In vivo preclinical PET/CT imaging of carbon-11-labeled aminoglycerol probe for the diagnosis of liver fibrosis

Staging Liver Fibrosis by Fibroblast Activation Protein Inhibitor PET in a Human-Sized Swine Model

Current methods of staging liver fibrosis have notable limitations. We investigated the utility of PET in staging liver fibrosis by correlating liver uptake of ⁶⁸Ga-labeled fibroblast activation protein inhibitor (FAPI) with histology in a human-sized swine model. Methods: Five pigs underwent baseline ⁶⁸Ga-FAPI-46 (⁶⁸Ga-FAPI) PET/MRI and liver biopsy, followed by liver parenchymal embolization, 8 wk of oral alcohol intake, endpoint ⁶⁸Ga-FAPI PET/MRI, and necropsy. Regions of interest were drawn on baseline and endpoint PET images, and SUV_mean was recorded. At the endpoint, liver sections corresponding to regions of interest were identified and cut out. Fibrosis was histologically evaluated using a modified METAVIR score for swine liver and quantitatively using collagen proportionate area (CPA). Box-and-whisker plots and linear regression were used to correlate SUV_mean with METAVIR score and CPA, respectively. Results: Liver ⁶⁸Ga-FAPI uptake strongly correlated with CPA (r = 0.89, P < 0.001). ⁶⁸Ga-FAPI uptake was significantly and progressively higher across F2 and F3/F4 fibrosis stages, with a respective median SUV_mean of 2.9 (interquartile range [IQR], 2.7-3.8) and 7.6 (IQR, 6.7-10.2) (P < 0.001). There was no significant difference between ⁶⁸Ga-FAPI uptake of baseline liver and endpoint liver sections staged as F0/F1, with a respective median SUV_mean of 1.7 (IQR, 1.3-2.0) and 1.7 (IQR, 1.5-1.8) (P = 0.338). Conclusion: The strong correlation between liver ⁶⁸Ga-FAPI uptake and the histologic stage of liver fibrosis suggests that ⁶⁸Ga-FAPI PET can play an impactful role in noninvasive staging of liver fibrosis, pending validation in patients.

Liver Fibrosis Assessment by Viewing Sinusoidal Capillarization: US Molecular Imaging versus Two-dimensional Shear-Wave Elastography in Rats

Background US elastography is a first-line assessment of liver fibrosis severity; however, its application is limited by its insufficient sensitivity in early-stage fibrosis detection and its measurements are affected by inflammation. Purpose To assess the sensitivity of US molecular imaging (USMI) in early-stage liver fibrosis detection and to determine whether USMI can specifically distinguish fibrosis regardless of inflammation when compared with two-dimensional (2D) shear-wave elastography (SWE). Materials and methods USMI and 2D SWE were performed prospectively (January to June 2021) in 120 male Sprague-Dawley rats with varying degrees of liver fibrosis and acute hepatitis and control rats. Liver sinusoidal capillarization was viewed at CD34-targeted USMI and quantitatively analyzed by the normalized intensity difference (NID). Data were compared by using a two-sided Student t test or one-way analysis of variance. Linear correlation analyses were used to evaluate the relationships between collagen proportionate area values and NID and liver stiffness measurement (LSM) values. Receiver operating characteristic curves were used to assess the diagnostic performance in detecting liver fibrosis. Results Both NID and LSM values showed good linear correlation with collagen proportionate area values (r = 0.91 and 0.87, respectively). No difference was observed between the areas under the receiver operating characteristic curve in detecting stage F0-F1 between USMI and 2D SWE (0.97 vs 0.91, respectively; P = .20). USMI depicted liver fibrosis at an early stage more accurately than 2D SWE (area under the curve, 0.97 vs 0.82, respectively; P = .01). Rats with hepatitis had higher liver stiffness values than control rats (9.83 kPa ± 0.79 vs 6.55 kPa ± 0.38, respectively; P < .001), with no difference in the NID values between control rats and rats with hepatitis (6.75% ± 1.43 vs 6.74% ± 0.86, respectively; P = .98). Conclusion Sinusoidal capillarization viewed at US molecular imaging helped to detect early-stage liver fibrosis more accurately than two-dimensional shear-wave elastography and helped assess fibrosis regardless of inflammation. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Barr in this issue.

Recent Progress in the Molecular Imaging of Nonalcoholic Fatty Liver Disease

Pathological fibrosis of the liver is a landmark feature in chronic liver diseases, including nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). Diagnosis and assessment of progress or treatment efficacy today requires biopsy of the liver, which is a challenge in, e.g., longitudinal interventional studies. Molecular imaging techniques such as positron emission tomography (PET) have the potential to enable minimally invasive assessment of liver fibrosis. This review will summarize and discuss the current status of the development of innovative imaging markers for processes relevant for fibrogenesis in liver, e.g., certain immune cells, activated fibroblasts, and collagen depositions.