Magnetic Resonance Elastography Measurements Research Articles

Nucleus pulposus structure and function assessed in shear using magnetic resonance elastography, quantitative MRI, and rheometry.

In vivo quantification of the structure-function relationship of the intervertebral disc (IVD) via quantitative MRI has the potential to aid objective stratification of disease and evaluation of restorative therapies. Magnetic resonance elastography (MRE) is an imaging technique that assesses tissue shear properties and combined with quantitative MRI metrics reflective of composition can inform structure-function of the IVD. The objectives of this study were to (1) compare MRE- and rheometry-derived shear modulus in agarose gels and nucleus pulposus (NP) tissue and (2) correlate MRE and rheological measures of NP tissue with composition and quantitative MRI. MRE and MRI assessment (i.e., T1ρ and T2 mapping) of agarose samples (2%, 3%, and 4% (w/v); n = 3-4/%) and of bovine caudal IVDs after equilibrium dialysis in 5% or 25% PEG (n = 13/PEG%) was conducted. Subsequently, agarose and NP tissue underwent torsional mechanical testing consisting of a frequency sweep from 1 to 100 Hz at a rotational strain of 0.05%. NP tissue was additionally evaluated under creep and stress relaxation conditions. Linear mixed-effects models and univariate regression analyses evaluated the effects of testing method, %agarose or %PEG, and frequency, as well as correlations between parameters. MRE- and rheometry-derived shear moduli were greater at 100 Hz than at 80 Hz in all agarose and NP tissue samples. Additionally, all samples with lower water content had higher complex shear moduli. There was a significant correlation between MRE- and rheometry-derived modulus values for homogenous agarose samples. T1ρ and T2 relaxation times for agarose and tissue were negatively correlated with complex shear modulus derived from both techniques. For NP tissue, shear modulus was positively correlated with GAG/wet-weight and negatively correlated with %water content. This work demonstrates that MRE can assess hydration-induced changes in IVD shear properties and further highlights the structure-function relationship between composition and shear mechanical behaviors of NP tissue.

Magnetic resonance elastography for the prediction of hepatocellular carcinoma in chronic hepatitis B.

Magnetic resonance elastography (MRE) is used for the evaluation of liver fibrosis; however, it remains unclear whether MRE-based liver stiffness is associated with hepatocellular carcinoma (HCC) development, particularly in patients with chronic hepatitis B. A total of 504 patients with chronic hepatitis B receiving MRE were enrolled. The primary endpoint was the association between MRE-based liver stiffness and HCC. In a cross-sectional analysis at the time of MRE measurement, the median (interquartile range) liver stiffness values in patients with presence or history of HCC and those without HCC were 3.68 (2.89-4.96) and 2.60 (2.22-3.45) kPa, respectively, and liver stiffness was significantly higher in patients with presence or history of HCC than in those without HCC (P < 0.001). In a longitudinal analysis of patients without HCC, the 1-, 3-, and 5-year cumulative incidence of HCC in patients with liver stiffness ≥3.6 kPa and those with liver stiffness <3.6 kPa were 3.8%, 7.0%, and 22.9%, and 0%, 0.9%, and 1.5%, respectively (P < 0.001). In the multivariable analysis, MRE-based liver stiffness (per 1 kPa) or liver stiffness ≥3.6 kPa was an independent factor for HCC development with an adjusted hazard ratio (aHR) of 1.61 (95% confidence interval [CI], 1.3-2.0) or aHR of 8.22 (95% CI, 2.1-31). MRE-based liver stiffness is associated with HCC risk in patients with chronic hepatitis B and may be used for the early prediction of HCC development and determination of indications for treatment.

Individual Muscle Force Estimation in the Human Forearm Using Multi-Muscle MR Elastography (MM-MRE.

To establish the sensitivity of magnetic resonance elastography (MRE) to active muscle contraction in multiple muscles of the forearm. We combined MRE of forearm muscles with an MRI-compatible device, the MREbot, to simultaneously measure the mechanical properties of tissues in the forearm and the torque applied by the wrist joint during isometric tasks. We measured shear wave speed of thirteen forearm muscles via MRE in a series of contractile states and wrist postures and fit these outputs to a force estimation algorithm based on a musculoskeletal model. Shear wave speed changed significantly upon several factors, including whether the muscle was recruited as an agonist or antagonist (p = 0.0019), torque amplitude (p = <0.0001), and wrist posture (p = 0.0002). Shear wave speed increased significantly during both agonist (p = <0.0001) and antagonist (p = 0.0448) contraction. Additionally, there was a greater increase in shear wave speed at greater levels of loading. The variations due to these factors indicate the sensitivity to functional loading of muscle. Under the assumption of a quadratic relationship between shear wave speed and muscle force, MRE measurements accounted for an average of 70% of the variance in the measured joint torque. This study shows the ability of MM-MRE to capture variations in individual muscle shear wave speed due to muscle activation and presents a method to estimate individual muscle force through MM-MRE derived measurements of shear wave speed. MM-MRE could be used to establish normal and abnormal muscle co-contraction patterns in muscles of the forearm controlling hand and wrist function.

Harmonized Multisite MRI-Based Quantification of Human Liver Fat and Stiffness: A Pilot Study.

Nonalcoholic fatty liver disease (NAFLD) is a leading cause of end-stage liver disease. NAFLD diagnosis and follow-up relies on a combination of clinical data, liver imaging, and/or liver biopsy. However, intersite imaging differences impede diagnostic consistency and reduce the repeatability of the multisite clinical trials necessary to develop effective treatments. The goal of this pilot study was to harmonize commercially available 3 T magnetic resonance imaging (MRI) measurements of liver fat and stiffness in human participants across academic sites and MRI vendors. Cohort. Four community-dwelling adults with obesity. 1.5 and 3 T, multiecho 3D imaging, PRESS, and GRE. Harmonized proton density fat fraction (PDFF) and magnetic resonance spectroscopy (MRS) protocols were used to quantify the FF of synthetic phantoms and human participants with obesity using standard acquisition parameters at four sites that had four different 3 T MRI instruments. In addition, a harmonized magnetic resonance elastography (MRE) protocol was used to quantify liver stiffness among participants at two different sites at 1.5 and 3 T field strengths. Data were sent to a single data coordinating site for postprocessing. Linear regression in MATLAB, ICC analyses using SAS 9.4, one-sided 95% confidence intervals for the ICC. PDFF and MRS FF measurements were highly repeatable among sites in both humans and phantoms. MRE measurements of liver stiffness in three individuals at two sites using one 1.5 T and one 3 T instrument showed repeatability that was high although lower than that of MRS and PDFF. We demonstrated harmonization of PDFF, MRS, and MRE-based quantification of liver fat and stiffness through synthetic phantoms, traveling participants, and standardization of postprocessing analysis. Multisite MRI harmonization could contribute to multisite clinical trials assessing the efficacy of interventions and therapy for NAFLD. 2 TECHNICAL EFFICACY STAGE: 2.

Abstract 583: Validating Noninvasive Indices Of Thoracic Aortic Dissection With Magnetic Resonance Elastography

Objective: Dissection-associated aneurysms (DAA) are the leading cause of death related to chronic Type-B aortic dissections (TBAD). Conventional imaging cannot distinguish high-risk DAAs that would benefit from early surgical intervention. We propose the feasibility of aortic stiffness as measured by magnetic resonance elastography (MRE) as a biomarker to help make this distinction. We validate MRE stiffness measures in 3D-printed PVA hydrogel phantoms with human-like dissection geometries and demonstrated the first successful application of MRE in a human thoracic aorta with a healthy volunteer. Methods: All phantoms had a 10% PVA true lumen and a 10%, 15%, 20%, or 25% false lumen. The phantoms and the thoracic aorta of a healthy volunteer were imaged in a 3T-MR scanner. A pneumatic driver created mechanical vibrations within the aorta. A cardiac-gated spin-echo echo planar imaging (SE-EPI) sequence was utilized. In vivo, end-diastolic images were chosen for analysis to minimize blood flow artifacts. Results: The MRE shear stiffness of the various PVA false lumen sides of the phantoms were 32.19, 51.48, 59.29, and 73.53 ± 2.66 kPa, respectively. Figure 1 shows the correlation (R 2 = 0.99) between MRE and rheometric stiffness measurements of the four phantoms with different PVA concentrations. Figure 2 shows MRE local frequency estimations of stiffness from the human aorta with a mean shear stiffness of 3.37±0.83kPa. Conclusion: We present a validation and feasibility study of MRE in the thoracic aorta. Future research will allow for developing predictive indices for TBAD DAA development.

Uniaxial prestress and waveguide effects on estimates of the complex shear modulus using magnetic resonance elastography in a transverse isotropic muscle phantom and excised muscle

Tensile prestress is inherent to the functional role of some biological tissues currently being studied using elastography, such as skeletal and cardiac muscle, arterial walls, and the cornea. Therefore, the impact of prestress coupled with waveguide effects due to small dimensions in one or more directions needs to be better understood. An experimental configuration is designed, fabricated and experimentally tested using magnetic resonance elastography (MRE). Cylindrically-shaped isotropic and transversely isotropic phantoms, as well as the excised cat soleus muscle are statically stretched along their main axis to specific prestrain levels while simultaneously conducting MRE measurements that enable synchronous motion-encoding in all three dimensions (polarization directions). In the case of the excised cat soleus, diffusion tensor imaging is also performed to enable a co-registered mapping of fiber structure. Guided by analytical models and numerical finite element simulations, experimental measurements are post-processed to obtain an estimate of the complex (viscoelastic) shear modulus as a function of prestress level and frequency of vibratory motion.

Elastography using torsional wave motion in transverse isotropic material

An experimental configuration for driving and measuring torsional wave motion is designed, fabricated and experimentally tested using magnetic resonance elastography (MRE) in both a ultra-high field preclinical MRI system and in a cryogen-free low-field tabletop MRI system. Cylindrically-shaped isotropic and transversely isotropic phantoms, as well as the excised cat soleus muscle are statically stretched along their main axis to specific prestrain levels while simultaneously conducting MRE measurements with torsional waves. In the case of the excised cat soleus, diffusion tensor imaging is also performed to enable a co-registered mapping of fiber structure. The potential advantage of torsional wave excitation to drive shear wave motion over a large volume with uniform amplitude, and hence SNR, is tested by comparison to excitation of shear waves using other methods.

Impact of Hepatic Iron Overload in the Evaluation of Steatosis and Fibrosis in Patients with Nonalcoholic Fatty Liver Disease Using Vibration-Controlled Transient Elastography (VCTE) and MR Imaging Techniques: A Clinical Study

PurposeThree main non-invasive imaging methods are routinely used for the assessment of liver fibrosis and steatosis in patients with nonalcoholic fatty liver disease (NAFLD): the vibration-controlled transient elastography (VCTE) using the FibroScan device, the magnetic resonance imaging (MRI) based on proton density fat fraction (PDFF), and the magnetic resonance elastography (MRE). The purpose of our study is to evaluate the efficiency of the VCTE findings compared to the two others methods, and to analyze the impact of hepatic iron overload on these comparisons. MethodsA clinical study was performed on 94 patients with NAFLD in the radiology department of ACRIM-Polyclinic Saint-Côme (France). The study also included 17 patients with hemochromatosis, measured from T2⁎ MRI. The liver tissues of all the patients were evaluated with 1) VCTE (including the controlled attenuation (CAP) and stiffness parameters), 2) MRI (fat fraction parameter), and 3) MRE (stiffness parameter) techniques. The performance of VCTE was assessed by estimating the area under the ROC curve (AUC) for patients without or with hemochromatosis. Spearman's correlation was used for the comparison of VCTE measurements to MRI and MRE. ResultsVCTE-based stiffness and CAP were significantly correlated with PDFF and MRE measurements (P<0.01) for the subgroup without hemochromatosis. The correlations failed for the subgroup with hemochromatosis. ConclusionVCTE and CAP measurements were not correlated with those from MR PDFF and MRE for patients with hemochromatosis. VCTE, PDFF and MRE modalities don't give concordant results for patients with hemochromatosis.

MR elastography identifies regions of extracellular matrix reorganization associated with shorter survival in glioblastoma patients.

Biomechanical tissue properties of glioblastoma tumors are heterogeneous, but the molecular mechanisms involved and the biological implications are poorly understood. Here, we combine magnetic resonance elastography (MRE) measurement of tissue stiffness with RNA sequencing of tissue biopsies to explore the molecular characteristics of the stiffness signal. MRE was performed preoperatively in 13 patients with glioblastoma. Navigated biopsies were harvested during surgery and classified as "stiff" or "soft" according to MRE stiffness measurements (|G*|norm). Twenty-two biopsies from eight patients were analyzed by RNA sequencing. The mean whole-tumor stiffness was lower than normal-appearing white matter. The surgeon's stiffness evaluation did not correlate with the MRE measurements, which suggests that these measures assess different physiological properties. Pathway analysis of the differentially expressed genes between "stiff" and "soft" biopsies showed that genes involved in extracellular matrix reorganization and cellular adhesion were overexpressed in "stiff" biopsies. Supervised dimensionality reduction identified a gene expression signal separating "stiff" and "soft" biopsies. Using the NIH Genomic Data Portal, 265 glioblastoma patients were divided into those with (n = 63) and without (n = 202) this gene expression signal. The median survival time of patients with tumors expressing the gene signal associated with "stiff" biopsies was 100 days shorter than that of patients not expressing it (360 versus 460 days, hazard ratio: 1.45, P < .05). MRE imaging of glioblastoma can provide noninvasive information on intratumoral heterogeneity. Regions of increased stiffness were associated with extracellular matrix reorganization. An expression signal associated with "stiff" biopsies correlated with shorter survival of glioblastoma patients.

Investigation of the contribution of viscoelastic polymer gel pad usage to the accuracy of magnetic resonance elastography measurements: A preliminary study

Investigation of the contribution of viscoelastic polymer gel pad usage to the accuracy of magnetic resonance elastography measurements: A preliminary study

Ex vivo bovine liver nonlinear viscoelastic properties: MR elastography and rheological measurements

IntroductionKnowledge of the nonlinear viscoelastic properties of the liver is important, but the complex tissue behavior outside the linear viscoelastic regime has impeded their characterization, particularly in vivo. Combining static compression with magnetic resonance (MR) elastography has the potential to be a useful imaging method for assessing large deformation mechanical properties of soft tissues in vivo. However, this remains to be verified. Therefore this study aims first to determine whether MR elastography can measure the nonlinear mechanical properties of ex vivo bovine liver tissue under varying levels of uniform and focal preloads (up to 30%), and second to compare MR elastography-derived complex shear modulus with standard rheological measurements. MethodNine fresh bovine livers were collected from a local abattoir, and experiments were conducted within 12hr of death. Two cubic samples (∼10 × 10 × 10 cm3) were dissected from each liver and imaged using MR elastography (60 Hz) under 4 levels of uniform and focal preload (1, 10, 20, and 30% of sample width) to investigate the relationship between MR elastography-derived complex shear modulus (G∗) and the maximum principal Right Cauchy Green Strain (C11). Three tissue samples from each of the same 9 livers underwent oscillatory rheometry under the same 4 preloads (1, 10, 20, and 30% strain). MR elastography-derived complex shear modulus (G∗) from the uniform preload was validated against rheometry by fitting the frequency dependence of G∗ with a power-law and extrapolating rheometry-derived G∗ to 60 Hz. ResultsMR elastography-derived G∗ increased with increasing compressive large deformation strain, and followed a power-law curve (G∗ = 1.73 × C11−0.38, R2 = 0.96). Similarly, rheometry-derived G∗ at 1 Hz, increasing from 0.66 ± 1.03 kPa (1% strain) to 1.84 ± 1.65 kPa (30% strain, RM one-way ANOVA, P < 0.001), and the frequency dependence of G∗ followed a power-law with the exponent decreasing from 0.13 to 0.06 with increasing preload. MR elastography-derived G∗ was 1.4–3.1 times higher than the extrapolated rheometry-derived G∗ at 60 Hz, but the strain dependence was consistent between rheometry and MR elastography measurements. ConclusionsThis study demonstrates that MR elastography can detect changes in ex vivo bovine liver complex shear modulus due to either uniform or focal preload and therefore can be a useful technique to characterize nonlinear viscoelastic properties of soft tissue, provided that strains applied to the tissue can be quantified. Although MR elastography could reliably characterize the strain dependence of the ex vivo bovine liver, MR elastography overestimated the complex shear modulus of the tissue compared to rheological measurements, particularly at lower preload (<10%). That is likely to be important in clinical hepatic MR elastography diagnosis studies if preload is not carefully considered. A limitation is the absence of overlapping frequency between rheometry and MR elastography for formal validation.

Decoupling Uniaxial Tensile Prestress and Waveguide Effects From Estimates of the Complex Shear Modulus in a Cylindrical Structure Using Transverse-Polarized Dynamic Elastography.

Dynamic elastography, whether based on magnetic resonance, ultrasound, or optical modalities, attempts to reconstruct quantitative maps of the viscoelastic properties of biological tissue, properties altered by disease and injury, by noninvasively measuring mechanical wave motion in the tissue. Most reconstruction strategies that have been developed neglect boundary conditions, including quasi-static tensile or compressive loading resulting in a nonzero prestress. Significant prestress is inherent to the functional role of some biological tissues currently being studied using elastography, such as skeletal and cardiac muscle, arterial walls, and the cornea. In the present article a configuration, inspired by muscle elastography but generalizable to other applications, is analytically and experimentally studied. A hyperelastic polymer phantom cylinder is statically elongated in the axial direction while its response to transverse-polarized vibratory excitation is measured. We examine the interplay between uniaxial prestress and waveguide effects in this muscle-like tissue phantom using computational finite element simulations and magnetic resonance elastography measurements. Finite deformations caused by prestress coupled with waveguide effects lead to results that are predicted by a coordinate transformation approach that has been previously used to simplify reconstruction of anisotropic properties using elastography. Here, the approach estimates material viscoelastic properties that are independent of the nonhomogeneous prestress conditions without requiring advanced knowledge of those stress conditions.

Ensemble Kalman inversion for magnetic resonance elastography

Magnetic resonance elastography (MRE) is an MRI-based diagnostic method for measuring mechanical properties of biological tissues. MRE measurements are processed by an inversion algorithm to produce a map of the biomechanical properties. In this paper a new and powerful method (ensemble Kalman inversion with level sets (EKI)) of MRE inversion is proposed and tested. The method has critical advantages: material property variation at disease boundaries can be accurately identified, and uncertainty of the reconstructed material properties can be evaluated by consequence of the probabilistic nature of the method. EKI is tested in 2D and 3D experiments with synthetic MRE data of the human kidney. It is demonstrated that the proposed inversion method is accurate and fast.

Structure-Function Dissociations of Human Hippocampal Subfield Stiffness and Memory Performance.

Aging and neurodegenerative diseases lead to decline in thinking and memory ability. The subfields of the hippocampus (HCsf) play important roles in memory formation and recall. Imaging techniques sensitive to the underlying HCsf tissue microstructure can reveal unique structure-function associations and their vulnerability in aging and disease. The goal of this study was to use magnetic resonance elastography (MRE), a noninvasive MR imaging-based technique that can quantitatively image the viscoelastic mechanical properties of tissue to determine the associations of HCsf stiffness with different cognitive domains across the lifespan. Eighty-eight adult participants completed the study (age 23-81 years, male/female 36/51), in which we aimed to determine which HCsf regions most strongly correlated with different memory performance outcomes and if viscoelasticity of specific HCsf regions mediated the relationship between age and performance. Our results revealed that both interference cost on a verbal memory task and relational memory task performance were significantly related to cornu ammonis 1-2 (CA1-CA2) stiffness (p = 0.018 and p = 0.011, respectively), with CA1-CA2 stiffness significantly mediating the relationship between age and interference cost performance (p = 0.031). There were also significant associations between delayed free verbal recall performance and stiffness of both the dentate gyrus-cornu ammonis 3 (DG-CA3; p = 0.016) and subiculum (SUB; p = 0.032) regions. This further exemplifies the functional specialization of HCsf in declarative memory and the potential use of MRE measures as clinical biomarkers in assessing brain health in aging and disease.SIGNIFICANCE STATEMENT Hippocampal subfields are cytoarchitecturally unique structures involved in distinct aspects of memory processing. Magnetic resonance elastography is a technique that can noninvasively image tissue viscoelastic mechanical properties, potentially serving as sensitive biomarkers of aging and neurodegeneration related to functional outcomes. High-resolution in vivo imaging has invigorated interest in determining subfield functional specialization and their differential vulnerability in aging and disease. Applying MRE to probe subfield-specific cognitive correlates will indicate that measures of subfield stiffness can determine the integrity of structures supporting specific domains of memory performance. These findings will further validate our high-resolution MRE method and support the potential use of subfield stiffness measures as clinical biomarkers in classifying aging and disease states.

The Associations Between Cardiorespiratory Fitness, Hippocampal Health, And Cognition In Mild Cognitive Impairment

Mild cognitive impairment (MCI), a prodromal stage of Alzheimer’s disease, has negative effects on cognition and is associated with structural changes in the brain, particularly the hippocampus. We utilized magnetic resonance elastography (MRE), an imaging technique that estimates brain mechanical properties, to quantify the integrity of the underlying tissue microstructure. MRE is an emerging method for evaluating hippocampal health and its relation to cognition. We used MRE to assess the relationship between aerobic fitness and hippocampal integrity in MCI and aging, as fitness is a modifiable lifestyle factor. Establishing these links can help identify those at risk of cognitive impairment and establish interventions. PURPOSE: To demonstrate the value of MRE measures of hippocampal health to assess the relationship between aerobic fitness, cognition, and MRE in MCI. METHODS: We recruited 47 healthy older adults (69 ± 6 yrs) and 13 with amnestic MCI (72 ± 9 yrs). Participants had an MRI, fitness and cognitive testing to collect hippocampal stiffness and damping ratio, reflecting the resistance of tissue, relative VO2,max, and a composite cognitive score. RESULTS: Older adults had significantly higher stiffness (p < .01) and lower damping ratio (p = .001). Stiffness significantly mediated the relationship between diagnosis and cognition (Estimated indirect effect, ACME (95% CI) = .04 (-.004, -.009)). VO2 was differentially associated with MRE measures in MCI compared healthy older adults. A significant diagnosis x fitness interaction effect was observed (Stiffness: β = .012, SE = .006, p = .041; Damping ratio: β = -.001, SE = .001, p = .041), with a stronger relationship between VO2 and MRE measures in the MCI group (Stiffness: p = .029, 95% CI = .075, .881; Damping ratio: p = .243, 95% CI = -.74, .33) compared to in the healthy older group (Stiffness: p = .191, 95% CI = -1.01, .49; Damping ratio: p = .764, 95% CI = -.36, .27). Only stiffness was associated with fitness in MCI participants. CONCLUSIONS: These preliminary findings suggest the utility of MRE in studying the mechanism of disease, with stiffness mediating the relationship between groups and cognition. Fitness is related to MRE outcomes in MCI, specifically stiffness, suggesting that higher aerobic fitness may be even more beneficial for those with MCI.

Evaluation of cerebral cortex viscoelastic property estimation with nonlinear inversion magnetic resonance elastography

Objective. Magnetic resonance elastography (MRE) of the brain has shown promise as a sensitive neuroimaging biomarker for neurodegenerative disorders; however, the accuracy of performing MRE of the cerebral cortex warrants investigation due to the unique challenges of studying thinner and more complex geometries. Approach. A series of realistic, whole-brain simulation experiments are performed to examine the accuracy of MRE to measure the viscoelasticity (shear stiffness, μ, and damping ratio, ξ) of cortical structures predominantly effected in aging and neurodegeneration. Variations to MRE spatial resolution and the regularization of a nonlinear inversion (NLI) approach are examined. Main results. Higher-resolution MRE displacement data (1.25 mm isotropic resolution) and NLI with a low soft prior regularization weighting provided minimal measurement error compared to other studied protocols. With the optimized protocol, an average error in μ and ξ was 3% and 11%, respectively, when compared with the known ground truth. Mid-line structures, as opposed to those on the cortical surface, generally display greater error. Varying model boundary conditions and reducing the thickness of the cortex by up to 0.67 mm (which is a realistic portrayal of neurodegenerative pathology) results in no loss in reconstruction accuracy. Significance. These experiments establish quantitative guidelines for the accuracy expected of in vivo MRE of the cortex, with the proposed method providing valid MRE measures for future investigations into cortical viscoelasticity and relationships with health, cognition, and behavior.

Performance of C-SENSE Accelerated Rapid Liver Shear Stiffness Measurement Using Displacement Wave Polarity-Inversion Motion Encoding: An Evaluation Study.

Liver shear stiffness measurement using magnetic resonance elastography (MRE) aids in the noninvasive diagnosis and staging of liver fibrosis. Inadequate breath-holds can lead to inaccurate stiffness estimation and/or failed MRE exams. To prospectively evaluate the performance of compressed sensitivity encoding (C-SENSE) accelerated rapid MRE measurement of liver shear stiffness using displacement wave polarity-inversion motion encoding. Retrospective. Eleven with liver disease and 10 asymptomatic subjects. 1.5 T; gradient-recalled-echo (GRE) MRE. All participants underwent: 1) two-dimensional (2D) GRE MRE with inflow saturation using SENSE acceleration factor (R) of 2 (standard of care [SC]); 2) 2D rapid MRE with (RwS); and 3) without (RnS) inflow saturation using C-SENSE R=3; and 4) spatial three-dimensional (3D) rapid MRE with inflow saturation (R3D) using C-SENSE R=4; with nominally identical spatial resolution and coverage. Image analyst (D.G., 2 years of experience) drew identical and maximal regions of interest (ROIs) in right hepatic lobe. Linear regression, intra-class correlation coefficients (ICC), Bland-Altman analyses, and the Wilcoxon signed-rank test were used to assess consistency and agreement of liver stiffness measurements for manually drawn identical and maximal ROIs. In 21 participants (37 ± 14 years) with liver stiffness (2.3 ± 0.7kPa), body mass index (BMI 27 ± 7kg/m2 ), proton density fat fraction (PDFF 9 ± 9%), and T2 * (27 ± 4msec); rapid MRE sequences showed excellent agreement (ICC > 0.95) with SC MRE and no correlation (r2 < 0.1) of the differences (mean difference <0.2kPa, <6%; limits of agreement <0.4kPa, <16%) with BMI, PDFF, and T2 *. Breath-hold times were: 14 seconds (SC), 5seconds (RnS), 7seconds (RwS) per slice, and 16 seconds for the R3D acquisition. C-SENSE accelerated GRE MRE sequences, using displacement wave polarity-inversion motion encoding, produce equivalent measurements of liver stiffness and have potential clinical benefit in patients with limited breath-holding capacity. 1 TECHNICAL EFFICACY: Stage 1.

Quantitative effects of off-resonance related distortion on brain mechanical property estimation with magnetic resonance elastography.

Off-resonance related geometric distortion can impact quantitative MRI techniques, such as magnetic resonance elastography (MRE), and result in errors to these otherwise sensitive metrics of brain health. MRE is a phase contrast technique to determine the mechanical properties of tissue by imaging shear wave displacements and estimating tissue stiffness through inverse solution of Navier's equation. In this study, we systematically examined the quantitative effects of distortion and corresponding correction approaches on MRE measurements through a series of simulations, phantom models, and in vivo brain experiments. We studied two different k-space trajectories, echo-planar imaging and spiral, and we determined that readout time, off-resonance gradient strength, and the combination of readout direction and off-resonance gradient direction, impact the estimated mechanical properties. Images were also processed through traditional distortion correction pipelines, and we found that each of the correction mechanisms works well for reducing stiffness errors, but are limited in cases of very large distortion. The ability of MRE to detect subtle changes to neural tissue health relies on accurate, artifact-free imaging, and thus off-resonance related geometric distortion must be considered when designing sequences and protocols by limiting readout time and applying correction where appropriate.

Tumor Solid Stress: Assessment with MR Elastography under Compression of Patient-Derived Hepatocellular Carcinomas and Cholangiocarcinomas Xenografted in Mice.

Simple SummaryTumor biomechanical properties, including high viscoelasticity and tumor pressure (solid stress and interstitial fluid pressure), are linked to tumor severity. While tumor viscoelasticity can be quantified with MR elastography, a non-invasive method to quantify tumor pressure remains elusive. In patient-derived hepatocellular carcinomas and cholangiocarcinomas xenografted in mice, we observed that basal elasticity determined during MR elastography under compression had high diagnostic performance in assessing tumor fibrosis content and was independently influenced by interstitial fluid pressure. In contrast, compression stiffening rate had high diagnostic performance in assessing solid stress. Assessment of compression stiffening with MR elastography may provide a non-invasive biomarker of tumor solid stress.Malignant tumors have abnormal biomechanical characteristics, including high viscoelasticity, solid stress, and interstitial fluid pressure. Magnetic resonance (MR) elastography is increasingly used to non-invasively assess tissue viscoelasticity. However, solid stress and interstitial fluid pressure measurements are performed with invasive methods. We studied the feasibility and potential role of MR elastography at basal state and under controlled compression in assessing altered biomechanical features of malignant liver tumors. MR elastography was performed in mice with patient-derived, subcutaneously xenografted hepatocellular carcinomas or cholangiocarcinomas to measure the basal viscoelasticity and the compression stiffening rate, which corresponds to the slope of elasticity versus applied compression. MR elastography measurements were correlated with invasive pressure measurements and digital histological readings. Significant differences in MR elastography parameters, pressure, and histological measurements were observed between tumor models. In multivariate analysis, collagen content and interstitial fluid pressure were determinants of basal viscoelasticity, whereas solid stress, in addition to collagen content, cellularity, and tumor type, was an independent determinant of compression stiffening rate. Compression stiffening rate had high AUC (0.87 ± 0.08) for determining elevated solid stress, whereas basal elasticity had high AUC for tumor collagen content (AUC: 0.86 ± 0.08). Our results suggest that MR elastography compression stiffening rate, in contrast to basal viscoelasticity, is a potential marker of solid stress in malignant liver tumors.

Stiffness change of the supraspinatus muscle can be detected by magnetic resonance elastography

Magnetic resonance elastography (MRE) and ultrasound shear wave elastography (SWE) are imaging techniques to measure stiffness of the soft tissue using magnetic resonance imaging (MRI) and ultrasound images, respectively. The purpose of this study was to explore the feasibility of the MRE measurement to evaluate the change in supraspinatus (SSP) muscle stiffness before and after rotator cuff tear, and to compare the result with those of SWE. Six swine shoulders were used. The skin and subcutaneous fat were removed, and the stiffness value of the SSP muscle was measured by MRE and SWE. The MRE measurement was performed with 0.3 T open MRI and the vibration from a pneumatic driver system with active driver to a passive driver to create the shear wave in the tissue. The passive driver was placed on the center of the SSP muscle. The stiffness was estimated from the wave images using local frequency estimation methods. In the SWE measurement, the probe of the ultrasound was placed on the center of the SSP muscle. The shear wave propagation speed was measured at a depth of 1 cm from the surface, and the stiffness was calculated. After those measurements, the rotator cuff tendon was detached from the greater tuberosity, and MRE and SWE measurements were then performed in the same manner again. The differences in the stiffness values were compared between before and after the rotator cuff tendon tear on both the MRE and SWE measurements. The results indicated that stiffness values on MRE and SWE were 9.3 ± 1.8 and 10.0 ± 1.2 kPa respectively before the rotator cuff tear, and 7.3 ± 1.3 and 8.0 ± 0.8 kPa respectively after the tendon detachment. Stiffness values were significantly lower after the tendon detachment on both the MRE and SWE measurements (p < 0.05). Our results demonstrated that stiffness values of the SSP muscle on MRE and SWE were lower after rotator cuff detachment. From this result, MRE may be a feasible method for quantification of the change in rotator cuff muscle stiffness.