| PurposeTo investigate MR imaging of HCC on plain and SPIO-enhanced MRI in rats, so as to clarify the pathologic basis of SPIO-enhanced MRI that is useful for estimation of histological grading in HCC, and to improve the detection rate and diagnostic accuracy of HCC.Materials and methods1. Ninety male rats of Wistar were divided into two groups randomly, 80 were test group and 10 were control group. Diethylnitrosamine(DEN) was dissolved in saline at a concentration of 2‰.This solution was fed to the test group during the first 14 weeks and substituted with normal drinking water afterward. The control group was fed with same amount of saline. 2. The test group received MR examinations in 16, 18, 20, 21, 22, 23, 24, 25 week. Seventy-eight nodules of 39 rats were studied.3. Before imaging, a catheter was inserted into external jugular vein of rat, then MR imaging was performed before and after SPIO injection using SE-T1WI, FMPSPGR-T1WI, GRE-T2WI, FSE-PDWI, FSE-T2WI, and the relative parameters were obtained.4. Rats were killed as soon as MRI finished, to match with the lesions seen on the MRI, tumors were observed grossly and drew for pathologic examination. All specimens were stained with HE and PerIs, and the degree of differentiation of tumorous tissues was determined, the number of Kupffer cell in tumorous and nontumorous tissues was counted.Results1. HCC developed in 39 rats, which were alive at test time. Of the 78 HCCs selected for study, 22 were well differentiated, 31 moderately differentiated and 25 poorly differentiated.2. Kupffer cells numbers in HCCs were significantly smaller than in liver tissues (P<0.01), and were correlated with the histological grading. Well differentiated HCCs had the most Kupffer cell number and the highest Kupffer-cell-count ratio, while poorly differentiated HCCs had the fewest Kupffer cell number and the lowest Kupffer-cell-count ratio. The Kupffer-cell-count ratio of well differentiated HCC was significantly difference from that of moderately or poorly differentiated HCC (P<0.01), there was no statistical difference between moderately differentiated and poorly differentiated HCC.3. Well differentiated HCC tended to be isointense on T1-, T2-weighted imaging; Moderately differentiated HCC was isointense or hypointense on T1-weighted imaging and isointense or hyperintense on T2-weighted imaging; Poorly differentiated HCC was mostly hypointense on T1-weighted imaging and hyperintense or heterogeneous intense on T2-weighted imaging. The signal patterns of well differentiated HCC were significantly different from the poorly differentiated(P<0.05).4. After SPIO enhancement, the signal intensity of liver decreased in all sequences, the signal intensity loss of liver and the CNR of HCC in GRE-T2WI was significantly greater than those in other sequences, and the SNR of HCC or liver in FSE-PDWI was significantly higher than that in other sequences. GRE-T2WI and FSE-PDWI were the sequences of choice in SPIO-enhanced MRI .5. The SIRSPIO of HCC was correlated with the histological grading and the Kupffer-cell-count ratio, SIRSPIO of well differentiated HCCs was significantly lower than those of moderately and poorly differentiated HCCs, while Kupffer-cell-count ratio of well differentiated HCCs was significantly higher than those of moderately and poorly differentiated HCCs, there was no statistical difference between moderately and poorly differentiated HCCs.6. SPIO-enhanced MRI detected more small lesions (below 4㎜ in diameter) than plain MRI. Conclusions1. HCC can be induced chronically with low dose of DEN in rats, the HCC model is ideal model for imaging study.2. The number of Kupffer cell in HCC was less than those in liver tissue, and decreased as the HCCs became less well differentiated. 3. The signal patterns on plain MRI can reflect the histological grading of HCC. 4. In SPIO-enhanced MRI, GRE-T2WI and FSE-PDWI were the sequences of choice.5. The SIRSPIO of HCC was correlated well with the histological grading and the Kupffer cel...
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