Early Assessment Of Post-radiofrequency Ablation With Contrast-enhanced CT And CT Perfusion Imaging In A Rabbit Hepatic VX2Tumor Model

Objective：To prospectively assess both contrast-enhanced computertomography(CT) and CT perfusion for evaluation of radiography signs in VX2liver carcinomas in rabbits after radiofrequency ablation therapy, andcontrast with the pathology to evaluate the value of clinical application.Materials and Methods: Twenty-eight healthy rabbits were assigned into4groups (named A, B, C, D),7rabbits each group. The hepatic VX2tumor modelswere made in the method of direct inoculation, and all rabbits underwent thecontrast-enhanced CT scan15days after the modeling, and then14rabbits wereselected randomly to do CT perfusion scan. All the28rabbits were undergoneopen radiofrequency ablation treatments soon after the CT scan completed. Didcontrast-enhanced CT and CT perfusion scan respectively to four groups ofpostoperative RFA rabbits on day1(group A), day3(group B), day7(groupC) and day14(group D). All rabbits in each group were euthanized afterexamination, and pathological specimens were taken and Hematein-Eosinpathologic evaluation was performed. The imaging findings of each lesion onthree-periods enhanced CT and CT perfusion imaging were observed, Perfusionparameters of blood flow (BF),blood volume (BV), time to peak (TTP), permeability (P), arterial liver perfusion (ALP), portal vein perfusion (PVP)and hepatic perfusion index (HPI) in pretherapeutic tumor rim, peripheral rimof ablated lesion in4groups, and residual or recurrence tumor were analyzed,and the character of the time density curve (TDC) and the color maps ofperfusion parameters were evaluated combined with pathology findings.Result:1. All of the twenty-eight VX2hepatic tumor model in rabbits weremade and done the radiofrequency ablation therapy successfully. Twenty-sixof them underwent the post-RFA enhanced CT and CT perfusion examination (tworabbits in14day group died), and six residual or recurrence tumor wereconfirmed by pathology.2. Results of enhanced CT:(1) Inflammatory reaction rim around the ablationlesion was noted as a thickness uniform peripheral rim-like enhancement inCT images, and the degree of enhancement was at its peak in day3and day7,and reduced obviously in day14. The residual/recurrence was noted as a lunateor nodular lesion which abnormal enhanced in arterial-phase CT images andwashed out quickly on portal vein phase.(2) Excepted the CT value on delayphase in group of14d after RFA therapy, There had no statistically significantdifference (P>0.05) on every enhanced phase between residual/recurrence andinflammatory reaction rim. There were no statistically significantdifferences between pretherapeutic tumor rim and inflammatory reaction rimin CT value on all three phases of post-RFA enhanced CT in1d and3d groups,but it had lower CT value in inflammatory reaction area compared withpretherapeutic tumor rim on portal vein phase in7d group and all there phasesin14dgroup, which had statistically significant differences (P<0.05).3. Time density curve in CT perfusion: The TDC in the pretherapeutic tumorrim, inflammatory reaction rim and residual/recurrence tumor showed different characteristics. The main type of TDC in pretherapeutic tumor rim isspeed-ascend and slow-descend (6/14), and the speed-ascend and plateau TDCtype was mainly in inflammatory reaction rim. The TDC of residual/recurrencetumor were composed mainly of speed-ascend and speed-descend (3/6) andspeed-ascend and plateau types.4. CT Perfusion parameters: The perfusion parameter PVP of inflammatoryreaction rim in all post-RFA groups were higher than residual/recurrence tumor,and the parameter HPI lower than residual/recurrence tumor. A significantdifference (P <0.01) was observed in mean values of both PVP and HPI. Allof the perfusion parameters in every post-RFA group had no significantdifference between inflammatory reaction rim and pretherapeutic tumor rim inthe group of1d and3d after RFA treatment, and the perfusion parameter PVPin7d group and the parameter BF, BV and ALP in14d group of inflammatoryreaction rim were lower than the value of pretherapeutic tumor rim, which hada significant difference (P<0.05).5. Pathological changes after RFA: It was showed that there were ablation tumor,ablation liver parenchyma, inflammatory reaction/fibrous tissue, hepatic celledema area and normal hepatic cell area observed in turn by the center ofablation lesion to peripheral area in pathology, and residual/recurrence tumorcould be existed on the edge of inflammatory reaction rim.Conclusion:1. Model of hepatic VX2tumor after RFA in rabbits can besuccessfully made, and the blood supply characteristics were alike thehepatocellular carcinoma in human.2. With the contrast-enhanced CT, it is hard to distinguish theresidual/recurrence tumor from inflammatory reaction area in the early stage(in a week) after RFA therapy only by measuring CT value.3. It can be effectively differentiate residual/recurrence tumor from inflammatory reaction around ablation zone by the perfusion parameters of PVPand HPI in the early stage (in a week) after RFA therapy, and the result ishighly coincident with the pathology. Therefore, CT perfusion imaging has alarge advantage in the early detection of residual/recurrent tumor after RFAtherapy.