Quantitative analysis of hepatic macro- and microvascular alterations during cirrhogenesis in the rat

LiverMap pipeline for 3D imaging of human liver reveals volumetric spatial dysregulation of cirrhotic vasculobiliary architecture

The liver contains an intricate microstructure that is critical for liver function. Architectural disruption of this spatial structure is pathologic. Unfortunately, 2D histopathology - the gold standard for pathological understanding of many liver diseases - can misrepresent or leave gaps in our understanding of complex 3D structural features. Here, we utilized immunostaining, tissue clearing, microscopy, and computational software to create 3D multilobular reconstructions of both non-fibrotic and cirrhotic human liver tissue. We found that spatial architecture in human cirrhotic liver samples with varying etiologies had sinusoid zonation dysregulation, reduction in glutamine synthetase-expressing pericentral hepatocytes, regression of central vein networks, disruption of hepatic arterial networks, and fragmentation of biliary networks, which together suggest a pro-portalization/decentralization phenotype in cirrhotic tissue. Further implementation of 3D pathological analyses may provide a deeper understanding of cirrhotic pathobiology and inspire novel treatments for liver disease.

The Utility of a Novel Stacked Microvascular Imaging for Enhanced Detection of Fibrosis in Chronic Liver Diseases

OBJECTIVE

Ultrasonographic imaging plays a primary role to detect fibrotic changes in patients with chronic liver disease (CLD). To enhance detectability of fibrosis in its early stage, we developed a novel stacked microvascular imaging (SMVI) that enables continuous visualization of fibrotic changes in intrahepatic vessels.

METHODS

SMVI was produced by accumulating 3-5 seconds of high-definition color images in tilted-scan mode. An SMVI score was devised by quantitating three hallmark vascular changes in liver fibrosis in 0-2 grades (total 0-6): narrowing, caliber irregularity, and tortuosity. To evaluate the clinical utility of the SMVI score, 469 well-defined CLD patients were enrolled and subgrouped by the stage of liver fibrosis defined based on elastography: F0-1Low, F0-1High, F2, F3, and F4. The diagnostic performance of the SMVI score was compared to conventional B-mode liver morphology score and various laboratory test markers of fibrosis.

RESULTS

Unlike conventional microvascular imaging that relies on a single image, SMVI enabled an undisrupted view of intrahepatic vessels for easy detection of fibrotic changes. SMVI detected microvascular narrowing in 92% at stage F0-1High. While detection rates for caliber irregularity and tortuosity were low at early stages but increased proportionately in advanced stages. Multiple logistic regression analysis revealed that SMVI score was most accurate in distinguishing F0-1Low from F0-1High cases compared to B-mode or laboratory test scores.

CONCLUSION

SMVI provides enhanced vascular images of liver fibrosis in CLD, especially in its early stage. The SMVI score can be used as a primary tool for determining fibrotic stages in CLD.

Fluid Mechanics Approach to Perfusion Quantification: Vasculature Computational Fluid Dynamics Simulation, Quantitative Transport Mapping (QTM) Analysis of Dynamics Contrast Enhanced MRI, and Application in Nonalcoholic Fatty Liver Disease Classification

OBJECTIVE

We quantify liver perfusion using quantitative transport mapping (QTM) method that is free of arterial input function (AIF). QTM method is validated in a vasculature computational fluid dynamics (CFD) simulation and is applied for processing dynamic contrast enhanced (DCE) MRI images in differentiating liver with nonalcoholic fatty liver disease (NAFLD) from healthy controls using pathology reference in a preclinical rabbit model.

METHODS

QTM method was validated on a liver perfusion simulation based on fluid dynamics using a rat liver vasculature model and the mass transport equation. In the NAFLD grading task, DCE MRI images of 7 adult rabbits with methionine choline-deficient diet-induced nonalcoholic steatohepatitis (NASH), 8 adult rabbits with simple steatosis (SS) were acquired and processed using QTM method and dual-input two compartment Kety's method respectively. Statistical analysis was performed on six perfusion parameters: velocity magnitude | u | derived from QTM, liver arterial blood flow LBFa, liver venous blood flow LBFv, permeability Ktrans, blood volume Vp and extravascular space volume Ve averaged in liver ROI.

RESULTS

In the simulation, QTM method successfully reconstructed blood flow, reduced error by 48% compared to Kety's method. In the preclinical study, only QTM |u| showed significant difference between high grade NAFLD group and low grade NAFLD group.

CONCLUSION

QTM postprocesses DCE-MRI automatically through deconvolution in space and time to solve the inverse problem of the transport equation. Comparing with Kety's method, QTM method showed higher accuracy and better differentiation in NAFLD classification task.

SIGNIFICANCE

We propose to apply QTM method in liver DCE MRI perfusion quantification.

Ultrasensitive US Microvessel Imaging of Hepatic Microcirculation in the Cirrhotic Rat Liver

Background Liver microcirculation dysfunction plays a vital role in the occurrence and development of liver diseases, and thus, there is a clinical need for in vivo, noninvasive, and quantitative evaluation of liver microcirculation. Purpose To evaluate the feasibility of ultrasensitive US microvessel imaging (UMI) in the visualization and quantification of hepatic microvessels in healthy and cirrhotic rats. Materials and Methods In vivo studies were performed to image hepatic microvasculature by means of laparotomy in Sprague-Dawley rats (five cirrhotic and five control rats). In vivo conventional power Doppler US and ex vivo micro-CT were performed for comparison. UMI-based quantifications of perfusion, tortuosity, and integrity of microvessels were compared between the control and cirrhotic groups by using the Wilcoxon test. Spearman correlations between quantification parameters and pathologic fibrosis, perfusion function, and hepatic hypoxia were evaluated. Results UMI helped detect minute vessels below the liver capsule, as compared with conventional power Doppler US and micro-CT. With use of UMI, lower perfusion indicated by vessel density (median, 22% [IQR, 20%-28%] vs 41% [IQR, 37%-46%]; P = .008) and fractional moving blood volume (FMBV) (median, 6.4% [IQR, 4.8%-8.6%] vs 13% [IQR, 12%-14%]; P = .008) and higher tortuosity indicated by the sum of angles metric (SOAM) (median, 3.0 [IQR, 2.9-3.0] vs 2.7 [IQR, 2.6-2.9]; P = .008) were demonstrated in the cirrhotic rat group compared with the control group. Vessel density (r = 0.85, P = .003), FMBV (r = 0.86, P = .002), and median SOAM (r = -0.83, P = .003) showed strong correlations with pathologically derived vessel density labeled with dextran. Vessel density (r = -0.81, P = .005) and median SOAM (r = 0.87, P = .001) also showed strong correlations with hepatic tissue hypoxia. Conclusion Contrast-free ultrasensitive US microvessel imaging provided noninvasive in vivo imaging and quantification of hepatic microvessels in cirrhotic rat liver. © RSNA, 2022 Supplemental material is available for this article. See also the editorial by Fetzer in this issue.

Anatomically and physiologically informed computational model of hepatic contrast perfusion for virtual imaging trials

PURPOSE

Virtual (in silico) imaging trials (VITs), involving computerized phantoms and models of the imaging process, provide a modern alternative to clinical imaging trials. VITs are faster, safer, and enable otherwise-impossible investigations. Current phantoms used in VITs are limited in their ability to model functional behavior such as contrast perfusion which is an important determinant of dose and image quality in CT imaging. In our prior work with the XCAT computational phantoms, we determined and modeled inter-organ (organ to organ) intravenous contrast concentration as a function of time from injection. However, intra-organ concentration, heterogeneous distribution within a given organ, was not pursued. We extend our methods in this work to model intra-organ concentration within the XCAT phantom with a specific focus on the liver.

METHODS

Intra-organ contrast perfusion depends on the organ's vessel network. We modeled the intricate vascular structures of the liver, informed by empirical and theoretical observations of anatomy and physiology. The developed vessel generation algorithm modeled a dual-input-single-output vascular network as a series of bifurcating surfaces to optimally deliver flow within the bounding surface of a given XCAT liver. Using this network, contrast perfusion was simulated within voxelized versions of the phantom by using knowledge of the blood velocities in each vascular structure, vessel diameters and length, and the time since the contrast entered the hepatic artery. The utility of the enhanced phantom was demonstrated through a simulation study with the phantom voxelized prior to CT simulation with the relevant liver vasculature prepared to represent blood and iodinated contrast media. The spatial extent of the blood-contrast mixture was compared to clinical data.

RESULTS

The vascular structures of the liver were generated with size and orientation which resulted in minimal energy expenditure required to maintain blood flow. Intravenous contrast was simulated as having known concentration and known total volume in the liver as calibrated from time-concentration curves. Measurements of simulated CT ROIs were found to agree with clinically observed values of early arterial phase contrast enhancement of the parenchyma (∼ 5 $ \sim 5$ HU). Similarly, early enhancement in the hepatic artery was found to agree with average clinical enhancement( 180 $(180$ HU).

CONCLUSIONS

The computational methods presented here furthered the development of the XCAT phantoms allowing for multi-timepoint contrast perfusion simulations, enabling more anthropomorphic virtual clinical trials intended for optimization of current clinical imaging technologies and applications.

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.

Fibrosis and hepatic regeneration mechanism

Liver cirrhosis is the final stage of continuous hepatic inflammatory activity derived by viral, metabolic or autoimmune origin. In the last years, cirrhosis was considered a unique and static condition; recently was accepted some patients subgroups with different liver injury degrees that coexist under the same diagnosis, with implications about the natural disease history. The liver growth factor (LGF) is a potent in vivo and in vitro mitogenic agent and an inducer of hepatic regeneration (HR) through the hepatocytes DNA synthesis. The clinical implications of the LGF levels in cirrhosis, are not clear and even with having a fundamental role in the liver regeneration processes, the studies suggest that it could be a cirrhosis severity marker, in acute liver failure and in chronic hepatitis. Its role as predictor of mortality in fulminant hepatic insufficiency patients has been suggested. HR is one of the most enigmatic and fascinating biological phenomena. The rapid volume and liver function restoration after a major hepatectomy (>70%) or severe hepatocellular damage and its strict regulation of tissue damage response after the cessation, is an exclusive property of the liver. HR is the clinical applications fundament, such as extensive hepatic resections (>70% of the liver parenchyma), segmental transplantation or living donor transplantation, sequential hepatectomies, isolated portal embolization or associated with in situ hepatic transection, temporary artificial support in acute liver failure and the possible cell therapy clinical applications.

Assessment of Vascular Network Connectivity of Hepatocellular Carcinoma Using Graph-Based Approach

BACKGROUND

The angiogenesis of liver cancer is a key condition for its growth, invasion, and metastasis. This study aims to investigate vascular network connectivity of hepatocellular carcinoma (HCC) using graph-based approach.

METHODS

Orthotopic HCC xenograft models (n=10) and the healthy controls (n=10) were established. After 21 days of modeling, hepatic vascular casting and Micro-CT scanning were performed for angiography, followed by blood vessels automatic segmentation and vascular network modeling. The topologic parameters of vascular network, including clustering coefficient (CC), network structure entropy (NSE), and average path length (APL) were quantified. Topologic parameters of the tumor region, as well as the background liver were compared between HCC group and normal control group.

RESULTS

Compared with normal control group, the tumor region of HCC group showed significantly decreased CC [(0.046 ± 0.005) vs. (0.052 ± 0.006), P=0.026], and NSE [(0.9894 ± 0.0015) vs. (0.9927 ± 0.0010), P<0.001], and increased APL [(0.433 ± 0.138) vs. (0.188 ± 0.049), P<0.001]. Compared with normal control group, the background liver of HCC group showed significantly decreased CC [(0.047 ± 0.004) vs. (0.052 ± 0.006), P=0.041] and increased NSE [0.9938 (0.9936~0.9940) vs. (0.9927 ± 0.0010), P=0.035]. No significant difference was identified for APL between the two groups.

CONCLUSION

Graph-based approach allows quantification of vascular connectivity of HCC. Disrupted vascular topological connectivity exists in the tumor region, as well as the background liver of HCC.

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.

Transarterial drug delivery for liver cancer: numerical simulations and experimental validation of particle distribution in patient-specific livers

Background: Transarterial therapies are routinely used for the locoregional treatment of unresectable hepatocellular carcinoma (HCC). However, the impact of clinical parameters (i.e. injection location, particle size, particle density etc.) and patient-specific conditions (i.e. hepatic geometry, cancer burden) on the intrahepatic particle distribution (PD) after transarterial injection of embolizing microparticles is still unclear. Computational fluid dynamics (CFD) may help to better understand this impact.Methods: Using CFD, both the blood flow and microparticle mass transport were modeled throughout the 3D-reconstructed arterial vasculature of a patient-specific healthy and cirrhotic liver. An experimental feasibility study was performed to simulate the PD in a 3D-printed phantom of the cirrhotic arterial network.Results: Axial and in-plane injection locations were shown to be effective parameters to steer particles toward tumor tissue in both geometries. Increasing particle size or density made it more difficult for particles to exit the domain. As cancer burden increased, the catheter tip location mattered less. The in vitro study and numerical results confirmed that PD largely mimics flow distribution, but that significant differences are still possible.Conclusions: Our findings highlight that optimal parameter choice can lead to selective targeting of tumor tissue, but that targeting potential highly depends on patient-specific conditions.

Effect of FibroScan test in antiviral therapy for HBV-infected patients with ALT <2 upper limit of normal

OBJECTIVE

The objective of this study is to detect the liver stiffness of hepatitis B virus (HBV)-infected patients with an alanine aminotransferase (ALT) level of <2 upper limit of normal (2ULN) by FibroScan and compare histological changes to assess the progression of liver lesions and its test results.

METHODS

There were 36 patients who had a liver FibroScan degree of >7.3 KD (F1), and a liver biopsy was conducted. Along with serology of liver fibrosis, indexes and hierarchical processing were used for evaluation. The correlation between these factors was analyzed.

RESULTS

The histopathological results of the liver were closely correlated with liver hardness. In the pathological diagnosis of chronic hepatitis, G represents the grade of inflammation and S represents the stage of hepatic fibrosis. Pathological examination results of H&E staining of liver tissue sections revealed that the area under the work characteristic curve of the subjects in G2S1, G2S2, G3S2, and G3S3 stages was 0.923, 0.916, 0.955, and 0.971, respectively, with diagnostic cut-off values of 9.03, 9.85, 15.14, and 30.67, respectively. Furthermore, hydroxyapatite, type III procollagen, laminin, and type IV collagen of serum fibrosis indexes are associated with liver stiffness values (P < 0.05).

CONCLUSION

FibroScan can be used as an alternative to liver biopsy. It is meaningful in determining whether HBV infected patients with an ALT level of <2 ULN should receive antiviral therapy.

Proportional vascularization along the fallopian tubes and ovarian fimbria: assessment by confocal microtomography

Objective

To evaluate and reconstruct three-dimensional images of vascularization along the fallopian tube (FT), as well as to determine its relationship with the ovary and ovarian fimbria, and to quantify the blood vessels along the FT according to its anatomical segments, using confocal microtomography (micro-CT).

Materials and Methods

Nine specimens (six FTs and three FTs with ovaries) were fixed in a solution of 10% formalin for > 24 h at room temperature. Iodine staining was performed by soaking the specimens in 10% Lugol’s solution for 24 h. All specimens were evaluated using micro-CT. A morphometric analysis was performed on the reconstructed images to quantify the vascular distribution along the FT.

Results

In the FTs evaluated, the density of blood vessels was significantly greater in the fimbrial segments than in the isthmic segments (p < 0.05). The ovarian fimbria was clearly identified, demonstrating the important relationship between these vessels and the FT fimbriae.

Conclusion

We believe that the vascularization in the fimbriae is greater than and disproportional that in the other segments of FT, and that the ovarian fimbria plays an important role in the development of that difference.

Quantification of the Whole Lymph Node Vasculature Based on Tomography of the Vessel Corrosion Casts

Lymph nodes (LN) are crucial for immune function, and comprise an important interface between the blood and lymphatic systems. Blood vessels (BV) in LN are highly specialized, featuring high endothelial venules across which most of the resident lymphocytes crossed. Previous measurements of overall lymph and BV flow rates demonstrated that fluid also crosses BV walls, and that this is important for immune function. However, the spatial distribution of the BV in LN has not been quantified to the degree necessary to analyse the distribution of transmural fluid movement. In this study, we seek to quantify the spatial localization of LNBV, and to predict fluid movement across BV walls. MicroCT imaging of murine popliteal LN showed that capillaries were responsible for approximately 75% of the BV wall surface area, and that this was mostly distributed around the periphery of the node. We then modelled blood flow through the BV to obtain spatially resolved hydrostatic pressures, which were then combined with Starling’s law to predict transmural flow. Much of the total 10 nL/min transmural flow (under normal conditions) was concentrated in the periphery, corresponding closely with surface area distribution. These results provide important insights into the inner workings of LN, and provide a basis for further exploration of the role of LN flow patterns in normal and pathological functions.

Combined ultrasound and nerve stimulator-guided deep nerve block may decrease the rate of local anesthetics systemic toxicity: a randomized clinical trial

Background

Ultrasound guidance might decrease the incidence of local anesthetics systemic toxicity (LAST) for many peripheral nerve blocks compared with nerve stimulator guidance. However, it remains uncertain whether ultrasound guidance is superior to nerve stimulator guidance for deep nerve block of the lower extremity. This study was designed to investigate whether deep nerve block with ultrasound guidance would decrease the incidence of LAST compared with that with nerve stimulator guidance, and to identify associated risk factors of LAST.

Methods

Three hundred patients undergoing elective lower limb surgery and desiring lumbar plexus blocks (LPBs) and sciatic nerve blocks (SNBs) were enrolled in this study. The patients were randomly assigned to receive LPBs and SNBs with ultrasound guidance (group U), nerve stimulator guidance (group N) or dual guidance (group M). The primary outcome was the incidence of LAST. The secondary outcomes were the number of needle redirection, motor and sensory block onset and nerve distribution restoration time, as well as associated risk factors.

Results

There were 18 patients with LAST, including 12 in group U, 4 in group N and 2 in group M. By multiple comparisons among the three groups, we found that the incidence of LAST in group U (12%) was significantly higher than that in group N (4%)(P = 0.037) and group M(2%)(P = 0.006). The OR of LAST with hepatitis B (HBV) infection and the female sex was 3.352 (95% CI,1.233–9.108, P = 0.013) and 9.488 (95% CI,2.142–42.093, P = 0.0004), respectively.

Conclusions

Ultrasound guidance, HBV infection and the female sex were risk factors of LAST with LPBs and SNBs. For patients infected with HBV or female patients receiving LPBs and SNBs, we recommended that combined ultrasound and nerve stimulator guidance should be used to improve the safety.

Trial registration

This study was approved by the Ethical Committee of the First Affiliated Hospital of Army Medical University. The protocol was registered prospectively with the Chinese Clinical Trial Registry (ChiCTR-IOR-16008099) on March 15, 2016.

Corrosion casting in anatomy: Visualizing the architecture of hollow structures and surface details

Corrosion casting is the technique by which a solid, negative replica is created from a hollow anatomical structure and liberated from its surrounding tissues. For centuries, different types of hardening substances have been developed to create such casts, but nowadays, thermosetting polymers are mostly used as casting medium. Although the principle and initial set-up are relatively easy, producing high-quality casts that serve their intended purpose can be quite challenging. This paper evaluates some of the more popular casting resins that are currently available and provides a step-by-step overview of the corrosion casting procedure, including surface casts of anatomical structures. Hurdles and pitfalls are discussed, along with possible solutions to circumvent them, based on personal experience by the authors.