Morales Humberto, Lemen Lisa, Samaratunga Ranasinghage, Nguyen Peter, Tomsick Thomas
Humberto Morales, Lisa Lemen, Ranasinghage Samaratunga, Peter Nguyen, Thomas Tomsick, Department of Radiology, University of Cincinnati Medical Center, Cincinnati, OH 45267-0761, United States.
World J Radiol. 2016 Jun 28;8(6):588-93. doi: 10.4329/wjr.v8.i6.588.
To characterize the effects of iodinated contrast material (ICM) on magnetic resonance imaging (MRI) comparing different sequences and magnetic fields, with emphasis to similarities/differences with well-known signal characteristics of hemorrhage in the brain.
Aliquots of iopamidol and iodixanol mixed with normal saline were scanned at 1.5T and 3T. Signal intensity (SI) was measured using similar spin-echo (SE)-T1, SE-T2, gradient-echo (GRE) and fluid-attenuation-inversion-recovery (FLAIR) sequences at both magnets. Contrast to noise ratio (CNR) (SI contrast-SI saline/SD noise) for each aliquot were calculated and Kruskall-wallis test and graphic analysis was used to compare different pulse sequences and ICMs.
Both ICM showed increased SI on SE-T1 and decreased SI on SE-T2, GRE and FLAIR at both 1.5T and 3T, as the concentration was increased. By CNR measurements, SE-T2 had the greatest conspicuity at 3T with undiluted iopamidol (92.6 ± 0.3, P < 0.00) followed by iodixanol (77.5 ± 0.9, P < 0.00) as compared with other sequences (CNR range: 15-40). While SE-T2 had greatest conspicuity at 1.5T with iopamidol (49.3 ± 1, P < 0.01), SE-T1 showed similar or slightly better conspicuity (20.8 ± 4) than SE-T2 with iodixanol (23 ± 1.7). In all cases, hypo-intensity on GRE was less conspicuous than on SE-T2.
Iodixanol and iopamidol shorten T1 and T2 relaxation times at both 1.5T and 3T. Hypo-intensity due to shortened T2 relaxation time is significantly more conspicuous than signal changes on T1-WI, FLAIR or GRE. Variations in signal conspicuity according to pulse sequence and to type of ICM are exaggerated at 3T. We postulate T2 hypointensity with less GRE conspicuity differentiates ICM from hemorrhage; given the well-known GRE hypointensity of hemorrhage. Described signal changes may be relevant in the setting of recent intra-arterial or intravenous ICM administration in translational research and/or human stroke therapy.
通过比较不同序列和磁场，描述碘化造影剂（ICM）对磁共振成像（MRI）的影响，重点关注与脑内出血的已知信号特征的异同。
将碘帕醇和碘克沙醇与生理盐水混合的等分试样在1.5T和3T磁场下进行扫描。在两个磁场中，使用相似的自旋回波（SE）-T1、SE-T2、梯度回波（GRE）和液体衰减反转恢复（FLAIR）序列测量信号强度（SI）。计算每个等分试样的对比噪声比（CNR）（SI造影剂 - SI生理盐水/标准差噪声），并使用克鲁斯卡尔 - 沃利斯检验和图形分析来比较不同的脉冲序列和ICM。
随着浓度增加，在1.5T和3T磁场下，两种ICM在SE-T1序列上均显示SI增加，而在SE-T2、GRE和FLAIR序列上SI降低。通过CNR测量，在3T磁场下，未稀释的碘帕醇在SE-T2序列上的显影效果最佳（92.6 ± 0.3，P < 0.00），其次是碘克沙醇（77.5 ± 0.9，P < 0.00），与其他序列相比（CNR范围：15 - 40）。在1.5T磁场下，碘帕醇在SE-T2序列上显影效果最佳（49.3 ± 1，P < 0.01），而对于碘克沙醇，SE-T1序列显示出与SE-T2序列相似或略好的显影效果（20.8 ± 4），而SE-T2序列显影效果为（23 ± 1.7）。在所有情况下，GRE序列上的低信号不如SE-T2序列明显。
碘克沙醇和碘帕醇在1.5T和3T磁场下均缩短T1和T2弛豫时间。由于T2弛豫时间缩短导致的低信号比T1加权成像（T1-WI）、FLAIR或GRE序列上的信号变化明显得多。根据脉冲序列和ICM类型的信号显影差异在3T磁场下更为明显。我们推测，GRE序列上低信号不明显的T2低信号可将ICM与出血区分开来；鉴于出血在GRE序列上众所周知的低信号。所描述的信号变化可能与转化研究和/或人类中风治疗中近期动脉内或静脉内给予ICM的情况相关。
