Department of Radiology, Research Institute of Radiological Science, Severance Hospital, Yonsei University College of Medicine, 50-1 Yonsei-ro, Seodaemun-gu, Seoul, 03722, South Korea.
Department of Internal Medicine, Division of Cardiology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, South Korea.
AJR Am J Roentgenol. 2022 Mar;218(3):454-461. doi: 10.2214/AJR.21.26654. Epub 2021 Oct 13.
Current methods for calculating the myocardial extracellular volume (ECV) fraction require blood sampling to determine the serum hematocrit. Synthetic hematocrit and thus synthetic ECV may be derived using unenhanced attenuation of blood. By use of virtual unenhanced (VUE) attenuation of blood, contrast-enhanced dual-energy CT (DECT) may allow synthetic ECV calculations without unenhanced acquisition. The purpose of this study was to compare synthetic ECV calculated using synthetic hematocrit derived from VUE images and conventional ECV calculated using serum hematocrit, both of which were obtained by contrast-enhanced DECT, with ECV derived from MRI used as the reference standard. This retrospective study included 51 patients (26 men and 25 women; mean age, 59.9 ± 15.6 [SD] years) with nonischemic cardiomyopathy who, as part of an earlier prospective investigation, underwent equilibrium phase contrast-enhanced cardiac DECT and cardiac MRI and had serum hematocrit measured within 6 hours of both tests. A separate retrospective sample of 198 patients who underwent contrast-enhanced thoracic DECT performed on the same day for suspected pulmonary embolism and serum hematocrit measurement was identified to derive a synthetic hematocrit formula using VUE attenuation of blood by linear regression analysis. In the primary sample, two radiologists independently used DECT iodine maps to obtain the conventional ECV using serum hematocrit and the synthetic ECV using synthetic hematocrit based on the independently derived formula. The concordance correlation coefficient (CCC) was computed between conventional ECV and synthetic ECV from DECT. Conventional ECV and synthetic ECV from DECT were compared with the ECV derived from MRI in Bland-Altman analyses. In the independent sample, the linear regression formula for synthetic hematocrit was as follows: synthetic hematocrit = 0.85 × (VUE attenuation of blood) - 5.40. In the primary sample, the conventional ECV and synthetic ECV from DECT showed excellent agreement (CCC, 0.95). Bland-Altman analysis showed a small bias of -0.44% (95% limits of agreement, -5.10% to 4.22%) between MRI-derived ECV and conventional ECV from DECT as well as a small bias of -0.78% (95% limits of agreement, -5.25% to 3.69%) between MRI-derived ECV and synthetic ECV from DECT. Synthetic ECV and conventional ECV derived from DECT show excel lent agreement and a comparable association with ECV derived from cardiac MRI. Synthetic hematocrit from VUE attenuation of blood may allow myocardial tissue characterization on DECT without the inconvenience of blood sampling.
当前计算心肌细胞外容积（ECV）分数的方法需要采血以确定血清血细胞比容。可以使用未增强的血液衰减来推导出合成血细胞比容和合成 ECV。通过使用虚拟未增强（VUE）血液衰减，对比增强双能 CT（DECT）可能允许在没有未增强采集的情况下进行合成 ECV 计算。本研究的目的是比较使用对比增强 DECT 获得的源自 VUE 图像的合成血细胞比容计算得出的合成 ECV 与使用血清血细胞比容计算得出的常规 ECV，并将其与 MRI 得出的 ECV 作为参考标准。这项回顾性研究纳入了 51 名（26 名男性和 25 名女性；平均年龄，59.9 ± 15.6[SD]岁）患有非缺血性心肌病的患者，他们作为先前前瞻性研究的一部分接受了平衡期对比增强心脏 DECT 和心脏 MRI 检查，并在两次检查后 6 小时内测量了血清血细胞比容。还确定了一个单独的回顾性样本，该样本由 198 名在同一天因疑似肺栓塞而接受对比增强胸部 DECT 检查的患者组成，使用线性回归分析通过 VUE 血液衰减来推导出合成血细胞比容公式。在主要样本中，两位放射科医生使用 DECT 碘图分别基于独立推导的公式使用血清血细胞比容获得常规 ECV 和使用合成血细胞比容获得的合成 ECV。计算了常规 ECV 和基于 DECT 的合成 ECV 之间的一致性相关系数（CCC）。在 Bland-Altman 分析中比较了来自 DECT 的常规 ECV 和合成 ECV 与 MRI 得出的 ECV。在独立样本中，合成血细胞比容的线性回归公式如下：合成血细胞比容=0.85×（VUE 血液衰减）-5.40。在主要样本中，DECT 上的常规 ECV 和合成 ECV 显示出极好的一致性（CCC，0.95）。Bland-Altman 分析显示 MRI 得出的 ECV 与 DECT 上的常规 ECV 之间存在 0.44%的小偏差（95%一致性界限，-5.10%至 4.22%），以及 MRI 得出的 ECV 与 DECT 上的合成 ECV 之间存在 0.78%的小偏差（95%一致性界限，-5.25%至 3.69%）。DECT 上的合成 ECV 和常规 ECV 与心脏 MRI 得出的 ECV 显示出极好的一致性和可比的相关性。VUE 血液衰减的合成血细胞比容可能允许在 DECT 上进行心肌组织特征描述，而无需采血的不便。
