Magnetic resonance elastography of the liver: preliminary results and estimation of inter-rater reliability. Jpn J Radiol. 2010;28:623-627. [PMID: 20972864 DOI: 10.1007/s11604-010-0478-1]

Liver stiffness assessed by magnetic resonance elastography predicts clinical outcomes in patients with heart failure and without chronic liver disease

OBJECTIVES

Evaluation of liver stiffness (LS) by magnetic resonance elastography (MRE) is useful for estimating right atrial pressure (RAP) in patients with heart failure (HF). However, its prognostic implications are unclear. We sought to investigate whether LS measured by MRE (LS-MRE) could predict clinical outcomes in patients with HF.

METHODS

We prospectively examined 207 consecutive HF patients between April 2018 and May 2021 after excluding those with organic liver disease. All patients underwent 3.0-T MRE. The primary outcome of interest was the composite of all-cause death and hospitalisation for HF.

RESULTS

During a median follow-up period of 720 (interquartile range [IQR] 434-1013) days, the primary outcome occurred in 44 patients (21%), including 15 (7%) all-cause deaths and 29 (14%) hospitalisations for HF. The patients were divided into two groups according to median LS-MRE of 2.54 (IQR 2.34-2.82) kPa. Patients with higher LS-MRE showed a higher incidence of the primary outcome compared to those with lower LS-MRE (p < 0.001). Multivariable Cox regression analyses revealed that LS-MRE value was independently associated with the risk of adverse events (hazard ratio 2.49, 95% confidence interval 1.46-4.24). In multivariable linear regression, RAP showed a stronger correlation with LS-MRE (β coefficient = 0.31, p < 0.001) compared to markers related to liver fibrosis.

CONCLUSIONS

In patients without chronic liver disease and presenting with HF, elevated LS-MRE was independently associated with worse clinical outcomes. Elevated LS-MRE may be useful for risk stratification in patients with HF and without chronic liver disease.

KEY POINTS

• Magnetic resonance elastography (MRE) is an emerging non-invasive imaging technique for evaluating liver stiffness (LS) which can estimate right atrial pressure. • Elevated LS-MRE, which mainly reflects liver congestion, was independently associated with worse clinical outcomes in patients with heart failure. • The assessment of LS-MRE would be useful for stratifying the risk of adverse events in heart failure patients without chronic liver disease.

Combining 99mTc-GSA single-photon emission-computed tomography and Gd-EOB-DTPA-enhanced magnetic resonance imaging for staging liver fibrosis

Preoperative assessment of the degree of liver fibrosis is important to determine treatment strategies. In this study, galactosyl human serum albumin single-photon emission-computed tomography and ethoxybenzyl (EOB) contrast-enhanced magnetic resonance imaging (MRI) were used to assess the changes in hepatocyte function after liver fibrosis, and the standardized uptake value (SUV) was combined with gadolinium EOB-diethylenetriaminepentaacetic acid to evaluate its added value for liver fibrosis staging. A total of 484 patients diagnosed with hepatocellular carcinoma who underwent liver resection between January 2010 and August 2018 were included. Resected liver specimens were classified based on pathological findings into nonfibrotic and fibrotic groups (stratified according to the Ludwig scale). Galactosyl human serum albumin-single-photon emission-computed tomography and EOB contrast-enhanced MRI examinations were performed, and the mean SUVs (SUVmean) and contrast enhancement indices (CEIs) were obtained. The diagnostic value of the acquired SUV and CEIs for fibrosis was assessed by calculating the area under the receiver operating characteristic curve (AUC). In the receiver operating characteristic analysis, SUV + CEI showed the highest AUC in both fibrosis groups. In particular, in the comparison between fibrosis groups, SUV + CEI showed significantly higher AUCs than SUV and CEI alone in discriminating between fibrosis (F3 and 4) and no or mild fibrosis (F0 and 2) (AUC: 0.879, vs SUV [P = 0.008], vs. CEI [P = 0.023]), suggesting that the combination of SUV + CEI has greater diagnostic performance than the individual indices. Combining the SUV and CEI provides high accuracy for grading liver fibrosis, especially in differentiating between grades F0 and 2 and F3-4. SUV and gadolinium EOB-diethylenetriaminepentaacetic acid-enhanced MRI can be noninvasive diagnostic methods to guide the selection of clinical treatment options for patients with liver diseases.

Updates on Quantitative MRI of Diffuse Liver Disease: A Narrative Review

Diffuse liver diseases are highly prevalent conditions around the world, including pathological liver changes that occur when hepatocytes are damaged and liver function declines, often leading to a chronic condition. In the last years, Magnetic Resonance Imaging (MRI) is reaching an important role in the study of diffuse liver diseases moving from qualitative to quantitative assessment of liver parenchyma. In fact, this can allow noninvasive accurate and standardized assessment of diffuse liver diseases and can represent a concrete alternative to biopsy which represents the current reference standard. MRI approach already tested for other pathologies include diffusion-weighted imaging (DWI) and radiomics, able to quantify different aspects of diffuse liver disease. New emerging MRI quantitative methods include MR elastography (MRE) for the quantification of the hepatic stiffness in cirrhotic patients, dedicated gradient multiecho sequences for the assessment of hepatic fat storage, and iron overload. Thus, the aim of this review is to give an overview of the technical principles and clinical application of new quantitative MRI techniques for the evaluation of diffuse liver disease.

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

OBJECTIVES

To 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.

METHODS

This 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.

RESULTS

ICC 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.

CONCLUSION

MRE-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.

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.

[Optimization of External Driver Amplitude in Magnetic Resonance Elastography of the Liver: Relationship between Appropriate External Driver Amplitude and Indicators of Physical Constitution]

PURPOSE

Magnetic resonance elastography (MRE) of the liver was performed to examine the appropriate external driver amplitude according to the physique of the subject and the index useful for determining the physique.

METHODS

For 60 subjects who underwent MRE examination, we measured the unmeasurable elastic modulus area in the liver based on the stiffness map obtained from MRE. The external driver amplitude with the smallest unmeasurable elastic modulus area was taken as the appropriate external driver amplitude for the subject. The receiver operating characteristic (ROC) analysis was performed on the indicators of physical constitution (abdominal depth, waist circumference, body weight and body mass index (BMI) ) and external driver amplitude of 30%, 50% and 70%. BMI was the most appropriate tool for the comparison of indicators of physical constitution.

RESULT

The appropriate external driver amplitude was 30% when the cutoff value of BMI was less than 25.3 kg/m², 70% when it was 31.0 kg/m² or more, and 50% when it was between them.

CONCLUSION

It is considered that an accurate elastic modulus can be obtained by setting an appropriate indicator of physical constitution and external driver amplitude according to physique in MRE.

Poroelasticity as a Model of Soft Tissue Structure: Hydraulic Permeability Reconstruction for Magnetic Resonance Elastography in Silico

Magnetic Resonance Elastography allows noninvasive visualization of tissue mechanical properties by measuring the displacements resulting from applied stresses, and fitting a mechanical model. Poroelasticity naturally lends itself to describing tissue - a biphasic medium, consisting of both solid and fluid components. This article reviews the theory of poroelasticity, and shows that the spatial distribution of hydraulic permeability, the ease with which the solid matrix permits the flow of fluid under a pressure gradient, can be faithfully reconstructed without spatial priors in simulated environments. The paper describes an in-house MRE computational platform - a multi-mesh, finite element poroelastic solver coupled to an artificial epistemic agent capable of running Bayesian inference to reconstruct inhomogenous model mechanical property images from measured displacement fields. Building on prior work, the domain of convergence for inference is explored, showing that hydraulic permeabilities over several orders of magnitude can be reconstructed given very little prior knowledge of the true spatial distribution.

Normative values for magnetic resonance elastography-based liver stiffness in a healthy population

INTRODUCTION Chronic liver disease resulting in fibrosis, and ultimately cirrhosis, is a significant cause of morbidity and mortality worldwide. None of the conventional imaging techniques are able to detect early fibrosis and compare its grade with the histopathologic scale. Liver biopsy, as the diagnostic standard for liver fibrosis, also has limitations and is not well accepted by patients. Magnetic resonance elastography is a well‑established technique for evaluating liver stiffness and may replace invasive procedures. Detection of liver fibrosis in its early stages, however, requires a detailed knowledge of normal liver stiffness. OBJECTIVES This study aimed to determine normal liver stiffness values in healthy volunteers. PATIENTS AND METHODS A total of 102 volunteers (mean age, 21.6 years; range, 20-28 years) with no history of gastrointestinal, hepatobiliary, or cardiovascular disease were enrolled in the study. Liver stiffness was evaluated by magnetic resonance elastography with a 1.5T clinical magnetic resonance scanner. Images of the induced transverse wave propagation were obtained and converted to tissue stiffness maps (elastograms). RESULTS The mean (SD) liver stiffness for the entire group of volunteers was 2.14 (0.28) kPa (range, 1.37-2.66 kPa). For women, the mean (SD) stiffness value was 2.14 (0.30) kPa (range, 1.37-2.66 kPa), and for men, 2.14 (0.25) kPa (range, 1.54-2.54 kPa). CONCLUSIONS Liver stiffness in a healthy adult cohort did not exceed 2.7 kPa and is not influenced by sex, body mass index, or fat content.

Narrowband Shear Wave Generation Using Sinusoidally Modulated Acoustic Radiation Force

Most transient ultrasound elastography methods use high-intensity ultrasound "push" pulses that generate a shear wave with a wide frequency spectrum. However, it is difficult to control how the energy of the wave is distributed within that spectrum. For this reason, the shear-wave group velocity may not match that of harmonic methods like magnetic resonance elastography (MRE). The objective of this study was to introduce a narrowband shear wave generation method produced by "push" pulses with sinusoidally modulated intensity. The method, named harmonic shear wave imaging (HSWI), successively transmits a series of push pulses with a periodic change in duration. The excited shear waves form a continuous shear wave with a known main frequency that can be controlled by the user. Push pulses are interleaved with imaging pulses so only one clinical transducer is used to generate and record the shear waves. The proposed method was compared to MRE and a transient shear wave elastography method using phantoms and in vivo measurements. It was found that HSWI produces narrowband waves with a speed that closely matches that measured by MRE. Measurement of the acoustic output parameters indicated that the acoustic intensities in HSWI are suitable for clinical applications. The ability of HSWI to generate narrowband shear waves using a single linear array transducer makes it amenable for clinical translation. HSWI can potentially use the same thresholds as MRE for diagnosis of diseases affecting the stiffness of soft tissues.

Rheological determinants for simultaneous staging of hepatic fibrosis and inflammation in patients with chronic liver disease

The purpose of this study is to investigate the use of fundamental rheological parameters as quantified by MR elastography (MRE) to measure liver fibrosis and inflammation simultaneously in humans. MRE was performed on 45 patients at 3 T using a vibration frequency of 56 Hz. Fibrosis and inflammation scores were obtained from liver biopsies. Biomechanical properties were quantified in terms of complex shear modulus G* as well as shear wave phase velocity c and shear wave attenuation α. A rheological fractional derivative order model was used to investigate the linear dependence of the free model parameters (dispersion slope y, intrinsic speed c0 , and intrinsic relaxation time τ) on histopathology. Leave-one-out cross-validation was then utilized to demonstrate the effectiveness of the model. The intrinsic speed c0 increases with hepatic fibrosis, while an increased relaxation time τ is reflective of more inflammation of the liver parenchyma. The dispersion slope y does not depend either on fibrosis or on inflammation. The proposed rheological model, given this specific parameterization, establishes the functional dependences of biomechanical parameters on histological fibrosis and inflammation. The leave-one-out cross-validation demonstrates that the model allows identification, from the MRE measurements, of the histology scores when grouped into low-/high-grade fibrosis and low-/high-grade inflammation with significance levels of P = 0.0004 (fibrosis) and P = 0.035 (inflammation). The functional dependences of intrinsic speed and relaxation time on fibrosis and inflammation, respectively, shed new light onto the impact hepatic pathological changes on liver tissue biomechanics in humans. The dispersion slope y appears to represent a structural parameter of liver parenchyma not impacted by the severity of fibrosis/inflammation present in this patient cohort. This specific parametrization of the well-established rheological fractional order model is valuable for the clinical assessment of both fibrosis and inflammation scores, going beyond the capability of the plain shear modulus measurement commonly used for MRE.

Magnetic resonance elastography of liver and spleen: Methods and applications

The viscoelastic properties of the liver and spleen can be assessed with magnetic resonance elastography (MRE). Several actuators, MRI acquisition sequences and reconstruction algorithms have been proposed for this purpose. Reproducible results are obtained, especially when the examination is performed in standard conditions with the patient fasting. Accurate staging of liver fibrosis can be obtained by measuring liver stiffness or elasticity with MRE. Moreover, emerging evidence shows that assessing the tissue viscous parameters with MRE is useful for characterizing liver inflammation, non-alcoholic steatohepatitis, hepatic congestion, portal hypertension, and hepatic tumors. Further advances such as multifrequency acquisitions and compression-sensitive MRE may provide novel quantitative markers of hepatic and splenic mechanical properties that may improve the diagnosis of hepatic and splenic diseases.

Diagnostic imaging in the management of patients with metabolic syndrome

Metabolic syndrome (MetS) is the constellation of metabolic risk factors that might foster development of type 2 diabetes and cardiovascular disease. Abdominal obesity and insulin resistance play a prominent role among all metabolic traits of MetS. Because intervention including weight loss can reduce these morbidity and mortality in MetS, early detection of the severity and complications of MetS could be useful. Recent advances in imaging modalities have provided significant insight into the development and progression of abdominal obesity and insulin resistance, as well as target organ injuries. The purpose of this review is to summarize advances in diagnostic imaging modalities in MetS that can be applied for evaluating each components and target organs. This may help in early detection, monitoring target organ injury, and in turn developing novel therapeutic target to alleviate and avert them.

Usefulness of virtual touch quantification for staging liver fibrosis in patients with hepatitis C, and factors affecting liver stiffness measurement failure compared with liver biopsy

AIM

The assessment of liver fibrosis in patients with hepatitis C is important to predict carcinogenesis. In this study, we evaluated the usefulness of virtual touch quantification (VTQ) for staging liver fibrosis, and investigated factors causing discrepancies between the estimated fibrosis stage using VTQ and the pathological fibrosis stage.

METHODS

Patients with hepatitis C (n = 302) were assessed using VTQ and underwent pathological liver investigation within 1 week before and after VTQ. A receiver operator characteristic (ROC) curve was obtained for VTQ, fibrosis-4 (FIB-4) index, and aspartate aminotransferase-to-platelet ratio index (APRI), and each area under the ROC curve (AUROC) was compared to predict fibrosis stage. We used univariate and multivariate analyses to investigate the factors related to the discrepancy between the estimated fibrosis stage using VTQ and the pathological fibrosis stage.

RESULTS

At any stage, VTQ was the most accurate for staging liver fibrosis. The VTQ cut-off values were 1.33 m/s (AUROC = 0.822) for ≥F2, 1.51 m/s (AUROC = 0.836) for ≥F3, and 1.92 m/s (AUROC = 0.890) for F4. Skin liver capsule distance (SCD) was the most relevant factor for the discrepancy between the estimated fibrosis stage using VTQ and the pathological fibrosis stage. The SCD cut-off value was 17.5 mm.

CONCLUSIONS

Virtual touch quantification is a non-invasive, simple method that is more accurate for staging liver fibrosis than the FIB-4 index and APRI. However, when the SCD is longer than 17.5 mm, there may be measurement failures.

Tegafur-uracil-induced rapid development of advanced hepatic fibrosis

Tegafur-uracil has been reported to have only minor adverse effects and is associated with liver injury in 1.79% of Japanese patients. The development of tegafur-uracil-induced hepatic fibrosis with portal hypertension is rare. Here, we report a case of a 74-year-old woman with rapidly developing tegafur-uracil-induced hepatic fibrosis. The patient had no history of liver disease and had been treated with tegafur-uracil for 8 mo after breast cancer surgery. The patient was admitted to our hospital for abdominal distension and leg edema associated with liver dysfunction. Computed tomography imaging revealed massive ascites and splenomegaly, and a non-invasive assessment of liver fibrosis indicated advanced fibrosis. The histopathological findings revealed periportal fibrosis and bridging fibrosis with septation. The massive ascites resolved after discontinuing tegafur-uracil. These findings suggest that advanced hepatic fibrosis can develop from a relatively short-term administration of tegafur-uracil and that non-invasive assessment is useful for predicting hepatic fibrosis.

Prevalence and clinical significance of incidental extra-mammary findings in breast magnetic resonance imaging: A retrospective study of 1070 patients

PURPOSE

The purpose of this study was to analyze the prevalence of extra-mammary findings in magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Data from 1070 consecutive breast MRI studies was analyzed. MR-BI-RADS (Breast Imaging Reporting and Data System) was used to classify the risk category.

RESULTS

According to MR-BI-RADS, 915 (85.5%) of 1070 women were classified into MR-BI-RADS categories 1-3, and 155 (14.5%) into MR-BI-RADS categories 4-5. MR-BI-RADS categories 4-5 had a 10-times higher risk for major extra-mammary findings (odds ratio 10.1, P<0.01).

CONCLUSION

Extra-mammary findings are common and may have important clinical consequences.

Magnetic Resonance Elastography for the Evaluation of Liver Fibrosis in Chronic Hepatitis B and C by Using Both Gradient-Recalled Echo and Spin-Echo Echo Planar Imaging: A Prospective Study

OBJECTIVES

Magnetic resonance elastography (MRE) with three-dimensional spin-echo echo planar imaging (3D-SE-EPI) is a newly emerging noninvasive method for assessing liver fibrosis. We hypothesized that 3D-SE-EPI might have better diagnostic accuracy than conventional two-dimensional gradient-recalled echo (2D-GRE).

METHODS

We prospectively included 179 consecutive patients with chronic hepatitis B (CHB) or C (CHC) who underwent both MRE and liver biopsy. Liver stiffness was measured by both 3D-SE-EPI and 2D-GRE for staging biopsy-proven liver fibrosis (using METAVIR scores). A receiver-operating characteristic analysis using the area under the receiver-operating characteristic curve (AUC) was used to compare the diagnostic performance in predicting liver fibrosis between these two techniques, and compared them to serum markers of fibrosis.

RESULTS

The technical failure rate of 3D-SE-EPI (2.2%, n=4/179) was lower compared with 2D-GRE (8.3%, n=15/179). The stiffness measured by 3D-SE-EPI was slightly lower compared with 2D-GRE, with the mean difference of 0.57 kPa (Bland and Altman plot, 95% limits of agreement: -0.32 and 1.45 kPa). AUCs for the characterization of ≥F1, ≥F2, ≥F3, and F4 were 0.957 (95% confidence interval (CI): 0.913-0.983), 0.971 (0.932-0.991), 0.991 (0.961-0.999), and 0.979 (0.942-0.995) for 3D-SE-EPI, which was slightly higher compared with the AUCs for 2D-GRE at each fibrosis stage (0.948 (0.901-0.977), 0.959 (0.915-0.981), 0.979 (0.943-0.995), and 0.976 (0.938-0.994), respectively), although none reached statistical significance (P=0.160-0.585). In an "intention-to-diagnose" analysis, the diagnostic accuracy (the proportion of well-classified patients) by EPI (86.7-91.3%, n=169) was higher compared with GRE (80.9-82.1%, n=158) after applying optimal cutoffs. Both 3D-SE-EPI and 2D-GRE performed better than serum fibrosis markers.

CONCLUSIONS

With respect to 2D-GRE, 3D-SE-EPI has the advantage of lower failure rate with equivalent high diagnostic performance for staging liver fibrosis in CHB/CHC patients, and thus more helpful for those challenging cases in 2D-GRE.

Non-invasive assessment of liver fibrosis: Between prediction/prevention of outcomes and cost-effectiveness

The assessment of the fibrotic evolution of chronic hepatitis has always been a challenge for the clinical hepatologist. Over the past decade, various non-invasive methods have been proposed to detect the presence of fibrosis, including the elastometric measure of stiffness, panels of clinical and biochemical parameters, and combinations of both methods. The aim of this review is to analyse the most recent data on non-invasive techniques for the evaluation of hepatic fibrosis with particular attention to cost-effectiveness. We searched for relevant studies published in English using the PubMed database from 2009 to the present. A large number of studies have suggested that elastography and serum markers are useful techniques for diagnosing severe fibrosis and cirrhosis and for excluding significant fibrosis in hepatitis C virus patients. In addition, hepatic stiffness may also help to prognosticate treatment response to antiviral therapy. It has also been shown that magnetic resonance elastography has a high accuracy for staging and differentiating liver fibrosis. Finally, studies have shown that non-invasive methods are becoming increasingly precise in either positively identifying or excluding liver fibrosis, thus reducing the need for liver biopsy. However, both serum markers and transient elastography still have “grey area” values of lower accuracy. In this case, liver biopsy is still required to properly assess liver fibrosis. Recently, the guidelines produced by the World Health Organization have suggested that the AST-to-platelet ratio index or FIB-4 test could be utilised for the evaluation of liver fibrosis rather than other, more expensive non-invasive tests, such as elastography or FibroTest.

General review of magnetic resonance elastography

Magnetic resonance elastography (MRE) is an innovative imaging technique for the non-invasive quantification of the biomechanical properties of soft tissues via the direct visualization of propagating shear waves in vivo using a modified phase-contrast magnetic resonance imaging (MRI) sequence. Fundamentally, MRE employs the same physical property that physicians utilize when performing manual palpation - that healthy and diseased tissues can be differentiated on the basis of widely differing mechanical stiffness. By performing “virtual palpation”, MRE is able to provide information that is beyond the capabilities of conventional morphologic imaging modalities. In an era of increasing adoption of multi-parametric imaging approaches for solving complex problems, MRE can be seamlessly incorporated into a standard MRI examination to provide a rapid, reliable and comprehensive imaging evaluation at a single patient appointment. Originally described by the Mayo Clinic in 1995, the technique represents the most accurate non-invasive method for the detection and staging of liver fibrosis and is currently performed in more than 100 centers worldwide. In this general review, the mechanical properties of soft tissues, principles of MRE, clinical applications of MRE in the liver and beyond, and limitations and future directions of this discipline -are discussed. Selected diagrams and images are provided for illustration.

Reliability of magnetic resonance elastography using multislice two-dimensional spin-echo echo-planar imaging (SE-EPI) and three-dimensional inversion reconstruction for assessing renal stiffness

BACKGROUND

To evaluate the reliability of MRE using a spin-echo echo-planar imaging (SE-EPI) renal MRE technique in healthy volunteers.

METHODS

Institutional review board approved prospective study in which all participants provided written informed consent. Sixteen healthy volunteers comprising seven males and nine females with a median age of 35 years (age range: 23 to 59 years) were included. Coronal 90 Hz and 60 Hz MRE acquisitions were performed twice within a 30-min interval between examinations. Renal MRE reliability was assessed by (i) test-retest repeatability, and (ii) inter-rater agreement between two independent readers. The MRE-measured averaged renal stiffness values were evaluated using: intraclass correlation coefficient (ICC), Bland-Altman and the within-subject coefficient of variation (COV).

RESULTS

For test-retest repeatability, Bland-Altman showed a mean stiffness difference between examinations of 0.07 kPa (95% limits of agreement: -1.41, 1.54) at 90 Hz and 0.01 kPa (95% limits of agreement: -0.51, 0.53) at 60 Hz. Coefficient of repeatability was 1.47 kPa and 0.52 kPa at 90 Hz and 60 Hz, respectively. The within-subject COV was 13.6% and 7.7% at 90 Hz and 60 Hz, respectively. ICC values were 0.922 and 0.907 for test-retest repeatability and 0.998 and 0.989 for inter-rater agreement, respectively (P < 0.001).

CONCLUSION

SE-EPI renal MRE is a reliable technique.

Use of magnetic resonance elastography for assessing liver functional reserve: A clinical study

AIM: To investigate the value of magnetic resonance elastography (MRE) with regard to assessing liver functional reserve.

METHODS: Data from inpatients diagnosed with a liver tumor at an interventional radiology department from July 2013 to June 2014 were analyzed. A 3.0 Tesla magnetic resonance unit was used to scan 32 patients with confirmed diagnoses of hepatocellular carcinoma (HCC); an MRE sequence was added to the protocol, and the data were reconstructed and analyzed by two attending radiologists. Regions of interest were identified in different slices of the non-tumor liver parenchyma to measure average stiffness. In addition, the indocyanine green (ICG) test was performed no more than 1 wk before or after the magnetic resonance examination for all 32 patients; the ICG retention rate at 15 min (ICGR-15) and the ICG plasma clearance rate (ICG-K) were recorded. Correlational analyses were performed between the liver stiffness values and the ICGR-15 as well as between the liver stiffness values and the ICG-K.

RESULTS: Magnetic resonance imaging, including an MRE sequence and the ICG test, was performed successfully in all 32 enrolled patients. None of the patients developed complications. The mean ± SD of the elasticity values measured by the two attending radiologists were 4.7 ± 2.2 kPa and 4.7 ± 2.1 kPa, respectively. The average liver stiffness value of the non-tumor parenchyma measured using MRE in HCC patients was 4.7 ± 2.2 kPa. The average ICGR-15 was 0.089 ± 0.077, and the average ICG-K was 0.19 ± 0.07. We found that the liver stiffness value of the non-tumor parenchyma was significantly and positively related to the ICGR-15 (r = 0.746, P < 0.01) as well as significantly and negatively related to the ICG-K (r = -0.599, P < 0.01). The ICGR-15 was significantly and negatively related to the ICG-K (r = -0.852, P < 0.01).

CONCLUSION: MRE is accurate and non-invasive; furthermore, it can be used to effectively assess the liver functional reserve of HCC patients.

MR elastography of the liver at 3.0 T in diagnosing liver fibrosis grades; preliminary clinical experience

OBJECTIVES

To clarify the usefulness of 3.0-T MR elastography (MRE) in diagnosing the histological grades of liver fibrosis using preliminary clinical data.

MATERIALS AND METHODS

Between November 2012 and March 2014, MRE was applied to all patients who underwent liver MR study at a 3.0-T clinical unit. Among them, those who had pathological evaluation of liver tissue within 3 months from MR examinations were retrospectively recruited, and the liver stiffness measured by MRE was correlated with histological results. Institutional review board approved this study, waiving informed consent.

RESULTS

There were 70 patients who met the inclusion criteria. Liver stiffness showed significant correlation with the pathological grades of liver fibrosis (rho = 0.89, p < 0.0001, Spearman's rank correlation). Areas under the receiver operating characteristic curve were 0.93, 0.95, 0.99 and 0.95 for fibrosis score greater than or equal to F1, F2, F3 and F4, with cut-off values of 3.13, 3.85, 4.28 and 5.38 kPa, respectively. Multivariate analysis suggested that grades of necroinflammation also affected liver stiffness, but to a significantly lesser degree as compared to fibrosis.

CONCLUSIONS

3.0-T clinical MRE was suggested to be sufficiently useful in assessing the grades of liver fibrosis.

KEY POINTS

MR elastography may help clinicians assess patients with chronic liver diseases. Usefulness of 3.0-T MR elastography has rarely been reported. Measured liver stiffness correlated well with the histological grades of liver fibrosis. Measured liver stiffness was also affected by necroinflammation, but to a lesser degree. 3.0-T MRE could be a non-invasive alternative to liver biopsy.

Validity and Reliability of Magnetic Resonance Elastography for Staging Hepatic Fibrosis in Patients with Chronic Hepatitis B

PURPOSE

We evaluated the validity and reliability of magnetic resonance elastography (MRE) for staging hepatic fibrosis in patients with chronic hepatitis B.

METHODS

The study included 73 patients with chronic hepatitis B and confirmed stages of pathological fibrosis. Two radiologists measured liver stiffness using MRE in all cases. We compared the area under the receiver operating characteristic (ROC) curve (Az) for distinguishing stages of fibrosis compared with MRE liver stiffness measurements and serum fibrosis markers. We used intraclass correlation coefficients to analyze interobserver agreement for measurements of liver stiffness and 2 one-sided t-tests to test the equivalence of the measurements by the 2 observers.

RESULTS

ROC analyses revealed the significantly superior discrimination abilities of MRE for liver fibrosis staging (Az = 0.945 to 0.978 [Observer 1] and 0.936 to 0.967 [Observer 2]) to those of serum fibrosis markers (0.491 to 0.742) for both observers (P < 0.0004). The intraclass correlation coefficient between the 2 observers was excellent (ρ = 0.971), and the measurements of liver stiffness by the 2 observers were statistically equivalent within a 0.1-kPa difference (P = 0.0157)CONCLUSION: MRE is a valid and reliable technique for discriminating the stage of hepatic fibrosis in patients with chronic hepatitis B.

Magnetic resonance elastography of abdomen

Many diseases cause substantial changes in the mechanical properties of tissue, and this provides motivation for developing methods to noninvasively assess the stiffness of tissue using imaging technology. Magnetic resonance elastography (MRE) has emerged as a versatile MRI-based technique, based on direct visualization of propagating shear waves in the tissues. The most established clinical application of MRE in the abdomen is in chronic liver disease. MRE is currently regarded as the most accurate noninvasive technique for detection and staging of liver fibrosis. Increasing experience and ongoing research is leading to exploration of applications in other abdominal organs. In this review article, the current use of MRE in liver disease and the potential future applications of this technology in other parts of the abdomen are surveyed.

Comparison of the diagnostic accuracies of magnetic resonance elastography and transient elastography for hepatic fibrosis

OBJECTIVES

To compare the diagnostic accuracies of magnetic resonance elastography (MRE) and transient elastography (TE) for hepatic fibrosis.

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board and included 113 patients (mean age, 63.1±12.2years; 84 men and 29 women) with chronic liver disease who underwent liver biopsy or resection, histopathologic assessment (METAVIR scoring system), and TE within 6months of MRE. Diagnostic accuracies of MRE and TE were compared using receiver operating characteristic curve analysis. Appropriate cutoff values of the two methods determined by maximum positive and minimum negative likelihood ratios were used to calculate the positive and negative predictive values for discriminating significant fibrosis (≥F2) from F0-F1 or cirrhosis (F4) from F0-F3.

RESULTS

Mean (95% confidence interval) area under the receiver operating characteristic curve values of MRE for cirrhosis (F4) (0.97 [0.93-0.99] vs. 0.93 [0.87-0.96]; P=0.0308), clinically significant fibrosis (≥F2) (0.98 [0.94-0.99] vs. 0.87 [0.79-0.92]; P=0.0003), and any fibrosis (≥F1) (0.97 [0.92-0.99] vs. 0.87 [0.76-0.93]; P=0.0126) were significantly higher than those of TE. By using the cutoff values derived from the maximum positive likelihood ratio, the positive and negative predictive values for≥F2 were 98.8% and 83.9%, respectively, by MRE and 98.2% and 44.8%, respectively, by TE; and for F4, 97.0% and 86.3%, respectively, by MRE and 95.8% and 77.5%, respectively, by TE.

CONCLUSION

MRE has better diagnostic accuracy than TE for staging hepatic fibrosis.

Diagnostic value of magnetic resonance elastography for detecting and staging of hepatic fibrosis: a meta-analysis

AIM

A meta-analysis was performed to evaluate the diagnostic value of magnetic resonance elastography (MRE) in detecting and staging hepatic fibrosis.

MATERIALS AND METHODS

A systematic search of PubMed, EMBASE, Web of Science, and Cochrane Library Database up to October 2013 was undertaken to find studies on the evaluation of MRE in patients suspected of hepatic fibrosis. Data from the articles were analysed using Meta-disc 1.4 and Stata 12.0 software. The sensitivity, specificity, and area under the summary receiver operating characteristic (ROC) curve (AUROC) were pooled for all stages of hepatic fibrosis (F ≥ 1, F ≥ 2, F ≥ 3, and F = 4). Publication bias was assessed through the Deeks' funnel plot asymmetry tests.

RESULTS

Thirteen studies comprising 989 patients met the inclusion criteria. The pooled sensitivity and specificity for F ≥ 1, F ≥ 2, F ≥ 3, and F = 4 were 0.87 (95% CI = 0.84-0.89) and 0.92 (95% CI = 0.87-0.96), 0.87 (95% CI = 0.84-0.90) and 0.92 (95% CI = 0.89-0.95), 0.88 (95% CI = 0.85-0.91) and 0.91 (95% CI = 0.88-0.93), 0.91 (95% CI = 0.87-0.94) and 0.92 (95% CI = 0.89-0.94), respectively. The pooled AUROC for F ≥ 1, F ≥ 2, F ≥ 3, and F = 4 were 0.9502, 0.9663, 0.9644, and 0.9768, respectively. The non-significant slope of Deeks' funnel plot asymmetry tests indicated that no significant bias was found.

CONCLUSIONS

MRE has a high diagnostic accuracy for the quantitative detection and staging of hepatic fibrosis.

Latest developments in the imaging of fibrotic liver disease

According to the World Health Organization, liver cirrhosis accounted for 1.8% of all deaths in Europe, causing about 170,000 deaths per year. Approximately 29 million persons in the EU suffer from chronic liver disease and this trend is on the rise. Liver disease is the EU's fifth most common cause of death accounting for at least one in six deaths. Early detection and monitoring of fibrosis has the potential to direct management of these chronic liver diseases and avert morbidity and mortality. Although the available techniques are in their infancy and the very early stages of fibrosis are difficult to detect, there have been significant advances in imaging over the last decade that has resulted in the use of these new imaging techniques being introduced into the patient pathway. This review explores the accuracies of these imaging techniques, their role in the management of patients, and the potential for the future.

Hepatitis activity should be considered a confounder of liver stiffness measured with MR elastography

PURPOSE

To evaluate the effect of hepatitis activity on liver stiffness measurements and the role of serum alanine aminotransferase (ALT) in liver fibrosis staging by MR elastography (MRE).

MATERIALS AND METHODS

We measured liver stiffness (kPa) in 135 patients by MRE and histologically assessed fibrosis and hepatitis activity within 2 months. Stepwise multiple linear regression was performed to determine the maximum adjusted R(2) against liver stiffness, after adjusting for nothing (model 1), ALT/upper limit of normal categories (model 2), and hepatitis activity (A grade) by METAVIR (model 3). Logistic regression was used to identify independent factors associated with pathologically proven cirrhosis.

RESULTS

Platelet count and METAVIR F score were strongly associated with liver stiffness. The adjusted R(2) value of model 3 (0.7026) was higher than those of models 1 (0.6472) and 2 (0.6564), showing that hepatitis activity affected liver stiffness measurement. High ALT levels (odds ratio, 0.0066; P = 0.0003) as well as MRE (odds ratio, 9.91; P < 0.0001) were independently associated with cirrhosis.

CONCLUSION

Hepatitis activity may be a confounder of liver stiffness measurement during liver fibrosis staging using MRE. MRE can potentially make an overdiagnosis of liver cirrhosis if the patient has high ALT levels.

Optimization of scanning parameters for MR elastography at 3.0 T clinical unit: volunteer study

PURPOSE

We sought to optimize scanning parameters for MR elastography at 3.0 T clinical unit.

MATERIALS AND METHODS

10 volunteers were scanned with various magnetization encoding gradient (MEG) frequencies from 60 to 120 Hz at every 10 Hz, with otherwise fixed parameters (external driver frequency/amplitude = 60 Hz/50 %, 10 mm slice thickness, etc.). Images were qualitatively assessed for the degree of image defects, and also quantitatively for the areas without cross-hatching. After determining optimal MEG frequency, external driver amplitudes of 70 % (vs 50 %) and slice thickness of 8 mm (vs 10 mm) were also tested. With the optimized parameters, scans were repeated 1 week after the initial scan, and the repeatability of the liver stiffness measurement was validated.

RESULTS

80 or 90 Hz was shown to be the best MEG frequency. There were no significant differences in the qualitative and quantitative assessment between the two amplitudes and two slice thicknesses; however, 70 % amplitude resulted in discomfort at the chest wall beneath the external acoustic driver. Thus, MEG 80 (or 90) Hz, amplitude 50 %, and thickness 10 (or 8) mm were considered optimal. Repeatability of the liver stiffness measurement was ±10 % (95 % confidence interval).

CONCLUSIONS

With the optimized parameters, repeatability of ±10 % in liver stiffness measurement was obtained.

Comparison of magnetic resonance elastography and gadoxetate disodium-enhanced magnetic resonance imaging for the evaluation of hepatic fibrosis

OBJECTIVES

The objective of this study was to compare the diagnostic performance of magnetic resonance elastography (MRE) and gadoxetate disodium-enhanced magnetic resonance imaging (MRI) in the staging of hepatic fibrosis (HF) in patients with liver diseases.

MATERIALS AND METHODS

This retrospective study was approved by our institutional review board, and the informed consent was waived. One hundred and sixty-eight patients with chronic liver disease or suspected focal hepatic lesions underwent MRE and gadoxetate disodium-enhanced MRI at 1.5 T. Liver stiffness values were measured on quantitative shear-stiffness maps. The contrast enhancement index (CEI) was calculated as SIpost / SIpre, where SIpost and SIpre are, respectively, the liver-to-muscle signal intensity (SI) ratio on hepatobiliary phase images and on unenhanced images. The diagnostic performance of MRE and CEI for staging HF was compared using the receiver operating characteristic curve analysis on the basis of the histopathologic analysis of HF.

RESULTS

The liver stiffness values measured on MRE (r = 0.802; P < 0.0001) were more strongly correlated with the HF stage than with the CEI (r = -0.378; P < 0.0001). The areas under the receiver operating characteristic curve values of the liver stiffness values were significantly larger than those of CEI were for discriminating all stages of HF (P < 0.001 for ≥ F1, ≥ F2, ≥ F3, and ≥ F4). Magnetic resonance elastography showed higher sensitivity and specificity for predicting HF ≥ F1 (91% and 87%), ≥ F2 (87% and 91%), ≥ F3 (80% and 89%), and F4 (81% and 85%) compared with CEI (46% and 85%, 46% and 82%, 63% and 68%, and 76% and 65%, respectively).

CONCLUSIONS

Magnetic resonance elastography was superior to the gadoxetate disodium-enhancement MRI for HF staging.

Magnetic resonance elastography for the detection and staging of liver fibrosis in chronic hepatitis B

OBJECTIVES

We measured the accuracy of magnetic resonance elastography (MRE) for the detection and staging of liver fibrosis in chronic hepatitis B (CHB) and compared it with serum fibrosis markers.

METHODS

Prospective comparison of MRE and routine serum fibrosis markers, namely serum alanine aminotransferase (ALT), serum aspartate aminotransferase (AST), ALT/AST ratio (AAR), AST to platelet ratio index (APRI) and prothrombin index (PI), was performed in 63 consecutive CHB patients who underwent MRE and histological confirmation of liver fibrosis within a 6-month interval. Diagnostic performance of MRE and serum markers for staging fibrosis (≥F1), significant fibrosis (≥F2), advanced fibrosis (≥F3) and cirrhosis (F4) was compared.

RESULTS

The study group comprised 63 patients (19 female; mean age ± SD, 50 ± 11.9 years). MRE (ρ = 0.94, P < 0.0001), APRI (ρ = 0.42, P = 0.0006), PI (ρ = 0.42, P = 0.0006) and AST (ρ = 0.28, P = 0.028) results correlated significantly with fibrosis stage. MRE was significantly more accurate than serum fibrosis markers for the detection of significant fibrosis (0.99 vs. 0.55-0.73) and cirrhosis (0.98 vs. 0.53-0.77). Sensitivity, specificity, positive predictive and negative predictive values for MRE for significant fibrosis and cirrhosis were 97.4 %, 100 %, 100 % and 96 %, and 100 %, 95.2 %, 91.3 % and 100 %, respectively.

CONCLUSION

MRE is an accurate non-invasive technique for the detection and staging of liver fibrosis in CHB.

KEY POINTS

• Magnetic resonance elastography is accurate for liver fibrosis detection and staging. • MR elastography is more accurate than serum tests for staging liver fibrosis. • MR elastography can potentially replace liver biopsy in chronic hepatitis B.

Magnetic resonance elastography of liver in healthy Asians: normal liver stiffness quantification and reproducibility assessment

PURPOSE

To determine normal liver stiffness values evaluated with magnetic resonance elastography (MRE) in healthy normal Asian volunteers and assess its reproducibility.

MATERIALS AND METHODS

Liver stiffness was evaluated with MRE in 41 healthy Asians (23 females, 18 males; mean age, 41.8 years, and mean body mass index [BMI], 23.4 kg/m(2) ) on a 1.5T clinical scanner. The correlations between mean liver stiffness and age, gender, BMI, and fat fraction percentage of the liver were studied. Another 12 volunteers underwent liver MRE exams on two separate days 4-6 weeks apart under similar conditions for reproducibility assessment. Intraclass correlation coefficient (ICC) analysis was performed and within-subject coefficient of variation (CV) of stiffness was estimated.

RESULTS

The mean ± standard deviation (SD) of liver stiffness in normal healthy Asian subjects was 2.09 ± 0.22 kPa (95% confidence interval [CI], 2.04-2.15 kPa; range 1.68-2.48 kPa). The mean liver stiffness did not significantly correlate with age, gender, BMI, or fat content of the liver. The ICC for mean liver stiffness was 0.90 (95% CI, 0.78-0.96) and CV ranged from 2.2%-11.4%.

CONCLUSION

The liver stiffness in normal Asians is not affected by age, gender, BMI, or fat content. Liver stiffness with MRE is highly reproducible.

Liver fibrosis assessment using transient elastography guided with real-time B-mode ultrasound imaging: a feasibility study

Liver fibrosis is a kind of chronic damage of the liver and can lead to cirrhosis, one of the top 10 causes of death in the Western world. However, there is still a lack of noninvasive methods for diagnosing liver fibrosis. Fibroscan (Echosens, Paris, France), a device based on A-mode transient elastography, has shown promising results. In this study, a transient elastography system with real-time B-mode imaging for non-invasive liver fibrosis assessment, named Liverscan, was developed; its performance was tested and compared with that of the Fibroscan. A specific measurement probe was designed and fabricated with a B-mode ultrasound transducer fixed along the axis of a mechanical vibrator. It was integrated with the Liverscan to measure liver stiffness based on the shear wave propagation in liver tissues. The system was validated by mechanical indentation test using custom-made agar-gelatin phantoms with different stiffness. To further test its feasibility, in vivo measurements were conducted in 67 volunteers (age, 34 ± 3 years; body mass index, 21.3 ± 2.8 kg/m(2); Mean ± SD., 34 male and 33 female), including 20 patients with various liver diseases, and 28 (19 male and 9 female) being tested by both Liverscan and Fibroscan. A significant linear correlation between the stiffness measured by the mechanical indentation test and that by the Liverscan (r = 0.973; p < 0.001) was obtained. The in vivo liver stiffness measured by Liverscan was also correlated with that by Fibroscan significantly (r = 0.886; p < 0.001). There was a significant difference in liver stiffness between the 20 patients and the other healthy subjects (14.1 ± 3.4 kPa vs. 10.5 ± 2.1 kPa; p = 0.001). The intra- and inter-observer tests indicated that the measurements were repeatable with intra-class correlation coefficients being 0.987 (p < 0.001) and 0.988 (p < 0.001), respectively. This study demonstrated that Liverscan with a specifically designed probe was able to measure and differentiate liver of different stiffness using the established measurement protocol under the guidance of real-time B-mode ultrasound imaging.

MR-based measurements of portal vein flow and liver stiffness for predicting gastroesophageal varices

OBJECTIVES

We evaluated flow parameters measured by phase-contrast magnetic resonance (MR) imaging (PC-MRI) of the portal venous system and liver stiffness measured by MR elastography (MRE) to determine the usefulness of these methods in predicting gastroesophageal varices (GEV) in patients with chronic liver disease (CLD).

METHODS

In patients with CLD and controls, we performed PC-MRI on the portal (PV) and superior mesenteric veins; calculated mean velocity (V, cm/s), cross-sectional area (S, mm²), and flow volume (Q, mL/min); and determined markers of liver fibrosis (liver stiffness [kPa]) and aspartate aminotransferase (AST) platelet ratio index [APRI]). We visually assessed GEV and development of collateral pathways of the PV on routine contrast-enhanced dynamic MR imaging and compared patient characteristics, flow parameters, liver stiffness markers, and visual analysis among 3GEV groups, those with mild, severe, or no GEV with reference to endoscopic findings.

RESULTS

Child-Pugh grade, VPV, SPV, liver stiffness, APRI, and visually identified GEV (visible GEV) differed significantly among the 3 groups (P<0.05). We investigated VPV, SPV, liver stiffness, and visible GEV as independent markers to distinguish patients with and without GEV and examined VPV and visible GEV to predict severe GEV. Visible GEV showed low sensitivity (14 to 30%) and high specificity (98%) for predicting GEV in patients with CLD. A subgroup analysis that excluded cases with collateral pathway demonstrated slightly improved diagnostic performance of VPV and liver stiffness.

CONCLUSIONS

Portal vein flow parameters and liver stiffness can be useful markers for predicting GEV in patients with CLD.

Measurement consistency of MR elastography at 3.0 T: comparison among three different region-of-interest placement methods

PURPOSE

To test inter- and intraobserver consistency of liver stiffness measurement on MR elastography (MRE) at 3.0 T.

MATERIALS AND METHODS

Two abdominal radiologists independently measured stiffness of the liver on MRE in three volunteers and seven patients with chronic liver diseases using three different region-of-interest (ROI) placement methods. Methods 1 and 2 involved placing circular and free-hand-drawn ROIs, respectively, visually referring to anatomical (three-dimensional T1-weighted) and wave images. Method 3 involved placing ROIs on the fused images of MRE and anatomical images developed on a work station, visually referring to wave images. The inter- and intraobserver consistency was assessed with regression and Bland-Altman analysis.

RESULTS

Thirty-eight images were available for measurement in total. As for interobserver consistency, method 3 showed the best regression coefficient, correlation coefficient, and y intercept. The absolute values of the interobserver differences for method 3 were significantly smaller than those of method 1 or method 2 (p < 0.05, each). Intraobserver consistency of method 3 was excellent for both observers.

CONCLUSION

Stiffness measurement of the liver on MRE performed with the fusion method at 3.0 T provides the highest inter- and intraobserver consistency.

Magnetic resonance elastography of liver: technique, analysis, and clinical applications

Many pathological processes cause marked changes in the mechanical properties of tissue. MR elastography (MRE) is a noninvasive MRI based technique for quantitatively assessing the mechanical properties of tissues in vivo. MRE is performed by using a vibration source to generate low frequency mechanical waves in tissue, imaging the propagating waves using a phase contrast MRI technique, and then processing the wave information to generate quantitative images showing mechanical properties such as tissue stiffness. Since its first description in 1995, published studies have explored many potential clinical applications including brain, thyroid, lung, heart, breast, and skeletal muscle imaging. However, the best-documented application to emerge has been the use of MRE to assess liver disease. Multiple studies have demonstrated that there is a strong correlation between MRE-measured hepatic stiffness and the stage of fibrosis at histology. The emerging literature indicates that MRE can serve as a safer, less expensive, and potentially more accurate alternative to invasive liver biopsy which is currently the gold standard for diagnosis and staging of liver fibrosis. This review describes the basic principles, technique of performing a liver MRE, analysis and calculation of stiffness, clinical applications, limitations, and potential future applications.

Review of MR elastography applications and recent developments

The technique of MR elastography (MRE) has emerged as a useful modality for quantitatively imaging the mechanical properties of soft tissues in vivo. Recently, MRE has been introduced as a clinical tool for evaluating chronic liver disease, but many other potential applications are being explored. These applications include measuring tissue changes associated with diseases of the liver, breast, brain, heart, and skeletal muscle including both focal lesions (e.g., hepatic, breast, and brain tumors) and diffuse diseases (e.g., fibrosis and multiple sclerosis). The purpose of this review article is to summarize some of the recent developments of MRE and to highlight some emerging applications.

Liver stiffness measured by magnetic resonance elastography as a risk factor for hepatocellular carcinoma: a preliminary case-control study

OBJECTIVE

To examine if liver stiffness measured by magnetic resonance elastography (MRE) is a risk factor for hepatocellular carcinoma (HCC) in patients with chronic liver disease.

METHODS

By reviewing the records of magnetic resonance (MR) examinations performed at our institution, we selected 301 patients with chronic liver disease who did not have a previous medical history of HCC. All patients underwent MRE and gadoxetic acid-enhanced MR imaging. HCC was identified on MR images in 66 of the 301 patients, who were matched to controls from the remaining patients without HCC according to age. MRE images were obtained by visualising elastic waves generated in the liver by pneumatic vibration transferred via a cylindrical passive driver. Risk factors of HCC development were determined by the odds ratio with logistic regression analysis; gender and liver stiffness by MRE and serum levels of aspartate transferase, alanine transferase, alpha-fetoprotein, and protein induced by vitamin K absence-II.

RESULTS

Multivariate analysis revealed that only liver stiffness by MRE was a significant risk factor for HCC with an odds ratio (95 % confidence interval) of 1.38 (1.05-1.84).

CONCLUSION

Liver stiffness measured by MRE is an independent risk factor for HCC in patients with chronic liver disease.

Multi-organ perfusion CT in the abdomen using a 320-detector row CT scanner: preliminary results of perfusion changes in the liver, spleen, and pancreas of cirrhotic patients

PURPOSE

To utilize 320-detector row CT in perfusion CT of multiple abdominal organs and to compare the tissue perfusion between patients with and without liver cirrhosis.

MATERIALS AND METHODS

This study included 21 patients with cirrhosis and 20 without cirrhosis. The 320-detector row CT scanner enabled multi-organ perfusion CT without requiring the scanner table to be moved. Perfusion was calculated using the maximum slope model for the aorta, the portal vein, the right and left lobes of the liver, the head and body of the pancreas, the spleen, and the corpus and antrum of the stomach. Perfusion in each organ of patients with and without cirrhosis was compared.

RESULTS

Portal venous perfusion of the right and left lobes of the liver in patients with cirrhosis (117 and 100 mL min(-1)100mL(-1), respectively) was significantly less than that in patients without cirrhosis (213 and 174 mL min(-1)100mL(-1), respectively; p=0.0081 and 0.0294, respectively). Arterial perfusion of the spleen (111 mL min(-1)100mL(-1)) and the body of the pancreas (112 mL min(-1)100mL(-1)) in patients with cirrhosis was also significantly decreased compared with that in patients without cirrhosis (spleen, 162 mL min(-1)100mL(-1), p=0.0020; body of pancreas, 133 mL min(-1)100mL(-1), p=0.0405).

CONCLUSION

The results of the perfusion CT suggest that arterial perfusion of the spleen and the body of the pancreas, as well as portal perfusion of the liver, in cirrhotic patients was decreased compared with that in non-cirrhotic patients.

Cross-validation of MR elastography and ultrasound transient elastography in liver stiffness measurement: discrepancy in the results of cirrhotic liver

PURPOSE

To evaluate individual differences in liver stiffness measurement using both MR elastography (MRE) and ultrasound transient elastography (UTE) in patients with chronic liver disease.

MATERIALS AND METHODS

This study included 80 patients with chronic liver disease who underwent both UTE and MRE. MRE and UTE were performed using a pneumatic driver (60 Hz) and an ultrasound probe with a vibrator (50 Hz), respectively. Liver stiffness data measured using the two techniques (μ(UTE) and μ(MRE) ) were compared with respect to shear modulus. The patients were subdivided into four quartiles on the basis of average of the μ(UTE) and μ(MRE) values for each patient.

RESULTS

The analysis of the 4 quartile groups revealed that μ(UTE) was significantly higher than μ(MRE) in the two most stiff liver groups: μ(UTE) versus μ(MRE) , 7.5 (1.2) versus 6.0 (0.72) kPa for the group with [μ(UTE) + μ(MRE) ]/2 of 5.6-8.0 kPa; 15.1(4.2) versus 6.7 (1.4) kPa for the group with >8.0 kPa. However, in the least stiff liver group (i.e., the group with [μ(UTE) + μ(MRE) ]/2 < 3.2 kPa), μ(UTE) was significantly lower than μ(MRE) .

CONCLUSION

The shear modulus measured by UTE and MRE are not equivalent, especially in patients with stiff livers.

Acoustic radiation force impulse elastography of the liver: can fat deposition in the liver affect the measurement of liver stiffness?

PURPOSE

The aim of this study was to compare acoustic radiation force impulse (ARFI) results between livers with and without fat deposition.

MATERIALS AND METHODS

We studied 200 consecutive healthy individuals who underwent health checkups at our institution. The subjects were divided into three groups according to the echogenicity of the liver on ultrasonography (US) and the liver-spleen attenuation ratio index (LSR) on computed tomography: normal liver group (n = 121, no evidence of bright liver on US and LSR > 1); fatty liver group (n = 46, bright liver on US and LSR < 1); others (n = 33, inconclusive results). Subjects in the inconclusive group and those who consumed alcohol >5 days a week (n = 18) were excluded from the analysis. The velocities measured by ARFI in the normal and fatty liver groups were compared using the two one-sided test.

RESULTS

The mean (SD) velocity measured in the normal and fatty liver groups were 1.03 (0.12) m/s and 1.02 (0.12) m/s, respectively. The ARFI results of the fatty liver group were similar to those of the normal liver group (P < 0.0001).

CONCLUSION

This study suggested that fat deposition in the liver does not affect the liver stiffness measurement determined by ARFI.

Effects of gadoxetic acid on liver elasticity measurement by using magnetic resonance elastography

The purpose of this study was to evaluate the effect of gadoxetic acid (Gd-EOB-DTPA) on measurements of liver stiffness by using magnetic resonance elastography (MRE). In this study, 104 consecutive patients (mean age, 67.7±9.4 years) underwent MRE using a 1.5-T MR scanner equipped with a cylindrical passive driver that was placed across the right chest wall for delivering vibrations. Axial gradient-echo images, which were automatically converted to elastograms that represented stiffness (kPa), were acquired using a continuous sinusoidal vibration of 60 Hz. Two raters independently placed a region of interest on the right lobe of the liver on the elastograms obtained before and after Gd-EOB-DTPA was administered. Liver stiffness was measured using these two elastograms and compared using a paired t test and correlation analysis. No significant difference was observed in liver stiffness before and after Gd-EOB-DTPA was administered (Rater 1, P=.1200; Rater 2, P=.3585). The correlation coefficients were 0.986 (Rater 1) and 0.984 (Rater 2), indicating excellent correlation between the stiffness values before and after Gd-EOB-DTPA was administered. Liver stiffness measured by MRE did not differ before and after Gd-EOB-DTPA was administered.