USPIO增强微血管成像新技术评价肝癌新生血管功能和形态异质性的实验研究

Hepatocellular carcinoma(HCC) is a hypervascular tumor. Tumor angiogenesis can be used to monitor its biological behavior and evaluate tumor response to therapeutic interventions. Perfusion MRI is one of the most frequently used techniques to assess the micro-vascular function of HCC. However,it does not provide morphological information on micro-vessel diameter and density. To date, most of these studies have been performed with low-molecular-weight gadolinium chelates, which readily pass through the endothelium of angiogenic vessels. Their enhancement is nonspecific which hinders the accurate assessment of the micro-vascular function. As a result current perfusion MRI is sub-optimal for comprehensive and accurate evaluation of micro-vascular heterogeneity of HCC both before and after anti-angiogenesis. USPIO is a macromolecular blood pool contrast agent which is more selective for tumor-induced angiogenesis than low-molecular weight gadolinium because of its reduced leakage. It markedly shortens the T1 value of the tissue and has a good susceptibility effect. By exploiting these characteristics of USPIO, we will integrate dynamic perfusion MRI and steady-state vessel size imaging after infusion of self-made USPIO particle in human HCC model in nude mice. Our purposes are to improve MRI's accuracy in the evaluation of micro-vascular function of HCC, as well as to provide morphological information on tumor micro-vessel diameter and density. Being compared with pathology and immunohistochemistry, the relevance or complementary relationship between these functional and morphological biomarkers will be established. The imaging biomarkers, before and after anti-angiogenesis, which most accurately reflect the micro-vascular pathology will be selected. The time window showing vascular normalization during anti-angiogenesis may be captured. Finally the ways of tumor angiogenesis of HCC， functionally and morphologically, both before and after therapy, may be better understood by using our novel MRI techniques.

肿瘤血管生成是衡量肝细胞癌生物学行为和评价药物疗效的重要指标。MR灌注常用于评价肝癌的微血管功能，但无法提供微血管直径和密度等形态学数据；另外该检查临床常用的对比剂是小分子钆，其非选择性跨血管渗透作用一定程度上阻碍了灌注对微血管功能的准确评价。因而难以全面和准确反映肝癌抗血管生成前后微血管功能与形态复杂的异质性改变。USPIO为大分子血池对比剂，对血管渗透具选择性，能明显缩短组织T1值，并有较好的磁敏感性。我们拟在裸鼠人肝癌模型上，将USPIO增强后动态灌注扫描和基于磁敏感性的稳态血管尺寸成像新技术有机结合，旨在提高肝癌微血管灌注功能成像的准确性，并同时获得反映微血管直径和密度的形态学指标。通过与病理对照，探索和印证功能与形态指标间的相关/互补性，筛选抗血管生成前后最能准确反映肝癌微血管病理的MR影像生物指标，捕捉治疗中血管正常化的窗口，全面准确地揭示肝癌生长中微血管功能与形态的演变规律。

本项目的重点在于探究肝细胞癌肿瘤血管功能与异质性。肝细胞癌具有很强的诱导肿瘤血管生成的能力，肿瘤血管生成程度与肿瘤的生长、转移及预后密切相关，可以作为监测肿瘤生物学特性、预测转移、判断预后和评价药物疗效的重要生物学指标。因此，对肿瘤血管功能和数目做干预前准确评估和干预后的动态随访至关重要。本项目的目标是评估肝细胞癌抗肿瘤血管生成治疗前后肿瘤血管功能和密度的变化，将超顺磁性对比剂超微超顺磁性氧化铁（USPIO）应用于显示肿瘤血管，结合磁共振实时、无创及软组织分辨率高的优势，开展了磁共振弥散灌注成像和USPIO稳态肿瘤大血管及微血管成像，用于评价肝细胞癌血管生成及抗肿瘤血管生成治疗后疗效的动物实验研究。在裸鼠原位肝细胞癌模型上，通过一站式磁共振扫描同时获得反映肝细胞癌肿瘤血管功能、大血管半定量计数（ITSS）和微血管密度（Q）的新的影像学指标，并与病理结果对照，得到以下结果：（1）使用剂量为8 mg Fe/kg 的USPIO磁敏感加权成像获得的ITSS和微血管密度成像的Q可以分别评估肝细胞癌抗肿瘤血管生成治疗前、后大血管和微血管数目的变化；（2）使用体素内不相干运动成像中f可以用来评估肝细胞癌抗肿瘤血管生成治疗前、后血管功能的变化；（3）使用表观弥散系数（ADCtotal）和体素内不相干运动成像中真扩散系数（D）可以评估肝细胞癌抗细胞增殖治疗前、后肿瘤坏死情况。从而客观揭示肝细胞癌自然生长和抗血管生成后的肿瘤大血管和微血管的演变规律。这些新的影像学指标（ITSS、Q、f、ADCtotal和D）可能也可用于揭示其他类型肿瘤的肿瘤血管的生长方式，并可用于评价新研发的各种抗肿瘤血管生成药物的临床前期动物实验。