Magnetic Resonance Elastography Sequence Research Articles

A Comparative Study of Three Systems for Liver Magnetic Resonance Elastography.

Different MR elastography (MRE) systems may produce different stiffness measurements, making direct comparison difficult in multi-center investigations. To assess the repeatability and reproducibility of liver stiffness measured by three typical MRE systems. Prospective. Thirty volunteers without liver disease history (20 males, aged 21-28)/5 gel phantoms. 3.0 T United Imaging Healthcare (UIH), 1.5 T Siemens Healthcare, 3.0 T General Electric Healthcare (GE)/Echo planar imaging-based MRE sequence. Wave images of volunteers and phantoms were acquired by three MRE systems. Tissue stiffness was evaluated by two observers, while phantom stiffness was assessed automatically by code. The reproducibility across three MRE systems was quantified based on the mean stiffness of each volunteer and phantom. Intraclass correlation coefficients (ICC), coefficients of variation (CV), and Bland-Altman analyses were used to assess the interobserver reproducibility, the interscan repeatability, and the intersystem reproducibility. Paired t-tests were performed to assess the interobserver and interscan variation. Friedman tests with Dunn's multiple comparison correction were performed to assess the intersystem variation. P values less than 0.05 indicated significant difference. The reproducibility of stiffness measured by the two observers demonstrated consistency with ICC > 0.92, CV < 4.32%, Mean bias < 2.23%, and P > 0.06. The repeatability of measurements obtained using the electromagnetic system for the liver revealed ICC > 0.96, CV < 3.86%, Mean bias < 0.19%, P > 0.90. When considering the range of reproducibility across the three systems for liver evaluations, results ranged with ICCs from 0.70 to 0.87, CVs from 6.46% to 10.99%, and Mean biases between 1.89% and 6.30%. Phantom studies showed similar results. The values of measured stiffness differed across all three systems significantly. Liver stiffness values measured from different MRE systems can be different, but the measurements across the three MRE systems produced consistent results with excellent reproducibility. 1 TECHNICAL EFFICACY: Stage 2.

Wavelet MRE: Imaging propagating broadband acoustic waves with wavelet-based motion-encoding gradients.

To demonstrate a novel MR elastography (MRE) technique, termed here wavelet MRE. With this technique, broadband motion sensitivity is achievable. Moreover, the true tissue displacement can be reconstructed with a simple inverse transform. A wavelet MRE sequence was developed with motion-encoding gradients based on Haar wavelets. From the phase images' displacement was estimated using an inverse transform. Simulations were performed using a frequency sweep and a transient as ground-truth motions. A PVC phantom was scanned using wavelet MRE and standard MRE with both transient (one and 10 cycles of 90-Hz motion) and steady-state dual-frequency motion (30 and 60 Hz) for comparison. The technique was tested in a human brain, and motion trajectories were estimated for each voxel. In simulation, the displacement information estimated from wavelet MRE closely matched the true motion. In the phantom test, the MRE phase data generated from the displacement information derived from wavelet MRE agreed well with standard MRE data. Testing of wavelet MRE to assess transient motion waveforms in the brain was successful, and the tissue motion observed was consistent with a previous study. The uniform and broadband frequency response of wavelet MRE makes it a promising method for imaging transient, multifrequency motion, or motion with unknown frequency content. One potential application is measuring the response of brain tissue undergoing low-amplitude, transient vibrations as a model for the study of traumatic brain injury.

Rapid MR elastography of the liver for subsecond stiffness sampling.

Depicting the stiffness of biological soft tissues, MR elastography (MRE) has a wide range of diagnostic applications. The purpose of this study was to improve the temporal resolution of 2D hepatic MRE in order to provide more rapid feedback on the quality of the wavefield and ensure better temporal sampling of respiration-induced stiffness changes. We developed a rapid MRE sequence that uses 2D segmented gradient-echo spiral readout to encode 40 Hz harmonic vibrations and generate stiffness maps within 625 ms. We demonstrate the use of this technique as a rapid test for shear wave amplitudes and overall MRE image quality and as a method for monitoring respiration-induced stiffness changes in the liver in comparison to 3D MRE and ultrasound-based time-harmonic elastography. Subsecond MRE allowed monitoring of increasing shear wave amplitudes in the liver with increasing levels of external stimulation within a single breath-hold. Furthermore, the technique detected respiration-induced changes in liver stiffness with peak values (1.83 ± 0.22 m/s) at end-inspiration, followed by softer values during forced abdominal pressure (1.60 ± 0.22 m/s) and end-expiration (1.49 ± 0.22 m/s). The effects of inspiration and expiration were confirmed by time-harmonic elastography. Our results suggest that subsecond MRE of the liver is useful for checking MRE driver settings and monitoring breathing-induced changes in liver stiffness in near real time.

Single Breath-Hold 3-Dimensional Magnetic Resonance Elastography Depicts Liver Fibrosis and Inflammation in Obese Patients.

Three-dimensional (3D) magnetic resonance elastography (MRE) measures liver fibrosis and inflammation but requires several breath-holds that hamper clinical acceptance. The aim of this study was to evaluate the technical and clinical feasibility of a single breath-hold 3D MRE sequence as a means of measuring liver fibrosis and inflammation in obese patients. From November 2020 to December 2021, subjects were prospectively enrolled and divided into 2 groups. Group 1 included healthy volunteers (n = 10) who served as controls to compare the single breath-hold 3D MRE sequence with a multiple-breath-hold 3D MRE sequence. Group 2 included liver patients (n = 10) who served as participants to evaluate the clinical feasibility of the single breath-hold 3D MRE sequence in measuring liver fibrosis and inflammation. Controls and participants were scanned at 60 Hz mechanical excitation with the single breath-hold 3D MRE sequence to retrieve the magnitude of the complex-valued shear modulus (|G*| [kPa]), the shear wave speed (Cs [m/s]), and the loss modulus (G" [kPa]). The controls were also scanned with a multiple-breath-hold 3D MRE sequence for comparison, and the participants had histopathology (Ishak scores) for correlation with Cs and G". For the 10 controls, 5 were female, and the mean age and body mass index were 33.1 ± 9.5 years and 23.0 ± 2.1 kg/m 2 , respectively. For the 10 participants, 8 were female, and the mean age and body mass index were 45.1 ± 16.5 years and 33.1 ± 4.0 kg/m 2 (obese range), respectively. All participants were suspected of having nonalcoholic fatty liver disease. Bland-Altman analysis of the comparison in controls shows there are nonsignificant differences in |G*|, Cs, and G" below 6.5%, suggesting good consensus between the 2 sequences. For the participants, Cs and G" correlated significantly with Ishak fibrosis and inflammation grades, respectively ( ρ = 0.95, P < 0.001, and ρ = 0.84, P = 0.002). The single breath-hold 3D MRE sequence may be effective in measuring liver fibrosis and inflammation in obese patients.

Comparison of spin-echo echo-planar imaging magnetic resonance elastography with gradient-recalled echo magnetic resonance elastography and their correlation with transient elastography

PURPOSE This study aimed to assess the agreement between liver stiffness (LS) values obtained by the gradient-recalled echo (GRE) magnetic resonance elastography (MRE) and spin-echo echo-planar imaging (SE-EPI) MRE with those of transient elastography (TE), respectively. METHODS We retrospectively included 48 participants who underwent liver MRE with both GRE and SE-EPI sequences in the same session and also TE within 1 year. We obtained LS values for MRE by drawing free-hand region of interest, and TE was performed using a FibroScan device. We assessed the relationship between the mean LS values obtained by each MRE sequence and TE using the correlation coefficients and Bland-Altman plots, respectively. We also compared LS values and technical failure rates of measured values from MRE between SE-EPI and GRE sequences using the paired t-test and McNemar's test. The MRE failure was defined as the absence of pixel value with a confidence index above 95%. RESULTS The LS values from SE-EPI and GRE sequences strongly correlated with those from TE (GRE; r = 0.73, P < .001 vs. SE-EPI; r = 0.79, P < .001). In addition, the LS values from the 2 MRE sequences showed excellent relationship (intraclass correlation coefficient, 0.94 [0.89-0.97], P < .001). The LS values from SE-EPI and GRE MRE were not significantly different (4.14 kPa vs. 3.88 kPa, P = .19). Furthermore, the technical success rate of SE-EPI MRE was superior to that of GRE (100% vs. 83.8%, P = .031). CONCLUSION The measured LS values obtained using TE correlated strongly with those obtained using GRE and SE-EPI MRE techniques, even though SE-EPI-MRE resulted a higher technical success rate than GRE-MRE. Therefore, we believe that TE, GRE, and SE-EPI MR elastography techniques may complement each other according to the appropriate individual situation.

Reliability of Gradient-Echo Magnetic Resonance Elastography of Lumbar Muscles: Phantom and Clinical Studies.

Magnetic resonance elastography (MRE) has been used to successfully characterize the mechanical behavior of healthy and diseased muscles, but no study has been performed to investigate the reliability of MRE on lumbar muscles. The objective of this work was to determine the reliability of MRE techniques on lumbar muscles in both ex vivo phantom and in vivo human studies. In this study, fresh porcine leg muscles were used in the phantom study, and 80 healthy adults (38.6 ± 11.2 years, 40 women) were recruited in the human study. Five repeated stiffness maps were obtained from both the phantom and human muscles by using a gradient-echo MRE sequence with a pneumatic vibration on a 1.5 T MR scanner. The technical failure rate, coefficient of variation (CV), and quality score were assessed to evaluate the reliability of MRE, respectively. Analysis of variance was performed to compare the stiffness between different lumbar muscles, and the difference was significant if p < 0.05 after Bonferroni correction. The results showed that the MRE achieved a zero technical failure rate and a low CV of stiffness (6.24 ± 1.41%) in the phantom muscles. However, in the human study, the MRE exhibited high CVs of stiffness (21.57%–25.24%) in the lumbar muscles, and the technical failure rate was higher in psoas muscles (60.0–66.3% in) than in paraspinal muscles (0.0–2.5%). Further, higher quality scores were noticed in paraspinal muscles (7.31–7.71) than those in psoas muscles (1.83–2.06). In conclusion, the MRE was a reliable technique to investigate the mechanical property of lumbar muscles, but it was less reliable to assess stiffness in psoas muscles than paraspinal muscles.

Magnetic Resonance Elastography of Intervertebral Discs: Spin-Echo Echo-Planar Imaging Sequence Validation.

Magnetic resonance elastography (MRE) is an imaging technique that can noninvasively assess the shear properties of the intervertebral disc (IVD). Unlike the standard gradient recalled echo (GRE) MRE technique, a spin-echo echo-planar imaging (SE-EPI) sequence has the potential to improve imaging efficiency and patient compliance. To validate the use of an SE-EPI sequence for MRE of the IVD compared against the standard GRE sequence. Cross-over. Twenty-eight healthy volunteers (15 males and 13 females, age range: 19-55). 3 T; GRE, SE-EPI with breath holds (SE-EPI-BH) and SE-EPI with free breathing (SE-EPI-FB) MRE sequences. MRE-derived shear stiffnesses were calculated via principal frequency analysis. SE-EPI derived shear stiffness and octahedral shear strain signal-to-noise ratios (OSS-SNR) were compared against those derived using the GRE sequence. The reproducibility and repeatability of SE-EPI stiffness measurements were determined. Shear stiffness was evaluated in the nucleus pulposus (NP) and annulus fibrosus (AF) regions of the disc. Scan times between sequences were compared. Linear mixed models, Bland-Altman plots, and Lin's concordance correlation coefficients (CCCs) were used with P < 0.05 considered statistically significant. Good correlation was observed between shear stiffnesses derived from the SE-EPI sequences with those derived from the GRE sequence with CCC values greater than 0.73 and 0.78 for the NP and AF regions, respectively. OSS-SNR was not significantly different between GRE and SE-EPI sequences (P > 0.05). SE-EPI sequences generated highly reproducible and repeatable stiffness measurements with CCC values greater than 0.97 in the NP and AF regions and reduced scan time by at least 51% compared to GRE. SE-EPI-BH and SE-EPI-FB stiffness measurements were similar with CCC values greater than 0.98 for both regions. SE-EPI-based MRE-derived stiffnesses were highly reproducible and repeatable and correlated with current standard GRE MRE-derived stiffness estimates while reducing scan times. 1 TECHNICAL EFFICACY STAGE: 1.

Prospective Evaluation of Virtual MR Elastography With Diffusion-Weighted Imaging in Subjects With Nonalcoholic Fatty Liver Disease.

Non-alcoholic fatty liver disease (NAFLD) is increasingly common worldwide and can lead to the development of cirrhosis, liver failure and cancer. Virtual magnetic resonance elastography (VMRE), which is based on a shifted apparent diffusion coefficient (sADC), is a potential noninvasive method to assess liver fibrosis without the specialized hardware and expertise required to implement traditional MR elastography (MRE). Although hepatic steatosis is known to confound ADC measurements, previous studies using VMRE have not corrected for hepatic fat fraction. To compare VMRE, corrected for the confounding effects of unsuppressed fat signal, to MRE and biopsy in subjects with suspected NAFLD. Prospective, cross-sectional. A total of 49 adult subjects with suspected NAFLD (18 male; median age 55 years, range 33-74 years) who underwent liver biopsy. 3T, diffusion-weighted spin echo planar, chemical-shift encoded (IDEAL IQ) and MRE sequences. Two observers drew regions of interest on sADC, proton density fat fraction and MRE-derived stiffness maps. Fat-corrected sADC values were used to calculate the diffusion-based shear modulus according to the VMRE method. Predicted fibrosis stage for MRE and VMRE was determined using previously published cut-off values. The relationship between VMRE and MRE was assessed with least-squares linear regression (coefficient of determination, R2 ). Agreement between MRE and VMRE-predicted fibrosis stage was evaluated with a kappa coefficient and accuracy compared using McNemar's test. A one-way ANOVA determined if the fat-corrected sADC (VMRE) and MRE differed by fibrosis stage. A P value < 0.05 was considered statistically significant. Least squares regression of VMRE vs. MRE revealed R2 =0.046 and a slope that was not significantly different from zero (P=0.14). There was no agreement between MRE and VMRE-predicted fibrosis stage (kappa=-0.01). The proportion of correctly predicted fibrosis stage was significantly higher for MRE compared to VMRE. MRE was significantly associated with fibrosis stage, but fat-corrected sADC was not (P=0.24). Fat-corrected VMRE was not associated with fibrosis stage in NAFLD. Further investigation is required if VMRE is to be considered in subjects with NAFLD. 1 TECHNICAL EFFICACY: Stage 2.

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.

Fast magnetic resonance elastography with multiphase radial encoding and harmonic motion sparsity based reconstruction

Objective. To achieve fast magnetic resonance elastography (MRE) at a low frequency for better shear modulus estimation of the brain. Approach. We proposed a multiphase radial DENSE MRE (MRD-MRE) sequence and an improved GRASP algorithm utilizing the sparsity of the harmonic motion (SH-GRASP) for fast MRE at 20 Hz. For the MRD-MRE sequence, the initial position encoded by spatial modulation of magnetization (SPAMM) was decoded by an arbitrary number of readout blocks without increasing the number of phase offsets. Based on the harmonic motion, a modified total variation and temporal Fourier transform were introduced to utilize the sparsity in the temporal domain. Both phantom and brain experiments were carried out and compared with that from multiphase Cartesian DENSE-MRE (MCD-MRE), and conventional gradient echo sequence (GRE-MRE). Reconstruction performance was also compared with GRASP and compressed sensing. Main results. Results showed the scanning time of a fully sampled image with four phase offsets for MRD-MRE was only 1/5 of that from GRE-MRE. The wave patterns and estimated stiffness maps were similar to those from MCD-MRE and GRE-MRE. With SH-GRASP, the total scan time could be shortened by additional 4 folds, achieving a total acceleration factor of 20. Better metric values were also obtained using SH-GRASP for reconstruction compared with other algorithms. Significance. The MRD-MRE sequence and SH-GRASP algorithm can be used either in combination or independently to accelerate MRE, showing the potentials for imaging the brain as well as other organs.

Spleen Stiffness By Magnetic Resonance Elastography or Ultrasound Elastography As a Surrogate Marker of Bone Marrow Fibrosis in Myelofibrosis Patients

▪IntroductionPrimary myelofibrosis (PM) is a myeloproliferative neoplasm characterised by bone marrow fibrosis and extramedullary hematopoiesis. Both clinical findings and laboratory parameters are used for prognostic scores in Myelofibrosis patients. In addition, the degree of bone marrow fibrosis has an important prognostic value and has correlation with overall survival. Recently, bone marrow fibrosis was correlated with degree of splenic stiffness (SS) measured by imaging elastography techniques. 1,2 Despite these findings, there were patients with insignificant measures that could not be classified according to marrow fibrosis. In order to advance knowledge in this field, we studied splenic and hepatic stiffness (HS) in patients with myelofibrosis using elastography by two methods, ultrasonography (EUS) and magnetic resonance elastography (MRE), and its correlation with prognostic scores and bone marrow fibrosis.Study Design and MethodsThis is a prospective, cross-sectional, observational study in patients from the outpatient clinic for myeloproliferative neoplasms who had given informed consent according to procedures approved by institution´s ethical committee. Patients with PM, as well as post-essential thrombocythemia (ET) or post-polycythemia vera (PV) myelofibrosis, were included in this study. Myelofibrosis patients with diagnosis of other associated pathologies that may alter SS, as portal hypertension or cirrhosis, were excluded from the study. Patients were assessed for splenic stiffness measured by ultrasound conducted by two examiners, with more than 10 years of experience. EUS was performed in US Epiq 7 equipment - Philips - with ARFI elastometry methodology. The SS measurements was reported in m/s. In addition, they were also evaluated for splenic and liver stiffness by MRI technique. All exams were performed in 1.5 T MR equipment (Magneton Aera, Siemens Healthineers, Erlangen, Germany) and the MRI protocol included T2-weighted and gradient-echo MRE sequences using steady-state 60-Hz excitation and an external driver placed on the right side and, on the left side of the abdomen. The measures of SS were also obtained by two experienced examinersResultsAt this moment we present the results of 16 patients with myelofibrosis (PM: 8 cases; post-PV myelofibrosis: 2 cases; post-ET myelofibrosis: 6 cases). The median age was 69y (41-88y) and 62,5% of participants were male. The JAK2 V617F mutation was detected in 9 cases; three cases were CALR positive, and three cases were triple negative. The CBC showed: Hb: 10.9 g/dL (6.5-18.7); WBC (x10 9/L): 9.17 (1.8-44.5) and platelets (x10 9/L): 393 (10-957). Our preliminary results show that bone marrow fibrosis increased according to splenic stiffness by EUS and MRE (Figure 1a; table 1). Patients with osteosclerosis also presented a higher SS by MRE (Figure 1b). We could not find correlation of splenic stiffness with prognostic score DIPSS plus, although Int-2/High risk patients presented a trend to be associated with higher liver stiffness.ConclusionTo the moment, our preliminary findings suggest a correlation between SS and degree of bone marrow fibrosis and osteosclerosis, though the correlation between both measures and prognostic scores is still to be determined. We expect to have a better definition for all correlations, as we progress through the assessment of the other patients in our service. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

SPLEEN STIFFNESS BY MAGNETIC RESONANCE ELASTOGRAPHY OR ULTRASOUND ELASTOGRAPHY AS A SURROGATE MARKER OF BONE MARROW FIBROSIS IN MYELOFIBROSIS PATIENTS

Primary myelofibrosis (PM) is a myeloproliferative neoplasm characterised by bone marrow fibrosis and extramedullary hematopoiesis. Both clinical findings and laboratory parameters are used for prognostic scores in Myelofibrosis patients. In addition, the degree of bone marrow fibrosis has an important prognostic value and has correlation with overall survival. Recently, bone marrow fibrosis was correlated with degree of splenic stiffness (SS) measured by imaging elastography techniques. Despite these findings, there were patients with insignificant measures that could not be classified according to marrow fibrosis. In order to advance knowledge in this field, we studied splenic and hepatic stiffness (HS) in patients with myelofibrosis using elastography by two methods, ultrasonography (EUS) and magnetic resonance elastography (MRE), and its correlation with prognostic scores and bone marrow fibrosis. This is a prospective, cross-sectional, observational study in patients from the outpatientclinic for myeloproliferative neoplasms who had given informed consent according to procedures approved by institutions ethical committee. Patients with PM, as well as post-essential thrombocythemia or post-polycythemia vera myelofibrosis, were included in this study. Myelofibrosis patients with diagnosis of other associated pathologies that may alter SS, as portal hypertension or cirrhosis, were excluded from the study. Patients were assessed for splenic stiffness measured by ultrasound conducted by two examiners, with more than 10 years of experience. EUS was performed in US Epiq 7 equipment - Philips – with ARFI elastometry methodology. The SS measurements was reported in m/s. In addition, they were also evaluated for splenic and liver stiffness by MRI technique. All exams were performed in 1.5 T MR equipment (Magneton Aera, Siemens Healthineers, Erlangen, Germany) and the MRI protocol included T2-weighted and gradient-echo MRE sequences using steady-state 60-Hzexcitation and an external driver placed on the right side and, on the left side of theabdomen. The measures of SS were also obtained by two experienced examiners. At this moment we present the results of 16 patients with myelofibrosis (PM: 8 cases; post-PV myelofibrosis: 2 cases; post-ET myelofibrosis: 6 cases). The median age was 69y (41-88y) and 62,5% of participants were male. The JAK2 V617F mutation was detected in 9 cases; three cases were CALR positive, and three cases were triple negative. The CBC showed: Hb: 10.9 g/dL (6.5-18.7); WBC (x10/L): 9.17 (1.8-44.5) and platelets (x10/L): 393 (10-957). Our preliminary results show that bone marrow fibrosis increased according to splenic stiffness by EUS and MRE. Patients with osteosclerosis also presented a higher SS by MRE. We could not find correlation of splenic stiffness with prognostic score DIPSS plus, although Int-2/High risk patients presented a trend to be associated with higher liver stiffness. To the moment, our preliminary findings suggest a correlation between SS and degree of bone marrow fibrosis and osteosclerosis, though the correlation between both measures and prognostic scores is still to be determined. We expect to have a better definition forall correlations, as we progress through the assessment of the other patients in our service.

Free-breathing MR elastography of the lungs: An in vivo study.

Lung stiffness alters with many diseases; therefore, several MR elastography (MRE) studies were performed earlier to investigate the stiffness of the right lung during breathhold at residual volume and total lung capacity. The aims of this study were 1) to estimate shear stiffness of the lungs using MRE under free breathing and demonstrate the measurements' repeatability and reproducibility, and 2) to compare lung stiffness under free breathing to breathhold and as a function of age and gender. Twenty-five healthy volunteers were scanned on a 1.5 Tesla MRI scanner. Spin-echo dual-density spiral and a spin-echo EPI MRE sequences were used to measure shear stiffness of the lungs during free breathing and breathhold at midpoint of tidal volume, respectively. Concordance correlation coefficient and Bland-Altman analyses were performed to determine the repeatability and reproducibility of the spin-echo dual-density spiral-derived shear stiffness. Repeated measures analyses of variances were used to investigate differences in shear stiffness between spin-echo dual-density spiral and spin-echo EPI, right and left lungs, males and females, and different age groups. Free-breathing MRE sequence was highly repeatable and reproducible (concordance correlation coefficient > 0.86 for both lungs). Lung stiffness was significantly lower in breathhold than in free breathing (P < .001), which can be attributed to potential stress relaxation of lung parenchyma or breathhold inconsistencies. However, there was no significant difference between different age groups (P = .08). The left lung showed slightly higher stiffness values than the right lung (P = .14). There is no significant difference in lung stiffness between genders. This study demonstrated the feasibility of free-breathing lung MRE with excellent repeatability and reproducibility. Stiffness changes with age and during the respiratory cycle. However, gender does not influence lungs stiffness.

Automated Analysis of Multiparametric Magnetic Resonance Imaging/Magnetic Resonance Elastography Exams for Prediction of Nonalcoholic Steatohepatitis.

Nonalcoholic fatty liver disease (NAFLD) affects 25% of the global population. The standard of diagnosis, biopsy, is invasive and affected by sampling error and inter-reader variability. We hypothesized that widely available rapid MRI techniques could be used to predict nonalcoholic steatohepatitis (NASH) noninvasively by measuring liver stiffness, with magnetic resonance elastography (MRE), and liver fat, with chemical shift-encoded (CSE) MRI. Besides, we validate an automated image analysis technique to maximize the utility of these methods. To implement and test an automated system for analyzing CSE-MRI and MRE data coupled with model-based prediction of NASH. Prospective. Eighty-three patients with suspected NAFLD. A 1.5 T using a flow-compensated motion-encoded gradient echo MRE sequence and a multiecho CSE-MRI sequence. The MRE and CSE-MRI data were analyzed by two readers (5+ and 1 years of experience) and an automated algorithm. A logistic regression model to predict pathology-diagnosed NASH was trained based on stiffness and proton density fat fraction, and the area under the receiver operating characteristic curve (AUROC) was calculated using 10-fold cross validation for models based on both automated and manual measurements. A separate model was trained to predict the NASH severity score (NAS). Pearson's correlation, Bland-Altman, AUROC, C-statistic. The agreement between automated measurements and the more experienced reader (R2 =0.87 for stiffness and R2 =0.99 for proton density fat fraction [PDFF]) was slightly better than the agreement between readers (R2 =0.85 and 0.98). The model for predicting biopsy-diagnosed NASH had an AUROC of 0.87. The NAS-prediction model had a C-statistic of 0.85. We demonstrated a workflow that used a limited MRI acquisition protocol and fully automated analysis to predict NASH with high accuracy. These methods show promise to provide a reliable noninvasive alternative to biopsy for NASH-screening in populations with NAFLD. 2 TECHNICAL EFFICACY STAGE: 2.

Magnetic resonance elastography for estimating in vivo stiffness of the abdominal aorta using cardiac‐gated spin‐echo echo‐planar imaging: a feasibility study

Magnetic resonance elastography (MRE)-derived aortic stiffness is a potential biomarker for multiple cardiovascular diseases. Currently, gradient-recalled echo (GRE) MRE is a widely accepted technique to estimate aortic stiffness. However, multi-slice GRE MRE requires multiple breath-holds (BHs), which can be challenging for patients who cannot consistently hold their breath. The aim of this study was to investigate the feasibility of a multi-slice spin-echo echo-planar imaging (SE-EPI) MRE sequence for quantifying in vivo aortic stiffness using a free-breathing (FB) protocol and a single-BH protocol. On Scanner 1, 25 healthy subjects participated in the validation of FB SE-EPI against FB GRE. On Scanner 2, another 15 healthy subjects were recruited to compare FB SE-EPI with single-BH SE-EPI. Among all volunteers, five participants were studied on both scanners to investigate the inter-scanner reproducibility of FB SE-EPI aortic MRE. Bland-Altman analysis, Lin's concordance correlation coefficient (LCCC) and coefficient of variation (COV) were evaluated. The phase-difference signal-to-noise ratios (PD SNR) were compared. Aortic MRE using FB SE-EPI and FB GRE yielded similar stiffnesses (paired t-test, P = 0.19), with LCCC = 0.97. The FB SE-EPI measurements were reproducible (intra-scanner LCCC = 0.96) and highly repeatable (LCCC = 0.99). The FB SE-EPI MRE was also reproducible across different scanners (inter-scanner LCCC = 0.96). Single-BH SE-EPI scans yielded similar stiffness to FB SE-EPI scans (LCCC = 0.99) and demonstrated a low COV of 2.67% across five repeated measurements. Multi-slice SE-EPI aortic MRE using an FB protocol or a single-BH protocol is reproducible and repeatable with advantage over multi-slice FB GRE in reducing acquisition time. Additionally, FB SE-EPI MRE provides a potential alternative to BH scans for patients who have challenges in holding their breath.

Fusing acceleration and saturation techniques with wave amplitude labeling of time-shifted zeniths MR elastography.

To design a new 2D gradient recalled echo MR elastography (MRE) pulse sequence with inflow saturation for measuring liver stiffness in half the breath-hold time compared to standard of care (SC) 2D GRE MRE sequences. FASTWALTZ (fusing acceleration and saturation techniques with wave amplitude labeling of time-shifted zeniths) MRE employs an interleaved dual TR strategy with wave amplitude labeling and compressed SENSE undersampling to reduce breath-hold time while incorporating inflow saturation to suppress flow artifacts. The sequence was implemented and compared with SC MRE both in phantoms and in vivo in 5 asymptomatic volunteers. Stiffness values, region of interest size, and breath-hold times were compared between sequences. Stiffness values were comparable between FASTWALTZ and SC MRE for both phantoms and in-vivo data. In volunteers, the group mean stiffness values at 60Hz and region of interest size were 1.96 ± 0.30 kilopascals and 2279 ± 516 mm2 for SC MRE, and 1.95 ± 0.29 kilopascals and 2061 ± 464 mm2 for FASTWALTZ. Breath-hold duration for FASTWALTZ was 6.3 s compared to 13.3 s for SC MRE. FASTWALTZ provides comparable stiffness values in half the breath-hold time compared to SC MRE and may have clinical benefits in patients with limited breath-holding capacity.

Quantitative analysis of vibration waves based on Fourier transform in magnetic resonance elastography.

We developed a novel magnetic resonance elastography (MRE) analysis method based on Fourier transform to assess the responsive characteristics for different tissue stiffness and degree of transmission of the vibration wave emanating from a passive driver during MRE. A phantom tissue study was conducted with an MRE sequence and vibration wave system using a clinical MR scanner. The phantom tissue consisted of two layers of agar: 0.75 wt% and 1.0 wt%. Phase-unwrapped images derived from acquired MRE phase images were used to generate a phase profile curve, with a line plotted for the phase-unwrapped images. Fourier transform was performed, and the peak value of the power spectrum was derived. The damping rate/ratio was calculated using the Hilbert transform of the phase profile. We found that the mean shear stiffness value of 1.0 wt% agar was higher than that of 0.75 wt% agar. The responsive frequency of the 0.75 wt% agar layer showed a wider range and the damping rate of the signal showed a higher value than the respective values of the 1.0 wt% agar layer. In conclusion, Fourier transform analysis of MRE enabled us to obtain more detailed information of the tissue characteristics and vibration-wave conditions.

TURBINE‐MRE: A 3D hybrid radial‐Cartesian EPI acquisition for MR elastography

To develop a novel magnetic resonance elastography (MRE) acquisition using a hybrid radial EPI readout scheme (TURBINE), and to demonstrate its feasibility to obtain wave images and stiffness maps in a phantom and in vivo brain. The proposed 3D TURBINE-MRE is based on a spoiled gradient-echo MRE sequence with the EPI readout radially rotating about the phase-encoding axis to sample a full 3D k-space. A polyvinyl chloride phantom and 6 volunteers were scanned on a compact 3T GE scanner with a 32-channel head coil at 80 Hz and 60 Hz external vibration, respectively. For comparison, a standard 2D, multislice, spin-echo (SE) EPI-MRE acquisition was also performed with the same motion encoding and resolution. The TURBINE-MRE images were off-line reconstructed with iterative SENSE algorithm. The regional ROI analysis was performed on the 6 volunteers, and the median stiffness values were compared between SE-EPI-MRE and TURBINE-MRE. The 3D wave-field images and the generated stiffness maps were comparable between TURBINE-MRE and standard SE-EPI-MRE for the phantom and the volunteers. The Bland-Altman plot showed no significant difference in the median regional stiffness values between the two methods. The stiffness measured with the 2 methods had a strong linear relationship with a Pearson correlation coefficient of 0.943. We demonstrated the feasibility of the new TURBINE-MRE sequence for acquiring the desired 3D wave-field data and stiffness maps in a phantom and in-vivo brains. This pilot study encourages further exploration of TURBINE-MRE for functional MRE, free-breathing abdominal MRE, and cardiac MRE applications.

Normal range for MR elastography measured liver stiffness in children without liver disease.

Magnetic resonance elastography (MRE) can determine the presence and stage of liver fibrosis. Data on normative MRE values, while reported in adults, are limited in children. To determine the distribution of MRE-measured liver stiffness in children without liver disease. Prospective, observational. Eighty-one healthy children (mean 12.6 ± 2.6 years, range 8-17 years). 3.0T Signa HDxt, General Electric MR Scanner; 2D GRE MRE sequence. History, examination, laboratory evaluation, and (MR) exams (proton density fat fraction, PDFF, and MRE) were performed. MR elastograms were analyzed manually at two reading centers and compared with each other for agreement and with published values in healthy adults and thresholds for fibrosis in adult and pediatric patients. Descriptive statistics, Bland-Altman analysis, t-test to compare hepatic stiffness values with reference standards. Stiffness values obtained at both reading centers were similar, without significant bias (P = 0.362) and with excellent correlation (intraclass correlation coefficient [ICC] = 0.782). Mean hepatic stiffness value for the study population was 2.45 ± 0.35 kPa (95th percentile 3.19 kPa), which was significantly higher than reported values for healthy adult subjects (2.10 ± 0.23 kPa, P < 0.001). In all, 74-85% of subjects had stiffness measurements suggestive of no fibrosis. Mean liver stiffness measured with MRE in this cohort was significantly higher than that reported in healthy adults. Despite rigorous screening, some healthy children had stiffness measurements suggestive of liver fibrosis using current published thresholds. Although MRE has the potential to provide noninvasive assessment in patients with suspected hepatic disease, further refinement of this technology will help advance its use as a diagnostic tool for evidence of fibrosis in pediatric populations. 1 Technical Efficacy: 5 J. Magn. Reson. Imaging 2020;51:919-927.

A new technique for motion encoding gradient-less MR elastography of the psoas major muscle: A gradient-echo type multi-echo sequence

The present study aimed to develop vibration techniques for magnetic resonance (MR) elastography (MRE) of the psoas major muscle (PM). Seven healthy volunteers were included. MRE was performed with motion-encoding gradient (MEG)-less multi-echo MRE sequence, which allows clinicians to perform MRE using conventional MR imaging. In order to transmit mechanical vibration of the pneumatic type to the PM, a long narrow vibration pad was designed using a 3D printer, and the optimum vibration techniques were verified. The vibration pad was placed under the lower back, with the volunteers in the supine position. The results indicated that the PM vibrated well through the transmitted vibration from the lumbar spine, which suggests that the placement of a narrow vibration pad under the supine body, along the lumbar spine, allows the vibration of the PM. The shear modulus of the PM (n = 7) was 1.23 ± 0.09 kPa (mean ± SEM) on the right side and 1.22 ± 0.15 kPa on the left side, with no significant difference (t-test, P > 0.05). Increased stiffness of the muscle due to continuous local contraction may be an important cause of non-specific low back pain (LBP). The present vibration techniques for MRE of the PM provide a quantitative diagnostic tool for changes in muscle stiffness associated with non-specific LBP.