Assessment of liver function in thioacetamide-induced rat acute liver injury using an empirical mathematical model and dynamic contrast-enhanced MRI with Gd-EOB-DTPA

Preclinical magnetic resonance imaging and spectroscopy in the fields of radiological technology, medical physics, and radiology

Magnetic resonance imaging (MRI) is an indispensable diagnostic imaging technique used in the clinical setting. MRI is advantageous over X-ray and computed tomography (CT), because the contrast provided depends on differences in the density of various organ tissues. In addition to MRI systems in hospitals, more than 100 systems are used for research purposes in Japan in various fields, including basic scientific research, molecular and clinical investigations, and life science research, such as drug discovery, veterinary medicine, and food testing. For many years, additional preclinical imaging studies have been conducted in basic research in the fields of radiation technology, medical physics, and radiology. The preclinical MRI research includes studies using small-bore and whole-body MRI systems. In this review, we focus on the animal study using small-bore MRI systems as "preclinical MRI". The preclinical MRI can be used to elucidate the pathophysiology of diseases and for translational research. This review will provide an overview of previous preclinical MRI studies such as brain, heart, and liver disease assessments. Also, we provide an overview of the utility of preclinical MRI studies in radiological physics and technology.

In vivo liver function reserve assessments in alcoholic liver disease by scalable photoacoustic imaging

We present a rapid and high-resolution photoacoustic imaging method for evaluating the liver function reserve (LFR). To validate its accuracy, we establish alcoholic liver disease (ALD) models and employ dual-wavelength spectral unmixing to assess oxygen metabolism. An empirical mathematical model fits the photoacoustic signals, obtaining liver metabolism curve and LFR parameters. Liver oxygen metabolism significantly drops in ALD with the emergence of abnormal hepatic lobular structure. ICG half-life remarkably extends from 241 to 568 s in ALD. A significant decline in LFR occurs in terminal region compared to central region, indicated by a 106.9 s delay in ICG half-life, likely due to hepatic artery and vein damage causing hypoxia and inadequate nutrition. Reduced glutathione repairs LFR with a 43% improvement by reducing alcohol-induced oxidative damage. Scalable photoacoustic imaging shows immense potential for assessing LFR in alcoholic-related diseases, providing assistance to early detection and management of liver disease.

In vivo quantitative photoacoustic evaluation of the liver and kidney pathology in tyrosinemia

Hereditary tyrosinemia type Ⅰ (HT1) is a severe autosomal recessive inherited metabolic disease, which can result in severe damage of liver and kidney. Photoacoustic imaging (PAI) uses pulsed laser light to induce ultrasonic signals to facilitate the visualization of lesions that are strongly related to disease progression. In this study, the structural and functional changes of liver and kidney in HT1 was investigated by cross-scale PAI. The results showed that the hepatic lobule and renal tubule were severely damaged during HT1 progression. The hemoglobin content, vessel density, and liver function reserve were decreased. The metabolic half-life of indocyanine green declined from 59.8 s in health to 262.6 s in the advanced stage. Blood oxygen saturation was much lower than that in health. This study highlights the potential of PAI for in vivo evaluation of the liver and kidney lesions in HT1.

Quantitative Functional Evaluation of Liver Fibrosis in Mice with Dynamic Contrast-enhanced Photoacoustic Imaging

Background Dynamic contrast-enhanced (DCE) photoacoustic (PA) imaging (PAI) is a novel noninvasive imaging modality that uses the differences in optical absorption of oxyhemoglobin and deoxyhemoglobin and may be performed in a dynamic fashion to image the indocyanine green (ICG) pharmacokinetics in the liver. Purpose To determine whether DCE PAI parameters (maximum peak time [T_max] and half-life [T_1/2]) derived from the PA liver function curve correlate with fibrosis determined using histopathologic analysis. Materials and Methods Between June 2020 and October 2020, 28 male mice aged 8 weeks were intraperitoneally injected with carbon tetrachloride solution every 2 days to establish a liver fibrosis model. At the 1st, 4th, and 8th week of modeling, the changes in liver structure were monitored dynamically by using a PA technique. The T_max and T_1/2 of ICG were calculated at different pathologic stages and within a control group. Corresponding liver histopathologic results and blood biochemical data were obtained. Spearman rank correlation was used to evaluate the relationship between the DCE PAI results and histologic scores. Results The PA liver function curve showed that the T_max and T_1/2 varied among groups (mean T_max: control group, 9 seconds ± 1.8 [standard deviation]; 1 week, 51 seconds ± 4.4; 4 weeks, 73 seconds ± 5.3; 8 weeks, 104 seconds ± 6.6; P < .001) (mean T_1/2: control group, 28 seconds ± 6.5; 1 week, 201 seconds ± 12.4; 4 weeks, 285 seconds ± 11; 8 weeks, 318 seconds ± 30.5; P < .001). There was a positive correlation between the dynamic parameters (T_max and T_1/2) and the histopathologic scores; the Spearman ρ ratios for the Sirius red and α-smooth muscle actin (αSMA)-positive areas versus the T_max were 0.93 and 0.94 (P < .001 for both), and the Spearman ρ ratios for the Sirius red and αSMA-positive areas versus T_1/2 were 0.87 and 0.89 (P < .001 for both). Conclusion Dynamic contrast-enhanced photoacoustic imaging demonstrated a higher maximum peak time and half-life in mice with induced fibrosis compared with control mice without fibrosis, and these values correlated with histologic measures of fibrosis. © RSNA, 2021 Online supplemental material is available for this article.

Liver-Targeted siRNA Lipid Nanoparticles Treat Hepatic Cirrhosis by Dual Antifibrotic and Anti-inflammatory Activities

Previous studies on the treatment of hepatic cirrhosis have been focusing on how to inhibit liver fibrosis, while ignoring liver inflammation, a key and underlying factor that promotes cirrhosis. High mobility group box-1 (HMGB1) protein, a pro-inflammatory factor and fibroblast chemokine, can promote the proliferation of hepatic stellate cells (HSCs) and the development of hepatic inflammation and fibrosis, playing a key role in cirrhosis formation. In this study, we prepared pPB peptide (C*SRNLIDC*)-modified and HMGB1-siRNA-loaded stable nucleic acid lipid nanoparticles (HMGB1-siRNA@SNALP-pPB) to effectively treat hepatic cirrhosis by their dual antifibrotic and anti-inflammatory activities. The pPB peptide-modified and heat shock protein 47 (HSP47)-siRNA-loaded stable nucleic acid lipid nanoparticles (HSP47-siRNA@SNALP-pPB), which have only an antifibrotic effect without an anti-inflammatory effect, was used as control. The results demonstrated that HMGB1-siRNA@SNALP-pPB were actively targeted to HSCs by the mediation of pPB peptide, effectively silenced the HMGB1 gene, inhibited the activation and proliferation of HSCs, reduced the release of HMGB1 protein, inhibited collagen deposition and fibrosis formation in the liver, and significantly prolonged the survival time of cirrhotic mice models. HMGB1-siRNA@SNALP-pPB showed a stronger therapeutic effect on liver cirrhosis than HSP47-siRNA@SNALP-pPB. This study provides an actively targeted siRNA delivery system for cirrhosis treatment based on the dual antifibrotic and anti-inflammatory effects. In addition, this study clarified the role of inflammatory problems in cirrhosis treatment in addition to liver fibrosis, providing a useful idea and scientific basis for the development of cirrhosis treatment strategies in the future.

Chemical induction of hepatic apoptosis in rodents

The urge of identifying new pharmacological interventions to prevent or attenuate liver injury is of critical importance and needs an expanded experimental toolbox. Hepatocyte injury and cellular death is a prominent feature behind the pathology of liver diseases. Several research activities focused on identifying chemicals and hepatotoxicants that induce cell death by apoptosis, in addition to presenting its corresponding signaling pathway. Although such efforts provided further understanding of the mechanisms of cell death, it has also raised confusion concerning identifying the involvement of several modes of cell death including apoptosis, necrosis and fibrosis. The current review highlights the ability of several chemicals and potential hepatotoxicants to induce liver damage in rodents by means of apoptosis while the probable involvement of other modes of cell death is also exposed. Thus, several chemical substances including hepatotoxins, mycotoxins, hyperglycemia inducers, metallic nanoparticles and immunosuppressant drugs are reviewed to explore the hepatic cytotoxic spectrum they could exert on hepatocytes of rodents. In addition, the current review address the mechanism by which hepatotoxicity is initiated in hepatocytes in different rodents aiding the researcher in choosing the right animal model for a better research outcome.

A multi-center preclinical study of gadoxetate DCE-MRI in rats as a biomarker of drug induced inhibition of liver transporter function

Drug-induced liver injury (DILI) is a leading cause of acute liver failure and transplantation. DILI can be the result of impaired hepatobiliary transporters, with altered bile formation, flow, and subsequent cholestasis. We used gadoxetate dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), combined with pharmacokinetic modelling, to measure hepatobiliary transporter function in vivo in rats. The sensitivity and robustness of the method was tested by evaluating the effect of a clinical dose of the antibiotic rifampicin in four different preclinical imaging centers. The mean gadoxetate uptake rate constant for the vehicle groups at all centers was 39.3 +/- 3.4 s^-1 (n = 23) and 11.7 +/- 1.3 s^-1 (n = 20) for the rifampicin groups. The mean gadoxetate efflux rate constant for the vehicle groups was 1.53 +/- 0.08 s^-1 (n = 23) and for the rifampicin treated groups was 0.94 +/- 0.08 s^-1 (n = 20). Both the uptake and excretion transporters of gadoxetate were statistically significantly inhibited by the clinical dose of rifampicin at all centers and the size of this treatment group effect was consistent across the centers. Gadoxetate is a clinically approved MRI contrast agent, so this method is readily transferable to the clinic. Conclusion: Rate constants of gadoxetate uptake and excretion are sensitive and robust biomarkers to detect early changes in hepatobiliary transporter function in vivo in rats prior to established biomarkers of liver toxicity.

Quantitative T1, T2, and T2* Mapping and Semi-Quantitative Neuromelanin-Sensitive Magnetic Resonance Imaging of the Human Midbrain

Purpose

Neuromelanin is a dark pigment granule present within certain catecholamine neurons of the human brain. Here, we aimed to clarify the relationship between contrast of neuromelanin-sensitive magnetic resonance imaging (MRI) and MR relaxation times using T₁, T₂, and T₂* mapping of the lower midbrain.

Methods

The subjects were 14 healthy volunteers (11 men and 3 women, mean age 29.9 ± 6.9 years). Neuromelanin-sensitive MRI was acquired using an optimized T₁-weighted two-dimensional (2D)-turbo spin-echo sequence. To quantitatively evaluate the relaxation time, 2D-image data for the T₁, T₂, and T₂* maps were also acquired. The regions of interest (substantia nigra pars compacta [SNc], superior cerebellar peduncles [SCP], cerebral peduncles [CP], and midbrain tegmentum [MT]) were manually drawn on neuromelanin-sensitive MRI to measure the contrast ratio (CR) and on relaxation maps to measure the relaxation times.

Results

The CR in the SNc was significantly higher than the CRs in the SCP and CP. Compared to the SCP and CP, the SNc had significantly higher T₁ relaxation times. Moreover, the SNc had significantly lower T₂ and T₂* relaxation times than the other three regions (SCP, CP, and MT). Correlation analyses showed no significant correlations between the CRs in the SNc, SCP, and CP and each relaxation time.

Conclusions

We demonstrated the relationship between the CR of neuromelanin-sensitive MRI and the relaxation times of quantitative maps of the human midbrain.

Hepatic Phospholipidosis Is Associated with Altered Hepatobiliary Function as Assessed by Gadoxetate Dynamic Contrast–enhanced Magnetic Resonance Imaging

To determine if amiodarone induces hepatic phospholipidosis (PLD) sufficient to detect changes in hepatobiliary transporter function as assessed by gadoxetate dynamic contrast–enhanced magnetic resonance imaging (DCE-MRI), rats were orally dosed with vehicle (1% methyl cellulose) or amiodarone (300 mg/kg/day) for 7 consecutive days. Gadoxetate DCE-MRI occurred at baseline, day 7, and following a 2-week washout of amiodarone. At day 7, the gadoxetate washout rate was significantly decreased compared to the vehicle group. Blood chemistry analysis revealed no significant changes in liver enzymes (alanine aminotransferase [ALT]/aspartate aminotransferase [AST]/alkaline phosphatase [ALP]), bilirubin, or bile acids between vehicle or amiodarone groups. Hepatic PLD was confirmed in all rats treated with amiodarone at day 7 by transmission electron microscopy. Following the 2-week washout, there was no ultrastructural evidence of hepatic PLD in rats and the gadoxetate washout rate returned to baseline levels. This is the first study to show the application of gadoxetate DCE-MRI to detect hepatobiliary functional changes associated with PLD and offer a potential new technique with clinical utility in patients suspected of having PLD. These results also suggest PLD itself has functional consequences on hepatobiliary function in the absence of biomarkers of toxicity, given the cause/effect relationship between PLD and function has not been fully established.

Usefulness of two-point Dixon fat-water separation technique in gadoxetic acid-enhanced liver magnetic resonance imaging

AIM: To compare differences between volumetric interpolated breath-hold examination (VIBE) using two-point Dixon fat-water separation (Dixon-VIBE) and chemically selective fat saturation (FS-VIBE) with magnetic resonance imaging examination.

METHODS: Forty-nine patients were included, who were scanned with two VIBE sequences (Dixon-VIBE and FS-VIBE) in hepatobiliary phase after gadoxetic acid administration. Subjective evaluations including sharpness of tumor, sharpness of vessels, strength and homogeneity of fat suppression, and artifacts that were scored using a 4-point scale. The liver-to-lesion contrast was also calculated and compared.

RESULTS: Dixon-VIBE with water reconstruction had significantly higher subjective scores than FS-VIBE in strength and homogeneity of fat suppression (< 0.0001) but lower scores in sharpness of tumor (P < 0.0001), sharpness of vessels (P = 0.0001), and artifacts (P = 0.034). The liver-to-lesion contrast on Dixon-VIBE images was significantly lower than that on FS-VIBE (16.6% ± 9.4% vs 23.9% ± 12.1%, P = 0.0001).

CONCLUSION: Dixon-VIBE provides stronger and more homogenous fat suppression than FS-VIBE, while has lower clarity of focal liver lesions in hepatobiliary phase after gadoxetic acid administration.

Assessing liver function in patients with HBV-related HCC: a comparison of T₁ mapping on Gd-EOB-DTPA-enhanced MR imaging with DWI

OBJECTIVES

To compare the potential of T1 mapping on gadoxetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance imaging (MRI) and diffusion-weighted imaging (DWI) for assessing liver function in patients with hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC).

METHODS

One hundred consecutive patients with known HBV-related HCCs were included. T1 relaxation time and apparent diffusion coefficient (ADC) of the liver were measured, and the reduction rate of T1 relaxation time (∆%) was calculated. T1 relaxation time measurements were compared with ADC values according to the Model for End-Stage Liver Disease (MELD) score.

RESULTS

Hepatobiliary phase (HBP) and ∆% of T1 relaxation time measurements showed significant correlations with MELD score (rho = 0.571, p < 0.0001; rho = -0.573, p < 0.0001, respectively). HBP and ∆% of T1 relaxation time were significantly different between good (MELD ≤8) and poor liver function (MELD ≥9) (p < 0.0001 for both). Areas under the receiver operating characteristic curves (AUCs) of T1 relaxation time for HBP (AUC 0.84) and ∆% (AUC 0.82) were significantly better than for ADC (AUC 0.53; p < 0.0001).

CONCLUSIONS

T1 mapping on Gd-EOB-DTPA-enhanced MRI showed promise for evaluating liver function in patients with HBV-related HCC, while DWI was not reliable. HBP T1 relaxation time measurement was equally accurate as ∆% measurement.

KEY POINTS

• T 1 mapping on Gd-EOB-DTPA MRI was accurate for assessing liver function. • HBP T 1 relaxation time measurement was as accurate as ∆% T 1 • T 1 mapping on Gd-EOB-DTPA MRI was more accurate than DWI-ADC measurement.