Division of Neuroradiology, Department of Radiology, Hospital of the University of Pennsylvania, 3600 Market Street, Philadelphia, PA 19014, USA.
Acad Radiol. 2010 Jun;17(6):686-95. doi: 10.1016/j.acra.2010.01.019.
The purpose of this study was to present a new methodology to compare accuracies of two imaging fluid attenuated inversion recovery (FLAIR) magnetic resonance sequences in detection of multiple sclerosis (MS) lesions in the brain in the absence of ground truth, and to determine whether the two sequences, which differed only in echo time (TE), have the same accuracy.
We acquired FLAIR images at TE(1) = 90 ms and TE(2) = 155 ms from 46 patients with MS (24-69 years old, mean 45.8, 15 males) and 11 healthy volunteers (23-54 years old, mean 37.1, 6 males). Seven experienced neuroradiologists segmented lesions manually on randomly presented corresponding TE(1) and TE(2) images. For every image pair, a "surrogate ground truth" for each TE was generated by applying probability thresholds, ranging from 0.3 to 0.5, to the weighted average of experts' segmentations. Jackknife alternative free-response receiver operating characteristic analysis was used to compare experts' performance on TE(1) and TE(2) images, using successively the TE(1)- and TE(2)-based ground truths.
Supratentorially, there were significant differences in relative accuracy between the two sequences, ranging from 8.4% to 12.1%. In addition, we found a higher ratio of false positives to true positives for the TE(2) sequence using the TE(2) ground truth, compared to the TE(1) equivalent. Infratentorially, differences in the relative accuracy did not reach statistical significance.
The presented methodology may be useful in assessing the value of new clinical imaging protocols or techniques in the context of replacing existing ones, when the absolute ground truth is not available, and in determining changes in disease progression in follow-up studies. Our results suggest that the sequence with shorter TE should be preferred because it generates relatively fewer false positives. The finding is consistent with results of previous computer simulation studies.
本研究旨在提出一种新的方法，以比较两种不同回波时间（TE）的脑磁共振液体衰减反转恢复（FLAIR）成像序列在检测多发性硬化（MS）病变时的准确性，同时确定这两种序列是否具有相同的准确性，因为它们仅在 TE 上有所不同。
我们从 46 例 MS 患者（24-69 岁，平均年龄 45.8 岁，15 名男性）和 11 名健康志愿者（23-54 岁，平均年龄 37.1 岁，6 名男性）中采集了 FLAIR 图像，TE(1) = 90 ms，TE(2) = 155 ms。7 位经验丰富的神经放射科医生在随机呈现的相应 TE(1)和 TE(2)图像上手动分割病变。对于每对图像，通过将专家分割的加权平均值应用于 0.3 至 0.5 的概率阈值，为每个 TE 生成“替代地面实况”。采用 Jackknife 替代自由响应接收器操作特征分析，使用基于 TE(1)和 TE(2)的地面实况，分别比较专家在 TE(1)和 TE(2)图像上的性能。
在幕上，两种序列的相对准确性存在显著差异，范围为 8.4%至 12.1%。此外，与 TE(1) 等效物相比，使用 TE(2) 地面实况时，TE(2)序列的假阳性率与真阳性率之比更高。在幕下，相对准确性的差异没有达到统计学意义。
当无法获得绝对地面实况时，本研究提出的方法可能有助于评估新的临床成像方案或技术在替代现有方案时的价值，并且可用于确定随访研究中疾病进展的变化。我们的结果表明，应优先选择 TE 较短的序列，因为它产生的假阳性相对较少。这一发现与之前的计算机模拟研究结果一致。
