Hayashida Minoru, Ito Katsuyoshi, Fujita Takeshi, Shimizu Ayame, Sasaki Katsumi, Tanabe Masahiro, Matsunaga Naofumi
Department of Radiology, Yamaguchi University School of Medicine, Ube, Yamaguchi 755-8505, Japan.
Magn Reson Imaging. 2008 Jan;26(1):65-71. doi: 10.1016/j.mri.2007.04.007. Epub 2007 Jun 13.
The purpose of this study was to evaluate differences in the degrees of contrast enhancement effects of small hepatocellular carcinomas (HCCs) in patients with cirrhosis between helical computed tomography (CT) and magnetic resonance (MR) imaging during multiphasic contrast-enhanced dynamic imaging and to determine the diagnostic value of MR imaging especially in assessing hypovascular HCCs detected as hypoattenuating nodules on late-phase CT.
This study included 64 small HCCs (<3 cm in diameter) in 40 patients with chronic hepatitis or cirrhosis who underwent multiphasic (arterial, portal and late phases) contrast-enhanced dynamic helical CT and MR imaging. The contrast enhancement patterns of each lesion in the arterial and late phases were evaluated by two radiologists experienced in liver MR imaging and categorized as one of five grades (1=hypoattenuated/hypointense; 2=slightly hypoattenuated/hypointense; 3=isoattenuated/isointense; 4=slightly hyperattenuated/hyperintense; 5=hyperattenuated/hyperintense), compared with the surrounding liver parenchyma.
Forty-three (67%) of 64 lesions showed Grade 4 (n=24) or Grade 5 (n=19) enhancement on arterial-phase CT, while 51 (80%) of 64 lesions showed Grade 4 (n=20) or Grade 5 (n=31) enhancement on arterial-phase MR imaging, indicating hypervascular HCCs. The grading score of hypervascular HCCs on arterial-phase MR imaging (mean: 4.61) was significantly (P<.01) higher than that for hypervascular HCCs on arterial-phase CT (mean: 4.20), showing better detection of the hypervascularity (arterial enhancement) of the lesion on arterial-phase MR imaging. Regarding hypovascular HCCs, all (100%) of 21 hypovascular HCCs on CT showed Grade 1 (n=10) or Grade 2 (n=11) enhancement on late-phase CT, seen as hypoattenuation. In contrast, 8 (62%) of 13 hypovascular HCCs on MR imaging showed Grade 1 (n=1) or Grade 2 (n=7) enhancement on late-phase MR imaging, seen as hypointensity. Grading scores of hypovascular HCCs on late-phase images were significantly (P<.001) lower on CT than on MR imaging (mean score: 1.52 vs. 2.31), indicating better washout effects for hypovascular HCCs on late-phase CT.
The washout effects for small HCCs on late-phase MR imaging were inferior to those for small HCCs on late-phase CT. Especially, hypovascular HCCs demonstrated as hypoattenuating nodules on late-phase CT were often not seen on late-phase MR imaging, requiring careful evaluation of other sequences, including unenhanced T(1)-weighted and T(2)-weighted MR images.
本研究旨在评估肝硬化患者中小肝细胞癌（HCC）在螺旋计算机断层扫描（CT）和磁共振（MR）成像多期对比增强动态成像过程中对比增强效果的差异程度，并确定MR成像在评估于CT晚期表现为低密度结节的乏血供HCC中的诊断价值。
本研究纳入了40例慢性肝炎或肝硬化患者的64个小HCC（直径<3 cm），这些患者均接受了多期（动脉期、门脉期和晚期）对比增强动态螺旋CT和MR成像检查。由两位精通肝脏MR成像的放射科医生评估每个病灶在动脉期和晚期的对比增强模式，并与周围肝实质比较，分为五个等级之一（1 = 低密度/低信号；2 = 轻度低密度/低信号；3 = 等密度/等信号；4 = 轻度高密度/高信号；5 = 高密度/高信号）。
64个病灶中有43个（67%）在CT动脉期表现为4级（n = 24）或5级（n = 19）增强，而64个病灶中有51个（80%）在MR成像动脉期表现为4级（n = 20）或5级（n = 31）增强，提示为富血供HCC。富血供HCC在MR成像动脉期的分级评分（均值：4.61）显著高于CT动脉期（均值：4.20）（P <.01），表明MR成像动脉期对病灶富血供（动脉期增强）的显示更佳。对于乏血供HCC，CT上21个乏血供HCC全部（100%）在晚期CT表现为1级（n = 10）或2级（n = 11）增强，呈低密度。相比之下，MR成像上13个乏血供HCC中有8个（62%）在晚期MR成像表现为1级（n = 1）或2级（n = 7）增强，呈低信号。乏血供HCC在晚期图像上的分级评分在CT上显著低于MR成像（P <.001）（平均评分：1.52对2.31），表明CT晚期对乏血供HCC的廓清效果更佳。
小HCC在MR成像晚期的廓清效果不如CT晚期。特别是，于CT晚期表现为低密度结节的乏血供HCC在MR成像晚期常不可见，需要仔细评估包括未增强T1加权和T2加权MR图像在内的其他序列。
