Advances in Magnetic Resonance Elastography of Liver

Postprandial splenic stiffness changes on magnetic resonance elastography in a young healthy population

Magnetic resonance elastography (MRE) is an accurate noninvasive diagnostic tool for assessing the stiffness of parenchymal organs, including the spleen. However, this measurement may be biased due to postprandial changes in splenic stiffness. The aim of the current study was to evaluate postprandial changes in spleen stiffness assessed by MRE in a large sample of healthy volunteers. This was a prospective institutional research ethics board-approved study. Healthy volunteers with no history of liver disease were recruited for an MRE test and blood draw from December 2018 to July 2019. Each participant underwent spleen MRE after at least 4 h of fasting and again 30 min after a 1000 kcal meal. Also, 14 randomly selected volunteers underwent additional MRE examinations at 1.5 and 2.5 h after food intake. The MRE data were acquired at 60 Hz using a 1.5-T MRI scanner. The spleen stiffness was assessed using a weighted mean of stiffness values from regions of interest manually drawn on three to five spleen slices. Spearman's rank correlation, Wilcoxon signed-rank, Friedman, and Mann-Whitney tests were used for statistical analysis. A total of 100 volunteers met the inclusion criteria and were eventually enrolled in this study (age 23 ± 2 years; 65 women). The mean spleen stiffness for the whole group increased by 7.9% (p < 0.001) from the mean ± SD value of 5.09 ± 0.63 (95% CI: 4.96-5.21) kPa in the fasting state to 5.47 ± 0.66 (95% CI 5.34-5.60) kPa 30 min after the meal and then gradually decreased. However, even 2 h 30 min after the meal, the spleen stiffness was higher than in the fasting state. This difference was statistically significant at p less than 0.001. It was concluded that meal intake results in a statistically significant elevation of spleen stiffness that persists for 2.5 h. This finding supports the recommendation for routine fasting for more than 2.5 h prior to assessing MRE-based spleen stiffness.

Imaging of Fontan-Associated Liver Disease

ABSTRACT

The Fontan procedure is the definitive treatment for patients with single-ventricle physiology. Surgical advances have led to a growing number of patients surviving into adulthood. Fontan-associated liver disease (FALD) encompasses a spectrum of pathologic liver changes that occur secondary to altered physiology including congestion, fibrosis, and the development of liver masses. Assessment of FALD is difficult and relies on using imaging alongside of clinical, laboratory, and pathology information. Ultrasound, computed tomography, and magnetic resonance imaging are capable of demonstrating physiologic and hepatic parenchymal abnormalities commonly seen in FALD. Several novel imaging techniques including magnetic resonance elastography are under study for use as biomarkers for FALD progression. Imaging has a central role in detection and characterization of liver masses as benign or malignant. Benign FNH-like masses are commonly encountered; however, these can display atypical features and be mistaken for hepatocellular carcinoma (HCC). Fontan patients are at elevated risk for HCC, which is a feared complication and has a poor prognosis in this population. While imaging screening for HCC is widely advocated, no consensus has been reached regarding an optimal surveillance regimen.

Noninvasive Fibrosis Assessment in Chronic Hepatitis C Infection: An Update

Liver biopsy is historically the gold standard for liver fibrosis assessment of chronic hepatitis C patients. However, with the introduction and validation of noninvasive tests (NITs) to evaluate advanced fibrosis, and the direct-acting antiviral agents for treatment of chronic hepatitis C virus (HCV), the role of NITs have become even more complex. There is now need for longitudinal monitoring and elucidation of cutoff values for prediction of liver-related complication after sustained virological response. The aim of this report is to provide a critical overview of the various NITs available for the assessment of liver fibrosis in HCV patients.

Gunshot wounds in parenchymatous organs: the morphology mainly depends on the physical properties of the affected tissues

In contrast to gunshot wounds in skin and bone, the medico-legal literature pays little attention to the appearance of bullet penetration sites in abdominal organs. It was only in 1983 that Metter and Schulz published an article entitled "Morphological features of gunshot wounds in the liver and spleen." According to their observations, the organs in question showed stellate tears at the bullet penetration sites resembling skin wounds from contact shots to body regions having a bony support. The study presented simulated the real conditions by means of test shots to composite models consisting of porcine organs embedded in ballistic gelatin. The ammunition used was pistol cartridges 9 mm Luger with full metal jacket round nose bullets. The shots were video-documented with a high-speed camera in order to record the bullet's travel through the target. In addition, the composite models fired at underwent CT examinations followed by a macroscopic assessment of the organs. The study confirmed the findings of Metter and Schulz with regard to the star-like appearance of gunshot wounds in the liver and spleen. Likewise, the kidney showed radiating tears originating from the bullet path, whereas the wound track in pulmonary tissue was tube-shaped and lacked additional cracks. The varying wound patterns in parenchymatous organs can reasonably be explained as a consequence of the respective viscoelastic tissue properties.

Evaluation of Spleen Stiffness in Young Healthy Volunteers Using Magnetic Resonance Elastography

PURPOSE

Magnetic resonance elastography (MRE) has been established as the most accurate noninvasive technique for diagnosing liver fibrosis. Recent publications have suggested that the measurement of splenic stiffness is useful in setting where portal hypertension may be present. The goal of the current study was to compile normative data for MRE-assessed stiffness measurements of the spleen in young adults.

MATERIALS AND METHODS

A total of 100 healthy young Caucasian volunteers (65 females and 35 males) in the age range of 20 to 32 years were enrolled in this study. The participants reported no history of chronic spleen and liver disease, normal alcohol consumption, and a normal diet. The MRE data were acquired by using a 1.5 T whole-body scanner and a 2D GRE pulse sequence with 60 Hz excitation. Spleen stiffness was calculated as a weighted mean of stiffness values in the regions of interest manually drawn by the radiologist on three to five spleen slices.

RESULTS

Mean spleen stiffness was 5.09 ± 0.65 kPa for the whole group. Male volunteers had slightly higher splenic stiffness compared to females: 5.28 ± 0.78 vs. 4.98 ± 0.51 kPa, however, this difference was not statistically significant (p = 0.12). Spleen stiffness did not correlate with spleen fat content and liver stiffness but a statistically significant correlation with spleen volume was found.

CONCLUSIONS

The findings of this study provide normative values for 2D MRE-based measurement of spleen stiffness in young adults, a basis for assessing the value of this biomarker in young patients with portal system pathologies.

Magnetic Resonance Imaging in Clinical Trials of Diabetic Kidney Disease

Chronic kidney disease (CKD) associated with diabetes mellitus (DM) (known as diabetic kidney disease, DKD) is a serious and growing healthcare problem worldwide. In DM patients, DKD is generally diagnosed based on the presence of albuminuria and a reduced glomerular filtration rate. Diagnosis rarely includes an invasive kidney biopsy, although DKD has some characteristic histological features, and kidney fibrosis and nephron loss cause disease progression that eventually ends in kidney failure. Alternative sensitive and reliable non-invasive biomarkers are needed for DKD (and CKD in general) to improve timely diagnosis and aid disease monitoring without the need for a kidney biopsy. Such biomarkers may also serve as endpoints in clinical trials of new treatments. Non-invasive magnetic resonance imaging (MRI), particularly multiparametric MRI, may achieve these goals. In this article, we review emerging data on MRI techniques and their scientific, clinical, and economic value in DKD/CKD for diagnosis, assessment of disease pathogenesis and progression, and as potential biomarkers for clinical trial use that may also increase our understanding of the efficacy and mode(s) of action of potential DKD therapeutic interventions. We also consider how multi-site MRI studies are conducted and the challenges that should be addressed to increase wider application of MRI in DKD.

Elastography of the Liver in Wilson's Disease

Staging of liver fibrosis is of special significance in Wilson's disease as it determines the patient's prognosis and treatment. Histopathological examination is a standard method for fibrosis assessment; however, non-invasive methods like transient elastography and share wave elastography are believed to be reliable and repetitive and are expected to replace liver biopsy in Wilson's disease. This article presents a short description of available elastography techniques and the results of the most recent studies on elastography of the liver in patients with Wilson's disease.

Regulators, functions, and mechanotransduction pathways of matrix stiffness in hepatic disease

The extracellular matrix (ECM) provides physical support and imparts significant biochemical and mechanical cues to cells. Matrix stiffening is a hallmark of liver fibrosis and is associated with many hepatic diseases, especially liver cirrhosis and carcinoma. Increased matrix stiffness is not only a consequence of liver fibrosis but is also recognized as an active driver in the progression of fibrotic hepatic disease. In this article, we provide a comprehensive view of the role of matrix stiffness in the pathological progression of hepatic disease. The regulators that modulate matrix stiffness including ECM components, MMPs, and crosslinking modifications are discussed. The latest advances of the research on the matrix mechanics in regulating intercellular signaling and cell phenotype are classified, especially for hepatic stellate cells, hepatocytes, and immunocytes. The molecular mechanism that sensing and transducing mechanical signaling is highlighted. The current progress of ECM stiffness's role in hepatic cirrhosis and liver cancer is introduced and summarized. Finally, the recent trials targeting ECM stiffness for the treatment of liver disease are detailed.

MR elastography in primary sclerosing cholangitis: a pictorial review

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease characterized by biliary ductal inflammation and fibrosis causing both intrahepatic and extrahepatic biliary strictures and dilatation. There is currently no effective medical treatment and the disease leads to cirrhosis and liver failure, with patients often requiring liver transplantation in end-stage disease. Liver fibrosis is one of the most important factors in determining patient outcome in PSC, and the diagnosis and monitoring of fibrosis are vital to patient care. MRI with magnetic resonance cholangiopancreatography is the non-invasive imaging modality of choice in PSC and is useful for the evaluation of parenchymal and biliary changes. Biliary ductal abnormalities, however, cannot always predict the presence of liver fibrosis and alternative means are needed. MR Elastography (MRE) is the most accurate non-invasive method for assessing liver fibrosis and is particularly helpful in PSC due to unique hepatic manifestations. Like other non-invasive modalities, MRE measures liver stiffness as an indirect method for assessing fibrosis. Given the ability of MRE to assess liver fibrosis and the importance of fibrosis in PSC patients, MRE can reliably predict patient outcome. In this pictorial review, we will review MR findings of PSC, with an emphasis on MRE, and demonstrate scenarios where MRE is particularly helpful in evaluating PSC patients.

Diagnostic Value of FibroTouch and Non-invasive Fibrosis Indexes in Hepatic Fibrosis with Different Aetiologies

BACKGROUND

Liver biopsy is the gold standard for staging liver fibrosis, but it has numerous drawbacks, mainly associated with bleeding and bile fistula risks. A number of non-invasive techniques have been investigated, but they all have their own disadvantages. To avoid the risks mentioned above and to improve the diagnostic value, we still need to search for a more accurate non-invasive method to evaluate the degree of liver fibrosis.

AIM

This study aimed to evaluate the diagnostic performance of FibroTouch versus other non-invasive fibrosis indexes in hepatic fibrosis of different aetiologies.

METHODS

This study retrospectively enrolled 227 patients with chronic hepatic liver disease admitted to the first hospital of Lanzhou University from 2017 to 2020. Liver biopsy was performed in all of the patients, and their biochemical indicators were all tested. Non-invasive indexes including the fibrosis index based on four factors (FIB-4), the aminotransferase-to-platelet ratio index (APRI), and the gamma-glutamyl transpeptidase-to-platelet ratio index (GPRI) were all calculated. Transient elastography was performed using FibroTouch.

RESULTS

The correlation between FibroTouch and the pathology of liver fibrosis was significantly higher than that between the non-invasive fibrosis indexes and the biopsy results (r = 0.771, p < 0.05). The area under the receiver operating curve (AUC) of FibroTouch was significantly higher than that of FIB-4, APRI, and GPRI for the diagnosis of significant fibrosis (≥ S2 fibrosis stage), advanced fibrosis (≥ S3 fibrosis stage), and cirrhosis (= S4 fibrosis stage) (p < 0.05). The patients were grouped according to different aetiologies. The diagnostic value of FibroTouch had much higher credibility in different fibrosis stages for different causes compared with other non-invasive indexes. The AUC of FibroTouch showed both higher specificity and higher sensitivity than FIB-4, APRI, and GPRI for different liver fibrosis stages with different aetiologies.

CONCLUSIONS

FibroTouch demonstrates the highest diagnostic value for liver fibrosis and cirrhosis among non-invasive methods, showing better results than FIB-4, APRI, and GPRI, and surpassed only by liver biopsy. FibroTouch is reliable in assessing liver fibrosis with different aetiologies.

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

PURPOSE

To evaluate performance of 3D magnetic resonance elastography (MRE) using spin-echo echo-planar imaging (seEPI) for assessment of hepatic stiffness compared with 2D gradient-recalled echo (GRE) and 2D seEPI sequences.

METHODS

Fifty-seven liver MRE examinations including 2D GRE, 2D seEPI, and 3D seEPI sequences were retrospectively evaluated. Elastograms were analyzed by 2 radiologists and polygonal regions of interests (ROIs) were drawn in 2 different fashions: "curated" ROI (avoiding liver edge, major vessels, and areas of wave interferences) and "non-curated" ROI (including largest cross section of liver, to assess the contribution of artifacts). Liver stiffness measurement (LSM) was calculated as the arithmetic mean of individual stiffness values for each technique. For 3D MRE, LSMs were also calculated based on 4 slices ("abbreviated LSM"). Intra-patient variations in LSMs and different methods of ROI placement were assessed by univariate tests. A p-value of < 0.05 was set as a statistically significant difference.

RESULTS

Mean surface areas of the ROIs were 50,723 mm², 12,669 mm², 5814 mm², and 10,642 mm² for 3D MRE, abbreviated 3D MRE, 2D GRE, and 2D seEPI, respectively. 3D LSMs based on curated and non-curated ROIs showed no clinically significant difference, with a mean difference less than 0.1 kPa. Abbreviated 3D LSMs had excellent correlation with 3D LSMs based on all slices (r = 0.9; p < 0.001) and were not significantly different (p = 0.927).

CONCLUSION

3D MRE allows more reproducible measurements due to its lower susceptibility to artifacts and provides larger areas of parenchyma, enabling a more comprehensive evaluation of the liver.

Magnetic resonance elastography of the prostate in patients with lower urinary tract symptoms: feasibility of the modified driver at high multi-frequencies

PURPOSE

To demonstrate the feasibility and diagnostic value of high-frequency magnetic resonance elastography (MRE) for evaluation of prostatic disease in patients with lower urinary tract symptoms (LUTS).

METHODS

41 patients who underwent preoperative prostate MRI and MRE with a modified driver were enrolled retrospectively from May 2016 to September 2021. All were included in the assessment of MRE image quality, using a qualitative visual inspection and a quantitative confidence map. 35 patients (prostate cancer (PCa), n = 13; non-PCa, n = 22) undergoing prostatectomy or biopsy were evaluated for the diagnostic performance of stiffness values. The confidence values and the stiffness values were analyzed by one-way analysis of variance (ANOVA) and independent samples T test, respectively. Area under the receiver operating characteristic (AUROC) analysis was performed.

RESULTS

Through the qualitative analysis, all MRE acquisitions were successful at 60, 90, 120 and 150 Hz. The quantitative confidence values were significantly lower at 60 Hz (0.683 ± 0.055) and 90 Hz (0.762 ± 0.048) than that at 120 Hz (0.814 ± 0.049) and 150 Hz (0.840 ± 0.049), all P < 0.001. The stiffness of PCa was higher than non-PCa at 90 Hz (P = 0.008), 120 Hz (P < 0.001) and 150 Hz (P < 0.001). The AUCs were 0.773, 0.881 and 0.944, respectively.

CONCLUSION

Prostate MRE using the modified driver is feasible at 60-150 Hz and image quality is better at higher frequencies. Prostate MRE may be useful and helpful to evaluate prostate diseases in patients with LUTS at higher frequencies; however, further study may be warranted with larger population in future.

Update on the Evaluation and Management of Portal Hypertension

The development of clinically significant portal hypertension (CSPH) in patients with chronic liver disease is an important predictor of varices, variceal hemorrhage, ascites, hepatic encephalopathy, and death. The nomenclature of compensated advanced chronic liver disease, revised from compensated cirrhosis, recognizes the importance of portal hypertension (PH), rather than the histologic finding of cirrhosis, in clinical outcomes. Recent advances in the field have focused on the development of noninvasive methods, including transient elastography (TE), magnetic resonance elastography, and multiparametric magnetic resonance imaging, for predicting PH. TE is evolving to be the most widespread clinical tool to estimate PH, with a liver stiffness (LS) measurement cutoff of greater than or equal to 25 kilopascals (kPa) ruling in CSPH, and that of less than 15 kPa combined with a platelet count of greater than 150 × 10⁹/L ruling out CSPH. Extending utilization of TE to not only LS measurement but also splenic stiffness measurement using the same probes may augment the sensitivity of detecting CSPH and thus selecting candidates warranting endoscopic evaluation for high-risk varices. With respect to management of PH, the role of nonselective β blockers continues to evolve and may extend beyond variceal bleed in preventing decompensation and development of ascites. Statins have a burgeoning well of data supporting their use, but large, prospective, controlled trials with clinical endpoints are awaited. Further data are still warranted regarding the use of long-term albumin therapy to prevent complications of PH.

Perspective: The Mechanobiology of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the second most deadly primary cancer in the world and is thus a major global health challenge. HCC primarily develops in patients with an underlying chronic liver disease, the vast majority with advanced cirrhosis, characterized by increased matrix deposition and liver stiffness. Liver stiffness is highly associated with cancer development and poor patient outcome and is measured clinically to assess cancer risk; cirrhotic livers greatly exceed the threshold stiffness shown to alter hepatocyte cell behavior and to increase the malignancy of cancer cells. Recent studies have shown that cirrhotic liver cells have highly irregular nuclear morphologies and that nuclear deformation mediates mechanosensitive signaling. Separate research has shown that nuclear deformation can increase genetic instability and the accumulation of DNA damage in migrating cancer cells. We hypothesize that the mechanical changes associated with chronic liver disease are drivers of oncogenesis, activating mechanosensitive signaling pathways, increasing rates of DNA damage, and ultimately inducing malignant transformation.

Non-invasive imaging biomarkers to assess nonalcoholic fatty liver disease: A review

This review summarizes the current state of non-invasive diagnosis of non-alcoholic fatty liver disease (NAFLD). This begins with a brief discussion of blood-based analysis (serum biomarkers) then progresses through various imaging modalities (imaging biomarkers) including magnetic resonance (MR), computed tomography (CT), and ultrasound-based imaging methods. The review concludes with comment on the advantages, disadvantages, and prospects of commercially available modalities and the impact they may have on diagnosis and management of patients with NAFLD.