Experimental Study On The Vascularity Of VX₂ Tumors In Rabbits With Contrasted Ultrasonography

Objective: It was designed to analyze the anatomical and pathological basis of the growing characteristics of the vascularity of rabbit VX2 tumors, and then, to evaluate the value of contrast enhanced color Doppler flowing imaging (CDFI), power Doppler imaging (PDI) and dynamic grey-scale enhanced ultrasonography in detecting tumor vascularity by using self-made perfluorocarbon gas filled albumin microbubbles. Methods: Twelve New Zealand rabbits with muscle VX2 tumors and twenty-four rabbits with hepatic VX₂ tumors were examined. The self-made contrast agent was administered through ear vein. The contrast agent was injected slowly and continuously when under CDFI and PDI screening, on the other hand, the contrast agent was bolus injected when screening grey-scale imaging. CDFI and PDI imaging before and after the injection of contrast agent were carefully observed under a HP5500 ultrasound system especially on the changes of the blood flow at the periphery and the inside of the muscle tumors, and then they were compared with the results of X-ray Digital Subtract Angiography. The vascular enhancement of hepatic VX₂ tumors after the injection of contrast agent was evaluated by using coherent contrast imaging (CCI) via a Sequoia-512 color Doppler ultrasound system. Meanwhile, blood vessel cast was proceeded to establish a three-dimensional model of liver VX₂ tumor. CDFI and PDI were imaged for the observation of blood perfusion of hepatic tumors. CD34 and vascular endothelial growth factor (VEGF) in were performed by immunohistochemistry method. Microvessel density (MVD) was counted and the expression levels of VEGF were analyzed. The results above were analyzed statistically. Results: 1. After the injection of contrast agent, there were significant improvements in detecting neovascularity of VX2 tumors under the mode of CDFI and PDI. The imaging of contrast Doppler ultrasonography and DSA were quite similar in demonstrating tumoral vascularity. 2. During the CCI contrast process, there appeared three dynamic phases sequentially including arterial phase, portal phase and parenchyma phase. Specific vascular enhancement of liver tumor emerged in 8 rabbits at the arterial phase, with network-like imaging of blood vessels with strong echo in the region of the tumor. Blood vessel cast showed that the hepatic artery was the nutrient arteries for the tumor lesion, with some branch arteries extending into the tumor, inside which anatomic arterial network could be seen as obviously as densely and disorderly. 3.Endothelium of the VX2 tumor vessels was positive to CD34 immunochemical staining, distributed as separated or concentrated cluster-like. Most of the CD34 positive cells concentrated at the surrounding of the lesions. There were significant difference in the MVD values between peri-tumor tissues and intratumor tissues (t=2.136,P<0.01). CD34 was not expressed in the normal liver tissues, while VEGF was weakly expressed or not expressed in the normal liver tissues, but expressed strongly inside the tumor tissues and at the surrounding tissues. MVD value in the VEGF strongly expressed group is significantly higher than that of VEGF weakly expressed group. There were no correlations between the results of CDFI and non-contrasted PDI and the MVD value, and the VEGF value. Graded blood signals in the tumor tissues under contrasted PDI was correlated with the value of MVD(r = 0.789, P<0.05), and also highly correlated with the expression of VEGF (r = 0.667, P<0.01). Conclusion : 1. Contrasted color Doppler ultrasonography may be a useful tool in the demonstration of tumor vascularity. Contrasted power Doppler imaging is much better than contrasted CDFI. 2. Blood vessel cast, which could reveal the tumor vascularity directly and clearly, could provide a reliable anatomical and morphological basis for the imaging evaluation on features of VX2 tumors vascularity. 3. Investigation of the MVD value and the expression of VEGF may help us understand the angiogenesis of tumor tissues, and that, they could also provide a pathological basis for the evaluation of tumor vascularity by ultrasonography. 4.New technology of contrasted ultrasonography (CCI) was helpful in the detection of tumor vascularity, it was also helpful in the evaluation on vascular type and features of tumor through the screening on vascular morphology and the changes of perfusion time phases. It is therefore of clinical importance to the diagnosis and differential diagnosis of tumor patients.5.The graded percentage of positive areas of the blood flow signals assessed by contrasted PDI can reflect the cancerous neoangiogenesis indirectly. It is suggested that contrast-enhanced power Doppler imaging may be helpful in evaluating the biological behavior of tumor and guiding the treatment or assessing prognosis.