Magnetic resonance elastography of liver and spleen: Methods and applications

Multiparametric magnetic resonance imaging of the liver and spleen in Gaucher disease

PURPOSE

To assess liver and spleen characteristics of a population with Gaucher disease (GD) using multiparametric MRI and MR elastography (MRE) for evaluation of diffuse liver and spleen disease, which includes liver fat fraction, liver and spleen volume and iron deposition, and liver and spleen stiffness correlated with DS3 Severity Scoring System for Gaucher disease (GD-DS3).

METHODS

We prospectively evaluated 41 patients with type 1 Gaucher disease using a 3.0 T MRI and MRE between January 2019 and February 2020. Clinical, laboratory, and imaging data was collected. Mann-Whitney, Kruskal-Wallis, and Spearman's correlation were applied to evaluate liver and spleen MRI and MRE, clinical and laboratory variables, and GD-DS3. ERT and SRT treatment groups were compared.

RESULTS

Hepatomegaly was seen in 15% and splenomegaly in 42% of the population. Moderate and strong and correlations were found between liver and spleen iron overload (rho = 0.537; p = 0.002); between liver and spleen volume (rho = 0.692, p < 0.001) and between liver and spleen stiffness (rho = 0.453, p = 0.006). Moderate correlations were found between liver stiffness and GD-DS3 (rho = 0.559; p < 0.001) and between splenic volume and GD-DS3 (rho = 0.524; p = 0.001).

CONCLUSION

The prevalence of hepatosplenomegaly, liver fibrosis, and liver iron overload in treated patients with GD is low, which may be related to the beneficial effect of treatment. Liver MRE and splenic volume correlate with severity score and may be biomarkers of disease severity.

Economic evaluation of non-invasive liver tests for the diagnosis of liver fibrosis in chronic liver diseases: a systematic review protocol

OBJECTIVE

The objective of this review is to determine the costs and benefits of non-invasive liver tests vs liver biopsy in patients with chronic liver diseases.

INTRODUCTION

Hepatic diseases can lead to liver fibrosis, cirrhosis, and hepatocellular carcinoma. In the past, liver biopsy was the only option for diagnosing fibrosis degree. Liver biopsy is an invasive procedure that depends on the sample size to be able to deliver an accurate diagnosis. In recent years, non-invasive liver tests have been increasingly used to estimate liver fibrosis degree; however, there is a lack of economic assessments of technology implementation outcomes.

INCLUSION CRITERIA

This review will include partial (cost studies) and complete economic evaluation studies on hepatitis B, hepatitis C, alcoholic liver disease, and non-alcoholic fatty liver disease that compare non-invasive liver tests with liver biopsies. Studies published in English, French, Spanish, German, Italian, or Portuguese will be included. No date limits will be applied to the search.

METHODS

This review will identify published and unpublished studies. Published studies will be identified using MEDLINE (PubMed), Cochrane Library (CENTRAL), Embase, Web of Science, Scopus, and LILACS. Sources of unpublished studies and gray literature will include sources from health technology assessment agencies, clinical practice guidelines, regulatory approvals, advisories and warnings, and clinical trial registries, as well as Google Scholar. Two independent reviewers will screen and assess studies, and extract and critically appraise the data. Data extracted from the included studies will be analyzed and summarized to address the review objective using narrative text, and the JBI dominance ranking matrix.

REVIEW REGISTRATION

PROSPERO CRD42023404278.

Rapid MR elastography of the liver for subsecond stiffness sampling

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Comparison of ultrasound elastography, magnetic resonance elastography and finite element model to quantify nonlinear shear modulus

Objective. The aim of this study is to validate the estimation of the nonlinear shear modulus (A) from the acoustoelasticity theory with two experimental methods, ultrasound (US) elastography and magnetic resonance elastography (MRE), and a finite element method.Approach. Experiments were performed on agar (2%)-gelatin (8%) phantom considered as homogeneous, elastic and isotropic. Two specific setups were built to ensure a uniaxial stress step by step on the phantom, one for US and a nonmagnetic version for MRE. The stress was controlled identically in both imaging techniques, with a water tank placed on the top of the phantom and filled with increasing masses of water during the experiment. In US, the supersonic shear wave elastography was implemented on an ultrafast US device, driving a 6 MHz linear array to measure shear wave speed. In MRE, a gradient-echo sequence was used in which the three spatial directions of a 40 Hz continuous wave displacement generated with an external driver were encoded successively. Numerically, a finite element method was developed to simulate the propagation of the shear wave in a uniaxially stressed soft medium.Main results. Similar shear moduli were estimated at zero stress using experimental methods,μ0US= 12.3 ± 0.3 kPa andμ0MRE= 11.5 ± 0.7 kPa. Numerical simulations were set with a shear modulus of 12 kPa and the resulting nonlinear shear modulus was found to be -58.1 ± 0.7 kPa. A very good agreement between the finite element model and the experimental models (AUS= -58.9 ± 9.9 kPa andAMRE= -52.8 ± 6.5 kPa) was obtained.Significance. These results show the validity of such nonlinear shear modulus measurement quantification in shear wave elastography. This work paves the way to develop nonlinear elastography technique to get a new biomarker for medical diagnosis.

Tissue mechanics coevolves with fibrillar matrisomes in healthy and fibrotic tissues

Fibrillar proteins are principal components of extracellular matrix (ECM) that confer mechanical properties to tissues. Fibrosis can result from wound repair in nearly every tissue in adults, and it associates with increased ECM density and crosslinking as well as increased tissue stiffness. Such fibrotic tissues are a major biomedical challenge, and an emerging view posits that the altered mechanical environment supports both synthetic and contractile myofibroblasts in a state of persistent activation. Here, we review the matrisome in several fibrotic diseases, as well as normal tissues, with a focus on physicochemical properties. Stiffness generally increases with the abundance of fibrillar collagens, the major constituent of ECM, with similar mathematical trends for fibrosis as well as adult tissues from soft brain to stiff bone and heart development. Changes in expression of other core matrisome and matrisome-associated proteins or proteoglycans contribute to tissue stiffening in fibrosis by organizing collagen, crosslinking ECM, and facilitating adhesion of myofibroblasts. Understanding how ECM composition and mechanics coevolve during fibrosis can lead to better models and help with antifibrotic therapies.

Application of multimodal imaging in the diagnosis of intrahepatic splenosis: Two case reports and a literature review

Intrahepatic splenosis is quite rare and is often misdiagnosed as other lesions. We present two cases of intrahepatic splenosis examined with hepatobiliary contrast agents, intravoxel incoherent motion diffusion-weighted imaging and magnetic resonance elastography. We discuss various imaging modalities and the roles of various magnetic resonance imaging methods in diagnosis. We also discuss the differentiating features that allow the correct diagnosis to be made and provide a brief review of the literature.

Clinical utility of 3D magnetic resonance elastography in patients with biliary obstruction

OBJECTIVES

Three-dimensional magnetic resonance elastography (3D-MRE) allows for multiparametric modeling of both elastic and viscous tissue characteristics. Our aim was to compare 3D-MRE with conventional liver shear stiffness assessment in gauging obstructive jaundice (OJ), predicting the adequacy of biliary decompression after drainage, and discriminating OJ from liver fibrosis.

METHODS

Patients with no histories of liver disease (n = 201) were studied in retrospect, grouped by bilirubin levels as no jaundice (NJ ≤ 2 mg/dL; n = 75), mild OJ (>2 mg/dL and ≤ 4 mg/dL; n = 56), and severe OJ (> 4 mg/dL; n = 70). For comparison, another 75 patients with chronic hepatitis B and C infections and histologically proven liver fibrosis were similarly analyzed. Each patient underwent spin-echo echo-planar-imaging MRE at 60 Hz with 3D wave postprocessing. Logistic regression and ordinary regression models were used to compare the 3D-MRE model with liver shear stiffness.

RESULTS

Liver shear stiffness, loss modulus, and damping ratio were incorporated into a 3D-MRE model, which significantly outperformed shear stiffness in predicting OJ severity (accuracy: 0.801 vs 0.672; p < 0.001). Both the 3D-MRE model and liver shear stiffness performed equally well in predicting the outcome of biliary drainage procedure (C-statistics: 0.852 vs 0.847; p = 0.48). The 3D-MRE model also demonstrated significantly better C-statistics than that of liver shear stiffness in discriminating mild OJ from F1-F2 liver fibrosis (0.765 vs 0.641; p = 0.005) and severe OJ from F3-F4 liver fibrosis (0.750 vs 0.635; p = 0.031).

CONCLUSIONS

3D-MRE is an innovative imaging method for gauging OJ severity, predicting the outcome of biliary drainage procedure, and discriminating OJ from liver fibrosis.

KEY POINTS

• 3D-MR elastography achieved promising results for predicting the severity of obstructive jaundice. • Advanced parameters of 3D-MR elastography demonstrated significantly better performance than that of shear stiffness of 2D-MR elastography in discriminating obstructive jaundice from liver fibrosis caused by chronic hepatitis B/C. • Both 3D-MR elastography and 2D-MR elastography were equivalent in predicting the outcome of biliary drainage procedure.

Magnetic resonance elastography biomarkers for detection of histologic alterations in nonalcoholic fatty liver disease in the absence of fibrosis

OBJECTIVES

To investigate associations between histology and hepatic mechanical properties measured using multiparametric magnetic resonance elastography (MRE) in adults with known or suspected nonalcoholic fatty liver disease (NAFLD) without histologic fibrosis.

METHODS

This was a retrospective analysis of 88 adults who underwent 3T MR exams including hepatic MRE and MR imaging to estimate proton density fat fraction (MRI-PDFF) within 180 days of liver biopsy. Associations between MRE mechanical properties (mean shear stiffness (|G*|) by 2D and 3D MRE, and storage modulus (G'), loss modulus (G″), wave attenuation (α), and damping ratio (ζ) by 3D MRE) and histologic, demographic and anthropometric data were assessed.

RESULTS

In univariate analyses, patients with lobular inflammation grade ≥ 2 had higher 2D |G*| and 3D G″ than those with grade ≤ 1 (p = 0.04). |G*| (both 2D and 3D), G', and G″ increased with age (rho = 0.25 to 0.31; p ≤ 0.03). In multivariable regression analyses, the association between inflammation grade ≥ 2 remained significant for 2D |G*| (p = 0.01) but not for 3D G″ (p = 0.06); age, sex, or BMI did not affect the MRE-inflammation relationship (p > 0.20).

CONCLUSIONS

2D |G*| and 3D G″ were weakly associated with moderate or severe lobular inflammation in patients with known or suspected NAFLD without fibrosis. With further validation and refinement, these properties might become useful biomarkers of inflammation. Age adjustment may help MRE interpretation, at least in patients with early-stage disease.

KEY POINTS

• Moderate to severe lobular inflammation was associated with hepatic elevated shear stiffness and elevated loss modulus (p =0.04) in patients with known or suspected NAFLD without liver fibrosis; this suggests that with further technical refinement these MRE-assessed mechanical properties may permit detection of inflammation before the onset of fibrosis in NAFLD. • Increasing age is associated with higher hepatic shear stiffness, and storage and loss moduli (rho = 0.25 to 0.31; p ≤ 0.03); this suggests that age adjustment may help interpret MRE results, at least in patients with early-stage NAFLD.

Impact of propofol sedation on the diagnostic accuracy of hepatic venous pressure gradient measurements in patients with cirrhosis

BACKGROUND

Measurement of the hepatic venous pressure gradient (HVPG) is the gold standard to evaluate the presence and severity of portal hypertension. The procedure is generally safe and well tolerated, but nevertheless, some patients demand for sedation. However, it is unknown whether propofol sedation would impair the accuracy of portal pressure measurements.

METHODS

This is a prospective observational cohort study including cirrhotic patients with suspected portal hypertension undergoing invasive measurement of HVPG. Measurements of HVPG were performed in awake condition as well as under sedation with propofol infusion.

RESULTS

In total, 37 patients were included. Mean HVPG in awake condition was 15.9 mmHg (IQR 13-19) and during sedation 14.1 mmHg (IQR 12-17). While measures of free hepatic vein pressure (FHVP) were not altered after propofol sedation (p = 0.34), wedged hepatic vein pressure values (WHVP) decreased in an average by  2.05 mmHg (95% CI - 2.46 to - 1.16; p < 0.001) which was proportional to the magnitude of HVPG. In 31 out of 37 patients (83.8%), portal hypertension with HVPG ≥ 12 mmHg was found. Under sedation with propofol, two patients (5.4%) with borderline values would have been incorrectly classified as < 12 mmHg. After adjustment for the average difference of - 10%, all patients were correctly classified. Intraclass correlation coefficient between HVPG measurement in awake condition and under propofol sedation was 0.927 (95% CI 0.594-0.975).

CONCLUSIONS

Propofol sedation during HVPG measurements is generally safe, however it may lead to relevant alterations of HVPG readings.

Added Value of Tomoelastography for Characterization of Pancreatic Neuroendocrine Tumor Aggressiveness Based on Stiffness

Simple Summary

The prediction of pancreatic neuroendocrine tumor (PNET) aggressiveness is important for treatment planning. The aim of this study was to evaluate the diagnostic performance of magnetic resonance elastography (MRE) with tomoelastography postprocessing (tomoelastography) in differentiating PNET from healthy pancreatic tissue and to correlate PNET stiffness with aggressiveness using asphericity derived from positron emission tomography (PET) as reference. In this prospective study we showed in a group of 13 patients with PNET that tomoelastography detected PNET by increased stiffness (p < 0.01) with a high diagnostic performance (AUC = 0.96). PNET was positively correlated with PET derived asphericity (r = 0.81). Tomoelastography provides quantitative imaging markers for the detection of PNET and the prediction of greater tumor aggressiveness by increased stiffness.

Abstract

Purpose: To evaluate the diagnostic performance of tomoelastography in differentiating pancreatic neuroendocrine tumors (PNETs) from healthy pancreatic tissue and to assess the prediction of tumor aggressiveness by correlating PNET stiffness with PET derived asphericity. Methods: 13 patients with PNET were prospectively compared to 13 age-/sex-matched heathy volunteers (CTR). Multifrequency MR elastography was combined with tomoelastography-postprocessing to provide high-resolution maps of shear wave speed (SWS in m/s). SWS of pancreatic neuroendocrine tumor (PNET-T) were compared with nontumorous pancreatic tissue in patients with PNET (PNET-NT) and heathy pancreatic tissue (CTR). The diagnostic performance of tomoelastography was evaluated by ROC-AUC analysis. PNET-SWS correlations were calculated with Pearson’s r. Results: SWS was higher in PNET-T (2.02 ± 0.61 m/s) compared to PNET-NT (1.31 ± 0.18 m/s, p < 0.01) and CTR (1.26 ± 0.09 m/s, p < 0.01). An SWS-cutoff of 1.46 m/s distinguished PNET-T from PNET-NT (AUC = 0.89; sensitivity = 0.85; specificity = 0.92) and a cutoff of 1.49 m/s differentiated pancreatic tissue of CTR from PNET-T (AUC = 0.96; sensitivity = 0.92; specificity = 1.00). The SWS of PNET-T was positively correlated with PET derived asphericity (r = 0.81; p = 0.01). Conclusions: Tomoelastography provides quantitative imaging markers for the detection of PNET and the prediction of greater tumor aggressiveness by increased stiffness.

Necro-inflammatory activity grading in chronic viral hepatitis with three-dimensional multifrequency MR elastography

The purpose of this study was to assess the diagnostic value of multifrequency MR elastography for grading necro-inflammation in the liver. Fifty participants with chronic hepatitis B or C were recruited for this institutional review board-approved study. Their liver was examined with multifrequency MR elastography. The storage, shear and loss moduli, and the damping ratio were measured at 56 Hz. The multifrequency wave dispersion coefficient of the shear modulus was calculated. The measurements were compared to reference markers of necro-inflammation and fibrosis with Spearman correlations and multiple regression analysis. Diagnostic accuracy was assessed. At multiple regression analysis, necro-inflammation was the only determinant of the multifrequency dispersion coefficient, whereas fibrosis was the only determinant of the storage, loss and shear moduli. The multifrequency dispersion coefficient had the largest AUC for necro-inflammatory activity A ≥ 2 [0.84 (0.71–0.93) vs. storage modulus AUC: 0.65 (0.50–0.79), p = 0.03], whereas the storage modulus had the largest AUC for fibrosis F ≥ 2 [AUC (95% confidence intervals) 0.91 (0.79–0.98)] and cirrhosis F4 [0.97 (0.88–1.00)]. The measurement of the multifrequency dispersion coefficient at three-dimensional MR elastography has the potential to grade liver necro-inflammation in patients with chronic vial hepatitis.

Three-dimensional MR Elastography Depicts Liver Inflammation, Fibrosis, and Portal Hypertension in Chronic Hepatitis B or C

Background The value of measuring mechanical properties to categorize various pathophysiologic states of the liver is as yet undetermined in chronic hepatitis B (CHB) or C (CHC). Purpose To evaluate multiparametric three-dimensional (3D) MR elastography as a means of detecting early necroinflammation, distinguishing necroinflammation from fibrosis, and gauging the severity of portal hypertension (PH) in CHB or CHC. Materials and Methods From January 2015 to September 2019, participants with CHB or CHC were prospectively enrolled from a single institution and were divided into two groups: those with liver biopsy and no evidence of PH (group 1) and those with PH and a hepatic venous pressure gradient (HVPG) measurement (group 2). For group 3, healthy volunteers were separately recruited from a nearby community. Multiple viscoelastic parameters (shear stiffness [SS], storage modulus, loss modulus, and damping ratio [DR]) were determined at 3D MR elastography at 60 Hz, and multivariable logistic or linear regression analysis was used to assess associations of mechanical parameters with histologic scores and HVPG. Results A total of 155 participants (median age, 41 years [interquartile range, 32-48 years]; 85 women) were in group 1 (training set: n = 78, validation set: n = 77), 85 participants (median age, 57 years [interquartile range, 43-61 years]; 51 women) in group 2, and 60 healthy volunteers (median age, 49 years [interquartile range, 27-64 years]; 38 men) in group 3. The liver DR was higher in participants with necroinflammation (DR, 0.13 ± 0.03) versus those without (at liver fibrosis stage F0) (DR, 0.10 ± 0.02; P < .001). Liver DR and SS together performed well in the diagnosis of necroinflammation (area under the receiver operating characteristic curve [AUC], 0.88 [95% CI: 0.79, 0.96]) and the scoring of moderate to severe activity (AUC, 0.88 [95% CI: 0.81, 0.95]) in the validation data set. Liver DR (regression coefficient [β] = -30.3 [95% CI: -58.0, -2.5]; P = .03) and splenic SS (β = 2.3 [95% CI: 1.7, 2.9]; P < .001) were independently associated with HVPG. Conclusion Three-dimensional MR elastography may detect early necroinflammation, distinguish necroinflammation from liver fibrosis, and correlate with hepatic venous pressure gradient in chronic hepatitis B and C. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Reeder in this issue.

Multifrequency magnetic resonance elastography for elasticity quantitation and optimal tissue discrimination: A two-platform liver fibrosis mimicking phantom study

In the framework of algebraic inversion, magnetic resonance elastography (MRE) repeatability, reproducibility and robustness were evaluated on extracted shear velocities (or elastic moduli). The same excitation system was implemented at two sites equipped with clinical MR scanners of 1.5 and 3 T. A set of four elastic, isotropic, homogeneous calibrated phantoms of distinct elasticity representing the spectrum of liver fibrosis severity was mechanically characterized. The repeatability of the measurements and the reproducibility between the two platforms were found to be excellent with mean coefficients of variations of 1.62% for the shear velocity mean values and 1.95% for the associated standard deviations. MRE velocities were robust to the amplitude and pattern variations of the displacement field with virtually no difference between outcomes from both magnets at identical excitation frequencies, even when the displacement field amplitude was six times smaller. However, MRE outcomes were very sensitive to the number of voxels per wavelength, s, of the recorded displacement field, with relative biases reaching 62% and precision loss by a factor of up to 23.5. For both magnetic field strengths, MRE accuracy and precision were largely degraded outside of established conditions of validity (6 ≲ s ≲ 9), resulting in estimated shear velocity values not significantly different between phantoms of increasing elasticity. When fulfilling the spatial sampling conditions, either prospectively in the acquisition or retrospectively before the reconstruction, MRE produced quantitative measurements that allowed to unambiguously discriminate, with infinitesimal p values, between the phantoms mimicking increasing severity of liver fibrosis.

Tissue engineered artificial liver model based on viscoelastic hyaluronan-collagen hydrogel and the effect of EGCG intervention on ALD

In alcoholic liver disease (ALD) research, animal models, as one of the most popular methods to explore pathology and therapeutic drug screening, show the limitations of expensive cost and ethic, as well as long modeling time. To minimize the use of animal models in ALD research, an artificial liver model has been developed by incorporating HepG2 cells into hydrogel matrix based on difunctional hyaluronan and collagen. And on this basis an alcohol-induced ALD model in vitro by adding alcohol in the engineering process has been established. Results showed that the construct exhibited a simulated synthetic and metabolic liver function thanks to the bionic fibrillar and viscoelastic characteristics of hydrogels. And the in vitro alcohol-induced ALD model was also proved to be successfully established, even presenting equal results with ALD mice. Furthermore, epigallocatechin gallate (EGCG) as an intervention on ALD was confirmed in both in vitro and in vivo model. The findings indicate our simple artificial liver model is not only highly predictive but also easy to apply to drug screening and implantation studies, suggesting a promising alternative to animal models. Moreover, as the main active ingredient of tea, EGCG's effective intervention and reversal effect on fatty liver provides support for the theory that green tea could prevent alcoholic fatty liver.

Establishing a novel method for assessing elasticity of internal anal sphincter using ultrasonic real-time tissue elastography

BACKGROUND

Evaluating anorectal function using real-time tissue elastography (RTE) has not been reported. A previous study reported that in the internal anal sphincter (IAS) of surgical specimens of patients with rectal cancer who underwent abdominoperineal resection, there was an increased fibrosis trend in those who underwent pre-operative chemoradiotherapy (CRT) compared with non-CRT. We speculated that CRT might have induced sclerosis of the IAS because of fibrosis. Therefore, we aimed to establish a method of quantitating the degree of IAS hardness using RTE on endoanal ultrasonography.

METHODS

RTE was performed with freehand manual compression under a defined pressure at the middle anal canal. Using the most compressive point in the strain graph, we traced the region of interest in the IAS. The strain histogram showed a frequency distribution of colours according to the degree of strain (numeric scan ranging from 0 to 255; smaller number indicated harder tissue). We defined the mean of the strain histogram as 'elasticity'. Ten patients with locally advanced rectal cancer who underwent pre-operative CRT were prospectively enrolled. We statistically evaluated the correlation between IAS elasticity and maximum resting pressure (MRP) values both at pre- and post-CRT. MRP was examined concurrently with the examination of IAS elasticity.

RESULTS

Representativity of elasticity measurements was demonstrated. It revealed a trend: IAS elasticity had a moderate inverse correlation with MRP (r = 0.41, P = 0.07), regardless of whether measurements were made before or after CRT.

CONCLUSION

We established a completely novel method for the assessment of elasticity of the IAS, using RTE on endoanal ultrasonography.

Reduction of breathing artifacts in multifrequency magnetic resonance elastography of the abdomen

PURPOSE

With abdominal magnetic resonance elastography (MRE) often suffering from breathing artifacts, it is recommended to perform MRE during breath-hold. However, breath-hold acquisition prohibits extended multifrequency MRE examinations and yields inconsistent results when patients cannot hold their breath. The purpose of this work was to analyze free-breathing strategies in multifrequency MRE of abdominal organs.

METHODS

Abdominal MRE with 30, 40, 50, and 60 Hz vibration frequencies and single-shot, multislice, full wave-field acquisition was performed four times in 11 healthy volunteers: once with multiple breath-holds and three times during free breathing with ungated, gated, and navigated slice adjustment. Shear wave speed maps were generated by tomoelastography inversion. Image registration was applied for correction of intrascan misregistration of image slices. Sharpness of features was quantified by the variance of the Laplacian.

RESULTS

Total scan times ranged from 120 seconds for ungated free-breathing MRE to 376 seconds for breath-hold examinations. As expected, free-breathing MRE resulted in larger organ displacements (liver, 4.7 ± 1.5 mm; kidneys, 2.4 ± 2.2 mm; spleen, 3.1 ± 2.4 mm; pancreas, 3.4 ± 1.4 mm) than breath-hold MRE (liver, 0.7 ± 0.2 mm; kidneys, 0.4 ± 0.2 mm; spleen, 0.5 ± 0.2 mm; pancreas, 0.7 ± 0.5 mm). Nonetheless, breathing-related displacement did not affect mean shear wave speed, which was consistent across all protocols (liver, 1.43 ± 0.07 m/s; kidneys, 2.35 ± 0.21 m/s; spleen, 2.02 ± 0.15 m/s; pancreas, 1.39 ± 0.15 m/s). Image registration before inversion improved the quality of free-breathing examinations, yielding no differences in image sharpness to uncorrected breath-hold MRE in most organs (P > .05).

CONCLUSION

Overall, multifrequency MRE is robust to breathing when considering whole-organ values. Respiration-related blurring can readily be corrected using image registration. Consequently, ungated free-breathing MRE combined with image registration is recommended for multifrequency MRE of abdominal organs.

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

PURPOSE

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.

METHODS

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.

RESULTS

Stiffness values were comparable between FASTWALTZ and SC MRE for both phantoms and in-vivo data. In volunteers, the group mean stiffness values at 60 Hz 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.

CONCLUSION

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.

Assessment of liver fibrosis with liver and spleen magnetic resonance elastography, serum markers in chronic liver disease

Background

The accurate assessment of liver fibrosis is essential for patients with chronic liver disease. A liver biopsy is an invasive procedure that has many potential defects and complications. Therefore, noninvasive assessment techniques are of considerable value for clinical diagnosis. Liver and spleen magnetic resonance elastography (MRE) and serum markers have been proposed for quantitative and noninvasive assessment of liver fibrosis. This study aims to compare the diagnostic performance of liver and spleen stiffness measured by MRE, fibrosis index based on the 4 factors (FIB-4), aspartate aminotransferase-to-platelet ratio index (APRI), and their combined models for staging hepatic fibrosis.

Methods

One hundred and twenty patients with chronic liver disease underwent MRE scans. Liver and spleen stiffness were measured by the MRE stiffness maps. Serum markers were collected to calculate FIB-4 and APRI. Liver biopsies were used to identify pathologic grading. Spearman's rank correlation analysis evaluated the correlation between the parameters and fibrosis stages. Receiver operating characteristic (ROC) analysis evaluated the performance of the four individual parameters, a liver and spleen stiffness combined model, and an all-parameters combined model in assessing liver fibrosis.

Results

Liver stiffness, spleen stiffness, FIB-4, and APRI were all correlated with fibrosis stage (r=0.87, 0.64, 0.65, and 0.51, respectively, all P<0.001). Among the 4 individual diagnostic markers, liver stiffness showed the highest values in staging F1-4, F2-4, F3-4 and F4 (AUC =0.89, 0. 97, 0.95, and 0.95, all P<0.001). The AUCs of the liver and spleen stiffness combined model in the F1-4, F2-4, F3-4, and F4 staging groups were 0.89, 0.97, 0.95, and 0.96, respectively (all P<0.001). The corresponding AUCs of the all-parameters combined model were 0.90, 0.97, 0.95, and 0.96 (all P<0.001). The AUCs of the liver and spleen stiffness combined model were significantly higher than those of APRI, FIB-4 in the F2-4, F3-4, and F4 staging groups (all P<0.05). Both combined models were not significantly different from liver stiffness in staging liver fibrosis (all P>0.05).

Conclusions

Liver stiffness measured with MRE had better diagnostic performance than spleen stiffness, APRI, and FIB-4 for fibrosis staging. The combined models did not significantly improve the diagnostic value compared with liver stiffness in staging fibrosis.

Magnetic resonance elastography-derived stiffness of the kidneys and its correlation with water perfusion

Stiffness plays an important role in diagnosing renal fibrosis. However, kidney stiffness is altered by perfusion changes in many kidney diseases. Therefore, the aim of the current study is to determine the correlation of kidney stiffness with water intake. We hypothesize that kidney stiffness will increase with 1 L of water intake due to increased water perfusion to the kidneys. Additionally, stiffness of the kidneys will correlate with apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values before and after water intake. A 3 T MRI scanner was used to perform magnetic resonance elastography and diffusion tensor imaging of the kidneys on 24 healthy subjects (age range: 22-66 years) before and after water intake of 1 L. A 3D T1-weighted bladder scan was also performed to measure bladder volume before and after water intake. A paired t-test was performed to evaluate the effect of water intake on the stiffness of kidneys, in addition to bladder volume. A Spearman correlation test was performed to determine the association between stiffness, bladder volume, ADC and FA values of both kidneys before and after water intake. The results show a significant increase in stiffness in different regions of the kidney (ie, percentage increase ranged from 3.6% to 7.5%) and bladder volume after water intake (all P < 0.05). A moderate significant negative correlation was observed between change in kidney stiffness and bladder volume (concordance correlation coefficient = -0.468, P < 0.05). No significant correlation was observed between stiffness and ADC or FA values before and after water intake in both kidneys (P > 0.05). Water intake caused a significant increase in the stiffness of the kidneys. The negative correlation between the change in kidney stiffness and bladder volume, before and after water intake, indicates higher perfusion pressure in the kidneys, leading to increased stiffness.

Magnetic Resonance Elastography of kidneys: SE-EPI MRE reproducibility and its comparison to GRE MRE

The purpose of this study is 1) to demonstrate reproducibility of spin echo-echo planar imaging (SE-EPI) magnetic resonance elastography (MRE) to estimate kidney stiffness; and 2) to compare SE-EPI MRE and gradient recalled echo (GRE) MRE-derived stiffness estimations in various anatomical regions of the kidney. Kidney MRE was performed on 33 healthy subjects (8 for SE-EPI MRE reproducibility and 25 for comparison with GRE MRE; age range: 22-66 years) in a 3 T MRI scanner. To demonstrate SE-EPI MRE reproducibility, subjects were scanned for the first scan and then asked to leave the scan room and repositioned again for the second (repeat) scan. Similar set-up was used for GRE MRE as well. The displacement data was then processed to obtain overall stiffness estimates of the kidney. Concordance correlation analyses were performed to determine SE-EPI MRE reproducibility and agreement between GRE MRE and SE-EPI MRE derived stiffness. A high concordance correlation (ρ_c  = 0.95; p-value<0.0001) was obtained for SE-EPI MRE reproducibility. Good concordance correlation was observed (ρ_c  = 0.84; p < 0.0001 for both kidneys, ρ_c  = 0.91; p < 0.0001 for right kidney and ρ_c  = 0.78; p < 0.0001 for left kidney) between GRE MRE and SE-EPI MRE derived stiffness measurements. Paired t-test results showed that stiffness value of medulla was significantly (p < 0.0001) greater than cortex using SE-EPI MRE as well as GRE MRE. SE-EPI MRE was reproducible and good agreement was observed in MRE-derived stiffness measurements obtained using SE-EPI and GRE sequences. Therefore, SE-EPI can be used for kidney MRE applications.

Diagnostic performance of quantitative magnetic resonance imaging biomarkers for predicting portal hypertension in children and young adults with autoimmune liver disease

BACKGROUND

Primary sclerosing cholangitis, autoimmune hepatitis and autoimmune sclerosing cholangitis are forms of chronic, progressive autoimmune liver disease (AILD) that can affect the pediatric population.

OBJECTIVE

To determine whether quantitative MRI- and laboratory-based biomarkers are associated with conventional imaging findings of portal hypertension (radiologic portal hypertension) in children and young adults with AILD.

MATERIALS AND METHODS

Forty-four patients with AILD enrolled in an institutional registry underwent a research abdominal MRI examination at 1.5 tesla (T). Five quantitative MRI techniques were performed: liver MR elastography, spleen MR elastography, liver iron-corrected T1 mapping, liver T2 mapping, and liver diffusion-weighted imaging (DWI, quantified as apparent diffusion coefficients). Two anatomical sequences were used to document splenomegaly, varices and ascites. We calculated aspartate aminotransferase (AST)-to-platelet ratio index (APRI) and fibrosis-4 (FIB-4) scores - laboratory-based biomarkers of liver fibrosis. We used receiver operating characteristic (ROC) curve analyses to establish the diagnostic performance of quantitative MRI and laboratory biomarkers for indicating the presence of radiologic portal hypertension.

RESULTS

Twenty-three (52%) patients were male; mean age was 15.2±4.0 years. Thirteen (30%) patients had radiologic portal hypertension. Liver and spleen stiffness demonstrated the greatest diagnostic performance for indicating the presence of portal hypertension (area-under-the-ROC-curve [AUROC]=0.98 and 0.96, respectively). The APRI and FIB-4 scores also demonstrated good diagnostic performance (AUROC=0.87 and 0.88, respectively).

CONCLUSION

MRI-derived measures of liver and spleen stiffness as well as laboratory-based APRI and FIB-4 scores are highly associated with imaging findings of portal hypertension in children and young adults with AILD and thus might be useful for predicting portal hypertension impending onset and directing personalized patient management.

Does gadoxetate disodium affect MRE measurements in the delayed hepatobiliary phase?

OBJECTIVES

To assess if the administration of gadoxetate disodium (Gd-EOB-DTPA) significantly affects hepatic magnetic resonance elastography (MRE) measurements in the delayed hepatobiliary phase (DHBP).

METHODS

A total of 47 patients (15 females, 32 males; age range 23-78 years, mean 54.28 years) were assigned to standard hepatic magnetic resonance imaging (MRI) with application of Gd-EOB-DTPA and hepatic MRE. MRE was performed before injection of Gd-EOB-DTPA and after 40-50 min in the DHBP. Liver stiffness values were obtained before and after contrast media application and differences between pre- and post-Gd-EOB-DTPA values were evaluated using a Bland-Altman plot and the Mann-Whitney-Wilcoxon test. In addition, the data were compared with regard to the resulting fibrosis classification.

RESULTS

Mean hepatic stiffness for pre-Gd-EOB-DTPA measurements was 4.01 kPa and post-Gd-EOB-DTPA measurements yielded 3.95 kPa. We found a highly significant individual correlation between pre- and post-Gd-EOB-DTPA stiffness values (Pearson correlation coefficient of r = 0.95 (p < 0.001) with no significant difference between the two measurements (p =0.49)). Bland-Altman plot did not show a systematic effect for the difference between pre- and post-stiffness measurements (mean difference: 0.06 kPa, SD 0.81). Regarding the classification of fibrosis stages, the overall agreement was 87.23% and the intraclass correlation coefficient was 96.4%, indicating excellent agreement.

CONCLUSIONS

Administration of Gd-EOB-DTPA does not significantly influence MRE stiffness measurements of the liver in the DHBP. Therefore, MRE can be performed in the DHBP.

KEY POINTS

• MRE of the liver can reliably be performed in the delayed hepatobiliary phase. • Gd-EOB-DTPA does not significantly influence MRE stiffness measurements of the liver. • MRE performed in the delayed hepatobiliary-phase is reasonable in patients with reduced liver function.