High-resolution 3D visualization of ductular proliferation of bile duct ligation-induced liver fibrosis in rats using x-ray phase contrast computed tomography

Multiscale reconstruction of various vessels in the intact murine liver lobe

The liver contains a variety of vessels and participates in miscellaneous physiological functions. While past studies generally focused on certain hepatic vessels, we simultaneously obtained all the vessels and cytoarchitectural information of the intact mouse liver lobe at single-cell resolution. Here, taking structural discrepancies of various vessels into account, we reconstruct and visualize the portal vein, hepatic vein, hepatic artery, intrahepatic bile duct, intrahepatic lymph of an intact liver lobe and peribiliary plexus in its selected local areas, providing a technology roadmap for studying the fine hepatic vascular structures and their spatial relationship, which will help research into liver diseases and evaluation of medical efficacies in the future.

Use of the volume-averaged Murray's deviation method for the characterization of branching geometry in liver fibrosis: a preliminary study on vascular circulation

Background

Vascular changes in liver fibrosis can result in increased intrahepatic vascular resistance and impaired blood circulation. This can hinder the recovery from fibrosis and may eventually lead to portal hypertension, a major cirrhosis complication. This report proposed a volume-averaged Murray's deviation method to characterize intrahepatic circulation in the liver during fibrosis and its subsequent regression via X-ray phase-contrast computed tomography (PCCT).

Methods

Liver fibrosis was induced in 24 Sprague-Dawley rats by exposure to carbon tetrachloride (CCl₄) for up to 10 weeks, after which, spontaneous regression commenced and continued until week 30. High-resolution three-dimensional (3D) imaging of the livers was performed with PCCT. The values of Murray's deviation based on the volume-averaged and the conventional diameter-based methods were compared. After that, the intrahepatic circulation at different stages of fibrosis was evaluated using the volume-averaged method. The increase in collagen during liver fibrosis was assessed by pathological analyses.

Results

A comparison of the 2 methods showed that with an increase in the number of diameter measurements, the value of Murrary's deviation obtained using the diameter-based method gradually approaches those of the volume-averaged method, with minimal variations. The value of Murray's deviation increased with the development of fibrosis. After reversal, the value rapidly decreased and approached that of the normal state in both the main branches (1.05±0.17, 1.17±0.21, 1.34±0.18, and 1.17±0.19 in the normal, moderate, severe, and regressive groups, respectively; P<0.05 between the severe group and other groups) and the small branches (1.05±0.09, 1.42±0.48, 1.79±0.57, and 1.18±0.28 in the normal, moderate, severe, and regressive group, respectively; P<0.05 between adjacent groups). An analysis of Murray's deviation and the pathological results showed that the vascular circulation in this disease model was consistent with the progression and recovery from fibrosis.

Conclusions

This study showed the validity of the volume-averaged method for calculating Murray's deviation and demonstrated that it could accurately evaluate the blood circulation state of the liver during fibrosis and its subsequent regression. Thus, the volume-averaged method of calculating Murray's deviation may be an objective and valuable staging criterion to evaluate intrahepatic circulation during liver fibrosis.

Insight into Bile Duct Reaction to Obstruction from a Three-dimensional Perspective Using ex Vivo Phase-Contrast CT

Background Biliary obstruction leads to an increase in biliary pressure within the biliary system, which induces the morphologic adaptation of the biliary tree. Purpose To observe and to quantify the morphologic characteristics of the adaptation in a bile duct ligation rat model and verify it in patients with biliary atresia in a three-dimensional (3D) manner using x-ray phase-contrast CT. Materials and Methods A bile duct ligation model was induced in 40 male Sprague-Dawley rats, which were divided into five groups: the control group (no ligation) and groups 2, 4, 6, and 8 weeks after bile duct ligation (eight animals in each group). Liver tissue samples (approximately 1.8 cm in length and 1.3 cm in height) were imaged by using phase-contrast CT and compared with histologic analysis. With a combination of phase-contrast CT and 3D visualization technology, the entire biliary system and the intrahepatic vascular system were quantitatively analyzed according to downstream, midstream, and upstream domains based on bile duct volume, surface area, and other parameters. Additionally, liver explant tissues from 28 patients with biliary atresia were studied to determine the impact of biliary tract reconstruction. Results To offset the increased biliary pressure within the biliary system, the ductular reaction in the downstream, midstream, and upstream domains manifested as dilatation, spiderweb-like looping, and interconnected honeycomb-like patterns, respectively. The most severe ductular reaction occurred in the upstream domain, and the relative surface area (mean, 0.02 μm^-1 ± 0.01, 0.04 μm^-1 ± 0.01, 0.07 μm^-1 ± 0.02, and 0.10 μm^-1 ± 0.02 for the 2-8-week groups, respectively; P < .01 among the groups) and volume fraction of ductules (mean, 16.54% ± 4.62, 19.69% ± 6.41, 26.92% ± 5.82, and 38.34% ± 10.36 for the 2-8-week groups, respectively; P < .01 among the groups except between the 2- and 4-week groups [P = .062]) significantly increased over time. In patients with biliary atresia, it was observed that both fibrosis and proliferative ductules regressed after successful biliary tract reconstruction following Kasai portoenterostomy. Furthermore, ductular reaction was accompanied by a progressive increase in the arterial supply but a loss of portal blood supply. Conclusion X-ray phase-contrast CT with three-dimensional rendering of the biliary system in a bile duct ligation rat model provides key insights into ductular reaction or biliary self-adaptation triggered by increased biliary pressure. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Vannier and Wang in this issue.

Fine-scale visualizing the hierarchical structure of mouse biliary tree with fluorescence microscopy method

The liver is a vital organ and the hepatic lobule serves as the most basic structural and functional unit which is mainly assembled with parenchymal cells including hepatocytes and biliary epithelial cells. The continuous tubular arrangement of biliary cells which constitutes the biliary tracts is critical for liver function, however, the biliary tracts are often disrupted in many liver diseases such as cirrhosis and some congenital disorders. Visualization of the biliary tracts in fine-scale and three-dimension will help to understanding the structure basis of these liver diseases. In the present study, we established several biliary tract injury mouse models by diet feeding, surgery or genetic modification. The cytoplasm and nuclei of the parenchymal cells were marked by active uptake of fluorescent dyes Rhodamine B (red) and Hoechst (blue), respectively. After the removal of liver en bloc, the biliary tracts were retrogradely perfused with green fluorescent dye, fluorescein isothiocyanate (FITC). The liver was then observed under confocal microscopy. The fine-scale and three-dimensional (3D) structure of the whole biliary tree, particularly the network of the end-terminal bile canaliculi and neighboring hepatocytes were clearly visualized. The biliary tracts displayed clear distinct characteristics in normal liver and diseased liver models. Taken together, we have developed a simple and repeatable imaging method to visualize the fine-scale and hierarchical architecture of the biliary tracts spreading in the mouse liver.

3D analysis of microvasculature in murine liver fibrosis models using synchrotron radiation-based microtomography

Cirrhosis describes the development of excess fibrous tissue around regenerative nodules in response to chronic liver injury and usually leads to irreversible organ damage and end-stage liver disease. During the development of cirrhosis, the formation of collagenous scar tissue is paralleled by a reorganization and remodeling of the hepatic vascular system. To date, macrovascular remodeling in various cirrhosis models has been examined using three-dimensional (3D) imaging modalities, while microvascular changes have been studied mainly by two-dimensional (2D) light microscopic and electron microscopic imaging. Here, we report on the application of high-resolution 3D synchrotron radiation-based microtomography (SRμCT) for the study of the sinusoidal and capillary blood vessel system in three murine models of advanced parenchymal and biliary hepatic fibrosis. SRμCT facilitates the characterization of microvascular architecture and identifies features of intussusceptive angiogenesis in progressive liver fibrosis in a non-destructive 3D manner.

Vascular branching geometry relating to portal hypertension: a study of liver microvasculature in cirrhotic rats by X-ray phase-contrast computed tomography

Background

Portal hypertension is one of the major complications of cirrhosis. The changes in hepatic microvasculature are considered as critical pathophysiological characteristics of portal hypertension. X-ray phase-contrast computed tomography (PCCT) is a new imaging technique that can detect liver vessels at a micrometric level without contrast agents.

Methods

In this study, male Sprague-Dawley rats with liver cirrhosis induced by carbon tetrachloride (CCl₄) or bile duct ligation (BDL) were investigated with PCCT. The portal pressures of rats were recorded before euthanasia. The branch angle and Murray's deviation (MD) were measured based on the branching geometry of the three-dimensional (3D) microvasculature of liver cirrhosis in rats. Statistical analyses were performed to determine the correlation between branching geometry and portal pressure in liver fibrosis.

Results

The results demonstrated that the branch angle and MD significantly increased in the CCl₄ model and BDL model compared with their corresponding normal group or sham group. The portal pressure was significantly correlated with the branching morphologic features (all R≥0.761 and P<0.01).

Conclusions

The branch angle and MD could accurately distinguish portal pressure in cirrhotic rats, suggesting that branching geometric characteristics of the microvasculature may be a promising marker in the prognosis of portal hypertension in liver cirrhosis.

Characterization of microvessels and parenchyma in in-line phase contrast imaging CT: healthy liver, cirrhosis and hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is a cancer with a poor prognosis, and approximately 80% of HCC cases develop from cirrhosis. Imaging techniques in the clinic seem to be insufficient for revealing the microstructures of liver disease. In recent years, phase contrast imaging CT (PCI-CT) has opened new avenues for biomedical applications owing to its unprecedented spatial and contrast resolution. The aim of this study was to present three-dimensional (3D) visualization of human healthy liver, cirrhosis and HCC using a PCI-CT technique called in-line phase contrast imaging CT (ILPCI-CT) and to quantitatively evaluate the variations of these tissues, focusing on the liver parenchyma and microvasculature.

Methods

Tissue samples from 9 surgical specimens of normal liver (n=3), cirrhotic liver (n=2), and HCC (n=4) were imaged using ILPCI-CT at the Shanghai Synchrotron Radiation Facility (SSRF) without contrast agents. 3D visualization of all ex vivo liver samples are presented. To quantitatively evaluate the vessel features, the vessel branch angles of each sample were clearly depicted. Additionally, radiomic features of the liver parenchyma extracted from the 3D images were measured. To evaluate the stability of the features, the percent coefficient of variation (%COV) was calculated for each radiomic feature. A %COV <30 was considered to be low variation. Finally, one-way ANOVA, followed by Tukey's test, was used to determine significant changes among the different liver specimens.

Results

ILPCI-CT allows for a clearer view of the architecture of the vessels and reveals more structural details than does conventional radiography. Combined with the 3D visualization technique, ILPCI-CT enables the acquisition of an accurate description of the 3D vessel morphology in liver samples. Qualitative descriptions and quantitative assessment of microvessels demonstrated clear differences among human healthy liver, cirrhotic liver and HCC. In total, 38 (approximately 51%) radiomic features had low variation, including 11 first-order features, 16 GLCM features, 6 GLRLM features and 5 GLSZM features. The differences in the mean vessel branch angles and 3 radiomic features (first-order entropy, GLCM-inverse variance and GLCM-sum entropy) were statistically significant among the three groups of samples.

Conclusions

ILPCI-CT may allow for morphologic descriptions and quantitative evaluation of vessel microstructures and parenchyma in human healthy liver, cirrhotic liver and HCC. Vessel branch angles and radiomic features extracted from liver parenchyma images can be used to distinguish the three kinds of liver tissues.