In patients with pulmonary embolism (PE), there is a growing interest in quantifying the pulmonary vascular obtruction index (PVOI), which may be an independent risk factor for PE recurrence. Perfusion SPECT/CT is a very attractive tool to provide an accurate quantification of the PVOI. However, there is currently no reliable method to automatically delineate and quantify it. The aim of this phantom study was to assess and compare 3 segmentation methods for PVOI quantification with perfusion SPECT/CT imaging. Three hundred ninety-six SPECT/CT scans, with various PE scenarios (n = 44), anterior to posterior perfusion gradients (n = 3), and lung volumes (n = 3) were simulated using Simind software. Three segmentation methods were assesssed: (1) using an intensity threshold expressed as a percentage of the maximal voxel value (MaxTh), (2) using a Z-score threshold (ZTh) after building a Z-score parametric lung map, and (3) using a relative difference threshold (RelDiffTh) after building a relative difference parametric map. Ninety randomly selected simulations were used to define the optimal threshold, and 306 simulations were used for the complete analysis. Spacial correlation between PE volumes from the phantom data and the delineated PE volumes was assessed by computing DICEPE indices. Bland-Altman statistics were used to calculate agreement for PVOI between the phantom data and the segmentation methods. Mean DICEPE index was higher with the RelDiffTh method (0.85 ± 0.08), as compared with the MaxTh method (0.78 ± 0.16) and the ZTh method (0.67 ± 0.15). Using the RelDiffTh method, mean DICEPE index remained high (> 0.81) regardless of the perfusion gradient and the lung volumes. Using the RelDiffTh method, mean relative difference in PVOI was − 12%, and the limits of agreement were − 40% to 16%. Values were 3% (− 75% to 81%) for MaxTh method and 0% (− 120% to 120%) for ZTh method. Graphycal analysis of the Bland-Altman graph for the RelDiffTh method showed very close estimation of the PVOI for small and medium PE, and a trend toward an underestimation of large PE. In this phantom study, a delineation method based on a relative difference parametric map provided a good estimation of the PVOI, regardless of the extent of PE, the intensity of the anterior to posterior gradient, and the whole lung volumes.

中文翻译：

---

Perfusion SPECT-CT自动勾画和量化肺栓塞患者肺血管阻塞指数：模拟研究

在肺栓塞 (PE) 患者中，量化肺血管阻塞指数 (PVOI) 越来越受到关注，该指数可能是 PE 复发的独立危险因素。灌注 SPECT/CT 是一种非常有吸引力的工具，可提供 PVOI 的准确量化。然而，目前还没有可靠的方法来自动描绘和量化它。这项体模研究的目的是评估和比较 PVOI 量化与灌注 SPECT/CT 成像的 3 种分割方法。使用 Simind 软件模拟了 396 次 SPECT/CT 扫描，具有各种 PE 场景（n = 44）、前后灌注梯度（n = 3）和肺容积（n = 3）。评估了三种分割方法：(1) 使用强度阈值表示为最大体素值 (MaxTh) 的百分比，(2) 在构建 Z-score 参数肺图后使用 Z-score 阈值 (ZTh)，以及 (3) 在构建相对差异参数图后使用相对差异阈值 (RelDiffTh)。90 个随机选择的模拟用于定义最佳阈值，306 个模拟用于完整分析。通过计算 DICEPE 指数评估来自幻像数据的 PE 体积与描绘的 PE 体积之间的空间相关性。Bland-Altman 统计用于计算体模数据和分割方法之间 PVOI 的一致性。与 MaxTh 方法 (0.78 ± 0.16) 和 ZTh 方法 (0.67 ± 0.15) 相比，RelDiffTh 方法 (0.85 ± 0.08) 的平均 DICEPE 指数更高。使用 RelDiffTh 方法，平均 DICEPE 指数仍然很高（> 0。81) 无论灌注梯度和肺容量如何。使用 RelDiffTh 方法，PVOI 的平均相对差异为 − 12%，一致限为 − 40% 至 16%。MaxTh 方法的值为 3%（- 75% 至 81%），ZTh 方法的值为 0%（- 120% 至 120%）。RelDiffTh 方法的 Bland-Altman 图的图形分析表明，对中小型 PE 的 PVOI 估计非常接近，并且有低估大型 PE 的趋势。在这项体模研究中，基于相对差异参数图的描绘方法提供了对 PVOI 的良好估计，无论 PE 的程度、前后梯度的强度以及整个肺容积如何。MaxTh 方法的值为 3%（- 75% 至 81%），ZTh 方法的值为 0%（- 120% 至 120%）。RelDiffTh 方法的 Bland-Altman 图的图形分析表明，对中小 PE 的 PVOI 估计非常接近，并且有低估大 PE 的趋势。在这项体模研究中，无论 PE 的程度、前后梯度的强度以及整个肺容积如何，基于相对差异参数图的描绘方法都提供了对 PVOI 的良好估计。MaxTh 方法的值为 3%（- 75% 至 81%），ZTh 方法的值为 0%（- 120% 至 120%）。RelDiffTh 方法的 Bland-Altman 图的图形分析表明，对中小 PE 的 PVOI 估计非常接近，并且有低估大 PE 的趋势。在这项体模研究中，无论 PE 的程度、前后梯度的强度以及整个肺容积如何，基于相对差异参数图的描绘方法都提供了对 PVOI 的良好估计。