Clinical Feasibility of MR Elastography in Patients With Biliary Obstruction

Liver Fibrosis, Fat, and Iron Evaluation with MRI and Fibrosis and Fat Evaluation with US: A Practical Guide for Radiologists

Quantitative imaging biomarkers of liver disease measured by using MRI and US are emerging as important clinical tools in the management of patients with chronic liver disease (CLD). Because of their high accuracy and noninvasive nature, in many cases, these techniques have replaced liver biopsy for the diagnosis, quantitative staging, and treatment monitoring of patients with CLD. The most commonly evaluated imaging biomarkers are surrogates for liver fibrosis, fat, and iron. MR elastography is now routinely performed to evaluate for liver fibrosis and typically combined with MRI-based liver fat and iron quantification to exclude or grade hepatic steatosis and iron overload, respectively. US elastography is also widely performed to evaluate for liver fibrosis and has the advantage of lower equipment cost and greater availability compared with those of MRI. Emerging US fat quantification methods can be performed along with US elastography. The author group, consisting of members of the Society of Abdominal Radiology (SAR) Liver Fibrosis Disease-Focused Panel (DFP), the SAR Hepatic Iron Overload DFP, and the European Society of Radiology, review the basics of liver fibrosis, fat, and iron quantification with MRI and liver fibrosis and fat quantification with US. The authors cover technical requirements, typical case display, quality control and proper measurement technique and case interpretation guidelines, pitfalls, and confounding factors. The authors aim to provide a practical guide for radiologists interpreting these examinations. ^© RSNA, 2023 See the invited commentary by Ronot in this issue. Quiz questions for this article are available in the supplemental material.

Noninvasive Fibrosis Testing in Chronic Liver Disease Including Caveats

Assessment of liver fibrosis is important as the range of liver disease management has expanded, rendering biopsy both imperfect and impractical in many situations. Noninvasive tests of fibrosis leverage laboratory, imaging and elastography techniques to estimate disease extent, often with the goal of identifying advanced fibrosis. This review attempts to summarize their utility across a broad range of possible clinical scenarios while considering the central tenets of health care quality: access, quality, and cost. For each test, it also discusses the caveats whereby each test may have reduced effectiveness and how to consider each in a typical clinical setting.

Noninvasive imaging of hepatic dysfunction: A state-of-the-art review

Hepatic dysfunction represents a wide spectrum of pathological changes, which can be frequently found in hepatitis, cholestasis, metabolic diseases, and focal liver lesions. As hepatic dysfunction is often clinically silent until advanced stages, there remains an unmet need to identify affected patients at early stages to enable individualized intervention which can improve prognosis. Passive liver function tests include biochemical parameters and clinical grading systems (e.g., the Child-Pugh score and Model for End-Stage Liver Disease score). Despite widely used and readily available, these approaches provide indirect and limited information regarding hepatic function. Dynamic quantitative tests of liver function are based on clearance capacity tests such as the indocyanine green (ICG) clearance test. However, controversial results have been reported for the ICG clearance test in relation with clinical outcome and the accuracy is easily affected by various factors. Imaging techniques, including ultrasound, computed tomography, and magnetic resonance imaging, allow morphological and functional assessment of the entire hepatobiliary system, hence demonstrating great potential in evaluating hepatic dysfunction noninvasively. In this article, we provide a state-of-the-art summary of noninvasive imaging modalities for hepatic dysfunction assessment along the pathophysiological track, with special emphasis on the imaging modality comparison and selection for each clinical scenario.

A proposed model on MR elastography for predicting postoperative major complications in patients with hepatocellular carcinoma

Objective

To develop a model for predicting post-operative major complications in patients with hepatocellular carcinoma (HCC).

Methods

In all, 186 consecutive patients with pre-operative MR elastography were included. Complications were categorised using Clavien‒Dindo classification, with major complications defined as ≥Grade 3. Liver-stiffness measurement (LSM) values were measured on elastogram. The indocyanine green clearance rate of liver remnant (ICG-Krem) was based on the results of CT volumetry, intraoperative data, and ICG-K value. For an easy application to the prediction model, the continuous variables were converted to categories. Moreover, logistic regression analysis and fivefold cross-validation were performed. The prediction model's discriminative performance was evaluated using the area under the receiver operating characteristic curve (AUC), and the calibration of the model was assessed by the Hosmer‒Lemeshow test.

Results

43 of 186 patients (23.1%) had major complications. The multivariate analysis demonstrated that LSM, albumin-bilirubin (ALBI) score, intraoperative blood loss, and ICG-Krem were significantly associated with major complications. The median AUC of the five validation subsets was 0.878. The Hosmer-Lemeshow test confirmed no evidence of inadequate fit (p = 0.13, 0.19, 0.59, 0.59, and 0.73) on the fivefold cross-validation. The prediction model for major complications was as follows: -2.876 + 2.912 [LSM (>5.3 kPa)]+1.538 [ALBI score (>-2.28)]+0.531 [Intraoperative blood loss (>860 ml)]+0.257 [ICG-Krem (<0.10)].

Conclusion

The proposed prediction model can be used to predict post-operative major complications in patients with HCC.

Advances in knowledge

The proposed prediction model can be used in routine clinical practice to identify post-operative major complications in patients with HCC and to strategise appropriate treatments of HCC.

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 of the Brain

Magnetic resonance elastography (MRE) is an emerging noninvasive technique, an alternative to palpation for quantitative assessment of biomechanical properties of tissue. In MRE, tissue stiffness information is obtained by a 3-step process, propagating mechanical waves in the tissues, measuring the wave propagation using modified magnetic resonance (MR) pulse sequences, and generating the quantitative stiffness maps from the MR images. MRE is clinically used in patients with liver diseases, whereas its applications in other organs are still being investigated. At present, the pediatric studies are in the initial stage and preliminary results promise to provide additional information about tissue characteristics.

Predictive value of combined computed tomography volumetry and magnetic resonance elastography for major complications after liver resection

PURPOSE

To retrospectively compare the predictive value of computed tomography volumetry (CTV), magnetic resonance elastography (MRE) of the liver, and their combination for major complications after liver resection.

METHODS

We enrolled 108 consecutive patients who underwent anatomical liver resection for liver tumors and preoperative contrast-enhanced CT and MRE. The future liver remnant (FLR) ratio was calculated by CTV, while the liver stiffness measurement (LSM) was obtained by MRE. FLR ratio alone, LSM alone, and combined FLR ratio and LSM were evaluated to predict major complications (Clavien-Dindo grade ≥ IIIa). Univariate and multivariate analyses of hepatic biochemical parameters and imaging data were performed to identify predictors of major complications. Receiver operating characteristic analyses of FLR ratio, LSM, and their combination were performed, and the sensitivity and specificity were calculated.

RESULTS

Twenty-two (20.4%) of the 108 patients experienced major complications. According to multiple regression analysis, the FLR ratio (odds ratio [OR] 0.96, 95% confidence interval [CI] 0.91-0.99, p = 0.040) and LSM (OR 1.72, 95% CI 1.01-2.94, p = 0.047) were independent predictors of major complications. The combined FLR ratio and LSM were predictive of major complications, with an area under the curve (AUC) of 0.818, sensitivity of 68.2%, and specificity of 84.9%. The AUC and specificity for combined FLR ratio and LSM were larger than those for FLR ratio (AUC: 0.711, specificity: 80.2%) and LSM (AUC: 0.793, specificity: 80.2%).

CONCLUSION

Combined CTV and MRE analysis can improve the AUC and specificity for predicting major complications after anatomical liver resection.

[Magnetic resonance elastography of the liver : Worth knowing for clinical routine]

BACKGROUND

Magnetic resonance elastography (MRE) is a noninvasive, quantitative, MRI-based method to evaluate liver stiffness. Beside biopsy and ultrasound elastography, this imaging method plays in many places a significant role in the detection and additive characterization of chronic liver disease.

OBJECTIVES, MATERIALS AND METHODS

Based on the literature, a brief review of the underlying method and the commercially available products is given. Furthermore, the practical procedure, the analysis, and the interpretation of clinically relevant questions are illustrated and a comparison with ultrasound elastography is provided.

RESULTS

This relative "young" MRI method allows extensive evaluation of mechanical properties of the liver and is an important diagnostic tool especially in follow-up examinations. The MRE of the liver is with a maximum technical failure rate of 5.8% a robust technique with high accuracy and an excellent re-test reliability as well as intra- and interobserver reproducibility. There is a high diagnostic certainty within the framework of most important clinical indications, the quantification of fibrosis, and with a very good correlation with the "gold standard" biopsy.

CONCLUSION

Based on its rising clinical relevance and the broad usage, MRE of the liver is increasingly used in many centers and in routine liver protocols. Therefore, basic knowledge of this method is essential for every radiologist.

Liver stiffness measurement in patients with nodular regenerative hyperplasia undergoing magnetic resonance elastography

PURPOSE

Nodular regenerative hyperplasia (NRH) may mimic cirrhosis at imaging. We aim to investigate the effect of NRH on liver stiffness measurement (LSM) obtained with magnetic resonance elastography (MRE).

METHODS

This retrospective, Institutional Review Board-approved study included 37 subjects with NRH (Group 1) and no or minimal fibrosis (F0-F1), a control group (Group 2) made of 30 subjects with non-advanced fibrosis (F0-F2), and a control group (Group 3) made of 30 subjects with advanced fibrosis (F3-F4), all with available MRE. LSM was measured in each subject along with assessment of hepatic morphological features of cirrhosis and signs of portal hypertension. The significance of the difference in mean LSM between Group 1 and 2 and between Group 1 and 3 was evaluated using the Mann-Whitney U test. The difference in distribution of imaging features among groups was assessed using the Pearson χ2 or Fisher exact test.

RESULTS

The mean ± SD LSM in Group 1 (3.56 ± 1.10 kPa) was significantly higher compared to Group 2 (2.91 ± 0.52 kPa, P = 0.019) and significantly lower compared to Group 3 (7.18 ± 2.08 kPa, P < 0.001). Twelve (32%) patients with NRH had LSM ≥ 4.11 kPa, and 6 (16%) patients had LSM ≥ 4.71 kPa. Surface nodularity (P = 0.032) and caudate lobe hypertrophy (P = 0.004) were more commonly visualized in Group 1 than in Group 2. At least one feature of portal hypertension was observed in 16 (43%) NRH subjects.

CONCLUSION

NRH may increase the LSM obtained with MRE and may represent a confounding factor when using liver stiffness for the non-invasive diagnosis of fibrosis.

Magnetic Resonance Elastography of Liver: Current Update

The first clinical application of magnetic resonance elastography (MRE) was in the evaluation of chronic liver disease (CLD) for detection and staging of liver fibrosis. In the past 10 years, MRE has been incorporated seamlessly into a standard magnetic resonance imaging (MRI) liver protocol worldwide. Liver MRE is a robust technique for evaluation of liver stiffness and is currently the most accurate noninvasive imaging technology for evaluation of liver fibrosis. Newer MRE sequences including spin-echo MRE and 3 dimensional MRE have helped in reducing the technical limitations of clinical liver MRE that is performed with 2D gradient recalled echo (GRE) MRE. Advances in MRE technology have led to understanding of newer mechanical parameters such as dispersion, attenuation, and viscoelasticity that may be useful in evaluating pathological processes in CLD and may prove useful in their management.This review article will describe the changes in CLD that cause an increase in stiffness followed by principle and technique of liver MRE. In the later part of the review, we will briefly discuss the advances in liver MRE.