority of its energy at the distal end of its track where the tumor is located. The proton range in a material is determined from the stopping power ratio (SPR) of the material. However, SPR is typically estimated based on a computed tomography (CT) scan which can lead to range estimation errors due to the difference in x-ray and proton interactions in matter, which can preclude the ability to utilize protons to their full potential. Applications of magnetic resonance imaging (MRI) in radiotherapy have increased over the past decade and using MRI to calculate SPR directly could provide numerous advantages. The purpose of this study was to develop a practical implementation of a novel multimodal imaging method for estimating SPR and compare the results of this method to physical measurements in which values were computed directly using tissue substitute materials fabricated to mimic skin, muscle, adipose, and spongiosa bone. METHODS For both the multimodal imaging method and physical measurements, SPR was calculated using the Bethe-Bloch equation from values of relative electron density and mean ionization potential determined for each tissue. Parameters used to estimate SPR using the multimodal imaging method were extracted from Dixon water-only and (1 H) proton density-weighted zero echo time MRI sequences and CT, with both kVCT and MVCT used separately to evaluate the performance of each. For comparison, SPR was also computed from kVCT using the stoichiometric method, the current clinical standard. RESULTS Results showed that our multimodal imaging approach using MRI with either kVCT or MVCT was in close agreement to SPR calculated from physical measurements for the four tissue substitutes evaluated. Using MRI and MVCT, SPR values estimated using our method were within 1% of physical measurements and were more accurate than the stoichiometric method for the tissue types studied. CONCLUSIONS We have demonstrated the methodology for improved estimation of SPR using the proposed multimodal imaging framework.
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Affiliation(s)
- Jessica E Scholey
- Department of Radiation Oncology, The University of California, San Francisco, CA, USA
| | - Dharshan Chandramohan
- Department of Radiation Oncology, The University of California, San Francisco, CA, USA
| | - Tarun Naren
- Department of Radiation Oncology, The University of California, San Francisco, CA, USA
| | - William Liu
- Department of Radiation Oncology, The University of California, San Francisco, CA, USA
| | - Peder Eric Zufall Larson
- Department of Radiology and Biomedical Imaging, The University of California, San Francisco, CA, USA
| | - Atchar Sudhyadhom
- Department of Radiation Oncology, The University of California, San Francisco, CA, USA
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Tesfai AS, Fischer J, Özen AC, Eppenberger P, Oehrstroem L, Rühli F, Ludwig U, Bock M. Multi-parameter Analytical Method for B1 and SNR Analysis (MAMBA): An open source RF coil design tool. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 319:106825. [PMID: 32947127 DOI: 10.1016/j.jmr.2020.106825] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Revised: 08/05/2020] [Accepted: 09/03/2020] [Indexed: 06/11/2023]
Abstract
In Magnetic Resonance Imaging (MRI), radio frequency (RF) coils of different forms and shapes are used to maximize signal-to-noise ratio (SNR). RF coils are designed for clinical applications and have dimensions comparable with the target body part to be imaged, and they perform best when loaded by human tissue majority of which have conductivity values higher than 0.5 S/m. However, they are not properly tuned and matched for samples having low conductivity such as solid samples with low water content. Moreover, for samples with low filling factor and low conductivity, the noise in MRI is dominated by RF coil losses. In this case, RF coil design can be optimized to improve image SNR. Here, a new software tool (Multi-parameter Analytical Method for B1 and SNR Analysis) MAMBA is presented to design and compare volume coils of birdcage, solenoid, and loop-gap design for these samples. The input parameters of the tool are the sample properties, the coil design and the hardware properties, of which a relative SNR is determined. For that, a figure of merit is calculated from the coil sensitivity, applied resonant frequency and the resistive losses of sample, coil and capacitive components. The tool was tested in an ancient Egyptian mummy head which represents an extreme case of MRI with short T2*. Two optimized birdcage coils were designed using MAMBA, constructed and compared to a commercial transmit receive head coil. Calculated relative SNR values are in good agreement with the measurements.
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Affiliation(s)
- Agazi Samuel Tesfai
- Dept. of Radiology, Medical Physics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
| | - Johannes Fischer
- Dept. of Radiology, Medical Physics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Ali Caglar Özen
- Dept. of Radiology, Medical Physics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany; German Consortium for Translational Cancer Research Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Patrick Eppenberger
- Institute of Evolutionary Medicine, Faculty of Medicine, University of Zurich, Switzerland
| | - Lena Oehrstroem
- Institute of Evolutionary Medicine, Faculty of Medicine, University of Zurich, Switzerland
| | - Frank Rühli
- Institute of Evolutionary Medicine, Faculty of Medicine, University of Zurich, Switzerland
| | - Ute Ludwig
- Dept. of Radiology, Medical Physics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Michael Bock
- Dept. of Radiology, Medical Physics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
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Ultrashort Time to Echo Magnetic Resonance Evaluation of Calcium Pyrophosphate Crystal Deposition in Human Menisci. Invest Radiol 2020; 54:349-355. [PMID: 30688685 DOI: 10.1097/rli.0000000000000547] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
OBJECTIVES In human menisci, we aimed to investigate whether calcium pyrophosphate crystal deposition (CPPD) affects biomechanical and quantitative MR properties, and their zonal distribution. MATERIALS AND METHODS From 9 cadaveric knees, sectioned triangular meniscus pieces were harvested. Samples were classified into "normal" or "CPPD" groups based upon visual inspection. Micro computed tomography scan verified CPPD. Using magnetic resonance imaging, ultrashort echo time (UTE) T2* and spin echo (SE) T2, quantitative values in 3 zones (red, red-white, and white) were determined. Using biomechanical test, indentation forces in the same zones were determined. Effects of CPPD and meniscal zone on indentation force and quantitative MR values were compared. RESULTS On UTE MRI scans, CPPD-affected menisci exhibited punctate dark regions, found mostly (92%) in avascular white and red-white zones. Indentation forces were significantly higher for CPPD samples in the red-white (all P < 0.02) and white (all P < 0.004) zones but not in the vascular red zone (all P > 0.2). Similarly, UTE T2* red zone values were similar between both groups (~6.6 milliseconds, P = 0.8), whereas in the red-white and white zones, CPPD samples had significantly lower values (~5.1 milliseconds, P = 0.005 to 0.007). In contrast, SE T2 values showed no difference with CPPD (P = 0.12 to 0.16). UTE T2*, but not SE T2, correlated significantly with indentation force (R = -0.29, P = 0.009). CONCLUSIONS Dark CPP deposits were detectable on UTE images featuring high signal intensity from surrounding meniscal tissue. Preliminary results indicate that CPP deposits were almost exclusively found in the avascular zones. Compared with normal, CPPD menisci featured higher indentation stiffness and lower UTE T2* values in the affected zones.
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Sudhyadhom A. Determination of mean ionization potential using magnetic resonance imaging for the reduction of proton beam range uncertainties: theory and application. ACTA ACUST UNITED AC 2017; 62:8521-8535. [DOI: 10.1088/1361-6560/aa8d9e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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Butler R, Gilbert G, Descoteaux M, Bernier PM, Whittingstall K. Application of polymer sensitive MRI sequence to localization of EEG electrodes. J Neurosci Methods 2016; 278:36-45. [PMID: 28017737 DOI: 10.1016/j.jneumeth.2016.12.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2016] [Revised: 11/05/2016] [Accepted: 12/20/2016] [Indexed: 11/17/2022]
Abstract
BACKGROUND The growing popularity of simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) opens up the possibility of imaging EEG electrodes while the subject is in the scanner. Such information could be useful for improving the fusion of EEG-fMRI datasets. NEW METHOD Here, we report for the first time how an ultra-short echo time (UTE) MR sequence can image the materials of an MR-compatible EEG cap, finding that electrodes and some parts of the wiring are visible in a high resolution UTE. Using these images, we developed a segmentation procedure to obtain electrode coordinates based on voxel intensity from the raw UTE, using hand labeled coordinates as the starting point. RESULTS We were able to visualize and segment 95% of EEG electrodes using a short (3.5min) UTE sequence. We provide scripts and template images so this approach can now be easily implemented to obtain precise, subject-specific EEG electrode positions while adding minimal acquisition time to the simultaneous EEG-fMRI protocol. COMPARISON WITH EXISTING METHOD(S) T1 gel artifacts are not robust enough to localize all electrodes across subjects, the polymers composing Brainvision cap electrodes are not visible on a T1, and adding T1 visible materials to the EEG cap is not always possible. We therefore consider our method superior to existing methods for obtaining electrode positions in the scanner, as it is hardware free and should work on a wide range of materials (caps). CONCLUSIONS EEG electrode positions are obtained with high precision and no additional hardware.
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Affiliation(s)
- Russell Butler
- Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Health Science, Université de Sherbrooke, Sherbrooke, Québec, Canada; Centre d'imagerie moléculaire de Sherbrooke (CIMS), Centre de Recherche CHUS, Canada.
| | - Guillaume Gilbert
- MR Clinical Science, Philips Healthcare Canada, 281 H illmount Road, Markham, Ontario, L6C 2S3, Canada
| | - Maxime Descoteaux
- Sherbrooke Connectivity Imaging Lab (SCIL), Computer Science department, Science Faculty, Université de Sherbrooke, Canada; Centre d'imagerie moléculaire de Sherbrooke (CIMS), Centre de Recherche CHUS, Canada
| | | | - Kevin Whittingstall
- Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Health Science, Université de Sherbrooke, Sherbrooke, Québec, Canada; Department of Diagnostic Radiology, Faculty of Medicine and Health Science, Université de Sherbrooke, 12e Avenue Nord, Sherbrooke, QC, J1H 5N4, Canada; Centre d'imagerie moléculaire de Sherbrooke (CIMS), Centre de Recherche CHUS, Canada
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Eldib M, Bini J, Faul DD, Oesingmann N, Tsoumpas C, Fayad ZA. Attenuation Correction for Magnetic Resonance Coils in Combined PET/MR Imaging: A Review. PET Clin 2016; 11:151-60. [PMID: 26952728 PMCID: PMC4785842 DOI: 10.1016/j.cpet.2015.10.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
With the introduction of clinical PET/magnetic resonance (MR) systems, novel attenuation correction methods are needed, as there are no direct MR methods to measure the attenuation of the objects in the field of view (FOV). A unique challenge for PET/MR attenuation correction is that coils for MR data acquisition are located in the FOV of the PET camera and could induce significant quantitative errors. In this review, current methods and techniques to correct for the attenuation of a variety of coils are summarized and evaluated.
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Affiliation(s)
- Mootaz Eldib
- Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, NY 10029, USA; Department of Biomedical Engineering, The City College of New York, 160 Convent Avenue, New York, NY 10031, USA
| | - Jason Bini
- Department of Diagnostic Radiology, PET Center, Yale School of Medicine, Yale University, 801 Howard Avenue, New Haven, CT 06520, USA
| | - David D Faul
- Siemens Healthcare, 527 Madison Avenue, New York, NY 10022, USA
| | | | - Charalampos Tsoumpas
- Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, NY 10029, USA; Division of Biomedical Imaging, Faculty of Medicine and Health, University of Leeds, 8.001a Worsley Building, Clarendon Way, Leeds LS2 9JT, UK
| | - Zahi A Fayad
- Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, NY 10029, USA; Department of Radiology, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, NY 10029, USA; Department of Cardiology, Zena and Michael A. Weiner Cardiovascular Institute, Marie-Josée and Henry R. Kravis Cardiovascular Health Center, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, NY 10029, USA.
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Ultrashort echo time and zero echo time MRI at 7T. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2015; 29:359-70. [PMID: 26702940 DOI: 10.1007/s10334-015-0509-0] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Revised: 10/23/2015] [Accepted: 11/06/2015] [Indexed: 10/22/2022]
Abstract
OBJECTIVE Zero echo time (ZTE) and ultrashort echo time (UTE) pulse sequences for MRI offer unique advantages of being able to detect signal from rapidly decaying short-T2 tissue components. In this paper, we applied 3D ZTE and UTE pulse sequences at 7T to assess differences between these methods. MATERIALS AND METHODS We matched the ZTE and UTE pulse sequences closely in terms of readout trajectories and image contrast. Our ZTE used the water- and fat-suppressed solid-state proton projection imaging method to fill the center of k-space. Images from healthy volunteers obtained at 7T were compared qualitatively, as well as with SNR and CNR measurements for various ultrashort, short, and long-T2 tissues. RESULTS We measured nearly identical contrast-to-noise and signal-to-noise ratios (CNR/SNR) in similar scan times between the two approaches for ultrashort, short, and long-T2 components in the brain, knee and ankle. In our protocol, we observed gradient fidelity artifacts in UTE, and our chosen flip angle and readout also resulted in shading artifacts in ZTE due to inadvertent spatial selectivity. These can be corrected by advanced reconstruction methods or with different chosen protocol parameters. CONCLUSION The applied ZTE and UTE pulse sequences achieved similar contrast and SNR efficiency for volumetric imaging of ultrashort-T2 components. Key differences include that ZTE is limited to volumetric imaging, but has substantially reduced acoustic noise levels during the scan. Meanwhile, UTE has higher acoustic noise levels and greater sensitivity to gradient fidelity, but offers more flexibility in image contrast and volume selection.
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Grosse U, Syha R, Gatidis S, Grözinger G, Martirosian P, Partovi S, Nikolaou K, Robbin MR, Schick F, Springer F. MR-basedin vivofollow-up study of Achilles tendon volume and hydration state after ankle-loading activity. Scand J Med Sci Sports 2015; 26:1200-8. [DOI: 10.1111/sms.12550] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/10/2015] [Indexed: 12/01/2022]
Affiliation(s)
- U. Grosse
- Department of Diagnostic and Interventional Radiology; University Hospital Tübingen; Tübingen Germany
- Department of Radiology; University Hospital Case Medical Center; Case Western Reserve University; Cleveland Ohio USA
| | - R. Syha
- Department of Diagnostic and Interventional Radiology; University Hospital Tübingen; Tübingen Germany
| | - S. Gatidis
- Department of Diagnostic and Interventional Radiology; University Hospital Tübingen; Tübingen Germany
| | - G. Grözinger
- Department of Diagnostic and Interventional Radiology; University Hospital Tübingen; Tübingen Germany
| | - P. Martirosian
- Section on Experimental Radiology; Department of Diagnostic and Interventional Radiology; University Hospital Tübingen; Tübingen Germany
| | - S. Partovi
- Department of Radiology; University Hospital Case Medical Center; Case Western Reserve University; Cleveland Ohio USA
| | - K. Nikolaou
- Department of Diagnostic and Interventional Radiology; University Hospital Tübingen; Tübingen Germany
| | - M. R. Robbin
- Department of Radiology; University Hospital Case Medical Center; Case Western Reserve University; Cleveland Ohio USA
| | - F. Schick
- Section on Experimental Radiology; Department of Diagnostic and Interventional Radiology; University Hospital Tübingen; Tübingen Germany
| | - F. Springer
- Department of Diagnostic and Interventional Radiology; University Hospital Tübingen; Tübingen Germany
- Musculoskeletal Centre X-Ray Department; Chapel Allerton Hospital; Leeds UK
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Eldib M, Bini J, Robson PM, Calcagno C, Faul DD, Tsoumpas C, Fayad ZA. Markerless attenuation correction for carotid MRI surface receiver coils in combined PET/MR imaging. Phys Med Biol 2015; 60:4705-17. [PMID: 26020273 DOI: 10.1088/0031-9155/60/12/4705] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The purpose of the study was to evaluate the effect of attenuation of MR coils on quantitative carotid PET/MR exams. Additionally, an automated attenuation correction method for flexible carotid MR coils was developed and evaluated. The attenuation of the carotid coil was measured by imaging a uniform water phantom injected with 37 MBq of 18F-FDG in a combined PET/MR scanner for 24 min with and without the coil. In the same session, an ultra-short echo time (UTE) image of the coil on top of the phantom was acquired. Using a combination of rigid and non-rigid registration, a CT-based attenuation map was registered to the UTE image of the coil for attenuation and scatter correction. After phantom validation, the effect of the carotid coil attenuation and the attenuation correction method were evaluated in five subjects. Phantom studies indicated that the overall loss of PET counts due to the coil was 6.3% with local region-of-interest (ROI) errors reaching up to 18.8%. Our registration method to correct for attenuation from the coil decreased the global error and local error (ROI) to 0.8% and 3.8%, respectively. The proposed registration method accurately captured the location and shape of the coil with a maximum spatial error of 2.6 mm. Quantitative analysis in human studies correlated with the phantom findings, but was dependent on the size of the ROI used in the analysis. MR coils result in significant error in PET quantification and thus attenuation correction is needed. The proposed strategy provides an operator-free method for attenuation and scatter correction for a flexible MRI carotid surface coil for routine clinical use.
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Affiliation(s)
- Mootaz Eldib
- Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA. Department of Biomedical Engineering, The City College of New York, New York, NY 10031, USA
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Abstract
OBJECTIVES Shrinkage and deformation of mesh implants used for hernia treatment can be the cause of long-term complications. The purpose of this study was to quantify noninvasively time-dependent mesh shrinkage, migration, and configuration changes in patients who were surgically treated for inguinal hernia using magnetic resonance imaging (MRI)-visible mesh implants. MATERIALS AND METHODS In an agarose phantom, meshes in different shrinkage and folding conditions were used to validate the quantification process. Seven patients who were surgically (3 bilaterally) treated for inguinal hernia using iron-loaded mesh implants were prospectively examined using MRI. Gradient echo sequences in sagittal and transverse orientations were performed on day 1 after surgery and at day 90. The mesh-induced signal voids were semiautomatically segmented and a polygonal surface model was generated. A comparison of area and centroid position was performed between the 2 calculated surfaces (day 1 vs day 90). RESULTS The phantom study revealed a maximum deviation of 3.6% between the MRI-based quantification and the actual mesh size. All 10 implants were successfully reconstructed. The mean (SD) observed mesh shrinkage 90 days after surgery was 20.9% (7.1%). The mean (SD) centroid movement was 1.17 (0.47) cm. Topographic analysis revealed mean (SD) local configuration changes of 0.23 (0.03) cm. CONCLUSIONS In this study, significant mesh shrinkage (20.9%) but marginal changes in local mesh configuration occurred within 90 days after mesh implantation. Centroid shift of the mesh implant can be traced back to different patient positioning and abdominal distension. The developed algorithm facilitates noninvasive assessment of key figures regarding MRI-visible meshes. Consequently, it might help to improve mesh technology as well as surgical skills.
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Wurnig MC, Calcagni M, Kenkel D, Vich M, Weiger M, Andreisek G, Wehrli FW, Boss A. Characterization of trabecular bone density with ultra-short echo-time MRI at 1.5, 3.0 and 7.0 T--comparison with micro-computed tomography. NMR IN BIOMEDICINE 2014; 27:1159-66. [PMID: 25088271 PMCID: PMC5730971 DOI: 10.1002/nbm.3169] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Revised: 05/30/2014] [Accepted: 06/23/2014] [Indexed: 05/16/2023]
Abstract
The goal of this study was to test the potential of ultra-short echo-time (UTE) MRI at 1.5, 3.0 and 7.0 T for depiction of trabecular bone structure (of the wrist bones), to evaluate whether T2* relaxation times of bone water and parametric maps of T2* of trabecular bone could be obtained at all three field strengths, and to compare the T2* relaxation times with structural parameters obtained from micro-computed tomography (micro-CT) as a reference standard. Ex vivo carpal bones of six wrists were excised en bloc and underwent MRI at 1.5, 3.0 and 7.0 T in a whole-body MR imager using the head coil. A three-dimensional radial fat-suppressed UTE sequence was applied with subsequent acquisitions, with six different echo times TE of 150, 300, 600, 1200, 3500 and 7000 µs. The T2* relaxation time and pixel-wise computed T2* parametric maps were compared with a micro-computed-tomography reference standard providing trabecular bone structural parameters including porosity (defined as the bone-free fraction within a region of interest), trabecular thickness, trabecular separation, trabecular number and fractal dimension (Dk). T2* relaxation curves and parametric maps could be computed from datasets acquired at all field strengths. Mean T2* relaxation times of trabecular bone were 4580 ± 1040 µs at 1.5 T, 2420 ± 560 µs at 3.0 T and 1220 ± 300 µs at 7.0 T, when averaged over all carpal bones. A positive correlation of T2* with trabecular bone porosity and trabecular separation, and a negative correlation of T2* relaxation time with trabecular thickness, trabecular number and fractal dimension, was detected (p < 0.01 for all field strengths and micro-CT parameters). We conclude that UTE MRI may be useful to characterize the structure of trabecular bone, comparable to micro-CT.
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Affiliation(s)
- Moritz C. Wurnig
- Department of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland
- Correspondence to: M. C. Wurnig, Department of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland.
| | - Maurizio Calcagni
- Division of Plastic and Reconstructive Surgery, University Hospital Zurich, Switzerland
| | - David Kenkel
- Department of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland
| | | | - Markus Weiger
- Institute for Biomedical Engineering, University and ETH Zurich, Switzerland
| | - Gustav Andreisek
- Department of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland
| | - Felix W. Wehrli
- Laboratory for Structural NMR Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, USA
| | - Andreas Boss
- Department of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland
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Assessing lung transplantation ischemia-reperfusion injury by microcomputed tomography and ultrashort echo-time magnetic resonance imaging in a mouse model. Invest Radiol 2014; 49:23-8. [PMID: 24056111 DOI: 10.1097/rli.0b013e3182a53111] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
PURPOSE Ischemia-reperfusion injury (I/R) is a common early complication after lung transplantation. The purpose of this study was to compare ultrashort echo-time (UTE) sequences in magnetic resonance imaging (MRI) with a microcomputed tomography (micro-CT) reference standard for detection of I/R injury in a lung transplantation mouse model. MATERIALS AND METHODS Six mice (C57BL/6) underwent orthotopic lung transplantation using donor grafts that were exposed to 6-hour cold ischemia. Imaging was performed within 24 hours after the transplantation with high-resolution micro-CT (tube voltage, 50 kV; current, 500 mA; aluminum filter, 0.5 mm; voxel size, 35 × 35 × 35 μm³) and small-animal MRI at 4.7 T with a linearly polarized whole-body mouse coil. The imaging protocol comprised radial 3-dimensional UTE sequences with different echo times (repetition time, 8 milliseconds; echo time, 50/75/100/500/1500/3000/4000/5000 μs; voxel size, 350 × 350 × 350 μm³). Images were assessed visually and through calculation of contrast-to-noise ratio (CNR) values. Calculated S0 values and T2* transverse relaxation times (MRI) of lung parenchyma were compared with Hounsfield unit (HU) density in micro-CT images. Receiver operating characteristic curves and area under the curve values were calculated for comparison of diagnostic power. All samples underwent a histologic examination. RESULTS The results of both UTE MRI and micro-CT showed an excellent depiction of pulmonary infiltration due to I/R injury, with MRI exhibiting a significantly higher CNR (mean [SD] CNR MRI, 19.7 [8.0]; mean [SD] CNR micro-CT, 10.3 [2.5]; P < 0.001). Measured parametrical values were as follows: mean (SD) HU, -416 (120); mean (SD) S0 value, 1655 (440); mean (SD) T2*, 895 (870) μs for the non-transplanted right lung and mean (SD) HU, 29 (35); mean (SD) S0 value, 2310 (300); and mean (SD) T2*, 4550 (3230) μs for the transplanted left lung. Slight infiltration could be better discriminated with micro-CT, whereas, in strong infiltration, a better contrast was provided by UTE MRI. The area under the curve values resulting from the receiver operating characteristic curve analysis were 0.99 for HU density, 0.89 for S₀, 0.96 for T2*, and 0.98 for the combination of S₀ and T2*. CONCLUSIONS Results show that MRI of the lung has a similar diagnostic power compared with that of micro-CT regarding the detection of I/R injury after experimental lung transplantation. Both modalities provide complementary information in the assessment of dense and slight infiltration in the early phase after lung transplantation. Therefore, UTE MRI seems to be a promising addition to computed tomographic imaging in the assessment of I/R injury after lung transplantation.
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In vivo MRI visualization of parastomal mesh in a porcine model. Hernia 2014; 18:663-70. [DOI: 10.1007/s10029-014-1270-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Accepted: 05/23/2014] [Indexed: 10/25/2022]
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Grosse U, Syha R, Hein T, Gatidis S, Grözinger G, Schabel C, Martirosian P, Schick F, Springer F. Diagnostic value of T1and T2* relaxation times and off-resonance saturation effects in the evaluation of achilles tendinopathy by MRI at 3T. J Magn Reson Imaging 2014; 41:964-73. [DOI: 10.1002/jmri.24657] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2014] [Revised: 04/10/2014] [Accepted: 04/13/2014] [Indexed: 12/21/2022] Open
Affiliation(s)
- Ulrich Grosse
- Department of Diagnostic and Interventional Radiology; University Hospital Tuebingen; Tuebingen Germany
- Section on Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Roland Syha
- Department of Diagnostic and Interventional Radiology; University Hospital Tuebingen; Tuebingen Germany
- Section on Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Tobias Hein
- Department of Sports Medicine; University Hospital Tuebingen; Tuebingen Germany
| | - Sergios Gatidis
- Department of Diagnostic and Interventional Radiology; University Hospital Tuebingen; Tuebingen Germany
- Section on Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Gerd Grözinger
- Department of Diagnostic and Interventional Radiology; University Hospital Tuebingen; Tuebingen Germany
- Section on Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Christoph Schabel
- Department of Diagnostic and Interventional Radiology; University Hospital Tuebingen; Tuebingen Germany
- Section on Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Petros Martirosian
- Section on Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Fritz Schick
- Section on Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Fabian Springer
- Department of Diagnostic and Interventional Radiology; University Hospital Tuebingen; Tuebingen Germany
- Section on Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
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Grosse U, Springer F, Hein T, Grözinger G, Schabel C, Martirosian P, Schick F, Syha R. Influence of physical activity on T1 and T2* relaxation times of healthy achilles tendons at 3T. J Magn Reson Imaging 2013; 41:193-201. [DOI: 10.1002/jmri.24525] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Accepted: 11/06/2013] [Indexed: 12/22/2022] Open
Affiliation(s)
- Ulrich Grosse
- Department of Diagnostic and Interventional Radiology; University Hospital Tuebingen; Tuebingen Germany
- Section of Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Fabian Springer
- Department of Diagnostic and Interventional Radiology; University Hospital Tuebingen; Tuebingen Germany
- Section of Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Tobias Hein
- Department of Sports Medicine; University Hospital Tuebingen; Tuebingen Germany
| | - Gerd Grözinger
- Department of Diagnostic and Interventional Radiology; University Hospital Tuebingen; Tuebingen Germany
- Section of Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Christoph Schabel
- Department of Diagnostic and Interventional Radiology; University Hospital Tuebingen; Tuebingen Germany
- Section of Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Petros Martirosian
- Section of Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Fritz Schick
- Section of Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
| | - Roland Syha
- Department of Diagnostic and Interventional Radiology; University Hospital Tuebingen; Tuebingen Germany
- Section of Experimental Radiology; University Hospital Tuebingen; Tuebingen Germany
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First In-Human Magnetic Resonance Visualization of Surgical Mesh Implants for Inguinal Hernia Treatment. Invest Radiol 2013; 48:770-8. [DOI: 10.1097/rli.0b013e31829806ce] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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In vivo visualization of polymer-based mesh implants using conventional magnetic resonance imaging and positive-contrast susceptibility imaging. Invest Radiol 2013; 48:200-5. [PMID: 23344516 DOI: 10.1097/rli.0b013e31827efd14] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE Polymer-based textile meshes for abdominal hernia treatment are invisible by conventional imaging methods, including magnetic resonance imaging (MRI). Integration of iron particles in the mesh base material allows MRI visualization of meshes. Positive-contrast susceptibility imaging (PCSI) was implemented to separate susceptibility-induced voids from proton-deficient voids. The purpose of this study was to compare PCSI with conventional gradient echo and turbo spin echo (TSE) sequences for the in vivo assessment of superparamagnetic iron oxide particle-loaded surgical meshes in an animal model. METHODS AND MATERIALS Iron-loaded polymer meshes were implanted into the abdominal wall of 10 rabbits. At days 1, 30, and 90 after surgery, conventional gradient echo, TSE, and PCSI were performed at 1.5 T in the sagittal and axial planes. Images were scored by 2 radiologists with respect to mesh visibility, delineation of the surrounding tissue, differentiation from other structures, and overall diagnostic use, on a 4-point scale ranging from 1 (insufficient) to 4 (excellent). The results were compared using Wilcoxon signed-rank tests. The mesh shape, possible deformation or fracture, and possible mesh migration were evaluated on the different pulse sequences and compared with the results at surgery and autopsy. RESULTS The iron-loaded meshes appeared as hypointense signal voids on gradient echo sequences, as a hyperintense line on PCSI, and as a very thin dark line on TSE images. In all animals, a precise depiction of the mesh location and its spatial configuration and integrity was possible by MRI and confirmed by surgical and autopsy results. In all 4 categories and at all 3 time points of imaging, image quality scores were significantly higher for gradient echo imaging (range, 3.60-3.80) compared with PCSI (range, 3.12-3.42) and TSE (range, 1.64-1.89). At day 90, the image quality ratings of gradient echo and PCSI were comparable. In 2 cases, the complete delineation of mesh borders was impossible because of signal voids of adjacent anatomical structures, whereas PCSI helped achieve this differentiation. CONCLUSION In this rabbit model of iron-loaded implanted abdominal meshes, standard gradient echo imaging was best suitable to assess implant location, integrity, and configuration. In 2 of 10 animals, PCSI helped achieve a complete delineation of mesh borders.
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Du J, Bydder GM. Qualitative and quantitative ultrashort-TE MRI of cortical bone. NMR IN BIOMEDICINE 2013; 26:489-506. [PMID: 23280581 PMCID: PMC4206448 DOI: 10.1002/nbm.2906] [Citation(s) in RCA: 114] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2012] [Revised: 10/19/2012] [Accepted: 11/18/2012] [Indexed: 05/08/2023]
Abstract
Osteoporosis causes over 1.5 million fractures per year, costing about $15 billion annually in the USA. Current guidelines utilize bone mineral density (BMD) to assess fracture risk; however, BMD alone only accounts for 30-50% of fractures. The other two major components of bone, organic matrix and water, contribute significantly to bone mechanical properties, but cannot be assessed with conventional imaging techniques in spite of the fact that they make up about 57% of cortical bone by volume. Conventional clinical MRI usually detects signals from water in tissues without difficulty, but cannot detect the water bound to the organic matrix, or the free water in the microscopic pores of the Haversian and the lacunar-canalicular system of cortical bone, because of their very short apparent transverse relaxation times (T2 *). In recent years, a new class of sequences, ultrashort-TE (UTE) sequences, with nominal TEs of less than 100 µs, which are much shorter than the TEs available with conventional sequences, have received increasing interest. These sequences can detect water signals from within cortical bone and provide an opportunity to study disease of this tissue in a new way. This review summarizes the recent developments in qualitative UTE imaging (techniques and contrast mechanisms to produce bone images with high contrast) and quantitative UTE imaging (techniques to quantify the MR properties, including T1 , T2 * and the magnetization transfer ratio, and tissue properties, including bone perfusion, as well as total, bound and free water content) of cortical bone in vitro and in vivo. The limitations of the current techniques for clinical applications and future directions are also discussed.
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Affiliation(s)
- Jiang Du
- Department of Radiology, University of California, San Diego, CA 92103-8226, USA.
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Magnetic resonance imaging of solid dental restoration materials using 3D UTE sequences: visualization and relaxometry of various compounds. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2013; 26:555-64. [PMID: 23525675 DOI: 10.1007/s10334-013-0373-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Revised: 02/19/2013] [Accepted: 02/20/2013] [Indexed: 10/27/2022]
Abstract
OBJECT Due to an increasing scientific interest in MR-imaging of carious lesions and teeth, an accurate signal characterization of dental restoration materials is necessary for optimization of MR sequence protocols and evaluation of material degradation. Therefore, signal yield and relaxation behavior of common dental restoration materials in comparison to those of dentine of extracted human teeth were assessed in vitro by ultrashort echo time (UTE) sequences. MATERIALS AND METHODS Eighteen material samples and dentine of two freshly extracted human teeth were investigated on a 3T whole-body clinical MR-scanner. Transverse (T2*) and longitudinal relaxation times (T1) were quantified using a recently published modified Ernst equation that takes relevant in-pulse relaxation effects into account. RESULTS All investigated samples could be successfully visualized but maximum signal yield was highly variable between samples. T1-values of the investigated dental restoration materials ranged between 28 and 365 ms, whereas T2*-values ranged between 96 and 917 μs. In contrast, T1-values of dentine (T1=545 ms±299 ms) were higher, while T2*-values (T2*=478 μs±271 μs) showed similar values. CONCLUSIONS Dental restoration materials and dentine of extracted human teeth can be visualized by UTE sequences and show a broad range of signal yield and relaxation times.
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Sun Y, Ventura M, Oosterwijk E, Jansen JA, Walboomers XF, Heerschap A. Zero echo time magnetic resonance imaging of contrast-agent-enhanced calcium phosphate bone defect fillers. Tissue Eng Part C Methods 2013; 19:281-7. [PMID: 22934755 DOI: 10.1089/ten.tec.2011.0745] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Calcium phosphate cements (CPCs) are widely used bone substitutes. However, CPCs have similar radiopacity as natural bone, rendering them difficult to be differentiated in classical X-ray and computed tomography imaging. As conventional magnetic resonance imaging (MRI) of bone is cumbersome, due to low water content and very short T(2) relaxation time, ultra-short echo time (UTE) and zero echo time (ZTE) MRI have been explored for bone visualization. This study examined the possibility to differentiate bone and CPC by MRI. T(1) and T(2)* values determined with UTE MRI showed little difference between bone and CPC; hence, these materials were difficult to separate based on T(1) or T(2) alone. Incorporation of ultra-small particles of iron oxide and gadopentetatedimeglumine (Gd-DTPA; 1 weight percentage [wt%] and 5 wt% respectively) into CPC resulted in visualization of CPC with decreased intensity on ZTE images in in vitro and ex vivo experiments. However, these additions had unfavorable effects on the solidification time and/or mechanical properties of the CPC, with the exception of 1% Gd-DTPA alone. Therefore, we tested this material in an in vivo experiment. The contrast of CPC was enhanced at an early stage postimplantation, and was significantly reduced in the 8 weeks thereafter. This indicates that ZTE imaging with Gd-DTPA as a contrast agent could be a valid radiation-free method to visualize CPC degradation and bone regeneration in preclinical experiments.
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Affiliation(s)
- Yi Sun
- Department of Radiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
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Rapid Assessment of Longitudinal Relaxation Time in Materials and Tissues With Extremely Fast Signal Decay Using UTE Sequences and the Variable Flip Angle Method. Invest Radiol 2011; 46:610-7. [DOI: 10.1097/rli.0b013e31821c44cd] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Generalized equation for describing the magnetization in spoiled gradient-echo imaging. Magn Reson Imaging 2011; 29:723-30. [DOI: 10.1016/j.mri.2011.02.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2010] [Revised: 02/02/2011] [Accepted: 02/20/2011] [Indexed: 11/20/2022]
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Horch RA, Wilkens K, Gochberg DF, Does MD. RF coil considerations for short-T2 MRI. Magn Reson Med 2011; 64:1652-7. [PMID: 20665825 DOI: 10.1002/mrm.22558] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
With continuing hardware and pulse sequence advancements, modern MRI is gaining sensitivity to signals from short-T(2) (1)H species under practical experimental conditions. However, conventional MRI coils are typically not designed for this type of application, as they often contain proton-rich construction materials that may contribute confounding (1)H background signal during short-T(2) measurements. An example of this is shown herein. Separately, a loop-gap style coil was used to compare different coil construction materials and configurations with respect to observed (1)H background signal sizes in a small animal imaging system. Background signal sources were spatially identified and quantified in a number of different coil configurations. It was found that the type and placement of structural coil materials around the loop-gap resonator, as well as the coil's shielding configuration, are critical determinants of the coil's background signal size. Although this study employed a loop-gap resonator design, these findings are directly relevant to standard volume coils commonly used for MRI.
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Affiliation(s)
- R Adam Horch
- Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee 37232-2310, USA
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Springer F, Steidle G, Martirosian P, Claussen CD, Schick F. Effects of in-pulse transverse relaxation in 3D ultrashort echo time sequences: analytical derivation, comparison to numerical simulation and experimental application at 3T. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 206:88-96. [PMID: 20637661 DOI: 10.1016/j.jmr.2010.06.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2009] [Revised: 05/21/2010] [Accepted: 06/17/2010] [Indexed: 05/29/2023]
Abstract
The introduction of ultrashort-echo-time-(UTE)-sequences to clinical whole-body MR scanners has opened up the field of MR characterization of materials or tissues with extremely fast signal decay. If the transverse relaxation time is in the range of the RF-pulse duration, approximation of the RF-pulse by an instantaneous rotation applied at the middle of the RF-pulse and immediately followed by free relaxation will lead to a distinctly underestimated echo signal. Thus, the regular Ernst equation is not adequate to correctly describe steady state signal under those conditions. The paper presents an analytically derived modified Ernst equation, which correctly describes in-pulse relaxation of transverse magnetization under typical conditions: The equation is valid for rectangular excitation pulses, usually applied in 3D UTE sequences. Longitudinal relaxation time of the specimen must be clearly longer than RF-pulse duration, which is fulfilled for tendons and bony structures as well as many solid materials. Under these conditions, the proposed modified Ernst equation enables adequate and relatively simple calculation of the magnetization of materials or tissues. Analytically derived data are compared to numerical results obtained by using an established Runge-Kutta-algorithm based on the Bloch equations. Validity of the new approach was also tested by systematical measurements of a solid polymeric material on a 3T whole-body MR scanner. Thus, the presented modified Ernst equation provides a suitable basis for T1 measurements, even in tissues with T2 values as short as the RF-pulse duration: independent of RF-pulse duration, the 'variable flip angle method' led to consistent results of longitudinal relaxation time T1, if the T2 relaxation time of the material of interest is known as well.
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Affiliation(s)
- Fabian Springer
- Section on Experimental Radiology, Department of Diagnostic and Interventional Radiology, University Hospital, 72076 Tübingen, Germany.
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Abstract
Current advances in magnetic resonance, as a diagnostic modality, are discussed in the context of publications from Investigative Radiology during 2007 and 2008. The articles relating to this topic, published during the past 2 years, are reviewed by anatomic region. The discussion concludes with a consideration of magnetic resonance contrast media, focusing on studies published in the journal, and examining in particular the potential impact of nephrogenic systemic fibrosis.
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