Reimer P, Tombach B
Institute of Clinical Radiology, Westphalian Wilhelms University Münster, Albert-Schweitzer Strasse 33, D-48129 Münster, Germany.
Eur Radiol. 1998;8(7):1198-204. doi: 10.1007/s003300050535.
A variety of parenterally administered iron oxides have been developed for contrast-enhanced MRI of the liver. Two different classes of iron oxides are currently clinically approved or in phase 3 trials: superparamagnetic iron oxides (SPIO) with a high R2/R1 relaxivity ratio and short blood half-life (AMI-25 and SH U 555 A), and ultrasmall paramagnetic iron oxides (USPIO) with a lower R2/R1 relaxivity ratio and longer blood half-life (AMI-227). All iron oxides significantly increase tumor-to-liver contrast and allow detection of more lesions than unenhanced MRI on T2-weighted images at a field strength of 0.2-1.5 T. Malignant lesions without phagocytic cells exhibit constant signal on T2-weighted accumulation phase images with all three iron oxides. All iron oxides cause a signal decrease of benign lesions with either phagocytic cells or a significant blood pool on T2-weighted accumulation phase images. The signal decrease of benign lesions is proportional to the Kupffer cell activity or tumor vascularity and is useful for lesion characterization. Another enhancement feature for the differentiation of benign from malignant lesions is ring enhancement of malignant lesions (metastases) on T1-weighted enhanced images either during the perfusion phase with SH U 555 A or during the accumulation phase with AMI-227, which is attributed to the blood pool effects of the compounds. Differentiation of lesions and vessels is easier on enhanced images with angiographic effects than on unenhanced images. Iron oxides improve the quality of two-dimensional MR angiography techniques of the portal venous system by decreasing background signal (liver tissue with all iron oxides) and increasing intravascular signal (AMI-227). The use of iron oxides for hepatic MRI provides an alternative to the existing multistep diagnosis with CT, CT portography, MRI and biopsy.
已研发出多种用于肝脏对比增强磁共振成像（MRI）的胃肠外给药氧化铁。目前有两类不同的氧化铁已获临床批准或处于3期试验阶段：具有高R2/R1弛豫率和短血液半衰期的超顺磁性氧化铁（SPIO，如AMI - 25和SH U 555 A），以及具有较低R2/R1弛豫率和较长血液半衰期的超小顺磁性氧化铁（USPIO，如AMI - 227）。在0.2 - 1.5 T场强下的T2加权图像上，所有氧化铁均能显著增加肿瘤与肝脏的对比度，且比未增强的MRI能检测到更多病变。在T2加权积聚期图像上，不含吞噬细胞的恶性病变在使用所有三种氧化铁时均表现出恒定信号。在T2加权积聚期图像上，所有氧化铁都会使具有吞噬细胞或显著血池的良性病变信号降低。良性病变的信号降低与库普弗细胞活性或肿瘤血管形成成正比，有助于病变特征的判定。另一个用于区分良性与恶性病变的增强特征是，在T1加权增强图像上，恶性病变（转移瘤）在使用SH U 555 A的灌注期或使用AMI - 227的积聚期会出现环形增强，这归因于化合物的血池效应。与未增强图像相比，具有血管造影效果的增强图像上更容易区分病变和血管。氧化铁通过降低背景信号（使用所有氧化铁时的肝脏组织）和增加血管内信号（AMI - 227），提高了门静脉系统二维磁共振血管造影技术的质量。将氧化铁用于肝脏MRI为现有的CT、CT门静脉造影、MRI和活检多步骤诊断提供了一种替代方法。
