Magnetic Resonance Elastography Research Articles

Simulation of a synchronized methodology for MR-based electromechanical property imaging during transcranial electrical stimulation

Introduction: Recent investigations into the biomechanics of the brain have unveiled alteration in tissue stiffness triggered by external stimuli. For instance, visual stimulation effects can be measured in elasticity images of the cortex generated by functional magnetic resonance elastography (MRE). Such a mechanical characterization method combined with non-invasive brain stimulation (NIBS), a technique that seeks to selectively modulate particular parts of the brain using weak electrical currents, has the potential to influence research on various neurological disorders. In this in silico study, we aimed to elucidate individual and interdependent aspects related to a synchronized biomechanical imaging and non-invasive brain stimulation methodology. Magnetic resonance electrical impedance tomography (MREIT) was incorporated to the pipeline, providing a promising way of evaluating NIBS-induced electrical current patterns in the brain while leveraging MRE and transcranial alternating current stimulation (tACS) experimental settings.Methods: A mouse head model was assembled using open-access atlases to include five anatomical structures: skin/subcutaneous tissue, skull, cerebrospinal fluid (CSF), brain white and grey matters. MRE, tACS, and MREIT experiments were simulated using Comsol Multiphysics with Matlab Livelink. Synthetic MRE and MREIT data were processed using the subzone non-linear inversion and harmonic Bz algorithm, respectively, to reconstruct images of the distributed complex shear modulus and electrical conductivity.Results and Discussion: Lorentz body forces arising from simultaneous MRE and tACS elicited elastic waves of negligible amplitude compared with the extrinsic actuation levels reported in the literature, which allowed accurate reconstructions of the complex shear modulus. Qualitative electrical conductivity maps retrieved by MREIT accurately delineated anatomical regions of the brain model and could be used to recover reasonably accurate distributions of tACS-induced currents. This multi-physics approach has potential for translation to human brain imaging, and may provide more possibilities for the characterization of brain function together than in isolation.

Shear wave speeds in a nearly incompressible fibrous material with two unequal fiber families.

The mechanical properties of soft biological tissues can be characterized non-invasively by magnetic resonance elastography (MRE). In MRE, shear wave fields are induced by vibration, imaged by magnetic resonance imaging, and inverted to estimate tissue properties in terms of the parameters of an underlying material model. Most MRE studies assume an isotropic material model; however, biological tissue is often anisotropic with a fibrous structure, and some tissues contain two or more families of fibers-each with different orientations and properties. Motivated by the prospect of using MRE to characterize such tissues, this paper describes the propagation of shear waves in soft fibrous material with two unequal fiber families. Shear wave speeds are expressed in terms of material parameters, and the effect of each parameter on the shear wave speeds is investigated. Analytical expressions of wave speeds are confirmed by finite element simulations of shear wave transmission with various polarization directions. This study supports the feasibility of estimating parameters of soft fibrous tissues with two unequal fiber families in vivo from local shear wave speeds and advances the prospects for the mechanical characterization of such biological tissues by MRE.

Velacur ACE outperforms FibroScan CAP for diagnosis of MASLD.

As the prevalence of metabolic dysfunction-associated steatotic liver disease increases, it is imperative to have noninvasive alternatives to liver biopsy. Velacur offers a non-invasive, point-of-care ultrasound-based method for the assessment of liver stiffness and attenuation. The aim of this study was to perform a head-to-head comparison of liver stiffness and liver fat determined by Velacur and FibroScan using MRI-based measurements as the reference standard. This prospective cross-sectional study included 164 adult participants with well-characterized metabolic dysfunction-associated steatotic liver disease. Patients underwent a research exam including Velacur, FibroScan and contemporaneous magnetic resonance elastography, and magnetic resonance imaging proton density fat fraction (MRI-PDFF) scans. The primary outcome was the presence of advanced fibrosis (>F2) as measured by magnetic resonance elastography and the presence of liver fat (>5%) as measured by MRI-PDFF. The mean age and body mass index were 57±12 years and 30.6±4.8kg/m2, respectively. The mean liver stiffness on magnetic resonance elastography was 3.22±1.39kPa and the mean liver fat on MRI-PDFF was 14.2±8%. The liver stiffness assessments by Velacur and FibroScan were similar for the detection of advanced fibrosis (AUC 0.95 vs. 0.97) and were not statistically different (p=0.43). Velacur was significantly better than FibroScan (AUC 0.94 vs. 0.79, p=0.01), for the detection of MRI-PDFF >5% (diagnosis of metabolic dysfunction-associated liver disease). Velacur was superior to FibroScan for liver fat detection with MRI-PDFF as the reference. Velacur and FibroScan were not statistically different for liver stiffness assessment as defined by magnetic resonance elastography.

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.

SWENet: A Physics-Informed Deep Neural Network (PINN) for Shear Wave Elastography.

Shear wave elastography (SWE) enables the measurement of elastic properties of soft materials in a non-invasive manner and finds broad applications in various disciplines. The state-of-the-art SWE methods rely on the measurement of local shear wave speeds to infer material parameters and suffer from wave diffraction when applied to soft materials with strong heterogeneity. In the present study, we overcome this challenge by proposing a physics-informed neural network (PINN)-based SWE (SWENet) method. The spatial variation of elastic properties of inhomogeneous materials has been introduced in the governing equations, which are encoded in SWENet as loss functions. Snapshots of wave motions have been used to train neural networks, and during this course, the elastic properties within a region of interest illuminated by shear waves are inferred simultaneously. We performed finite element simulations, tissue-mimicking phantom experiments, and ex vivo experiments to validate the method. Our results show that the shear moduli of soft composites consisting of matrix and inclusions of several millimeters in cross-section dimensions with either regular or irregular geometries can be identified with excellent accuracy. The advantages of the SWENet over conventional SWE methods consist of using more features of the wave motions and enabling seamless integration of multi-source data in the inverse analysis. Given the advantages of SWENet, it may find broad applications where full wave fields get involved to infer heterogeneous mechanical properties, such as identifying small solid tumors with ultrasound SWE, and differentiating gray and white matters of the brain with magnetic resonance elastography.

Severe hepatic steatosis promotes increased liver stiffness in the early stages of metabolic dysfunction-associated steatotic liver disease.

The predictors of progression from steatosis to more advanced stages of metabolic dysfunction-associated steatotic liver disease (MASLD) remain unclear. We evaluated the association between the quantity of hepatic steatosis and longitudinal changes in liver stiffness measurements (LSMs) using magnetic resonance elastography (MRE) in patients with MASLD. We retrospectively analysed patients with MASLD who underwent at least two serial MRE and magnetic resonance imaging-based proton density fat fraction (MRI-PDFF) examinations at least 1 year apart. Fine-Gray competitive proportional hazard regression was used to identify LSM progression and regression factors. A total of 471 patients were enrolled. Factors linked to LSM progression were steatosis grade 3 (MRI-PDFF ≥17.1%, adjusted hazard ratio [aHR] 2.597; 95% confidence interval [CI] 1.483-4.547) and albumin-bilirubin grade 2 or 3 (aHR 2.790; 95% CI 1.284-6.091), while the only factor linked to LSM regression was % decrease rate of MRI-PDFF ≥5% (aHR 2.781; 95% CI 1.584-4.883). Steatosis grade 3 correlated with a higher incidence rate of LSM progression than steatosis grade 1 (MRI-PDFF <11.3%) in patients with LSM stage 0 (<2.5 kilopascal [kPa]), and a % annual decrease rate of MRI-PDFF ≥5% correlated with a higher incidence rate of LSM regression than that of MRI-PDFF >-5% and <5% in patients with LSM stage 1 or 2-4 (≥2.5 kPa). Severe hepatic steatosis was linked to significant LSM progression in patients with MASLD and low LSM (<2.5 kPa).

Application of continuous shear wave elastography method with multiple frequency selection to liver viscoelasticity measurement

In this study, we present a method for evaluating liver viscoelasticity using continuous shear wave elastography with an arbitrary frequency selection. In the Voigt model, viscosity depends on the frequency of shear waves, thus allowing viscosity evaluation by combining measurements at different frequencies. The shear wave frequency must satisfy the continuous shear-wave elastography frequency conditions. Therefore, the shear-wave frequency was selected as an integer fraction of the pulse repetition frequency of the ultrasound device. Low-viscosity phantoms were used in this study. The frequency dependence of shear-wave velocity was confirmed using a viscous phantom. The shear wave velocity dispersion measured using the proposed method was 5.41–8.98 m/s/kHz for four healthy liver volunteers, which are similar to that of a healthy liver reported by magnetic resonance elastography (5.76–7.52 m/s/kHz). It has been demonstrated that the frequency dependence of shear wave propagation can be measured.

Multiparametric MRI-based whole-liver radiomics for predicting early-stage liver fibrosis in rabbits.

To develop and validate a whole-liver radiomic model using multiparametric MRI for predicting early-stage liver fibrosis (LF) in rabbits. A total of 134 rabbits (early-stage LF, n = 91; advanced-stage LF, n = 43) who underwent liver magnetic resonance elastography (MRE), hepatobiliary phase, dynamic contrast enhanced (DCE), intravoxel incoherent motion (IVIM), diffusion kurtosis imaging, and T2* scanning were enrolled and randomly allocated to either the training or validation cohort. Whole-liver radiomic features were extracted and selected to develop a radiomic model and generate quantitative Rad-scores. Then, multivariable logistic regression was utilized to determine the Rad-scores associated with early-stage LF, and effective features were integrated to establish a combined model. The predictive performance was assessed by the area under the curve (AUC). The MRE model achieved superior AUCs of 0.95 in the training cohort and 0.86 in the validation cohort, followed by the DCE-MRI model (0.93 and 0.82), while the IVIM model had lower AUC values of 0.91 and 0.82, respectively. The Rad-scores of MRE, DCE-MRI and IVIM were identified as independent predictors associated with early-stage LF. The combined model demonstrated AUC values of 0.96 and 0.88 for predicting early-stage LF in the training and validation cohorts, respectively. Our study highlights the remarkable performance of a multiparametric MRI-based radiomic model for the individualized diagnosis of early-stage LF. This is the first study to develop a combined model by integrating multiparametric radiomic features to improve the accuracy of LF staging.

Acute effects of high-intensity exercise on brain mechanical properties and cognitive function

Previous studies have shown that engagement in even a single session of exercise can improve cognitive performance in the short term. However, the underlying physiological mechanisms contributing to this effect are still being studied. Recently, with improvements to advanced quantitative neuroimaging techniques, brain tissue mechanical properties can be sensitively and noninvasively measured with magnetic resonance elastography (MRE) and regional brain mechanical properties have been shown to reflect individual cognitive performance. Here we assess brain mechanical properties before and immediately after engagement in a high-intensity interval training (HIIT) regimen, as well as one-hour post-exercise. We find that immediately after exercise, subjects in the HIIT group had an average global brain stiffness decrease of 4.2% (p < 0.001), and an average brain damping ratio increase of 3.1% (p = 0.002). In contrast, control participants who did not engage in exercise showed no significant change over time in either stiffness or damping ratio. Changes in brain mechanical properties with exercise appeared to be regionally dependent, with the hippocampus decreasing in stiffness by 10.4%. We also found that one-hour after exercise, brain mechanical properties returned to initial baseline values. The magnitude of changes to brain mechanical properties also correlated with improvements in reaction time on executive control tasks (Eriksen Flanker and Stroop) with exercise. Understanding the neural changes that arise in response to exercise may inform potential mechanisms behind improvements to cognitive performance with acute exercise.

Prospective head-to-head comparison of non-invasive scores for diagnosis of fibrotic MASH in patients with type 2 diabetes

Non-invasive scores have been proposed to identify patients with fibrotic, metabolic dysfunction-associated steatohepatitis (MASH), who are at the highest risk of progression to complications of cirrhosis and may benefit from pharmacologic treatments. However, data in patients with type 2 diabetes (T2DM) are lacking. The aim of this multicenter prospective study was to perform a head-to-head comparison of FAST (FibroScan-aspartate aminotransferase [AST]), MAST (MRI-AST), MEFIB (magnetic resonance elastography [MRE] plus FIB-4), and FNI (fibrotic NASH index) for detecting fibrotic MASH in patients with T2DM. A total of 330 outpatients with T2DM and biopsy-proven metabolic dysfunction-associated steatotic liver disease (MASLD) from the QUID-NASH study (NCT03634098), who underwent FibroScan, MRI-proton density fat fraction and MRE at the time of liver biopsy were studied. The main outcome was fibrotic MASH, defined as NAS ≥4 (with at least one point for each parameter) and fibrosis stage ≥2 (centrally reviewed). All data for score comparisons were available for 245 patients (median age 59 years, 65% male, median BMI 31kg/m2; fibrotic MASH in 39%). FAST and MAST had similar accuracy (AUROCs 0.81 vs. 0.79, p=0.41) but outperformed FNI (0.74; p=0.01) and MEFIB (0.68; p<0.0001). When using original cut-offs, MAST outperformed FAST, MEFIB and FNI when comparing the percentage of correctly classified patients, in whom liver biopsy would be avoided (69% vs. 48%, 46%, 39%, respectively; p<0.001). When using cut-offs specific to our population, FAST outperformed FNI and MAST (56% vs. 40%, and 38%, respectively; p<0.001). Our findings show that FAST, MAST, MEFIB and FNI are accurate non-invasive tools to identify patients with T2DM and fibrotic MASH in secondary/tertiary diabetes clinics. Cut-offs adapted to the T2DM population should be considered. Among patients with type 2 diabetes (T2DM), identifying those with metabolic dysfunction-associated steatohepatitis and significant fibrosis, who are the most at risk of developing clinical liver-related outcomes and who may benefit from pharmacologic treatments, is an unmet need. In this prospective multicenter study, we compared four non-invasive scores, three based on imaging (MRI or ultrasound technologies) and one on laboratory blood tests, for this purpose, using original and study-specific cut-offs. Our findings show that FAST, MAST, MEFIB and FNI are accurate non-invasive tools to identify patients with T2DM and fibrotic MASH in secondary/tertiary diabetes clinics. Cut-offs adapted to the T2DM population should be considered. NCT03634098.

Viscoelastic parameters derived from multifrequency MR elastography for depicting hepatic fibrosis and inflammation in chronic viral hepatitis

ObjectivesThe capability of MR elastography (MRE) to differentiate fibrosis and inflammation, and to provide precise diagnoses is crucial, whereas the coexistence of fibrosis and inflammation may obscure the diagnostic accuracy.MethodsIn this retrospective study, from June 2020 to December 2022, chronic viral hepatitis patients who underwent multifrequency MRE (mMRE) were included in, and further divided into, training and validation cohorts. The hepatic viscoelastic parameters [shear wave speed (c) and loss angle (φ) of the complex shear modulus] were obtained from mMRE. The logistic regression and receiver operating characteristic (ROC) curves were generated to evaluate performance of viscoelastic parameters for fibrosis and inflammation.ResultsA total of 233 patients were assigned to training cohort and validation cohorts (mean age, 52 years ± 13 (SD); 51 women; training cohort, n = 170 (73%), and validation cohort, n = 63 (27%)). Liver c exhibited superior performance in detecting fibrosis with ROC (95% confidence interval) of ≥ S1 (0.96 (0.92–0.99)), ≥ S2 (0.86 (0.78–0.92)), ≥ S3 (0.89 (0.84–0.95)), and S4 (0.88 (0.83–0.93)). Similarly, φ was effective in diagnosing inflammation with ROC values of ≥ G2 (0.72 (0.63–0.81)), ≥ G3 (0.88 (0.83–0.94)), and G4 (0.92 (0.87–0.98)). And great predictive discrimination for fibrosis and inflammation were shown in validation cohort (all AUCs > 0.75).ConclusionThe viscoelastic parameters derived from multifrequency MRE could realize simultaneous detection of hepatic fibrosis and inflammation.Critical relevance statementFibrosis and inflammation coexist in chronic liver disease which obscures the diagnostic performance of MR elastography, whereas the viscoelastic parameters derived from multifrequency MR elastography could realize simultaneous detection of hepatic fibrosis and inflammation.Key points• Hepatic biomechanical parameters derived from multifrequency MR elastography could effectively detect fibrosis and inflammation.• Liver stiffness is useful for detecting fibrosis independent of inflammatory activity.• Fibrosis could affect the diagnostic efficacy of liver viscosity in inflammation, especially in early-grade of inflammation.Graphical

MR elastography-based slip interface imaging (SII) for functional assessment of myofascial interfaces: A feasibility study.

Abnormal adherence at functional myofascial interfaces is hypothesized as an important phenomenon in myofascial pain syndrome. This study aimed to investigate the feasibility of MR elastography (MRE)-based slip interface imaging (SII) to visualize and assess myofascial mobility in healthy volunteers. SII was used to assess local shear strain at functional myofascial interfaces in the flexor digitorum profundus (FDP) and thighs. In the FDP, MRE was performed at 90 Hz vibration to each index, middle, ring, and little finger. Two thigh MRE scans were performed at 40 Hz with knees flexed and extended. The normalized octahedral shear strain (NOSS) maps were calculated to visualize myofascial slip interfaces. The entropy of the probability distribution of the gradient NOSS was computed for the two knee positions at the intermuscular interface between vastus lateralis and vastus intermedius, around rectus femoris, and between vastus intermedius and vastus medialis. NOSS map depicted distinct functional slip interfaces in the FDP for each finger. Compared to knee flexion, clearer slip interfaces and larger gradient NOSS entropy at the vastus lateralis-vastus intermedius interface were observed during knee extension, where the quadriceps are not passively stretched. This suggests the optimal position for using SII to visualize myofascial slip interface in skeletal muscles is when muscles are not subjected to any additional force. The study demonstrated that MRE-based SII can visualize and assess myofascial interface mobility in extremities. The results provide a foundation for investigating the hypothesis that myofascial pain syndrome is characterized by changes in the mobility of myofascial interfaces.

Viscoelastic polyacrylamide MR elastography phantoms with tunable damping ratio independent of shear stiffness

Physiologically modeled test samples with known properties and characteristics, or phantoms, are essential for developing sensitive, repeatable, and accurate quantitative MRI techniques. Magnetic resonance elastography (MRE) is one such technique used to estimate tissue mechanical properties, and it is advantageous to use phantoms with independently tunable mechanical properties to benchmark the accuracy of MRE methods. Phantoms with tunable shear stiffness are commonly used for MRE, but tuning the viscosity or damping ratio has proven to be difficult. A promising candidate for MRE phantoms with tunable damping ratio is polyacrylamide (PAA). While pure PAA has very low attenuation, viscoelastic hydrogels have been made by entrapping linear polyacrylamide strands (LPAA) within the PAA network. In this study, we evaluate the use of LPAA/PAA gels as physiologically accurate phantoms with tunable damping ratio, independent of shear stiffness, via MRE. Phantoms were made with 15.3 wt% PAA while the LPAA concentration ranged from 4.5 wt% to 8.0 wt%. MRE was performed at 9.4 T with 400 Hz vibration on all phantoms revealing a strong, positive correlation between damping ratio and LPAA content (p < 0.001). There was no significant correlation between shear stiffness and LPAA content, confirming a constant PAA concentration yielded constant shear stiffness. Rheometry at 10 Hz was performed to verify the damping ratio of the phantoms. Nearly identical slopes for damping ratio versus LPAA content were found from both MRE and rheometry (0.0073 and 0.0075 respectively). Ultimately, this study validates the adaptation of polyacrylamide gels into physiologically-relevant MRE phantoms to enable testing of MRE estimates of damping ratio.

Magnetic resonance elastography as a preoperative assessment for predicting intrahepatic recurrence in patients with hepatocellular carcinoma

PurposeMagnetic resonance elastography (MRE) is a noninvasive tool for diagnosing hepatic fibrosis with high accuracy. We investigated the preoperative clinical and imaging predictors of intrahepatic recurrence after curative resection of hepatocellular carcinoma (HCC), and evaluated MRE as a predictor of intrahepatic recurrence. MethodsWe retrospectively evaluated 80 patients who underwent preoperative contrast-enhanced magnetic resonance imaging (MRI) with two-dimensional MRE and curative resection for treatment-naïve HCC between May 2019 and December 2021. Liver stiffness (LS) was measured on the elastograms, and the optimal cutoff of LS for predicting intrahepatic recurrence was obtained using receiver operating characteristic (ROC) analysis. An LS above this cutoff was defined as MRE-recurrence. Preoperative imaging features of the tumor were assessed on MRI, including features in the Liver Imaging Reporting and Data System and microvascular invasion (MVI). Recurrence-free survival (RFS) rates were estimated using the Kaplan-Meier method, and differences were compared using the log-rank test. Using a Cox proportional hazards model, we conducted a multivariable analysis to investigate the factors affecting recurrence-free survival. ResultsDuring a median follow-up period of 32 months (range, 4–52 months), thirteen patients (16.3%) developed intrahepatic recurrence. ROC analysis determined an LS cutoff of ≥4.35 kPa to define MRE-recurrence. The 4-year RFS rate was significantly higher in patients without MRE-recurrence than in those with MRE-recurrence (93.4% vs. 48.9%; p = 0.001). In multivariable analysis, MRE-recurrence (Hazard ratio [HR], 5.9; 95% confidence interval [CI], 1.5–23.1) and MVI (HR, 3.4; 95% CI, 1.0–11.3) were independent predictors of intrahepatic recurrence. ConclusionsPatients without MRE-recurrence had significantly higher RFS rates than those with MRE-recurrence. MRE-recurrence and MVI were independent predictors of intrahepatic recurrence in patients after curative resection for HCC.

Differentiation of salivary gland tumors using diffusion-weighted image-based virtual MR elastography: A pilot study.

Differentiation among benign salivary gland tumors, Warthin tumors, and malignant salivary gland tumors is crucial to treatment planning and predicting patient prognosis. However, differentiation of those tumors using imaging findings remains difficult. This study evaluated the usefulness of elasticity determined from Diffusion-weighted image (DWI)-based virtual MR elastography (MRE) compared with conventional MRI findings in differentiating the tumors. This study included 17 benign salivary gland tumors, six Warthin tumors, and 11 malignant salivary gland tumors scanned on neck MRI. The long and short diameters, T1 and T2 signal intensities, tumor margins, ADC values, and elasticity from DWI-based virtual MRE of the tumors were evaluated. The interobserver agreement in measuring tumor elasticity and the ROC curves were also assessed. The long and short diameters and the T1 and T2 signal intensities showed no significant difference among the three tumor groups. Tumor margins and the mean ADC values showed significant differences among some tumor groups. The elasticity from virtual MRE showed significant differences among all three tumor groups and the interobserver agreement was excellent. The area under the ROC curves of the elasticity were higher than those of tumor margins and mean ADC values. Elasticity values based on DWI-based virtual MRE of benign salivary gland tumors, Warthin tumors, and malignant salivary gland tumors were significantly different. The elasticity of Warthin tumors was the highest and that of benign tumors was the lowest. The elasticity from DWI-based virtual MRE may aid in the differential diagnosis of salivary gland tumors.

Feasibility of assessing non-invasive intracranial compliance using FSI simulation-based and MR elastography-based brain stiffness.

Intracranial compliance (ICC) refers to the change in intracranial volume per unit change in intracranial pressure (ICP). Magnetic resonance elastography (MRE) quantifies brain stiffness by measuring the shear modulus. Our objective is to investigate the relationship between ICC and brain stiffness through fluid-structure interaction (FSI) simulation, and to explore the feasibility of using MRE to assess ICC based on brain stiffness. This is invaluable due to the clinical importance of ICC, as well as the fast and non-invasive nature of the MRE procedure. We employed FSI simulation in hydrocephalus patients with aqueductal stenosis to non-invasively calculate ICP which is the basis of the calculation of ICC and FSI-based brain stiffness. The FSI simulated parameters used have been validated with experimental data. Our results showed that there is no relationship between FSI simulated-based brain stiffness and ICC in hydrocephalus patients. However, MRE-based brain stiffness may be sensitive to changes in intracranial fluid dynamic parameters such as cerebral perfusion pressure (CPP), cerebral blood flow (CBF), and ICP, as well as to mechano-vascular changes in the brain, which are determining parameters in ICC assessment. Although optimism has been found regarding the assessment of ICC using MRE-based brain stiffness, especially for acute-onset brain disorders, further studies are necessary to clarify their direct relationship.

Imaging-based noninvasive liver disease assessment for staging liver fibrosis in chronic liver disease: A systematic review supporting the AASLD Practice Guideline.

Transient elastography (TE), shear wave elastography, and/or magnetic resonance elastography (MRE), each providing liver stiffness measurement (LSM), are the most studied imaging-based noninvasive liver disease assessment (NILDA) techniques. To support the American Association for the Study of Liver Diseases guidelines on NILDA, we summarized the evidence on the accuracy of these LSM methods to stage liver fibrosis (F). A comprehensive search for studies assessing LSM by TE, shear wave elastography, or MRE for the identification of significant fibrosis (F2-4), advanced fibrosis (F3-4), or cirrhosis (F4), using histopathology as the standard of reference by liver disease etiology in adults or children from inception to April 2022 was performed. We excluded studies with <50 patients with a single disease entity and mixed liver disease etiologies (with the exception of HCV/HIV coinfection). Out of 9447 studies, 240 with 61,193 patients were included in this systematic review. In adults, sensitivities for the identification of F2-4 ranged from 51% to 95%, for F3-4 from 70% to 100%, and for F4 from 60% to 100% across all techniques/diseases, whereas specificities ranged from 36% to 100%, 74% to 100%, and 67% to 99%, respectively. The largest body of evidence available was for TE; MRE appeared to be the most accurate method. Imaging-based NILDA outperformed blood-based NILDA in most comparisons, particularly for the identification of F3-4/F4. In the pediatric population, imaging-based NILDA is likely as accurate as in adults. LSM from TE, shear wave elastography, and MRE shows acceptable to outstanding accuracy for the detection of liver fibrosis across various liver disease etiologies. Accuracy increased from F2-4 to F3-4 and was the highest for F4. Further research is needed to better standardize the use of imaging-based NILDA, particularly in pediatric liver diseases.

Development of a suitable vibration pad for renal MR elastography

The aim of this study was to develop a vibration pad suitable for renal MR elastography (MRE). Chronic kidney disease (CKD) is a progressive condition affecting >800 million people worldwide. Renal fibrosis is a common pathological feature of CKD that causes fibrotic regions to be much stiffer than those in normal renal tissues. Therefore, MRE can be used to diagnose CKD because it can image organ stiffness. In MRE, the shear modulus is obtained from the wavelength of the shear waves. Therefore, it is highly important to propagate shear waves with sufficient vibration strength in the tissue. By using a three-dimensional (3D) printer, we created a “Flexible Pad” suitable for renal MRE. The Flexible Pad was placed under the back of the participant in the supine position and deformed in response to the participant's weight, adhering closely to the body surface. Six healthy volunteers participated in this study. Our Flexible Pad allowed for coherent shear waves (clear waves with little scattering and interference) to be efficiently transmitted to the kidney deep-lying tissues in the abdomen. The shear moduli of the kidney (n = 6) were 8.95 ± 0.84 kPa in the right kidney and 9.70 ± 0.99 kPa in the left kidney. Our results indicate that using our Flexible Pad for renal MRE can provide a more reliable measurement of renal shear modulus.

Evaluation of MR Elastography as a Noninvasive Diagnostic Test for Spontaneous Intracranial Hypotension.

Spontaneous intracranial hypotension is a condition resulting from a leak of CSF from the spinal canal arising independent of a medical procedure. Spontaneous intracranial hypotension can present with normal brain MR imaging findings and nonspecific symptoms, leading to the underdiagnosis in some patients and unnecessary invasive myelography in others who are found not to have the condition. Given the likelihood that spontaneous intracranial hypotension alters intracranial biomechanics, the goal of this study was to evaluate MR elastography as a potential noninvasive test to diagnose the condition. We performed MR elastography in 15 patients with confirmed spontaneous intracranial hypotension from September 2022 to April 2023. Age, sex, symptom duration, and brain MR imaging Bern score were collected. MR elastography data were used to compute stiffness and damping ratio maps, and voxelwise modeling was performed to detect clusters of significant differences in mechanical properties between patients with spontaneous intracranial hypotension and healthy control participants. To evaluate diagnostic accuracy, we summarized each examination by 2 spatial pattern scores (one each for stiffness and damping ratio) and evaluated group-wise discrimination by receiver operating characteristic curve analysis. Patients with spontaneous intracranial hypotension exhibited significant differences in both stiffness and damping ratio (false discovery rate-corrected, Q < 0.05). Pattern analysis discriminated patients with spontaneous intracranial hypotension from healthy controls with an area under the curve of 0.97 overall, and the area under the curve was 0.97 in those without MR imaging findings of spontaneous intracranial hypotension. Results from this pilot study demonstrate MR elastography as a potential imaging biomarker and a noninvasive method for diagnosing spontaneous intracranial hypotension, including patients with normal brain MR imaging findings.

Shear-wave elastography to predict hepatocellular carcinoma after hepatitis C virus eradication: A systematic review and meta-analysis.

Direct-acting antiviral agents (DAAs) are highly effective treatment for chronic hepatitis C (CHC) with a significant rate of sustained virologic response (SVR). The achievement of SVR is crucial to prevent additional liver damage and slow down fibrosis progression. The assessment of fibrosis degree can be performed with transient elastography, magnetic resonance elastography or shear-wave elastography (SWE). Liver elastography could function as a predictor for hepatocellular carcinoma (HCC) in CHC patients treated with DAAs. To explore the predictive value of SWE for HCC development after complete clearance of hepatitis C virus (HCV). A comprehensive literature search of clinical studies was performed to identify the ability of SWE to predict HCC occurrence after HCV clearance. In accordance with the study protocol, a qualitative and quantitative analysis of the evidence was planned. At baseline and after 12 wk of follow-up, a trend was shown towards greater liver stiffness (LS) in those who go on to develop HCC compared to those who do not [baseline LS standardized mean difference (SMD): 1.15, 95% confidence interval (95%CI): 020-2.50; LS SMD after 12 wk: 0.83, 95%CI: 0.33-1.98]. The absence of a statistically significant difference between the mean LS in those who developed HCC or not may be related to the inability to correct for confounding factors and the absence of raw source data. There was a statistically significant LS SMD at 24 wk of follow-up between patients who developed HCC vs not (0.64; 95%CI: 0.04-1.24). SWE could be a promising tool for prediction of HCC occurrence in patients treated with DAAs. Further studies with larger cohorts and standardized timing of elastographic evaluation are needed to confirm these data.