Liver Magnetic Resonance Elastography Research Articles

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.

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.

Individualized driver amplitude in liver MR elastography: a linear regression study.

Current liver magnetic resonance elastography (MRE) scans often require adjustments to driver amplitude to produce acceptable images. This could lead to time wastage and the potential loss of an opportunity to capture a high-quality image. To construct a linear regression model of individualized driver amplitude to improve liver MRE image quality. Data from 95 liver MRE scans of 61 participants, including abdominal missing volume ratio (AMVR), breath-holding status, the distance from the passive driver on the skin surface to the liver edge (Dd-l), body mass index (BMI), and lateral deflection of the passive driver with respect to the human sagittal plane (Angle α), were continuously collected. The Spearman correlation analysis and lasso regression were conducted to screen the independent variables. Multiple linear regression equations were developed to determine the optimal amplitude prediction model. The optimal formula for linear regression models: driver amplitude (%) = -16.80 + 78.59 × AMVR - 11.12 × breath-holding (end of expiration = 1, end of inspiration = 0) + 3.16 × Dd-l + 1.94 × BMI + 0.34 × angle α, with the model passing the F test (F = 22.455, P <0.001) and R2 value of 0.558. The individualized amplitude prediction model based on AMVR, breath-holding status, Dd-l, BMI, and angle α is a valuable tool in liver MRE examination.

Liver Magnetic Resonance Elastography: Focus on Methodology, Technique, and Feasibility.

Magnetic resonance elastography (MRE) is an imaging technique that combines low-frequency mechanical vibrations with magnetic resonance imaging to create visual maps and quantify liver parenchyma stiffness. As in recent years, diffuse liver diseases have become highly prevalent worldwide and could lead to a chronic condition with different stages of fibrosis. There is a strong necessity for a non-invasive, highly accurate, and standardised quantitative assessment to evaluate and manage patients with different stages of fibrosis from diagnosis to follow-up, as the actual reference standard for the diagnosis and staging of liver fibrosis is biopsy, an invasive method with possible peri-procedural complications and sampling errors. MRE could quantitatively evaluate liver stiffness, as it is a rapid and repeatable method with high specificity and sensitivity. MRE is based on the propagation of mechanical shear waves through the liver tissue that are directly proportional to the organ's stiffness, expressed in kilopascals (kPa). To obtain a valid assessment of the real hepatic stiffness values, it is mandatory to obtain a high-quality examination. To understand the pearls and pitfalls of MRE, in this review, we describe our experience after one year of performing MRE from indications and patient preparation to acquisition, quality control, and image analysis.

Liver magnetic resonance elastography and fat fraction in pediatric patients withcystic fibrosis versus healthy children.

Liver involvement is an important cause of morbidity and mortality in patients withcystic fibrosis (CF). While liver biopsy is the gold standard for demonstrating involvement, its invasiveness prompts a search for noninvasive alternatives. To evaluate liver involvement in pediatric patients with CF(versus healthy controls) using magnetic resonance (MR) elastography/spectroscopy and to correlate the imaging findings with clinical/laboratory characteristics. This was a single-center, prospective cross-sectional study conducted between April 2020 and March 2022 in patients withCF versus healthy controls. Patients with CF were divided into two subgroups: those with CF-related liver disease and those without. MR images were acquired on a 1.5-tesla machine. Kilopascal (kPa) values were derived from processing MR elastography images. MR spectroscopy was used to measure liver fat fraction, as an indication of hepatosteatosis. Groups were compared using either the Student's t test or the Mann‒Whitney U test. The chi-square test or Fisher's exact test were used to compare qualitative variables. Fifty-one patients with CF (12 ± 3.3years, 32 boys) and 24 healthy volunteers (11.1 ± 2.4years, 15 boys) were included in the study. Median liver stiffness (P=0.003) and fat fraction (P=0.03) were higher in the CF patients than in the controls. Median liver stiffness values were higher in CF patients with CF-related liver disease than in those without CF-related liver disease (P=0.002). Liver stiffness values of CF patients with high alanine aminotransferase (ALT), high gamma-glutamyl transferase, and thrombocytopenia were found to be higher than those without (P=0.004, P<0.001, P<0.001, respectively). Only the high ALT group showed a high fat fraction (P=0.002). Patients withCF had higher liver stiffness than the control group, and patients withCF-related liver disease had higher liver stiffness than both the CF patients without CF-related liver disease and the control group. Patients withCF had a higher fat fraction than the control group. Noninvasive assessment of liver involvement using MR elastography/spectroscopy can support the diagnosis of CF-related liver disease and the follow-up of patients withCF.

Comparison of spin-echo echo planar imaging and gradient-recalled echo sequences in magnetic resonance elastography of liver at 1.5T same MRI scanner.

Magnetic resonance elastography (MRE) is used to measure liver stiffness with gradient-recalled echo (GRE)-based and spin-echo echo planar imaging (SE-EPI)-based sequences. We compared the liver stiffness (LS) values of the two sequences on a 1.5-T MR imaging scanner. This is a retrospective study. An MRE imaging section was obtained from a horizontal section of the liver. Region of interest was drawn on the elastogram, and the mean LS and pixel values were measured and compared. The correlations between proton density fat fraction, R2* values, and biochemical data from electronic medical records were confirmed, and multivariate analysis was performed. The mean LS values were 3.01±1.78kPa for GRE and 3.13±1.57kPa for SE-EPI, showing excellent agreement and a strong correlation between the two sequences (correlation coefficient r=0.96). The mean pixel values were 369.5±142.7 pixels for GRE and 490.1±197.9 pixels for SE-EPI, showing a significant difference by the Wilcoxon rank sum test (p<0.01). There were no LS unmeasurable cases in SE-EPI, but seven (2.5%) were unmeasurable in GRE, and multivariate analysis showed a significant difference with p<0.001 in R2* values (mean, 92.7Hz) for the GRE method. The GRE and SE-EPI methods were comparable for LS measurements in 1.5-T liver MRE, indicating that SE-EPI MRE is more useful because GRE MRE may not measure cases with high R2* values and the region of interest tends to be smaller.

A combination of non-invasive tests for the detection of significant fibrosis in patients with metabolic dysfunction-associated steatotic liver disease is not superior to magnetic resonance elastography alone.

The aims of the present study were to investigate a combination of magnetic resonance elastography (MRE) and vibration-controlled transient elastography (VCTE) or MRE and fibrosis score 4 (FIB-4) in the detection of significant fibrosis in patients with metabolic dysfunction-associated steatotic liver disease (MASLD). Between November 5, 2021, and March 4, 2022, a total of 119 consecutive patients with MASLD were included. Liver stiffness was measured using liver biopsy, MRE, VCTE, and FIB-4. Data were collected from outpatient visit charts. Significant fibrosis was defined as ≥ stage 2 fibrosis. All 119 MASLD patients were Caucasian, and their median age was 55 years. MRE, VCTE, and FIB-4 demonstrated significant accuracy in the detection of significant fibrosis with an area under the ROC curve (AUC) of 0.848 ± 0.036 (p < 0.001), 0.632 ± 0.052 (p = 0.012), and 0.664 ± 0.051 (p = 0.001), respectively. However, the diagnostic performance of MRE was superior compared to that of VCTE (AUC difference: 0.216 ± 0.053, p < 0.001) and FIB-4 (AUC difference: 0.184 ± 0.058, p = 0.001). With logistic regression analysis, it was determined that when compared to MRE alone, a combination of MRE and TE (p = 0.880) or MRE and FIB-4 (p = 0.455) were not superior for detecting significant fibrosis. MRE alone is an accurate and non-invasive method for the identification of MASLD patients with significant fibrosis. Magnetic resonance elastography alone accurately detects significant fibrosis in patients with metabolic dysfunction-associated steatotic liver disease. • In routine clinical practice, several non-invasive biochemical-based biomarkers and imaging methods are widely used to assess liver fibrosis in patients with metabolic dysfunction-associated steatotic liver disease. • Magnetic resonance elastography (MRE) is more accuratethanvibration-controlled transient elastography (VCTE) or fibrosis score 4 (FIB-4) for assessing liver fibrosis and identifying significant fibrosis in patients with metabolic dysfunction-associated steatotic liver disease. • The combination of MRE andVCTE or MRE and FIB-4 was not superior to MRE alone.

A Three-Dimensional Digital Model for Early Diagnosis of Hepatic Fibrosis Based on Magnetic Resonance Elastography.

Hepatic fibrosis is an early stage of liver cirrhosis, and there are no better non-invasive and convenient methods for the detection and evaluation of the disease. Despite the good progress made with the liver stiffness map (LSM) based on magnetic resonance elastography (MRE), there are still some limitations that need to be overcome, including manual focus determination, manual selection of regions of interest (ROIs), and discontinuous LSM data without structural information, which makes it impossible to evaluate the liver as a whole. In this study, we propose a novel three-dimensional (3D) digital model for the early diagnosis of hepatic fibrosis based on MRE. MRE is a non-invasive imaging technique that employs magnetic resonance imaging (MRI) to measure the liver stiffness at the scanning site through human-computer interaction. Studies have indicated a significant positive correlation between the LSM obtained through MRE and the degree of hepatic fibrosis. However, for clinical purposes, a comprehensive and precise quantification of the degree of hepatic fibrosis is necessary. To address this, the concept of Liver Stiffness Distribution (LSD) was proposed in this study, which refers to the 3D stiffness volume of each liver voxel obtained by the alignment of 3D liver tissue images and MRE indicators. This provides a more effective clinical tool for the diagnosis and treatment of hepatic fibrosis.

Phase-regularized and displacement-regularized compressed sensing for fast magnetic resonance elastography.

Liver magnetic resonance elastography (MRE) is a noninvasive stiffness measurement technique that captures the tissue displacement in the phase of the signal. To limit the scanning time to a single breath-hold, liver MRE usually involves advanced readout techniques such as simultaneous multislice (SMS) or multishot methods. Furthermore, all these readout techniques require additional in-plane acceleration using either parallel imaging capabilities, such as sensitivity encoding (SENSE), or -space undersampling, such as compressed sensing (CS). However, these methods apply a single regularization function on the complex image. This study aims to design and evaluate methods that use separate regularization on the magnitude and phase of MRE to exploit their distinct spatiotemporal characteristics. Specifically, we introduce two compressed sensing methods. The first method, termed phase-regularized compressed sensing (PRCS), applies a two-dimensional total variation (TV) prior to the magnitude and two-dimensional wavelet regularization to the phase. The second method, termed displacement-regularized compressed sensing (DRCS), exploits the spatiotemporal redundancy using 3D total variation on the magnitude. Additionally, DRCS includes a displacement fitting function to apply wavelet regularization to the displacement phasor. Both DRCS and PRCS were evaluated with different levels of compression factors in three datasets: an in silico abdomen dataset, an in vitro tissue-mimicking phantom, and an in vivo liver dataset. The reconstructed images were compared with the full sampled reconstruction, zero-filling reconstruction, wavelet-regularized compressed sensing, and a low rank plus sparse reconstruction. The metrics used for quantitative evaluation were the structural similarity index (SSIM) of magnitude (M-SSIM), displacement (D-SSIM), and shear modulus (S-SSIM), and mean shear modulus. Results from highly undersampled in silico and in vitro datasets demonstrate that the DRCS method provides higher reconstruction quality than the conventional compressed sensing method for a wide range of stiffness values. Notably, DRCS provides 24% and 22% increase in D-SSIM compared with CS for the in silico and in vitro datasets, respectively. Comparison with liver stiffness measured from full sampled data and highly undersampled data (CR=4) demonstrates that the DRCS method provided the strongest correlation ( =0.95), second-lowest mean bias (-0.18 kPa, lowest for CS with -0.16 kPa), and lowest coefficient of variation (CV=3.6%). Our results demonstrate the potential of using DRCS to improve the reconstruction quality of accelerated MRE.

A tailored passive driver for liver MRE in pediatric patients.

Magnetic resonance elastography (MRE) is increasingly used in the pediatric population for diagnosis and staging of liver fibrosis. However, the MR-compatible driver and sequences are usually those used for adult patients. Our feasibility study aimed to adapt the standardized adult MRE passive driver and vibrational parameters to a pediatric population. We designed an elliptic passive driver shaped on a torus equipped with an elastic membrane and adapted to children's morphologies. As a first step, eight children (aged 8-18 years) were enrolled in a prospective pilot study aiming to determine the threshold vibrational amplitude for MRE using a custom passive driver, based on phase aliasing assessment and the occurrence of signal void artifacts on magnitude MR images. In the second step, the practicality and the consistency of the custom driver were assessed in a further 11 pediatric patients (aged 7-18 years). In the third step, we compared our custom driver vs. the commercial driver on six adult volunteers, in terms of the reliable region of interest area within the acquired MRE slices, the shear wave maps' quality, and measured stiffness values obtained. Based on pediatric patient data, the threshold vibrational amplitude expressed as percentage of maximum output was found to be 0.4 and 1.1 times the body weight (kg) at 40 and 60 Hz frequencies, respectively. In comparison to the commercial passive driver, the custom driver improved threefold the contact with the body surface, also enabling a more comfortable examination as self-assessed by the volunteers. Our custom driver was more comfortable for the volunteers and was able to generate more homogenous shear waves, yielding larger usable hepatic area, and more reliable stiffness values.

Noninvasive Prediction of Advanced Fibrosis in Pediatric Liver Disease-Discriminatory Performance of 2D Shear Wave Elastography, Transient Elastography and Magnetic Resonance Elastography in Comparison to Histopathology.

Background: Elastography can be measured with different imaging techniques and is increasingly used for noninvasive assessment of hepatic fibrosis. Little is known about the performance, and interrelation of different elastographic techniques, in prediction of hepatic fibrosis in pediatric liver disease. Objectives: We aimed to determine the discriminatory value for advanced fibrosis (Metavir F3-4) and evaluate the applicability of 2D shear wave ultrasound elastography (USe), Transient Elastography (TE) and Magnetic Resonance elastography (MRe) in pediatric liver disease. Methods: In patients with pediatric liver disease aged 0-19 years, USe, TE and MRe were compared with histopathological fibrosis stage. Multivariate logistic regression models for advanced fibrosis were considered. Discriminative performance was assessed by the area under the receiver operating characteristic curve and the Brier Score. Primary analyses included complete cases. Multiple imputation was used as sensitivity analysis. Results: In 93 histologically evaluated patients USe, TE and MRe were performed 89, 93 and 61 times respectively. With increased liver stiffness values, significantly increased odds for presenting F3-4 were seen in individual models for ALT &lt; 470 U/L, whereas the effect for ALT &gt; 470 U/L was non-significant. Area under the curve and Brier Score for discrimination of advanced fibrosis were 0.798 (0.661-0.935) and 0.115 (0.064-0.166); 0.862 (0.758-0.966) and 0.118 (0.065-0.171); 0.896 (0.798-0.994) and 0.098 (0.049-0.148) for USe, TE and MRe respectively. No significant increase in discriminatory ability was found when combining elastographic modalities. Conclusions: In pediatric liver disease, USe, TE and MRe had a good discriminatory ability for assessment of advanced liver fibrosis, although TE and MRe performed best. In most children with pediatric liver disease, TE is a reliable and easily applicable measure.

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.

Intra-patient comparison of 3D and 2D magnetic resonance elastography techniques for assessment of liver stiffness.

To evaluate performance of 3D magnetic resonance elastography (MRE) using spin-echo echo-planar imaging (seEPI) for assessment of hepatic stiffness compared with 2D gradient-recalled echo (GRE) and 2D seEPI sequences. Fifty-seven liver MRE examinations including 2D GRE, 2D seEPI, and 3D seEPI sequences were retrospectively evaluated. Elastograms were analyzed by 2 radiologists and polygonal regions of interests (ROIs) were drawn in 2 different fashions: "curated" ROI (avoiding liver edge, major vessels, and areas of wave interferences) and "non-curated" ROI (including largest cross section of liver, to assess the contribution of artifacts). Liver stiffness measurement (LSM) was calculated as the arithmetic mean of individual stiffness values for each technique. For 3D MRE, LSMs were also calculated based on 4 slices ("abbreviated LSM"). Intra-patient variations in LSMs and different methods of ROI placement were assessed by univariate tests. A p-value of < 0.05 was set as a statistically significant difference. Mean surface areas of the ROIs were 50,723 mm2, 12,669 mm2, 5814 mm2, and 10,642 mm2 for 3D MRE, abbreviated 3D MRE, 2D GRE, and 2D seEPI, respectively. 3D LSMs based on curated and non-curated ROIs showed no clinically significant difference, with a mean difference less than 0.1kPa. Abbreviated 3D LSMs had excellent correlation with 3D LSMs based on all slices (r = 0.9; p < 0.001) and were not significantly different (p = 0.927). 3D MRE allows more reproducible measurements due to its lower susceptibility to artifacts and provides larger areas of parenchyma, enabling a more comprehensive evaluation of the liver.

MR elastography in nonalcoholic fatty liver disease: inter-center and inter-analysis-method measurement reproducibility and accuracy at 3T

ObjectivesTo assess reproducibility and fibrosis classification accuracy of magnetic resonance elastography (MRE)–determined liver stiffness measured manually at two different centers, and by automated analysis software in adults with nonalcoholic fatty liver disease (NAFLD), using histopathology as a reference standard.MethodsThis retrospective, cross-sectional study included 91 adults with NAFLD who underwent liver MRE and biopsy. MRE-determined liver stiffness was measured independently for this analysis by an image analyst at each of two centers using standardized manual analysis methodology, and separately by an automated analysis. Reproducibility was assessed pairwise by intraclass correlation coefficient (ICC) and Bland-Altman analysis. Diagnostic accuracy was assessed by receiver operating characteristic (ROC) analyses.ResultsICC of liver stiffness measurements was 0.95 (95% CI: 0.93, 0.97) between center 1 and center 2 analysts, 0.96 (95% CI: 0.94, 0.97) between the center 1 analyst and automated analysis, and 0.94 (95% CI: 0.91, 0.96) between the center 2 analyst and automated analysis. Mean bias and 95% limits of agreement were 0.06 ± 0.38 kPa between center 1 and center 2 analysts, 0.05 ± 0.32 kPa between the center 1 analyst and automated analysis, and 0.11 ± 0.41 kPa between the center 2 analyst and automated analysis. The area under the ROC curves for the center 1 analyst, center 2 analyst, and automated analysis were 0.834, 0.833, and 0.847 for distinguishing fibrosis stage 0 vs. ≥ 1, and 0.939, 0.947, and 0.940 for distinguishing fibrosis stage ≤ 2 vs. ≥ 3.ConclusionMRE-determined liver stiffness can be measured with high reproducibility and fibrosis classification accuracy at different centers and by an automated analysis.Key Points• Reproducibility of MRE liver stiffness measurements in adults with nonalcoholic fatty liver disease is high between two experienced centers and between manual and automated analysis methods.• Analysts at two centers had similar high diagnostic accuracy for distinguishing dichotomized fibrosis stages.• Automated analysis provides similar diagnostic accuracy as manual analysis for advanced fibrosis.

In silico evaluation and optimisation of magnetic resonance elastography of the liver

Objective. Magnetic resonance elastography (MRE) is widely adopted as a biomarker of liver fibrosis. However, in vivo MRE accuracy is difficult to assess. Approach. Finite element model (FEM) simulation was employed to evaluate liver MRE accuracy and inform methodological optimisation. MRE data was simulated in a 3D FEM of the human torso including the liver, and compared with spin-echo echo-planar imaging MRE acquisitions. The simulated MRE results were compared with the ground truth magnitude of the complex shear modulus (∣G*∣) for varying: (1) ground truth liver ∣G*∣; (2) simulated imaging resolution; (3) added noise; (4) data smoothing. Motion and strain-based signal-to-noise (SNR) metrics were evaluated on the simulated data as a means to select higher-quality voxels for preparation of acquired MRE summary statistics of ∣G*∣. Main results. The simulated MRE accuracy for a given ground truth ∣G*∣ was found to be a function of imaging resolution, motion-SNR and smoothing. At typical imaging resolutions, it was found that due to under-sampling of the MRE wave-field, combined with motion-related noise, the reconstructed simulated ∣G*∣ could contain errors on the scale of the difference between liver fibrosis stages, e.g. 54% error for ground truth ∣G*∣ = 1 kPa. Optimum imaging resolutions were identified for given ground truth ∣G*∣ and motion-SNR levels. Significance. This study provides important knowledge on the accuracy and optimisation of liver MRE. For example, for motion-SNR ≤ 5, to distinguish between liver ∣G*∣ of 2 and 3 kPa (i.e. early-stage liver fibrosis) it was predicted that the optimum isotropic voxel size is 4–6 mm.

Magnetic resonance elastography of the liver: everything you need to know to get started.

Magnetic resonance elastography (MRE) of the liver has emerged as the non-invasive standard for the evaluation of liver fibrosis in chronic liver diseases (CLDs). The utility of MRE in the evaluation of different CLD in both adults and children has been demonstrated in several studies, and MRE has been recommended by several clinical societies. Consequently, the clinical indications for evaluation of CLD with MRE have increased, and MRE is currently used as an add-on test during routine liver MRI studies or as a standalone test. To meet the increasing clinical demand, MRE is being installed in many academic and private practice imaging centers. There is a need for a comprehensive practical guide to help these practices to deliver high-quality liver MRE studies as well as troubleshoot the common issues with MRE to ensure smooth running of the service. This comprehensive clinical practice review summarizes the indications and provides an overview on why to use MRE, technical requirements, system set-up, patient preparation, acquiring the data, and interpretation.

Effect of different driver power amplitudes on liver stiffness measurement in pediatric liver MR elastography.

To assess how different driver power amplitudes affect the measurement of liver stiffness in pediatric liver magnetic resonance elastography (MRE). From January 2018 to May 2018, pediatric patients (≤ 18years) who underwent liver MRE with 20% and 56% driver power amplitudes were included in this retrospective study. Region-of-interests (ROIs) were drawn on four stiffness maps to include the largest area of the liver parenchyma. Intraclass correlation coefficients (ICCs) were used to assess agreements for the area, mean, maximum, minimum and standard deviation of liver stiffness between the driver power amplitudes. 128 MRE stiffness maps from 16 patients (M:F = 10:6, median 12.5years old) were included. On MRE, median ROI areas of liver were 83.1 cm2 (range, 46.9-144.1 cm2) and 63.0 cm2 (range, 5.4-123.4 cm2) for the driver power amplitudes of 20% and 56%, respectively. Median liver stiffness values were 2.3kPa (range, 1.7-8.0kPa) and 2.8kPa (range, 1.7-8.5kPa). Maximum and minimum liver stiffness values were 5.3kPa and 1.0kPa for 20% and 7.8kPa and 1.1kPa for 56%. Standard deviation was 0.6kPa for 20% and 1.0kPa for 56%. ICC values between the two power amplitudes were 0.33-0.51 for the ROI area and the maximum, minimum and standard deviation values of liver stiffness. The ICC value for liver stiffness was 0.857 (95% confidence interval, 0.760-0.915). Liver stiffness with two driver power amplitudes on MRE showed good reliability in pediatric patients. Driver power amplitudes need to be optimized according to the pediatric liver size.

Two-dimensional (2D) morphologic measurements can quantify the severity of liver disease in children with autosomal recessive polycystic kidney disease (ARPKD).

To evaluate the correlation of 2D shape-based features with magnetic resonance elastography (MRE)-derived liver stiffness and portal hypertension (pHTN) in children with ARPKD-associated congenital hepatic fibrosis. In a prospective IRB-approved study, 14 children with ARPKD (mean age ± SD = 13.8 ± 5.8years) and 14 healthy controls (mean age ± SD = 13.7 ± 3.9years) underwent liver MRE. A 2D region of interest (ROI) outlining the left liver lobe at the level of the abdominal aorta was drawn on sagittal T2-weighted images. Eight shape features (perimeter, major axis length, maximum diameter, perimeter to surface ratio (PSR), elongation, sphericity, minor axis length, and mesh surface) describing the 2D-ROI were calculated. Spearman's correlation was calculated between shape features and MRE-derived liver stiffness (kPa) (n = 28). Shape features were compared between participants with ARPKD with pHTN (splenomegaly and thrombocytopenia), (n = 4) and without pHTN (n = 8) using the Mann Whitney U test. Receiver operating characteristic (ROC) curves were generated to examine the diagnostic accuracy of shape features in identifying cases with liver stiffness > 2.9kPa. In ARPKD participants and healthy controls, all eight shape features, except elongation, showed moderate to strong correlation with liver stiffness (kPa); the perimeter surface ratio had the strongest correlation (rho = - 0.75, p < 0.001). In ROC analysis, a cut-off of PSR ≤ 0.057mm-1 gave 100% (95% CI: 59.0-100.0) sensitivity and 100% (95% CI: 83.9-100.0) specificity in identifying ARPKD participants with liver stiffness > 2.9kPa, with an area under the ROC curve (AUC) of 1.0 (95% CI: 0.88-1.00). Individuals with pHTN had a lower median PSR (mean ± SD = 0.05 ± 0.01) than those without (0.07 ± 0.01; p = 0.027) with an AUC of 0.91 (95% CI: 0.60-0.99) in differentiating the participants with and without pHTN. Shape-based features of the left liver lobe show potential as non-invasive biomarkers of liver fibrosis and portal hypertension in children with ARPKD.

Liver fibrosis in patients with tetralogy of Fallot, an unrecognised complication?

Improved survival has led to a growing population of adults with congenital heart disease (CHD), followed by numerous reports of late complications. Liver disease is a known complication in some patients, with most studies focusing on Fontan associated liver disease. Whether liver disease also exists in other patients with CHD is not fully investigated. Elevated central venous pressure is considered pivotal in the development of liver disease in Fontan associated liver disease, and other patients with alterations in central venous pressure may also be at risk for developing liver fibrosis. We wanted to see if liver fibrosis is present in patients with tetralogy of Fallot. Many patients with tetralogy of Fallot have severe pulmonary regurgitation, which can lead to elevated central venous pressure. Patients with tetralogy of Fallot may be at risk of developing liver fibrosis. Ten patients (24-56 years) with tetralogy of Fallot and pulmonary regurgitation were investigated for liver fibrosis. All patients were examined with magnetic resonance elastography of liver, hepatobiliary iminodiacetic acid scan, indocyanine green elimination by pulse spectrophotometry, elastography via FibroScan, abdominal ultrasound including liver elastography, and blood samples including liver markers. Three out of ten patients had findings indicating possible liver fibrosis. Two of these had a liver biopsy performed, which revealed fibrosis stage 1 and 2, respectively. The same three patients had an estimated elevated central venous pressure in previous echocardiograms. Mild liver fibrosis was present in selected patients with tetralogy of Fallot and may be related to elevated central venous pressure.

Magnetic resonance elastography to quantify liver disease severity in autosomal recessive polycystic kidney disease.

To evaluate whether liver and spleen magnetic resonance elastography (MRE) can measure the severity of congenital hepatic fibrosis (CHF) and portal hypertension (pHTN) in individuals with autosomal recessive polycystic kidney disease (ARPKD), and to examine correlations between liver MRE and ultrasound (US) elastography. Cross-sectional study of nine individuals with ARPKD and 14 healthy controls. MRE was performed to measure mean liver and spleen stiffness (kPa); US elastography was performed to measure point shear wave speed (SWS) in both liver lobes. We compared: (1) MRE liver and spleen stiffness between controls vs. ARPKD; and (2) MRE liver stiffness between participants with ARPKD without vs. with pHTN, and examined correlations between MRE liver stiffness, spleen length, platelet counts, and US elastography SWS. Receiver operating characteristic (ROC) analysis was performed to examine diagnostic accuracy of liver MRE. Participants with ARPKD (median age 16.8 [IQR 13.3, 18.9] years) had higher median MRE liver stiffness than controls (median age 14.7 [IQR 9.7, 16.7years) (2.55 vs. 1.92kPa, p = 0.008), but MRE spleen stiffness did not differ. ARPKD participants with pHTN had higher median MRE liver stiffness than those without (3.60kPa vs 2.49kPa, p = 0.05). Liver MRE and US elastography measurements were strongly correlated. To distinguish ARPKD vs. control groups, liver MRE had 78% sensitivity and 93% specificity at a proposed cut-off of 2.48kPa [ROC area 0.83 (95% CI 0.63-1.00)]. Liver MRE may be a useful quantitative method to measure the severity of CHF and pHTN in individuals with ARPKD.