Hepatic CT Perfusion Imaging: Experimental Studies And Application In The Evaluation Of Hepatocarcinomatous Hemodynamics

IntroductionPathological changes in microcirculation structure often lead to abnormalitie in tissue hemodynamics. It will be helpful for determining the property and severity of disease to monitor such changes. It has been proved by many researches that the structure of hepatic sinuses would change gradually from normal liver to cirrhosis and at last to hepatocarcinoma. It still demands further studies to clarify the corresponding relationship between such changes and the hemody-namic changes.CT perfusion imaging (CTPI) is a new functional imaging method which is based on the principle of calculating organ blood flow used in Nuclear Medcine. It can evaluate the hemodynamic status of microcirculation with the advantages of simplicity and precise quantification. Hepatic CT perfusion imaging can provide the hemodynamic parameters like hepatic arterial perfusion (HAP), portal venous perfusion (PVP) and hepatic arterial perfusion index in the region of interest. At present, slope method is generally adopted to calculate these parameters in clinic, but the limitation to contrast medium dosage and injection rate should be considered. Theoretically, the less the contrast medium dosage is and the higher the injection rate is, the more precise the results are. If the contrast medium is insufficient, the signal -noise ratio will be influenced. If the injection rate is excessively high, the contrast medium will exosmose easily. Therefore, a balance should be found.In order to solve the problems above, the following aspects were involved in this study: (1) An experimental study on influence of the contrast medium dosage and injection rate on hepatic CT perfusion imaging: the influence on the perfusion parameters was observed by changing the contrast medium dosage and injection rate, and the optimal condition was determined. (2) CT perfusion imaging of inductive hepatocarcinoma on rats: CTPI was performed on the rats during different stages of Diethylnitroamine ( DENA) induction. The regularity of liver hemodynamic changes during hepatocarcinoma evolution was discussed. (3) the application of CTPI in the evaluation of blood supply of hepatocarcinoma : CTPI was applied to the study on blood supply of hepatocarcinoma and its clinical significance was evaluated.Materials and MethodsPart I9 healthy adult dogs received anesthesia in the abdominal cavity. Regular plain scans of the upper abdomen were performed on a multi - slice CT machine. The slices of interest (SOI) were selected which should include the right hepatic lobe, the spleen, the portal vein and the aorta. Then, contrast medium was administered through a superficial vein in the hind limb with a power injector when single - location dynamic scans started with the SOI at the center. Each dosage of contrast medium (0. 5, 1 ml/kg of body weight) and each injection rate (3, 5, 7, 9ml/s) should be combined respectively in each contrast scanning. So 8 perfusion imagings under different conditions were performed on each dog. The raw data of the perfusion imaging were exported to a personal computer and HAP, PVP and HPI were calculated with dedicated perfusion software. The results were expressed as mean value and standard deviation, and two - way analysis of variance was performed. Part H105 male Wistar rats of 2 - 3 months old were randomized into four groups: A, B, Al and Bl. A was the cirrhosis group (35 rats). B was the hepatocarcinoma group {60 rats). Al was the control group of A (5 rats). Bl was the con-trol group of B (5 rats). Group A and group B were induced with lOOppm di-ethylnitroamine (DENA) water solution for 14 weeks and 20 weeks respectively. Group Al and group Bl were fed normally. Hepatic perfusion imaging was performed with 0.6ml of contrast medium and 0.2ml/s of injection rate, and the HAP, PVP and HPI of the whole liver were measured. After the perfusion imaging, the rats were sacrificed immediately for routine pathological examination. Perfusion parameters of each group were expressed as mean value and standard deviation, and one - way analysis of variance was performed. Partm26 patients who had received a definite diagnosis of hepatocarcinoma underwent CT perfusion imaging before interventional therapy. Perfusion parameters of the carcinoma focus, the tissue around it and the distant liver tissue were measured. Results were expressed as median and put to rank sum test with Wilcoxon method. Correlation between each perfusion parameters of the carcinoma focus and its diameter was assessed by Pearson correlation coefficient.ResultsPart I1. Hepatic perfusion parameters at different dosages and injection rates were successively measured in only 6 of the 9 dogs.2. When the dosage was 0.5 ml/kg of body weight, the HAP and PVP of 5, 7 and 9 ml/s groups showed significant difference from those of 3 ml/s group, but there was no significant difference of the HAP and PVP between 5, 7 and 9 ml/s groups. HPI showed a gradually descending tendency, but there was no significant difference between each group.3. When the dosage was 1 ml/kg of body weight, the HAP showed no significant difference between each group of injection rate. PVP ascended gradually with the increase of injection rate, but began to descend at the injection rate of 9 ml/s. HPI showed no obvious changes.Part IIThe HAP and HPI of the cirrhosis group and the hepatocarcinoma groupwere obviously higher than those of their control groups, and the PVPs were lower than their control groups. The HAP showed no significant difference between the cirrhosis group and the hepatocarcinoma group. But the PVP of the hepatocarcinoma group was lower and the HPI was higher. No significant difference was found in each perfusion parameter of the two control groups. Part III1. On the HAP images, all carcinoma foci showed hyperperfusion, obviously different from the distant liver tissue. On the PVP and TLP images, the carcinoma foci showed hypoperfusion. On the HPI images, the proportion of the arterial blood supply in the carcinoma focus was obviously higher than that in the distant liver tissue. The necrosis zone of the focal center showed hypoperfusion on both HAP and PVP images. As to the carcinoma focus with a clear edge, the demarcation from the adjacent tissue was distinct on HAP and PVP images. But to the focus with a blurring edge, there was no obvious demarcation from the adjacent tissue on HAP and PVP images, and its size was larger than that on raw images.2. The HAP and HPI of the carcinoma focus were obviously higher than those of the distant liver tissue, but the PVP and TLP were lower. The perfusion parameters of the tissue around the carcinoma focus with a clear edge showed no significant difference from those of the distant liver tissue. On the contrary, the tissue around the focus with a blurring edge showed changes similar to the carcinoma. Its HAP ascended obviously, twice higher than that of the distant liver tissue. And the PVP decreased. But the TLP showed no significant changes. All perfusion parameters of the hepatocarcinoma showed no obvious correlation with its diameter.Conclusion1. When slope method was adopted in hepatic CT perfusion imaging, the HAP and PVP would be influenced by the dosage of contrast medium and the injection rate while the HPI was relatively stable. In view of safety and accuracy, the dosage of 0. 5 ml/kg and the injection rate of 5 ml/s were the optimal condi-o .