Liver fibrosis: noninvasive assessment with MR elastography versus aspartate aminotransferase-to-platelet ratio index

Acquisition Efficiency and Technical Repeatability of Dual-Frequency 3D Vector MR Elastography of the Liver

BACKGROUND

MR elastography (MRE) at 60 Hz is widely used for staging liver fibrosis. MRE with lower frequencies may provide inflammation biomarkers.

PURPOSE

To establish a practical simultaneous dual-frequency liver MRE protocol at both 30 Hz and 60 Hz during a single examination and validate the occurrence of second harmonic waves at 30 Hz.

STUDY TYPE

Retrospective.

SUBJECTS

One hundred six patients (48 females, age: 50.0 ± 13.4 years) were divided as follows: Cohort One (15 patients with chronic liver disease [CLD] and 25 healthy volunteers) with simultaneous dual-frequency MRE. Cohort Two (66 patients with CLD) with second harmonic MRE.

FIELD STRENGTH/SEQUENCE

3-T, single- or dual-frequency MRE at 30 Hz and 60 Hz.

ASSESSMENT

Liver stiffness (LS) in both cohorts was evaluated with manually placed volumetric ROIs by two independent analyzers. Image quality was assessed by three independent readers on a 4-point scale (0-3: none/failed, fair, moderate, excellent) based on the depth of wave propagation with 1/3 incremental penetration. The success rate was derived from the percentage of nonzero quality scores.

STATISTICAL TESTS

Measurement agreement, bias, and repeatability of LS were assessed using intraclass correlation coefficients (ICCs), Bland-Altman plots, and repeatability coefficient (RC). Mann-Whitney U tests were used to evaluate the differences in image quality between different methods. A P-value <0.05 was considered statistically significant.

RESULTS

Success rate was 97.5% in Cohort One and 91% success rate for the second harmonic MRE in Cohort Two. The second harmonic and conventional MRE showed excellent agreement in LS (all ICCs >0.90). The quality scores for the second harmonic wave images were lower than those from the conventional MRE (Z = -4.523).

DATA CONCLUSION

Compared with conventional and second harmonic methods, simultaneous dual-frequency had better image quality, high success rate and the advantage of intrinsic co-registration, while the second harmonic method can be an alternative if custom waveform is not available.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 1.

Potential role of two-dimensional shear wave elastography, including liver stiffness measurement and dispersion slope, for management of chronic hepatitis B

PURPOSE

This study assessed the use of liver stiffness (LS) and dispersion slope (DS) in classifying patients with chronic hepatitis B (CHB) by the necessity of antiviral treatment.

METHODS

A retrospective review examined 249 patients with CHB (male:female, 107:142; mean age, 53±14 years) between April 2018 and March 2022. Patients for whom treatment was indicated, termed group 1, exhibited either serum alanine transaminase (ALT) and aspartate aminotransferase levels not exceeding five times the upper limit of normal and LS >13 kPa, or hepatitis B virus DNA >2,000 IU/mL and ALT >40 IU/L. The remaining patients comprised group 2 (treatment not required). In subgroup analysis, patients with LS <13 kPa were further examined.

RESULTS

Overall, group 1 exhibited significantly higher LS (12.64±6.76 vs. 6.31±1.67 kPa, P<0.001) and DS (15.52±4.95 vs. 11.04±1.93 [m/s]/kHz, P<0.001) than group 2. In subgroup analysis, group 1 also demonstrated significantly higher values (LS: 8.05±2.12 vs 6.31±1.67 kPa, P<0.001, DS: 13.06±2.75 vs. 11.04±1.93 [m/s]/kHz, P<0.001). The areas under the curve (AUCs) for LS and DS in group 1 were 0.855 (95% confidence interval [CI], 0.80 to 0.90; P<0.001) and 0.810 (95% CI, 0.75 to 0.86; P<0.001), respectively. In subgroup analysis, the AUCs for LS and DS in group 1 were 0.751 (95% CI, 0.69 to 0.81; P<0.001) and 0.711 (95% CI, 0.64 to 0.77; P<0.001), respectively. Within group 1, the AUCs for LS and DS did not differ significantly (P>0.05).

CONCLUSION

LS and DS assist in classifying patients with CHB by their need for antiviral treatment.

Making sense of scattering: Seeing microstructure through shear waves

The physics of shear waves traveling through matter carries fundamental insights into its structure, for instance, quantifying stiffness for disease characterization. However, the origin of shear wave attenuation in tissue is currently not properly understood. Attenuation is caused by two phenomena: absorption due to energy dissipation and scattering on structures such as vessels fundamentally tied to the material's microstructure. Here, we present a scattering theory in conjunction with magnetic resonance imaging, which enables the unraveling of a material's innate constitutive and scattering characteristics. By overcoming a three-order-of-magnitude scale difference between wavelength and average intervessel distance, we provide noninvasively a macroscopic measure of vascular architecture. The validity of the theory is demonstrated through simulations, phantoms, in vivo mice, and human experiments and compared against histology as gold standard. Our approach expands the field of imaging by using the dispersion properties of shear waves as macroscopic observable proxies for deciphering the underlying ultrastructures.

Changes in nonalcoholic fatty liver disease and M2BPGi due to lifestyle intervention in primary healthcare

BACKGROUND

A healthy lifestyle is the most important method for managing nonalcoholic fatty liver disease (NAFLD). Mac-2-binding protein glycosylated isomer (M2BPGi) has been suggested as a biomarker for NAFLD. This study aimed to determine the efficacy of personalized lifestyle interventions on NAFLD remission.

METHODS

This single-arm intervention study recruited participants with NAFLD who underwent health checkups at seven health-promotion centers in five South Korean cities. Fatty liver diagnosis was based on ultrasonography (US). The 109 individuals were recruited for personalized lifestyle interventions of hypocaloric diets and exercise. The participants attended the lifestyle intervention programs once per month for the first 3 months, and once every 3 months for the subsequent 6 months. In addition to sessions through center visits, phone-based intervention and self-monitoring at 4-, 5-, 7-, and 8-month were provided during the 9-month intervention period. And phone-based self-monitoring were also provided monthly during the 3-month follow-up period. The primary outcome was NAFLD remission at month 12 as measured on US and magnetic resonance elastography. The secondary outcomes were the changes in metabolic factors and M2BPGi.

RESULTS

The 108 individuals (62 males and 46 females; age 51.1±12.4 years, mean±standard deviation) were finally analyzed after the 12month intervention. Body mass index, waist circumference (WC), blood pressure, blood lipids (total cholesterol, triglycerides, and HDL-C), and fasting blood sugar levels were improved relative to baseline (all P<0.05). Fatty liver at or above the moderate grade according to US was decreased at month 12 relative to baseline (67.6% vs 50.9%) (P = 0.002). M2BPGi levels decreased during the 12-month study period (P<0.001). M2BPGi levels were moderately correlated with hepatic fat fraction by magnetic resonance imaging (r = 0.33, P = 0.05). WC (OR = 0.82, 95% CI = 0.67-1.00, P = 0.05) and HDL-C (OR = 1.17, 95% CI = 1.03-1.32, P = 0.014) were associated with remission of fatty liver in the multivariate analysis.

CONCLUSION

The personalized lifestyle intervention was effective in improving fatty liver and metabolic factors, but not hepatic stiffness, in NAFLD.

TRIAL REGISTRATION

ICTRP, cris.nih.go.kr (KCT0006380).

The role of shear viscosity as a biomarker for improving chronic kidney disease detection using shear wave elastography: A computational study using a validated finite element model

The application of ultrasound shear wave elastography for detecting chronic kidney disease, namely renal fibrosis, has been widely studied. A good correlation between tissue Young's modulus and the degree of renal impairment has been established. However, the current limitation of this imaging modality pertains to the linear elastic assumption used in quantifying the stiffness of renal tissue in commercial shear wave elastography systems. As such, when underlying medical conditions such as acquired cystic kidney disease, which may potentially influence the viscous component of renal tissue, is present concurrently with renal fibrosis, the accuracy of the imaging modality in detecting chronic kidney disease may be affected. The findings in this study demonstrate that quantifying the stiffness of linear viscoelastic tissue using an approach similar to those implemented in commercial shear wave elastography systems led to percentage errors as high as 87%. The findings presented indicate that use of shear viscosity to detect changes in renal impairment led to a reduction in percentage error to values as low as 0.3%. For cases in which renal tissue was affected by multiple medical conditions, shear viscosity was found to be a good indicator in gauging the reliability of the Young's modulus (quantified through a shear wave dispersion analysis) in detecting chronic kidney disease. The findings show that percentage error in stiffness quantification can be reduced to as low as 0.6%. The present study demonstrates the potential use of renal shear viscosity as a biomarker to improve the detection of chronic kidney disease.

Diagnostic accuracy of magnetic resonance elastography and point-shear wave elastography for significant hepatic fibrosis screening: Systematic review and meta-analysis

The hepatic diseases are extremely common in clinical practice. The correct classification of liver fibrosis is extremely important, as it influences therapy and predicts disease outcomes. The purpose of this study is to compare the diagnostic performance of point-shear wave elastography (pSWE) and magnetic resonance elastography (MRE) in the hepatic fibrosis diagnostic. A meta-analysis was carried out based on articles published until October 2020. The articles are available at following databases: MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Scientific Electronic Library Online, LILACS, Scopus, and CINAHL. Diagnostic performances were analyzed per METAVIR F2, using 3.5kPa as target fibrosis. Assessment of the methodological quality of the incorporated papers by the QUADAS-2 tool for pSWE and MRE. A total 2,153 studies articles were evaluated and 44 studies, comprising 6,081 patients with individual data, were included in the meta-analysis: 28 studies for pSWE and 16 studies for MRE. The pooled sensitivity and specificity were 0.86 (95%CI 0.80-0.90) and 0.88 (95%CI 0.85-0.91), respectively, for pSWE, compared with 0.94 (95%CI 0.89-0.97) and 0.95 (95%CI 0.89-0.98) respectively, for MRE. The pooled SROC curve for pSWE shows in the area under the curve (AUC) of 0.93 (95%CI 0.90-0.95), whereas the AUC for MRE was 0.98 (95%CI 0.96-0.99). The diagnostic odds ratio for pSWE and MRE were 41 (95%CI 24-72) and 293 (95%CI 86-1000), respectively. There was statistically significant heterogeneity for pSWE sensitivity (I² = 85.26, P<0.001) and specificity (I² = 89.46, P<0.001). The heterogeneity for MRE also was significant for sensitivity (I² = 73.28, P<0.001) and specificity (I² = 87.24, P<0.001). Therefore, both pSWE and MRE are suitable modalities for assessing liver fibrosis. In addition, MRE is a more accurate imaging technique than pSWE and can be used as alternative to invasive biopsy.

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.

Noninvasive Liver Fibrosis Staging: Comparison of MR Elastography with Extracellular Volume Fraction Analysis Using Contrast-Enhanced CT

Purpose: To compare the accuracy of liver fibrosis staging with MR elastography and of staging with extracellular volume fraction (fECV) analysis using contrast-enhanced CT. Methods: This retrospective study included 60 patients who underwent both MR elastography and contrast-enhanced CT before liver surgery between October 2013 and July 2020. Two radiologists independently measured liver stiffness of MR elastography and fECV of CT images. Accuracy for liver fibrosis staging was assessed using receiver operating characteristic (ROC) analysis. Correlations between liver stiffness or fECV and liver fibrosis were also evaluated by means of the Spearman rank correlation coefficient. Results: The areas under the ROC curves for MR elastography for each stage differentiation of ≥F1 (0.85, 0.82 for the two radiologists), ≥F2 (0.88, 0.89), ≥F3 (0.87, 0.86), and F4 (0.84, 0.83) were greater than those for fECV analysis with CT (0.64, p = 0.06, 0.69, p = 0.2; 0.62, p < 0.005, 0.63, p < 0.005; 0.62, p < 0.005, 0.62, p < 0.01; and 0.70, p = 0.08, 0.71, p = 0.2, respectively). The correlation coefficients between liver stiffness and liver fibrosis in A0 (0.67, 0.69 for the two radiologists), A1 (0.64, 0.66) and A2 group (0.58, 0.51) were significantly higher than those between fECV and liver fibrosis (0.28, 0.30; 0.27, 0.31; and 0.23, 0.07; p < 0.05 for all comparisons). Conclusion: MR elastography allows for more accurate liver fibrosis staging compared with fECV analysis with CT. In addition, MR elastography may be less affected than fECV analysis by the inflammatory condition.

US Shear-Wave Elastography Dispersion for Characterization of Chronic Liver Disease

Background Little is known about the benefits of the use of dispersion slope (DS) as a viscosity-related parameter derived from two-dimensional (2D) shear-wave elastography (SWE) in the stratification of hepatic pathologic stages. Purpose To evaluate whether DS as an additional parameter can improve the diagnostic performance in detecting liver necroinflammation, fibrosis, and steatosis. Materials and Methods In this prospective study, consecutive participants with chronic liver disease who underwent liver biopsy and 2D SWE were recruited between July 2019 and September 2020. DS and liver stiffness (LS) measurements were obtained with use of a 2D SWE system immediately before biopsy. The biopsy specimens were assessed to obtain the scores of fibrosis, necroinflammation, and steatosis. Differences in the area under the receiver operating characteristic curve (AUC) were used to compare the diagnostic performance of DS, LS, and a combination of DS and LS. Results There were 159 participants evaluated (among them, 79 participants with chronic hepatitis B and 11 participants with nonalcoholic fatty liver disease). The distributions of DS values among various necroinflammatory activities (P = .02) and fibrosis stages (P < .001) were different. Moreover, DS was only associated with fibrosis after subgroup analysis based on the fibrosis stages and necroinflammatory activities (P < .001). The AUCs of DS in detecting clinically significant fibrosis (fibrosis stage ≥F2), cirrhosis (fibrosis stage of F4), and moderate to severe necroinflammatory activity (necroinflammatory activity ≥A2) were 0.72 (95% CI: 0.64, 0.79), 0.71 (95% CI: 0.63, 0.78), and 0.64 (95% CI: 0.55, 0.71), respectively. The differences of AUCs were not apparent for the DS and LS combination model after excluding DS (fibrosis stage ≥F2: 0.00 [95% CI: 0.00, 0.01], fibrosis stage of F4: -0.01 [95% CI: -0.02, 0.00], and necroinflammatory activity ≥A2: 0.00 [95% CI: 0.00, 0.01]). Conclusion The addition of dispersion slope derived from two-dimensional shear-wave elastography did not improve the diagnostic performance in detecting liver fibrosis, necroinflammation, or steatosis in patients with primarily viral hepatitis. ClinicalTrials.gov registration no.: NCT03777293 © RSNA, 2022 Online supplemental material is available for this article.

Characteristics of Urine Organic Acid Metabolites in Nonalcoholic Fatty Liver Disease Assessed Using Magnetic Resonance Imaging with Elastography in Korean Adults

The liver is an essential organ that manufactures energy through various metabolic pathways; thus, exploring the intermediate metabolites in nonalcoholic fatty liver disease (NAFLD) may help discover novel parameters in hepatic steatosis or fibrosis. The present study aimed to investigate the traits of urine organic acid metabolites in participants with hepatic steatosis and fibrosis in nonalcoholic Korean adults. Hepatic steatosis and fibrosis, in 68 men and 65 women, were evaluated using quantification by proton density fat fraction with magnetic resonance (MR) imaging and MR elastography, respectively. Urine metabolites were obtained using a high-performance liquid chromatography–mass spectrometry analysis. The candidate metabolites were included in the logistic regression models for hepatic steatosis and fibrosis. The association between high p-hydroxyphenyllactate levels and hepatic steatosis was not independent of body mass index and Homeostatic Model Assessment-insulin resistance. High ethylmalonate, β-hydroxybutyrate, and sulfate levels were significantly related to a low probability of hepatic fibrosis, independent of covariates. In conclusion, urine metabolites were not related to hepatic steatosis independent of obesity and insulin resistance, while several metabolites were specifically associated with hepatic fibrosis. Further study is required to verify the diagnostic value of the metabolites in a population with wide-spectrum NAFLD.

Mapping heterogenous anisotropic tissue mechanical properties with transverse isotropic nonlinear inversion MR elastography

The white matter tracts of brain tissue consist of highly-aligned, myelinated fibers; white matter is structurally anisotropic and is expected to exhibit anisotropic mechanical behavior. In vivo mechanical properties of tissue can be imaged using magnetic resonance elastography (MRE). MRE can detect and monitor natural and disease processes that affect tissue structure; however, most MRE inversion algorithms assume locally homogenous properties and/or isotropic behavior, which can cause artifacts in white matter regions. A heterogeneous, model-based transverse isotropic implementation of a subzone-based nonlinear inversion (TI-NLI) is demonstrated. TI-NLI reconstructs accurate maps of the shear modulus, damping ratio, shear anisotropy, and tensile anisotropy of in vivo brain tissue using standard MRE motion measurements and fiber directions estimated from diffusion tensor imaging (DTI). TI-NLI accuracy was investigated with using synthetic data in both controlled and realistic settings: excellent quantitative and spatial accuracy was observed and cross-talk between estimated parameters was minimal. Ten repeated, in vivo, MRE scans acquired from a healthy subject were co-registered to demonstrate repeatability of the technique. Good resolution of anatomical structures and bilateral symmetry were evident in MRE images of all mechanical property types. Repeatability was similar to isotropic MRE methods and well within the limits required for clinical success. TI-NLI MRE is a promising new technique for clinical research into anisotropic tissues such as the brain and muscle.

Noninvasive Assessment of Liver Fibrosis with ElastPQ in Patients with Chronic Viral Hepatitis: Comparison Using Histopathological Findings

Chronic viral hepatitis is a major cause of chronic liver disease leading to liver fibrosis. This study aimed to assess the diagnostic performance of elastography point quantification (ElastPQ), transient elastography (TE), and aspartate aminotransferase-to-platelet count ratio index (APRI) for the staging of liver fibrosis in patients with chronic viral hepatitis using histopathological findings as a reference standard. For 122 patients with chronic viral hepatitis, diagnostic performance was evaluated using area under the receiver operating characteristic curve (AUROC) analysis and correlations were determined using Spearman’s correlation coefficient. The AUROC of ElastPQ for the diagnosis of the fibrosis stage ≥ F2 was 0.917 with a cut-off value of 3.935. There was a significant positive correlation between the different stages of histologic liver fibrosis and stiffness values obtained using ElastPQ, TE, and APRI (ρ = 0.556, ρ = 0.657, ρ = 0.375, respectively; p < 0.001). ElastPQ showed a higher diagnostic accuracy than APRI, resembling that of TE; AUROC values of ElastPQ, TE, and APRI were 0.917, 0.964, and 0.896, respectively, for a fibrosis stage ≥ F2. ElastPQ is a promising noninvasive technique with a diagnostic accuracy comparable with that of TE for the evaluation of liver fibrosis in patients with chronic viral hepatitis.

Magnetic resonance relaxometry of the liver - a new imaging biomarker to assess right heart failure in pulmonary hypertension

BACKGROUND

Right heart failure (RHF) in pulmonary hypertension (PH) patients is manifested by increased right atrial (RA) pressure. We hypothesized liver relaxation times measured at cardiovascular magnetic resonance (CMR) can be used to noninvasively assess increased right-sided filling pressure.

METHODS

Forty-five consecutive patients, that is, 37 PH patients and 8 chronic thromboembolic pulmonary disease patients without PH underwent right heart catheterization and CMR. CMR findings were compared to 40 control subjects. Native T1, T2, and extracellular volume (ECV) liver values were measured on the cardiac maps.

RESULTS

Patients with increased RA pressure (i.e.,≥8 mm Hg)(n = 19, RA+ group) showed higher NT-proBNP and CRP values, lower LVEF, MAPSE values, larger atrial size, and higher native T1 and T2 values of the myocardium than patients with normal RA pressure (RA- group, n = 26). Liver T1, T2 and ECV was significantly higher in RA+ than RA- patients and controls, that is, T1: 684 ± 129 ms vs 563 ± 72 ms and 540 ± 34 ms; T2: 60 ± 10 ms vs 49 ± 6 ms and 46 ± 4 ms; ECV: 36 ± 8% vs 29 ± 4% and 30 ± 3%. A positive correlation was found between liver T1, T2 and ECV and RA pressure, that is, r² of 0.61, 0.82, and 0.58, respectively (p < 0.001). ROC analysis to depict increased RA pressure showed an AUC of 0.847, 0.904, 0.816, and 0.645 for liver T1, T2, NT-proNBP and gamma-glutamyl transpeptidase, respectively. Excellent intra- and inter-observer agreement was found for assessment of T1/T2/ECV liver values.

CONCLUSIONS

Assessment of liver relaxation times as part of a comprehensive CMR exam in PH patients may provide valuable information with regard to the presence of passive liver congestion.

Accuracy comparison of MR elastography and biological markers in detecting liver fibrosis and predicting postoperative ascites

BACKGROUND

This retrospective study aimed to compare the discriminative performance between magnetic resonance elastography (MRE) and biological markers in detecting liver fibrosis and in predicting postoperative ascites (PA).

METHODS

We enrolled 77 patients consecutively who underwent hepatectomy between March 2017 and June 2019. Liver fibrosis was histopathologically graded using the METAVIR scoring system as reference. Discriminative performance of non-invasive assessments in detecting different stages of liver fibrosis and predicting PA was evaluated by receiver-operator curve analysis.

RESULTS

The concordance indices (C-indices) for MRE and biological markers for detecting significant fibrosis (≥F2) and cirrhosis (F4) were: MRE, 0.84 and 0.86; Wisteria floribunda agglutinin + Mac-2 binding protein (WM2BP), 0.63 and 0.71; Hyaluronic acid (HA), 0.72 and 0.75; 7 S-type 4 collagen (T4C), 0.61 and 0.66; APRI, 0.76 and 0.83; and Fib-4, 0.75 and 0.76. Univariable logistic analysis for predicting PA showed that C-indices were 0.751 (p = 0.007), 0.798 (p = 0.106), 0.771 (p = 0.050), 0.674 (p = 0.855), 0.655 (p = 0.263), and 0.560 (p = 0.640) for MRE, WM2BP, Fib-4, HA, APRI, and T4C, respectively.

CONCLUSION

MRE has a higher diagnostic performance than biological markers in detecting the stages of liver fibrosis and is a predictor for PA after hepatectomy.

Performance of noninvasive tools for identification of minimal liver fibrosis in patients with hepatitis B virus infection

Background

Various noninvasive liver fibrosis assessment tools are available. Here, we evaluated the performance of the asparagine aminotransferase‐to‐platelet ratio index (APRI), the fibrosis‐4 index (FIB‐4), transient elastography (TE), and the globulin–platelet (GP) ratio for identifying liver fibrosis in patients with hepatitis B virus (HBV) infection.

Methods

A total of 146 patients were assessed using TE, FIB‐4, APRI, the GP ratio, and liver biopsy. Three patient grouping methods were applied: any fibrosis (AF; F0 vs. F1/2/3/4); moderate fibrosis (MF; F0/1 vs. F2/3/4); and severe fibrosis (SF; F0/1/2 vs. F3/4). Receiver operating characteristic (ROC) curve analysis, univariate analyses, and multivariate logistic regression were conducted.

Results

Regardless of patient‐grouping method, the area under the curve (AUC) of TE and the GP ratio were similar. Using the AF grouping method, the GP ratio showed superior performance compared with APRI and FIB‐4: the AUCs for the GP ratio, TE, APRI, and FIB‐4 were 0.76, 0.75, 0.70, and 0.66, respectively. Using the MF grouping method, the GP ratio also showed superior performance compared with APRI and FIB‐4: the AUCs for the GP ratio, TE, APRI, and FIB‐4 were 0.66, 0.68, 0.57, and 0.53, respectively. Using the SF grouping method, the AUCs for the GP ratio, TE, APRI, and FIB‐4 were not significantly different.

Conclusion

Compared with FIB‐4 and APRI, the GP ratio had higher accuracy for identifying liver fibrosis, especially early‐stage fibrosis, in patients with HBV infection.

Shear Wave Elastography: A Review on the Confounding Factors and Their Potential Mitigation in Detecting Chronic Kidney Disease

Early detection of chronic kidney disease is important to prevent progression of irreversible kidney damage, reducing the need for renal transplantation. Shear wave elastography is ideal as a quantitative imaging modality to detect chronic kidney disease because of its non-invasive nature, low cost and portability, making it highly accessible. However, the complexity of the kidney architecture and its tissue properties give rise to various confounding factors that affect the reliability of shear wave elastography in detecting chronic kidney disease, thus limiting its application to clinical trials. The objective of this review is to highlight the confounding factors presented by the complex properties of the kidney, in addition to outlining potential mitigation strategies, along with the prospect of increasing the versatility and reliability of shear wave elastography in detecting chronic kidney disease.

Feasibility of Intestinal MR Elastography in Inflammatory Bowel Disease

BACKGROUND

While MR enterography allows detection of inflammatory bowel disease (IBD), the findings continue to be of limited use in guiding treatment-medication vs. surgery.

PURPOSE

To test the feasibility of MR elastography of the gut in healthy volunteers and IBD patients.

STUDY TYPE

Prospective pilot.

POPULATION

Forty subjects (healthy volunteers: n = 20, 37 ± 14 years, 10 women; IBD patients: n = 20 (ulcerative colitis n = 9, Crohn's disease n = 11), 41 ± 15 years, 11 women).

FIELD STRENGTH/SEQUENCE

Multifrequency MR elastography using a single-shot spin-echo echo planar imaging sequence at 1.5 T with drive frequencies of 40, 50, 60, and 70 Hz.

ASSESSMENT

Maps of shear-wave speed (SWS, in m/s) and loss angle (φ, in rad), representing stiffness and solid-fluid behavior, respectively, were generated using tomoelastography data processing. Histopathological analysis of surgical specimens was used as reference standard in patients.

STATISTICAL TESTS

Unpaired t-test, one-way analysis of variance followed by Tukey post hoc analysis, Pearson's correlation coefficient and area under the receiver operating characteristic curve (AUC) with 95%-confidence interval (CI). Significance level of 5%.

RESULTS

MR elastography was feasible in all 40 subjects (100% technical success rate). SWS and φ were significantly increased in IBD by 21% and 20% (IBD: 1.45 ± 0.14 m/s and 0.78 ± 0.12 rad; healthy volunteers: 1.20 ± 0.14 m/s and 0.65 ± 0.06 rad), whereas no significant differences were found between ulcerative colitis and Crohn's disease (P = 0.74 and 0.90, respectively). In a preliminary assessment, a high diagnostic accuracy in detecting IBD was suggested by an AUC of 0.90 (CI: 0.81-0.96) for SWS and 0.84 (CI: 0.71-0.95) for φ.

DATA CONCLUSION

In this pilot study, our results demonstrated the feasibility of MR elastography of the gut and showed an excellent diagnostic performance in predicting IBD.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 1.

Viscoelasticity Imaging of Biological Tissues and Single Cells Using Shear Wave Propagation

Changes in biomechanical properties of biological soft tissues are often associated with physiological dysfunctions. Since biological soft tissues are hydrated, viscoelasticity is likely suitable to represent its solid-like behavior using elasticity and fluid-like behavior using viscosity. Shear wave elastography is a non-invasive imaging technology invented for clinical applications that has shown promise to characterize various tissue viscoelasticity. It is based on measuring and analyzing velocities and attenuations of propagated shear waves. In this review, principles and technical developments of shear wave elastography for viscoelasticity characterization from organ to cellular levels are presented, and different imaging modalities used to track shear wave propagation are described. At a macroscopic scale, techniques for inducing shear waves using an external mechanical vibration, an acoustic radiation pressure or a Lorentz force are reviewed along with imaging approaches proposed to track shear wave propagation, namely ultrasound, magnetic resonance, optical, and photoacoustic means. Then, approaches for theoretical modeling and tracking of shear waves are detailed. Following it, some examples of applications to characterize the viscoelasticity of various organs are given. At a microscopic scale, a novel cellular shear wave elastography method using an external vibration and optical microscopy is illustrated. Finally, current limitations and future directions in shear wave elastography are presented.

Noninvasive assessment of congestive hepatopathy in patients with constrictive pericardial physiology using MR relaxometry

BACKGROUND

Constrictive pericarditis represents a treatable cause of mainly right heart failure (RHF), characterized by increased filling pressures and congestive hepatopathy. We hypothesized assessment of T1 and T2 liver relaxation times enables to depict liver congestion, and thus to diagnose RHF.

METHODS

Cardiovascular magnetic resonance imaging (CMR) was performed in 45 pericarditis patients i.e., 25 with constrictive physiology (CP+), 20 with normal physiology (CP-), and 30 control subjects. CMR included morphologic and functional assessment of the heart and pericardium. Liver relaxation times were measured on T1 and T2 cardiac maps.

RESULTS

CP+ and CP- patients were predominantly male, but CP+ patients were on average 13 years older than CP- patients (p = 0.003). T1 and T2 Liver values were significantly higher in CP+ than in CP- patients and controls, i.e. T1: 765 ± 102 ms vs 581 ± 56 ms and 537 ± 30 ms (both p < 0.001); T2: 63 ± 13 ms vs 50 ± 4 ms and 46 ± 4 ms (both p < 0.001). Extracellular volume (ECV) liver values were also increased, i.e. 42 ± 7% CP+ vs 31 ± 3% CP- and 30 ± 3% control (both p < 0.001). Using a cut-off right atrial pressure of >5 mmHg to discriminate between normal and increased pressure, native T1 liver yielded the highest AUC (0.926) at ROC analysis with a sensitivity of 79.3% and specificity of 95.6%. Gamma-glutamyl transpeptidase correlated well withT1 liver (r² = 0.43) and ECV liver (r² = 0.30). Excellent intra- and inter-reader agreement was found for T1, T2 and ECV measurement of the liver.

CONCLUSIONS

Assessment of liver relaxation times in pericarditis patients provide valuable information on the presence of concomitant congestive hepatopathy, reflecting RHF.

Influence of fibrosis progression on the viscous properties of in vivo liver tissue elucidated by shear wave dispersion in multifrequency MR elastography

PURPOSE

Many elastography studies have shown that liver stiffness increases with fibrosis and thus can be used as a reliable marker for noninvasively staging fibrosis. However, the sensitivity of viscosity-related mechanical parameters, such as shear wave dispersion, to liver fibrosis is less well understood.

METHODS

In this proof-of-concept study, 15 healthy volunteers and 37 patients with chronic liver disease and biopsy-proven fibrosis were prospectively investigated by MR elastography at six drive frequencies of 35-60 Hz. Maps of shear wave speed (SWS, in m/s) and loss angle (φ, in rad), as a marker of stiffness and viscous properties, respectively, were generated using tomoelastography data processing. The Child-Pugh score was used to assess cirrhosis severity.

RESULTS

While SWS increased with fibrosis (F0: 1.53 ± 0.11 m/s, F1-F3: 1.71 ± 0.17 m/s, F4: 2.50 ± 0.39 m/s; P < 0.001), φ remained unchanged during mild to severe fibrosis (F0: 0.63 ± 0.05 rad, F1-F3: 0.60 ± 0.05 rad, P = 0.21) but increased in cirrhosis (F4: 0.81 ± 0.16 rad; P < 0.001). Correspondingly, the slope of SWS-dispersion within the investigated range of vibration frequencies increased from insignificant (F0-F3: 0.010 ± 0.007 m/s/Hz) to significant (F4: 0.038 ± 0.025 m/s/Hz; P = 0.005). Significant correlation with the Child-Pugh score was found for φ (R = 0.60, P = 0.01) but not for SWS.

CONCLUSION

Although cirrhosis is associated with liver stiffening and, intuitively, transition towards more rigid material properties, the observed increases in φ and slope of SWS-dispersion indicate abnormally high mechanical friction in cirrhotic livers. This biophysical signature might provide a prognostic imaging marker for the detection of pathological processes associated with fibrosis independent of stiffness.

Spatial heterogeneity of hepatic fibrosis in primary sclerosing cholangitis vs. viral hepatitis assessed by MR elastography

Spatial heterogeneity of hepatic fibrosis in primary sclerosing cholangitis (PSC) in comparison to viral hepatitis was assessed as a potential new biomarker using MR elastography (MRE). In this proof-of-concept study, we hypothesized a rather increased heterogeneity in PSC and a rather homogeneous distribution in viral hepatitis. Forty-six consecutive subjects (PSC: n = 20, viral hepatitis: n = 26) were prospectively enrolled between July 2014 and April 2017. Subjects underwent multifrequency MRE (1.5 T) using drive frequencies of 35–60 Hz and generating shear-wave speed (SWS in m/s) maps as a surrogate of stiffness. The coefficient of variation (CV in %) was determined to quantify fibrosis heterogeneity. Mean SWS and CV were 1.70 m/s and 21% for PSC, and 1.84 m/s and 18% for viral hepatitis. Fibrosis heterogeneity was significantly increased for PSC (P = 0.04) while no difference was found for SWS of PSC and viral hepatitis (P = 0.17). Global hepatic stiffness was similar in PSC and viral hepatitis groups, but spatial heterogeneity may reveal spatial patterns of stiffness changes towards enhanced biophysics-based diagnosis by MRI.

Prevalence of liver fibrosis and associated risk factors in the Korean general population: a retrospective cross-sectional study

OBJECTIVES

The health burden of chronic liver disease is increasing worldwide. Its main histological consequence is liver fibrosis, and eventually cirrhosis. This process is rarely diagnosed at the pre-cirrhotic stage due to it being asymptomatic. Little is known about the prevalence of liver fibrosis and associated risk factors in the general population. The aims of this study were to determine the prevalence and distribution of liver fibrosis using magnetic resonance elastography (MRE), as well as the risk factors associated with liver fibrosis in the asymptomatic general population.

DESIGN, SETTING AND PARTICIPANTS

This cross-sectional retrospective study consecutively selected subjects who underwent health check-ups including MRE at 13 health promotion centres in Korea between 2018 and 2020. Liver fibrosis was estimated using MRE with cut-off values for significant and advanced liver fibrosis of 2.90 and 3.60 kPa, respectively.

PRIMARY AND SECONDARY OUTCOME MEASURES

The Χ² test was used to compare the prevalence of liver fibrosis according to sex and age groups. Multivariable logistic regression analyses were performed to identify the factors for significant and advanced liver fibrosis.

RESULTS

Among the 8183 subjects, 778 (9.5%) had ≥significant fibrosis (≥2.9 kPa), which included 214 (2.6%) subjects with ≥advanced fibrosis (≥3.6 kPa). Multivariable analysis revealed that liver fibrosis was associated with age (OR=1.34, 95% CI=1.18 to 1.51), male sex (OR=3.18, 95% CI=1.97 to 5.13), diabetes (OR=2.43, 95% CI=1.8 to 3.28), HBsAg positivity (OR=3.49, 95% CI=2.55 to 4.79), abnormal liver function test (OR=1.9, 95% CI=1.49 to 2.42) and obesity (OR=1.77, 95% CI=1.35 to 2.32) (all p<0.001), as well as metabolic syndrome (OR=1.4, 95% CI=1.05 to 1.87) (p=0.024).

CONCLUSIONS

The prevalence of significant or more liver fibrosis was high in the Korean general population and much higher among individuals with risk factors. This suggests that screening of liver fibrosis should be considered in general population, especially among high-risk groups.

[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.

Noninvasive assessment of liver fibrosis by dual-layer spectral detector CT

PURPOSE

To elucidate the diagnostic ability of liver fibrosis using (1) liver parenchymal iodine density on equilibrium computed tomographic imaging and (2) extracellular volume (ECV) measured by dual-layer spectral detector CT.

METHODS

From April 2018 to June 2019, 68 patients [mean age, 62 years; 39 males, 29 females] underwent dynamic contrast-enhanced CT by a dual-layer spectral detector CT system before liver transplantation or liver resection. The iodine densities of liver parenchyma (I _liver) and aorta (I _aorta) were independently measured by two radiologists at the equilibrium phase. The iodine-density ratio (I-ratio) (I _liver/ I _aorta) and the CT-ECV were calculated. Spearman's rank correlation coefficient was used to analyze the relationship between the I-ratio or the CT-ECV and the fibrosis stage. A receiver operating characteristic (ROC) curve analysis was performed to determine the accuracy of the I-ratio and the CT-ECV for discriminating fibrosis stages.

RESULTS

For both readers, the I-ratio and the CT-ECV increased significantly as the fibrosis stage advanced (I-ratio: rho = 0.380 and 0.443, p < 0.01; CT-ECV: rho = 0.423 and 0.469, p < 0.01). The CT-ECV showed better diagnostic accuracy for staging fibrosis, and the area under the ROC curve values for discriminating F4 stage were 0.884 and 0.925. The two readers' cutoff values of the CT-ECV for diagnosing fibrosis as F4 were 26.2 % and 29.3 %, with 95.0 % and 90.0 % sensitivity and 72.9 % and 85.4 % specificity, respectively.

CONCLUSION

The liver parenchymal iodine density on the equilibrium phase and the CT-ECV can be useful for predicting a high stage of liver fibrosis.

Shear Wave Dispersion Predicts Liver Fibrosis and Adverse Outcomes in Patients with Heart Failure

Background: It has been recently reported that liver stiffness assessed by transient elastography reflects right atrial pressure (RAP) and is associated with worse outcomes in patients with heart failure (HF). However, the relationship between shear wave dispersion (SWD, a novel indicator of liver viscosity) determined by abdominal ultrasonography and RAP, and the prognostic impact of SWD on HF patients have not been fully examined. We aimed to clarify the associations of SWD with parameters of liver function test (LFT) and right heart catheterization (RHC), as well as with cardiac events such as cardiac death and worsening HF, in patients with HF. Methods: We performed abdominal ultrasonography, LFT and RHC in HF patients (n = 195), and followed up for cardiac events. We examined associations between SWD and parameters of LFT and RHC. Results: There were significant correlations between SWD and circulating levels of direct bilirubin (R = 0.222, p = 0.002), alkaline phosphatase (R = 0.219, p = 0.002), cholinesterase (R = −0.184, p = 0.011), and 7S domain of collagen type IV (R = 0.177, p = 0.014), but not with RAP (R = 0.054, p = 0.567) or cardiac index (R = −0.015, p = 0.872). In the Kaplan–Meier analysis, cardiac event rate was significantly higher in the high SWD group (SWD ≥ 10.0 (m/s)/kHz, n = 103) than in the low SWD group (SWD < 10.0 (m/s)/kHz, n = 92; log-rank, p = 0.010). In the Cox proportional hazard analysis, high SWD was associated with high cardiac event rates (hazard ratio, 2.841; 95% confidence interval, 1.234–6.541, p = 0.014). In addition, there were no interactions between SWD and all subgroups, according to the subgroup analysis. Conclusions: SWD assessed by abdominal ultrasonography reflects liver fibrosis rather than liver congestion, and is associated with adverse prognosis in HF patients.

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.

A parametric evaluation of shear wave speeds estimated with time-of-flight calculations in viscoelastic media

Shear wave elasticity imaging (SWEI) uses an acoustic radiation force to generate shear waves, and then soft tissue mechanical properties are obtained by analyzing the shear wave data. In SWEI, the shear wave speed is often estimated with time-of-flight (TOF) calculations. To characterize the errors produced by TOF calculations, three-dimensional (3D) simulated shear waves are described by time-domain Green's functions for a Kelvin-Voigt model evaluated for multiple combinations of the shear elasticity and the shear viscosity. Estimated shear wave speeds are obtained from cross correlations and time-to-peak (TTP) calculations applied to shear wave particle velocities and shear wave particle displacements. The results obtained from these 3D shear wave simulations indicate that TTP calculations applied to shear wave particle displacements yield effective estimates of the shear wave speed if noise is absent, but cross correlations applied to shear wave particle displacements are more robust when the effects of noise and shear viscosity are included. The results also show that shear wave speeds estimated with TTP methods and cross correlations using shear wave particle velocities are more sensitive to increases in shear viscosity and noise, which suggests that superior estimates of the shear wave speed are obtained from noiseless or noisy shear wave particle displacements.

A parametric evaluation of shear wave speeds estimated with time-of-flight calculations in viscoelastic media

Shear wave elasticity imaging (SWEI) uses an acoustic radiation force to generate shear waves, and then soft tissue mechanical properties are obtained by analyzing the shear wave data. In SWEI, the shear wave speed is often estimated with time-of-flight (TOF) calculations. To characterize the errors produced by TOF calculations, three-dimensional (3D) simulated shear waves are described by time-domain Green's functions for a Kelvin-Voigt model evaluated for multiple combinations of the shear elasticity and the shear viscosity. Estimated shear wave speeds are obtained from cross correlations and time-to-peak (TTP) calculations applied to shear wave particle velocities and shear wave particle displacements. The results obtained from these 3D shear wave simulations indicate that TTP calculations applied to shear wave particle displacements yield effective estimates of the shear wave speed if noise is absent, but cross correlations applied to shear wave particle displacements are more robust when the effects of noise and shear viscosity are included. The results also show that shear wave speeds estimated with TTP methods and cross correlations using shear wave particle velocities are more sensitive to increases in shear viscosity and noise, which suggests that superior estimates of the shear wave speed are obtained from noiseless or noisy shear wave particle displacements.

Uterine leiomyomas: correlation between histologic composition and stiffness via magnetic resonance elastography - a Pilot Study

OBJECTIVES

To evaluate magnetic resonance elastography as a tool for characterizing uterine leimyomas.

MATERIAL AND METHODS

At total of 12 women with symptomatic leiomyomas diagnosed in physical and ultrasound examinations were enrolled in this pilot study. Before surgery, all patients underwent magnetic resonance elastography of the uterus using a 1.5 T MR whole-body scanner (Optima, GE Healthcare, Milwaukee, WI, USA). Surgical specimens were forwarded for histological examination. The findings were allocated into 3 categories depending on the percentage content of connective tissue: below 15%, from 15 to 30% and more than 30%. The median stiffness of leiomyomas for each of the group was calculated. The U-Mann Whitney test was used for statistical analysis.

RESULTS

The stiffness of the leiomyomas ranged between 3.7-6.9 kPa (median value 4.9 kPa). The concentration of extracellular components in the leiomyomas did not exceed 40%. An increasing trend of the stiffness with the growing percentage of extracellular component was observed. Stiffness of the leiomyomas obtained by MRE varies depending on microscopic composition.

CONCLUSIONS

The value of stiffness shows a trend of increasing with the percentage of extracellular component of the leiomyoma. Further studies are required to assess the usefulness of MRE in diagnostics of uterine leiomyomas.

Deep residual nets model for staging liver fibrosis on plain CT images

PURPOSE

The early diagnosis of liver fibrosis is crucial for the prevention of liver cirrhosis and liver cancer. As gold standard for staging liver fibrosis, liver biopsy is an invasive procedure that carries the risk of serious complications. The aim of this study was to evaluate the performance of the residual neural network (ResNet), a non-invasive methods, for staging liver fibrosis using plain CT images.

METHODS

This retrospective study involved 347 patients subjected to liver CT scanning and liver biopsy. For each patient, we selected three axial images adjacent to the puncture location in the eighth or ninth inter-space on the right side. After processing and enhancement (rotation, translation, and amplification), these images were used as input data for the ResNet model. The model used a fivefold cross-validation method. In each fold, the images of approximately 80% of the total sample size (278 patients) were used for training the ResNet model, the other 20% (69 patients) were used for testing the trained network, with the liver biopsy pathology results as gold standard. The proportion of patients in each fibrosis stage was equal for training and test groups. The final result was the mean of the fivefold cross-validation in the test group. The performance of the ResNet model was evaluated for the test group by receiver operating characteristic (ROC) analysis.

RESULTS

For the ResNet model, the area under the ROC curve (AUC) for assessing cirrhosis (F4), advanced fibrosis (F3 or higher), significant fibrosis (F2 or higher), and mild fibrosis (F1 or higher) was 0.97, 0.94, 0.90, and 0.91, respectively.

CONCLUSIONS

The ResNet model analysis of plain CT images exhibited high diagnostic efficiency for liver fibrosis staging. As a convenient, fast, and economical non-invasive diagnostic method, the ResNet model can be used to assist radiologists and clinicians in liver fibrosis evaluations.

Liver extracellular volume fraction values obtained with magnetic resonance imaging can quantitatively stage liver fibrosis: a validation study in monkeys with nonalcoholic steatohepatitis

OBJECTIVES

This study was to evaluate the diagnostic value of liver extracellular volume (LECV) for the staging of liver fibrosis in a cynomolgus monkey model of nonalcoholic steatohepatitis (NASH).

METHODS

Forty-eight cynomolgus monkeys were enrolled in this prospective study. There are 17 healthy monkeys and 31 monkeys with NASH. Ten of these monkeys were used for repeatability assessment. The remaining 38 monkeys were used to compare LECV with other indicators including pathology fibrosis score, native T1, and serum chemical indexes by Spearman, Pearson correlation test, and ROC curves. The inter-reader variability was assessed by interclass correlation. The repeatability measurement of LECV was analyzed using Bland-Altman plots and the coefficient of variation. Partial correlation analysis was performed to assess the effects of fat content and inflammation scores on the correlation between LECV/T1 and liver fibrosis score.

RESULTS

This study demonstrated a good intra-reader agreement (intraclass correlation = 0.79) of LECV in all monkeys and an excellent repeatability in 10 monkeys (coefficient of variation = 2.01%). The LECV has a strong correlation with the fibrosis score (r = 0.949; p < 0.0001), low-density lipoprotein (r = 0.72; p < 0.0001), and cholesterol (r = 0.70; p < 0.0001). LECV showed high diagnostic efficacy in the diagnosis of liver fibrosis (area under the curve of ROC, 0.945~1; p < 0.001).

CONCLUSIONS

LECV may serve as a noninvasive valuable biomarker for the quantification and differentiating of the non-severe liver fibrosis (stage ≤ F3). However, circulating serum markers low-density lipoprotein and cholesterol (CHO) may not serve for this purpose.

KEY POINTS

• This paper demonstrated the excellent repeatability (intraclass correlation coefficient = 0.79) of LECV in monkey animal model. • LECV-MRI has a strong correlation with histopathological fibrosis score stage (r = 0.949; p < 0.0001) and shows high diagnostic efficacy in the staging of non-severe liver fibrosis (the area under ROC curve ≥ 0.945). • The new fibrosis score maps appeared to provide a better imaging tool for the spatial assessment of liver fibrosis. It may eventually facilitate the diagnosis of liver fibrosis distribution.

Artificial neural networks for magnetic resonance elastography stiffness estimation in inhomogeneous materials

PURPOSE

To test the hypothesis that removing the assumption of material homogeneity will improve the spatial accuracy of stiffness estimates made by Magnetic Resonance Elastography (MRE).

METHODS

An artificial neural network was trained using synthetic wave data computed using a coupled harmonic oscillator model. Material properties were allowed to vary in a piecewise smooth pattern. This neural network inversion (Inhomogeneous Learned Inversion (ILI)) was compared against a previous homogeneous neural network inversion (Homogeneous Learned Inversion (HLI)) and conventional direct inversion (DI) in simulation, phantom, and in-vivo experiments.

RESULTS

In simulation experiments, ILI was more accurate than HLI and DI in predicting the stiffness of an inclusion in noise-free, low-noise, and high-noise data. In the phantom experiment, ILI delineated inclusions ≤ 2.25 cm in diameter more clearly than HLI and DI, and provided a higher contrast-to-noise ratio for all inclusions. In a series of stiff brain tumors, ILI shows sharper stiffness transitions at the edges of tumors than the other inversions evaluated.

CONCLUSION

ILI is an artificial neural network based framework for MRE inversion that does not assume homogeneity in material stiffness. Preliminary results suggest that it provides more accurate stiffness estimates and better contrast in small inclusions and at large stiffness gradients than existing algorithms that assume local homogeneity. These results support the need for continued exploration of learning-based approaches to MRE inversion, particularly for applications where high resolution is required.

Why Are Viscosity and Nonlinearity Bound to Make an Impact in Clinical Elastographic Diagnosis?

The adoption of multiscale approaches by the biomechanical community has caused a major improvement in quality in the mechanical characterization of soft tissues. The recent developments in elastography techniques are enabling in vivo and non-invasive quantification of tissues' mechanical properties. Elastic changes in a tissue are associated with a broad spectrum of pathologies, which stems from the tissue microstructure, histology and biochemistry. This knowledge is combined with research evidence to provide a powerful diagnostic range of highly prevalent pathologies, from birth and labor disorders (prematurity, induction failures, etc.), to solid tumors (e.g., prostate, cervix, breast, melanoma) and liver fibrosis, just to name a few. This review aims to elucidate the potential of viscous and nonlinear elastic parameters as conceivable diagnostic mechanical biomarkers. First, by providing an insight into the classic role of soft tissue microstructure in linear elasticity; secondly, by understanding how viscosity and nonlinearity could enhance the current diagnosis in elastography; and finally, by compounding preliminary investigations of those elastography parameters within different technologies. In conclusion, evidence of the diagnostic capability of elastic parameters beyond linear stiffness is gaining momentum as a result of the technological and imaging developments in the field of biomechanics.

Liver stiffness measured by MR elastography is a predictor of early HCC recurrence after treatment

OBJECTIVES

Magnetic resonance elastography (MRE) is a non-invasive tool for measuring liver stiffness (LS) with high diagnostic accuracy. This study investigated whether quantified LS by MRE could predict early recurrence of patients with hepatocellular carcinoma (HCC) within the Milan criteria.

METHODS

A prospectively collected cohort, which included the HCC patients who underwent MRE before treatment (an HCC-MRE cohort), was analyzed. In the HCC-MRE cohort, only patients under the Milan criteria, who underwent hepatic resection, radiofrequency ablation (RFA), or transarterial chemoembolization (TACE), were reviewed. We investigated whether LS assessed by MRE was an independent predictor of early recurrence using Cox regressions and Kaplan-Meier analyses.

RESULTS

A total of 192 HCC patients under the Milan criteria who underwent hepatic resection (n = 96), RFA (n = 23), or TACE (n = 73) were included. Higher LS ratings (kPa; hazard ratio [HR] = 1.12; 95% confidence interval [CI] = 1.01-1.25; p = 0.040) emerged as an independent risk factor for early tumor recurrence. In the subgroup analysis, higher LS ratings were associated with higher risks of early HCC recurrence in both the resection/RFA group (> 4.5 kPa; HR = 2.95; 95% CI = 1.26-6.94; p = 0.013) and the TACE group (> 6 kPa; HR = 2.94; 95% CI = 1.27-6.83; p = 0.012).

CONCLUSION

LS assessed by MRE was an independent predictor of early recurrence among HCC patients under the Milan criteria after achieving a complete response.

KEY POINTS

• Liver parenchymal stiffness measured by MRE predicts early recurrence of treated HCC under Milan criteria. • A liver stiffness > 5.5 kPa was associated with worse recurrence-free survival. • Patients with high pre-treatment LS may benefit from stringent follow-up.

Multiparametric MR Index for the Diagnosis of Non-Alcoholic Steatohepatitis in Patients with Non-Alcoholic Fatty Liver Disease

Non-alcoholic steatohepatitis (NASH) is a complex disease consisting of various components including steatosis, lobular inflammation, and ballooning degeneration, with or without fibrosis. Therefore, it is difficult to diagnose NASH with only one imaging modality. This study was aimed to evaluate the feasibility of magnetic resonance imaging (MRI) for predicting NASH and to develop a non-invasive multiparametric MR index for the detection of NASH in non-alcoholic fatty liver disease (NAFLD) patients. This prospective study included 47 NAFLD patients who were scheduled to undergo or underwent ultrasound-guided liver biopsy within 2 months. Biopsy specimens were graded as NASH or non-NASH. All patients underwent non-enhanced MRI including MR spectroscopy (MRS), MR elastography (MRE), and T1 mapping. Diagnostic performances of MRS, MRE, and T1 mapping for grading steatosis, activity, and fibrosis were evaluated. A multiparametric MR index combining fat fraction (FF), liver stiffness (LS) value, and T1 relaxation time was developed using linear regression analysis. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the diagnostic performance of the newly devised MR index. Twenty NASH patients and 27 non-NASH patients were included. Using MRS, MRE, and T1 mapping, the mean areas under the curve (AUCs) for grading steatosis, fibrosis, and activity were 0.870, 0.951, and 0.664, respectively. The multiparametric MR index was determined as 0.037 × FF (%) + 1.4 × LS value (kPa) + 0.004 × T1 relaxation time (msec) −3.819. ROC curve analysis of the MR index revealed an AUC of 0.883. The cut-off value of 6 had a sensitivity of 80.0% and specificity of 85.2%. The multiparametric MR index combining FF, LS value, and T1 relaxation time showed high diagnostic performance for detecting NASH in NAFLD patients.

Segmental Liver Stiffness Evaluated with Magnetic Resonance Elastography Is Responsive to Endovascular Intervention in Patients with Budd-Chiari Syndrome

OBJECTIVE

To assess segmental liver stiffness (LS) with MRI before and after endovascular intervention in patients with Budd-Chiari syndrome (BCS).

MATERIALS AND METHODS

Twenty-three patients (13 males and 10 females; mean age, 42.6 ± 12.6 years; age range, 31-56 years) with BCS as a primary liver disease were recruited for this study. Two consecutive magnetic resonance elastography (MRE) examinations were performed before the endovascular treatment. Fifteen patients who underwent endovascular intervention treatment also had follow-up MRE scans within three days after the procedure. LS was measured in three liver segments: the right posterior, right anterior, and left medial segments. Inter-reader and inter-exam repeatability were analyzed with intraclass correlation coefficients (ICCs) and Bland-Altman analysis. Segmental LS and clinical characteristics before and after the intervention were also compared.

RESULTS

Within three days of the endovascular intervention, all three segmental LS values decreased: LS of the right posterior segment = 7.23 ± 0.88 kPa (before) vs. 4.94 ± 0.84 kPa (after), LS of the right anterior segment = 7.30 ± 1.06 kPa (before) vs. 4.77 ± 0.85 kPa (after), and LS of the left medial segment = 7.22 ± 0.87 kPa (before) vs. 4.87 ± 0.72 kPa (after) (all p = 0.001). There was a significant correlation between LS changes and venous pressure gradient changes before and after treatments (r = 0.651, p = 0.009). The clinical manifestations of all 15 patients significantly improved after therapy. The MRE repeatability was excellent, with insignificant variations (inter-reader, ICC = 0.839-0.943: inter-examination, ICC = 0.765-0.869). Bland-Altman analysis confirmed excellent agreement (limits of agreement, 13.4-19.4%).

CONCLUSION

Segmental LS measured by MRE is a promising repeatable quantitative biomarker for monitoring the treatment response to minimally invasive endovascular intervention in patients with BCS.

Non-invasive assessment of hepatic fibrosis: comparison of MR elastography to transient elastography and intravoxel incoherent motion diffusion-weighted MRI

OBJECTIVE

To compare the ability of MR elastography (MRE) with transient elastography (TE) and intravoxel incoherent motion (IVIM) diffusion-weighted MRI in staging hepatic fibrosis (HF).

MATERIALS AND METHODS

100 patients with chronic liver disease and 25 healthy volunteers underwent preoperative MRE, IVIM on a 3T MRI unit, and ultrasound-based TE. Liver stiffness measurement from MRE (LSM-MRE) and liver stiffness measurement from TE (LSM-TE) were measured; four diffusion parameters including the true diffusion coefficient (D_t), pseudo-diffusion coefficient, perfusion fraction (f), and apparent diffusion coefficient (ADC) were calculated. Receiver operating characteristic (ROC) curves were performed for significant parameters to compare the diagnosis performance for detecting HF.

RESULTS

LSM-MRE and LSM-TE values showed positive correlation with the fibrosis stage (r = 0.910 and 0.813, P < 0.001). D_t, f, and ADC values showed negative correlation with the fibrosis stage (r = - 0.727, - 0.503, and - 0.601, all P < 0.001). The area under the ROC curve (AUC) of LSM-MRE (AUC = 0.965, 0.957, 0.983) was significantly higher than that of LSM-TE (AUC = 0.906, 0.913, 0.931) and D_t (AUC = 0.875, 0.879, 0.861) in discriminating significant HF (≥ F2), advanced HF (≥ F3), or cirrhosis (F4) (all P < 0.05). Although LSM-TE showed higher AUCs than D_t in detecting fibrosis stages, there were no significant differences between LSM-TE and D_t (P > 0.05) except for detecting F4 (P < 0.05).

CONCLUSION

MRE shows excellent diagnostic performance for predicting significant fibrosis, advanced fibrosis compared with TE and IVIM, while TE and IVIM have comparable diagnostic performance.

Viscoelasticity in natural tissues and engineered scaffolds for tissue reconstruction

Viscoelasticity of living tissues plays a critical role in tissue homeostasis and regeneration, and its implication in disease development and progression is being recognized recently. In this review, we first explored the state of knowledge regarding the potential application of tissue viscoelasticity in disease diagnosis. In order to better characterize viscoelasticity with local resolution and non-invasiveness, emerging characterization methods have been developed with the potential to be supplemented to existing facilities. To understand cellular responses to matrix viscoelastic behaviors in vitro, hydrogels made of natural polymers have been developed and the relationships between their molecular structure and viscoelastic behaviors, are elucidated. Moreover, how cells perceive the viscoelastic microenvironment and cellular responses including cell attachment, spreading, proliferation, differentiation and matrix production, have been discussed. Finally, some future perspective on an integrated mechanobiological comprehension of the viscoelastic behaviors involved in tissue homeostasis, cellular responses and biomaterial design are highlighted. STATEMENT OF SIGNIFICANCE: Tissue- or organ-scale viscoelastic behavior is critical for homeostasis, and the molecular basis and cellular responses of viscoelastic materials at micro- or nano-scale are being recognized recently. We summarized the potential applications of viscoelasticity in disease diagnosis enabled by emerging non-invasive characterization technologies, and discussed the underlying mechanism of viscoelasticity of hydrogels and current understandings of cell regulatory functions of them. With a growing understanding of the molecular basis of hydrogel viscoelasticity and recognition of its regulatory functions on cell behaviors, it is important to bring the clinical insights on how these characterization technologies and engineered materials may contribute to disease diagnosis and treatment. This review explains the basics in characterizing viscoelasticity with our hope to bridge the gap between basic research and clinical applications.

Clinical utilization of shear wave dispersion imaging in diffuse liver disease

Shear wave (SW) dispersion imaging is a newly developed imaging technology for assessing the dispersion slope of SWs, which is related to tissue viscosity in diffuse liver disease. Our preclinical and preliminary clinical studies have shown that SW speed is more useful than dispersion slope for predicting the degree of fibrosis and that dispersion slope is more useful than SW speed for predicting the degree of necroinflammation. Thus, dispersion slope, which reflects viscosity, may provide additional pathophysiological insight into diffuse liver disease.

Ristretto MRE: A generalized multi-shot GRE-MRE sequence

In order to acquire consistent k-space data in MR elastography, a fixed temporal relationship between the MRI sequence and the underlying period of the wave needs to be ensured. To this end, conventional GRE-MRE enforces synchronization through repeated triggering of the transducer and forcing the sequence repetition time to be equal to an integer multiple of the wave period. For wave frequencies below 100 Hz, however, this leads to prolonged acquisition times, as the repetition time scales inversely with frequency. A previously developed multi-shot approach (eXpresso MRE) to multi-slice GRE-MRE tackles this issue by acquiring an integer number of slices per wave period, which allows acquisition to be accelerated in typical scenarios by a factor of two or three. In this work, it is demonstrated that the constraints imposed by the eXpresso scheme are overly restrictive. We propose a generalization of the sequence in three steps by incorporating sequence delays into imaging shots and allowing for interleaved wave-phase acquisition. The Ristretto scheme is compared in terms of imaging shot and total scan duration relative to eXpresso and conventional GRE-MRE and is validated in three different phantom studies. First, the agreement of measured displacement fields in different stages of the sequence generalization is shown. Second, performance is compared for 25, 36, 40, and 60 Hz actuation frequencies. Third, the performance is assessed for the acquisition of different numbers of slices (13 to 17). In vivo feasibility is demonstrated in the liver and the breast. Here, Ristretto is compared with an optimized eXpresso sequence, leading to scan accelerations of 15% and 5%, respectively, without compromising displacement field and stiffness estimates in general. The Ristretto concept allows us to choose imaging shot durations on a fine grid independent of the number of slices and the wave frequency, permitting 2- to 4.5-fold acceleration of conventional GRE-MRE acquisitions.

Magnetic resonance elastography: basic principles, technique, and clinical applications in the liver

Magnetic resonance elastography (MRE) is a constantly advancing technique for assessment of stiffness of tissues with newer technology and sequences. It is being increasingly used for the assessment of liver fibrosis. In this article, we discuss the advantages of MRE over biopsy and noninvasive methods such as US elastography in the assessment of liver fibrosis. Image acquisition and interpretation of liver MRE is also discussed.

Magnetic resonance elastography in nonlinear viscoelastic materials under load

Characterisation of soft tissue mechanical properties is a topic of increasing interest in translational and clinical research. Magnetic resonance elastography (MRE) has been used in this context to assess the mechanical properties of tissues in vivo noninvasively. Typically, these analyses rely on linear viscoelastic wave equations to assess material properties from measured wave dynamics. However, deformations that occur in some tissues (e.g. liver during respiration, heart during the cardiac cycle, or external compression during a breast exam) can yield loading bias, complicating the interpretation of tissue stiffness from MRE measurements. In this paper, it is shown how combined knowledge of a material's rheology and loading state can be used to eliminate loading bias and enable interpretation of intrinsic (unloaded) stiffness properties. Equations are derived utilising perturbation theory and Cauchy's equations of motion to demonstrate the impact of loading state on periodic steady-state wave behaviour in nonlinear viscoelastic materials. These equations demonstrate how loading bias yields apparent material stiffening, softening and anisotropy. MRE sensitivity to deformation is demonstrated in an experimental phantom, showing a loading bias of up to twofold. From an unbiased stiffness of [Formula: see text] Pa in unloaded state, the biased stiffness increases to 9767.5 [Formula: see text]1949.9 Pa under a load of [Formula: see text] 34% uniaxial compression. Integrating knowledge of phantom loading and rheology into a novel MRE reconstruction, it is shown that it is possible to characterise intrinsic material characteristics, eliminating the loading bias from MRE data. The framework introduced and demonstrated in phantoms illustrates a pathway that can be translated and applied to MRE in complex deforming tissues. This would contribute to a better assessment of material properties in soft tissues employing elastography.

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.

Predicting gastroesophageal varices through spleen magnetic resonance elastography in pediatric liver fibrosis

BACKGROUND

A recent retrospective study confirmed that hepatic stiffness and splenic stiffness measured with magnetic resonance elastography (MRE) are strongly associated with the presence of esophageal varices. In addition, strong correlations have been reported between splenic stiffness values measured with MRE and hepatic venous pressure gradients in animal models. However, most studies have been conducted on adult populations, and previous pediatric MRE studies have only demonstrated the feasibility of MRE in pediatric populations, while the actual clinical application of spleen MRE has been limited.

AIM

To assess the utility of splenic stiffness measurements by MRE to predict gastroesophageal varices in children.

METHODS

We retrospectively reviewed abdominal MRE images taken on a 3T system in pediatric patients. Patients who had undergone Kasai operations for biliary atresia were selected for the Kasai group, and patients with normal livers and spleens were selected for the control group. Two-dimensional spin-echo echo-planar MRE acquisition centered on the liver, with a pneumatic driver at 60 Hz and a low amplitude, was performed to obtain hepatic and splenic stiffness values. Laboratory results for aspartate aminotransferase to platelet ratio index (APRI) were evaluated within six months of MRE, and the normalized spleen size ratio was determined with the upper normal size limit. All Kasai group patients underwent gastroesophageal endoscopy during routine follow-up. The Mann-Whitney U test, Kendall's tau b correlation and diagnostic performance analysis using the area under the curve (AUC) were performed for statistical analysis.

RESULTS

The median spleen MRE value was 5.5 kPa in the control group (n = 9, age 9-18 years, range 4.7-6.4 kPa) and 8.6 kPa in the Kasai group (n = 22, age 4-18 years, range 5.0-17.8 kPa). In the Kasai group, the APRI, spleen size ratio and spleen MRE values were higher in patients with portal hypertension (n = 11) than in patients without (n = 11) (all P < 0.001) and in patients with gastroesophageal varices (n = 6) than in patients without (n = 16) (all P < 0.05), even though their liver MRE values were not different. The APRI (τ = 0.477, P = 0.007), spleen size ratio (τ = 0.401, P = 0.024) and spleen MRE values (τ = 0.426, P = 0.016) also correlated with varices grades. The AUC in predicting gastroesophageal varices was 0.844 at a cut-off of 0.65 (100% sensitivity and 75% specificity) for the APRI, and 0.844 at a cut-off of 9.9 kPa (83.3% sensitivity and 81.3% specificity) for spleen MRE values.

CONCLUSION

At a cut-off of 9.9 kPa, spleen MRE values predicted gastroesophageal varices as well as the APRI and spleen size ratio in biliary atresia patients after the Kasai operation. However, liver MRE values were not useful for this purpose.

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.

Acoustic radiation force optical coherence elastography for elasticity assessment of soft tissues

Biomechanical properties of soft tissues are important indicators of tissue functions which can be used for clinical diagnosis and disease monitoring. Elastography, incorporating the principles of elasticity measurements into imaging modalities, provides quantitative assessment of elastic properties of biological tissues. Benefiting from high-resolution, noninvasive and three-dimensional optical coherence tomography (OCT), optical coherence elastography (OCE) is an emerging optical imaging modality to characterize and map biomechanical properties of soft tissues. Recently, acoustic radiation force (ARF) OCE has been developed for elasticity measurements of ocular tissues, detection of vascular lesions and monitoring of blood coagulation based on remote and noninvasive ARF excitation to both internal and superficial tissues. Here, we describe the advantages of the ARF-OCE technique, the measurement methods in ARF-OCE, the applications in biomedical detection, current challenges and advances. ARF-OCE technology has the potential to become a powerful tool for in vivo elasticity assessment of biological samples in a non-contact, non-invasive and high-resolution nature.

Association Between Obesity and Discordance in Fibrosis Stage Determination by Magnetic Resonance vs Transient Elastography in Patients With Nonalcoholic Liver Disease

BACKGROUND & AIMS

Magnetic resonance elastography (MRE) and transient elastography (TE) are noninvasive techniques used to detect liver fibrosis in nonalcoholic fatty liver disease. MRE detects fibrosis more accurately than TE, but MRE is more expensive, and the concordance between MRE and TE have not been optimally assessed in obese patients. It is important to determine under which conditions TE and MRE produce the same readings, so that some patients can simply undergo TE evaluation to detect fibrosis. We aimed to assess the association between body mass index (BMI) and discordancy between MRE and TE findings, using liver biopsy as the reference, and validated our findings in a separate cohort.

METHODS

We performed a cross-sectional study of 119 adults with nonalcoholic fatty liver disease who underwent MRE, TE with M and XL probe, and liver biopsy analysis from October 2011 through January 2017 (training cohort). MRE and TE results were considered to be concordant if they found patients to have the same stage fibrosis as liver biopsy analysis. We validated our findings in 75 adults with nonalcoholic fatty liver disease who underwent contemporaneous MRE, TE, and liver biopsy at a separate institution from March 2010 through May 2013. The primary outcome was rate of discordance between MRE and TE in determining stage of fibrosis (stage 2-4 vs 0-1). Secondary outcomes were the rate of discordance between MRE and TE in determining dichotomized stage of fibrosis (1-4 vs 0, 3-4 vs 0-2, and 4 vs 0-3).

RESULTS

In the training cohort, there was 43.7% discordance in findings from MRE versus TE. BMI associated significantly with discordance in findings from MRE versus TE (odds ratio, 1.69; 95% confidence interval, 1.15-2.51; P = .008) after multivariable adjustment by age and sex. The findings were confirmed in the validation cohort: there was 45.3% discordance in findings from MRE versus TE. BMI again associated significantly with discordance in findings from MRE versus TE (odds ratio, 1.52; 95% confidence interval, 1.04-2.21; P = .029) after multivariable adjustment by age and sex.

CONCLUSIONS

We identified and validated BMI as a factor significantly associated with discordance of findings from MRE versus TE in assessment of fibrosis stage. The degree of discordancy increases with BMI.

Diffusion kurtosis imaging in the assessment of liver function: Its potential as an effective predictor of liver function

OBJECTIVES:

We aimed to determine whether diffusion kurtosis imaging (DKI) analysis with the breath-hold technique can replace liver function results obtained from laboratory tests.

METHODS:

Patients (n = 79) suspected of having a hepatobiliary disease, and control group without liver diseases (n = 15) were examined with non-Gaussian diffusion-weighted imaging using a 3.0 T magnetic resonance imaging unit. Based on the findings of DKI, various blood serum parameters, including the indocyanine green (ICG) retention rate 15 min after an intravenous injection of ICG (ICG-R15) and mean kurtosis values and Child-Pugh and albumin-bilirubin (ALBI) scores, were calculated. In total, 17 patients were tested using ICG-R15. For evaluating liver function, correlations between the mean kurtosis value and the Child-Pugh score, ALBI score, and ICG-R15 value as indicators of liver function obtained from blood data were assessed using Spearman's rank correlation. In apparent diffusion coefficient as well, we assessed correlations with these indicators.

RESULTS:

The mean kurtosis value correlated with the Child-Pugh score (Spearman's rank-correlation coefficient, ρ = 0.3992; p < 0.0001). Moreover, the mean kurtosis value revealed a correlation with the ICG-R15 value (Spearman's rank-correlation coefficient, ρ = 0.5972; p = 0.00114). The correlation between the mean kurtosis value and the ALBI score was the poorest among these (Spearman's rank-correlation coefficient, ρ = 0.3395; p = 0.0008).

CONCLUSION:

Liver function correlating with the Child-Pugh score and ICG-R15 value can be quantitatively estimated using the mean kurtosis value obtained from DKI analysis. DKI analysis with the breath-hold technique can be used to determine liver function instead of performing laboratory tests.

ADVANCES IN KNOWLEDGE:

Previous studies have not evaluated liver function in vivo using DKI.

Soft tissue rheology and its implications for elastography: Challenges and opportunities

Magnetic resonance elastography and related shear wave ultrasound elastography techniques can be used to estimate the mechanical properties of soft tissues in vivo by using the relationships between wave propagation and the elastic properties of materials. These techniques have found numerous clinical and research applications, tracking changes in tissue properties as a result of disease or other interventions. Most dynamic elastography approaches estimate tissue elastic (or viscoelastic) properties from a simplified version of the equations for the propagation of acoustic waves through a homogeneous linear (visco)elastic medium. However, soft tissue rheology is complex and departs significantly from this idealized picture. In particular, soft tissues are nonlinearly viscoelastic, inhomogeneous and often anisotropic, and their apparent stiffness can vary with the current loading state. All of these features have implications for the reliability and reproducibility of elastography measurements, from data acquisition to analysis and interpretation. New developments in inversion algorithms for elastography are beginning to offer solutions to account for the complex rheology of tissues, including inhomogeneity and anisotropy. There remains considerable potential to further refine elastography to capture the full spectrum of tissue rheology, and thus to better understand the underlying tissue microstructural changes in a broad range of clinical disorders.