Diffusion MRI alteration following the induction of mild liver fibrosis in a rabbit model
Matteo Figini1, Liang Pan1,2, Chong Sun1,3, Bin Wang1,4, Junjie Shangguan1, Kang Zhou1,5, Na Shang1, Quanhong Ma1, and Zhuoli Zhang1

1Radiology, Northwestern University, Chicago, IL, United States, 2Radiology, The Third Affiliated Hospital of Soochow University, Changzhou, China, 3Orthopedics, Qilu Hospital, Shandong University, Jinan, China, 4General Surgery, Nanfang Hospital, Southern Medical University, Guangzhou, China, 5Radiology, Peking Union Medical College Hospital, Chinese Academy of Medical Science and Peking Union Medical College, Beijing, China


Nine rabbits were injected with carbon tetrachloride for 6 weeks to induce liver fibrosis. At the end of this period, these rabbits and 15 controls injected with saline underwent an imaging protocol including diffusion MRI. Histology showed mild fibrosis throughout the liver of the CCl4-injected animals. The Apparent Diffusion Coefficient in the liver of the fibrotic rabbits was significantly higher than in the controls. This counterintuitive result can be explained by the presence of many conflicting mechanisms during the early stage of fibrosis. If confirmed, the ADC could become a valuable tool for the early detection of liver fibrosis .


Liver fibrosis is reversible in its early stages, whereas advanced liver fibrosis can lead to cirrhosis, liver failure, portal hypertension, and liver cancer, which often requires liver transplantation as a life-saving procedure. Therefore, early diagnosis of liver fibrosis is essential for treatment and prognosis. The gold-standard technique for the staging of liver fibrosis, which has several disadvantages: it is invasive, sometimes associated with pain and even major complications, and it suffers from sampling errors and inter-observer variability. MRI techniques have been proposed for the assessment and staging of liver fibrosis, with contradictory results1-4. Here we report Diffusion MRI results in a rabbit model of liver fibrosis.


Nine healthy New Zealand white rabbits (Experimental Animal Center of Lanzhou University) received weekly subcutaneous injections comprising 50% carbon tetrachloride (CCl4) in oily solution for 6 weeks (0.1 ml/kg for the first 3 weeks, 0.2 ml/kg from 4th to 6th week) in the neck and back. Fifteen control rabbits received subcutaneous injections with the same amount of normal saline solution instead. MRI was performed at the end of the 6 weeks on a 3 T clinical MR unit (Verio 3.0T, Siemens Medical Solutions, Erlangen, Germany) with a 32-channel head phased-array coil. Before being imaged, rabbits were anesthetized with intramuscular administration of 0.3 mL per kilogram of body weight of 2% xylazine hydrochloride and 30 mg/kg of ketamine hydrochloride. After a T2-weighted turbo spin-echo sequence for anatomical reference (TR/TE = 4000/30 ms, FOV = 210 x 210 mm2, matrix = 256 x 256, slice thickness = 4 mm), Diffusion-weighted images were acquired (TR/TE = 6600/100 ms, FOV = 210 x 210 mm2, matrix = 192 x 192, slice thickness = 4 mm) with 3 orthogonal directions of the diffusion-sensitizing gradients and 3 degrees of diffusion weighting: b = 0, 200, 500 s/mm2

Regions of interest (ROIs) were delineated in the liver parenchyma paying attention to avoid vessels and other structures. The diffusion-weighted signal was averaged in each ROI and a mono-exponential model was fitted to it using a custom code in Matlab (Mathworks, Natick, MA, USA) to compute the Apparent Diffusion Coefficient (ADC). The resulting ADC values were compared between fibrotic and control animals. Histologic slices were excised from the left lateral, right lateral, and medium lateral liver lobes of each rabbit, properly processed and stained for Masson's trichrome staining to identify collagen tissue.


The ADC values obtained in the fibrotic rabbits after 6 weeks of CCl4 injections were much higher than those obtained in control rabbits, as shown in the boxplots in figure 1. The difference between the two groups was statistically significant according to an unpaired two-tail t-test (p<10-6). Representative histology slides are represented in figure 2, showing a mild degree of fibrosis in the treated rabbits compared to the controls.


This study shows a dramatic ADC increase in the liver of rabbits with mild fibrosis. This result is unexpected, because fibrosis would be more intuitively associated with slow diffusion because of the presence of collagen fibers. However, this interpretation may be too simplistic and many other factors may influence the ADC, such as the total water content, inflammation, the presence of fat and iron, etc.5-6 Previous studies generally reported a poor correlation between diffusion MRI parameters and liver fibrosis, and they often focused on later stages. Our results certainly need to be confirmed, validated and understood more thoroughly, but they could be important to provide a non-invasive imaging tool for liver fibrosis detection at an early stage.


This work was supported by grants R01CA196967 and R01CA209886 funded by the USA National Cancer Institute (National Institutes of Health)


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Boxplots showing the ADC values for the control (left) and mild fibrosis (right) group. The red horizontal line is the median, the upper and lower limits of the blue box are the first (Q1) and third (Q3) quartile, respectively. The upper and lower whiskers reach the minimum data point above Q1-1.5(Q3-Q1) and the maximum below Q3+1.5(Q3-Q1) respectively; the data out of this range are considered as outliers and represented as red crosses

Masson trichrome–stained histologic slices excised from normal and 6-week rabbit livers during the pathogenesis of CCl4-induced hepatic fibrosis. (Original magnification, ×80.). Histologic slices show normal liver tissue (left) and liver tissue with CCl4-induced mild fibrosis (right).

Proc. Intl. Soc. Mag. Reson. Med. 26 (2018)