Magnetic resonance elastography (MRE) can visualize and measure acoustic shear waves in tissue-li... more Magnetic resonance elastography (MRE) can visualize and measure acoustic shear waves in tissue-like materials subjected to harmonic mechanical excitation. This allows the calculation of local values of material parameters such as shear modulus and attenuation. Various inversion algorithms to perform such calculations have been proposed. Under certain assumptions (discussed in detail), the problem reduces to local inversion of the Helmholtz
Magnetic resonance elastography (MRE) is a phase-contrast-based MRI imaging technique that can di... more Magnetic resonance elastography (MRE) is a phase-contrast-based MRI imaging technique that can directly visualize and quantitatively measure propagating acoustic strain waves in tissue-like materials subjected to harmonic mechanical excitation. The data acquired allows the calculation of local quantitative values of shear modulus and the generation of images that depict tissue elasticity or stiffness. This is significant because palpation, a physical examination that assesses the stiffness of tissue, can be an effective method of detecting tumors, but is restricted to parts of the body that are accessible to the physician's hand. MRE shows promise as a potential technique for 'palpation by imaging', with possible applications in tumor detection (particularly in breast, liver, kidney and prostate), characterization of disease, and assessment of rehabilitation (particularly in muscle). We describe MRE in the context of other recent techniques for imaging elasticity, discuss the processing algorithms for elasticity reconstruction and the issues and assumptions they involve, and present recent ex vivo and in vivo results.
Journal of Applied Clinical Medical Physics, Mar 25, 2022
PurposeTo describe and report longitudinal quality assurance (QA) measurements for the magnetic r... more PurposeTo describe and report longitudinal quality assurance (QA) measurements for the magnetic resonance imaging (MRI) component of the Elekta Unity MR‐linac during the first year of clinical use in our institution.Materials and methodsThe performance of the MRI component of Unity was evaluated with daily, weekly, monthly, and annual QA testing. The measurements monitor image uniformity, signal‐to‐noise ratio (SNR), resolution/detectability, slice position/thickness, linearity, central frequency, and geometric accuracy. In anticipation of routine use of quantitative imaging (qMRI), we characterize B0/B1 uniformity and the bias/reproducibility of longitudinal/transverse relaxation times (T1/T2) and apparent diffusion coefficient (ADC). Tolerance levels for QA measurements of qMRI biomarkers are derived from weekly monitoring of T1, T2, and ADC.ResultsThe 1‐year assessment of QA measurements shows that daily variations in each MR quality metric are well below the threshold for failure. Routine testing procedures can reproducibly identify machine issues. The longitudinal three‐dimensional (3D) geometric analysis reveals that the maximum distortion in a diameter of spherical volume (DSV) of 20, 30, 40, and 50 cm is 0.4, 0.6, 1.0, and 3.1 mm, respectively. The main source of distortion is gradient nonlinearity. Maximum peak‐to‐peak B0 inhomogeneity is 3.05 ppm, with gantry induced B0 inhomogeneities an order of magnitude smaller. The average deviation from the nominal B1 is within 2%, with minimal dependence on gantry angle. Mean ADC, T1, and T2 values are measured with high reproducibility. The median coefficient of variation for ADC, T1, and T2 is 1.3%, 1.1%, and 0.5%, respectively. The median bias for ADC, T1, and T2 is −0.8%, −0.1%, and 3.9%, respectively.ConclusionThe MRI component of Unity operates within the guidelines and recommendations for scanner performance and stability. Our findings support the recently published guidance in establishing clinically acceptable tolerance levels for image quality. Highly reproducible qMRI measurements are feasible in Unity.
Page 1. COMPARATIVE EVALUATION OF INVERSION ALGORITHMS FOR MAGNETIC RESONANCE ELASTOGRAF'HY ... more Page 1. COMPARATIVE EVALUATION OF INVERSION ALGORITHMS FOR MAGNETIC RESONANCE ELASTOGRAF'HY Armando Manduca, Travis E. Oliphant, M Alex Dresner, David S. Lake, James F. Greenleaj Richard L. Ehman ... 2.4. Variational Method (VM) Romano et al. ...
In order to improve head and neck radiotherapy treatment planning, a series of 3D fat-suppressed ... more In order to improve head and neck radiotherapy treatment planning, a series of 3D fat-suppressed T2-weighted sequences were developed with varying pulse sequence parameters. One non-fat-suppressed and five fat-suppressed sequences were acquired on five patients, and on each image, four structures were segmented by six radiation oncology physicians (observers). Robust and comprehensive analysis was performed to assess qualitative and quantitative image quality metrics. This included geometric distortion, SNR and CNR measurements, structure conspicuity, interobserver segmentation variability, and qualitative image quality rankings. The results of these were used to determine the optimal fat-suppressed sequence for head and neck radiation treatment planning.
Magnetic resonance elastography (MRE) can visualize and measure acoustic shear waves in tissue-li... more Magnetic resonance elastography (MRE) can visualize and measure acoustic shear waves in tissue-like materials subjected to harmonic mechanical excitation. This allows the calculation of local values of material parameters such as shear modulus and attenuation. Various inversion algorithms to perform such calculations have been proposed. Under certain assumptions (discussed in detail), the problem reduces to local inversion of the Helmholtz
Magnetic resonance elastography (MRE) is a phase-contrast-based MRI imaging technique that can di... more Magnetic resonance elastography (MRE) is a phase-contrast-based MRI imaging technique that can directly visualize and quantitatively measure propagating acoustic strain waves in tissue-like materials subjected to harmonic mechanical excitation. The data acquired allows the calculation of local quantitative values of shear modulus and the generation of images that depict tissue elasticity or stiffness. This is significant because palpation, a physical examination that assesses the stiffness of tissue, can be an effective method of detecting tumors, but is restricted to parts of the body that are accessible to the physician's hand. MRE shows promise as a potential technique for 'palpation by imaging', with possible applications in tumor detection (particularly in breast, liver, kidney and prostate), characterization of disease, and assessment of rehabilitation (particularly in muscle). We describe MRE in the context of other recent techniques for imaging elasticity, discuss the processing algorithms for elasticity reconstruction and the issues and assumptions they involve, and present recent ex vivo and in vivo results.
Journal of Applied Clinical Medical Physics, Mar 25, 2022
PurposeTo describe and report longitudinal quality assurance (QA) measurements for the magnetic r... more PurposeTo describe and report longitudinal quality assurance (QA) measurements for the magnetic resonance imaging (MRI) component of the Elekta Unity MR‐linac during the first year of clinical use in our institution.Materials and methodsThe performance of the MRI component of Unity was evaluated with daily, weekly, monthly, and annual QA testing. The measurements monitor image uniformity, signal‐to‐noise ratio (SNR), resolution/detectability, slice position/thickness, linearity, central frequency, and geometric accuracy. In anticipation of routine use of quantitative imaging (qMRI), we characterize B0/B1 uniformity and the bias/reproducibility of longitudinal/transverse relaxation times (T1/T2) and apparent diffusion coefficient (ADC). Tolerance levels for QA measurements of qMRI biomarkers are derived from weekly monitoring of T1, T2, and ADC.ResultsThe 1‐year assessment of QA measurements shows that daily variations in each MR quality metric are well below the threshold for failure. Routine testing procedures can reproducibly identify machine issues. The longitudinal three‐dimensional (3D) geometric analysis reveals that the maximum distortion in a diameter of spherical volume (DSV) of 20, 30, 40, and 50 cm is 0.4, 0.6, 1.0, and 3.1 mm, respectively. The main source of distortion is gradient nonlinearity. Maximum peak‐to‐peak B0 inhomogeneity is 3.05 ppm, with gantry induced B0 inhomogeneities an order of magnitude smaller. The average deviation from the nominal B1 is within 2%, with minimal dependence on gantry angle. Mean ADC, T1, and T2 values are measured with high reproducibility. The median coefficient of variation for ADC, T1, and T2 is 1.3%, 1.1%, and 0.5%, respectively. The median bias for ADC, T1, and T2 is −0.8%, −0.1%, and 3.9%, respectively.ConclusionThe MRI component of Unity operates within the guidelines and recommendations for scanner performance and stability. Our findings support the recently published guidance in establishing clinically acceptable tolerance levels for image quality. Highly reproducible qMRI measurements are feasible in Unity.
Page 1. COMPARATIVE EVALUATION OF INVERSION ALGORITHMS FOR MAGNETIC RESONANCE ELASTOGRAF'HY ... more Page 1. COMPARATIVE EVALUATION OF INVERSION ALGORITHMS FOR MAGNETIC RESONANCE ELASTOGRAF'HY Armando Manduca, Travis E. Oliphant, M Alex Dresner, David S. Lake, James F. Greenleaj Richard L. Ehman ... 2.4. Variational Method (VM) Romano et al. ...
In order to improve head and neck radiotherapy treatment planning, a series of 3D fat-suppressed ... more In order to improve head and neck radiotherapy treatment planning, a series of 3D fat-suppressed T2-weighted sequences were developed with varying pulse sequence parameters. One non-fat-suppressed and five fat-suppressed sequences were acquired on five patients, and on each image, four structures were segmented by six radiation oncology physicians (observers). Robust and comprehensive analysis was performed to assess qualitative and quantitative image quality metrics. This included geometric distortion, SNR and CNR measurements, structure conspicuity, interobserver segmentation variability, and qualitative image quality rankings. The results of these were used to determine the optimal fat-suppressed sequence for head and neck radiation treatment planning.
Uploads
Papers by Alex Dresner