Cardiac MR PET CT Program, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
Invest Radiol. 2013 Sep;48(9):646-53. doi: 10.1097/RLI.0b013e31828fdf9f.
In coronary computed tomographic angiography (CTA), low attenuation of coronary atherosclerotic plaque is associated with lipid-rich plaques. However, an overlap in Hounsfield units (HU) between fibrous and lipid-rich plaque as well as an influence of luminal enhancement on plaque attenuation was observed and may limit accurate detection of lipid-rich plaques by CTA. We sought to determine whether the quantitative histogram analysis improves accuracy of the detection of lipid-core plaque (LCP) in ex vivo hearts by validation against histological analysis.
Human donor hearts were imaged with a 64-slice computed tomographic scanner using a standard coronary CTA protocol, optical coherence tomography (OCT), a histological analysis. Lipid-core plaque was defined in the histological analysis as any fibroatheroma with a lipid/necrotic core diameter of greater than 200 μm and a circumference greater than 60 degrees as well as a cap thickness of less than 450 μm. In OCT, lipid-rich plaque was determined as a signal-poor region with diffuse borders in 2 quadrants or more. In CTA, the boundaries of the noncalcified plaque were manually traced. The absolute and relative areas of low attenuation plaque based on pixels with less than 30, less than 60, and less than 90 HU were calculated using quantitative histogram analysis.
From 5 hearts, a total of 446 cross sections were coregistered between CTA and the histological analysis. Overall, 55 LCPs (12%) were identified by the histological analysis. In CTA, the absolute and relative areas of low attenuation plaque less than 30, less than 60, and less than 90 HU were 0.14 (0.31) mm2 (4.22% [9.02%]), 0.69 (0.95) mm2 (18.28% [21.22%]), and 1.35 (1.54) mm2 (35.65% [32.07%]), respectively. The low attenuation plaque area correlated significantly with histological lipid content (lipid/necrotic core size [in square millimeter] and a portion of lipid/necrotic core on the entire plaque) at all thresholds but was the strongest at less than 60 HU (r = 0.53 and r = 0.48 for the absolute and relative areas, respectively). Using a threshold of 1.0 mm2 or greater, the absolute plaque area of less than 60 HU in CTA yielded 69% sensitivity and 80% specificity to detect LCP, whereas sensitivity and specificity were 73% and 71% for using 25.0% or higher relative area less than 60 HU. The discriminatory ability of CTA for LCP was similar between the absolute and relative areas (the area under the curve, 0.744 versus 0.722; P = 0.37). Notably, the association of the low attenuation plaque area in CTA with LCP was not altered by the luminal enhancement for the relative (P = 0.48) but for the absolute measurement (P = 0.03). Similar results were achieved when validated against lipid-rich plaque by OCT in a subset of 285 cross sections.
In ex vivo conditions, the relative area of coronary atherosclerotic plaque less than 60 HU in CTA as derived from quantitative histogram analysis has good accuracy to detect LCP as compared with a histological analysis independent of differences in luminal contrast enhancement.
在冠状动脉计算机断层血管造影术（CTA）中，冠状动脉粥样硬化斑块的低衰减与富含脂质的斑块有关。然而，纤维斑块和富含脂质的斑块之间的 Hounsfield 单位（HU）存在重叠，以及管腔增强对斑块衰减的影响，可能会限制 CTA 对富含脂质斑块的准确检测。我们试图通过与组织学分析对照，确定定量直方图分析是否能提高 CT 检测脂质核心斑块（LCP）的准确性。
使用 64 层 CT 扫描仪对人类供体心脏进行成像，采用标准冠状动脉 CTA 协议、光学相干断层扫描（OCT）和组织学分析。组织学分析中，脂质核心斑块定义为任何纤维脂瘤，其脂质/坏死核心直径大于 200 μm，周长大于 60 度，帽厚度小于 450 μm。在 OCT 中，富含脂质的斑块被确定为信号较弱的区域，边界弥漫，在 2 个或更多象限中有弥漫边界。在 CTA 中，手动追踪非钙化斑块的边界。使用定量直方图分析，根据像素的 HU 值小于 30、小于 60 和小于 90 来计算低衰减斑块的绝对和相对面积。
从 5 个心脏中，共对 CTA 和组织学分析之间的 446 个横截面进行了配准。总的来说，组织学分析确定了 55 个 LCP（12%）。在 CTA 中，HU 值小于 30、小于 60 和小于 90 的低衰减斑块的绝对和相对面积分别为 0.14（0.31）mm²（4.22%[9.02%]）、0.69（0.95）mm²（18.28%[21.22%]）和 1.35（1.54）mm²（35.65%[32.07%]）。低衰减斑块面积与组织学脂质含量（脂质/坏死核心大小[平方毫米]和脂质/坏死核心在整个斑块中的比例）在所有阈值下均呈显著相关，但在 HU 值小于 60 时相关性最强（绝对面积和相对面积的相关系数分别为 0.53 和 0.48）。使用 1.0 mm²或更大的阈值，CTA 中 HU 值小于 60 的绝对斑块面积对检测 LCP 的灵敏度为 69%，特异性为 80%，而使用 HU 值小于 60 的相对面积 25.0%或更高的灵敏度和特异性分别为 73%和 71%。CTA 对 LCP 的鉴别能力在绝对和相对面积之间相似（曲线下面积，0.744 对 0.722；P=0.37）。值得注意的是，CTA 中低衰减斑块面积与 LCP 的相关性不受管腔增强的影响（相对面积，P=0.48；绝对测量，P=0.03）。在 285 个横截面的亚组中，与 OCT 检测富含脂质的斑块相对照，也得到了类似的结果。
在离体条件下，与组织学分析相比，基于定量直方图分析的 CTA 冠状动脉粥样硬化斑块 HU 值小于 60 的相对面积具有良好的准确性，可用于检测 LCP，而不受管腔对比增强差异的影响。
