Rodriguez Rosendo A, Rubens Fraser, Rodriguez Carlos D, Nathan Howard J
Department of Surgery, Division of Cardiac Surgery, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, Ontario K1Y 4W7, Canada.
J Neuroimaging. 2006 Apr;16(2):126-32. doi: 10.1111/j.1552-6569.2006.00035.x.
The application of intensity thresholds for embolus detection with transcranial Doppler (TCD) can exclude from analysis an unrecognized proportion of high-intensity transient signals (HITS))whose intensities are below the threshold. The lack of consistent threshold criteria between clinical trials may explain part of the discrepancy in the reported HITS counts. We investigated the effect of choosing different thresholds on the sensitivity and specificity of detecting HITS during cardiopulmonary bypass (CPB).
Two observers independently analyzed TCD recordings from 8 patients under CPB. Doppler signals were classified as true HITS, equivocal HITS, artifacts, and Doppler speckles according to preestablished criteria. The relative intensity of Doppler signals was measured by two different methods (TCD software vs manual). Receiver Operating Characteristic curves determined the optimal threshold for each of the two intensity methods.
Reviewers achieved agreement in 96% of 2190 Doppler signals (kappa = 0.90). Relative intensities calculated with the TCD-software method were 3 dB (95% CI: 3.0-3.4) higher than the manual method. The optimal threshold was found at 10 dB (sensitivity: 99%; specificity: 90.8%) with the software method and at 7 dB with the manual method (sensitivity: 96%; specificity: 83%). The use of an intensity threshold 2 dB higher than the optimal increased the rejection of true HITS by 8% and 14%, respectively.
Using intensity thresholds higher than the optimal for embolus detection decreases HITS counts. Choosing a threshold depends on the type of method used for measuring the signal intensity. Uniform threshold criteria and comparative studies between different Doppler devices are necessary for making clinical trials more comparable.
经颅多普勒（TCD）检测栓子时应用强度阈值会将强度低于阈值的未被识别的高强度瞬态信号（HITS）排除在分析之外。临床试验之间缺乏一致的阈值标准可能是报告的HITS计数存在差异的部分原因。我们研究了选择不同阈值对体外循环（CPB）期间检测HITS的敏感性和特异性的影响。
两名观察者独立分析8例CPB患者的TCD记录。根据既定标准，将多普勒信号分为真正的HITS、可疑的HITS、伪像和多普勒斑点。通过两种不同方法（TCD软件与手动）测量多普勒信号的相对强度。受试者工作特征曲线确定了两种强度方法各自的最佳阈值。
在2190个多普勒信号中，两位观察者的一致性为96%（kappa = 0.90）。用TCD软件方法计算的相对强度比手动方法高3 dB（95% CI：3.0 - 3.4）。软件方法的最佳阈值为10 dB（敏感性：99%；特异性：90.8%），手动方法的最佳阈值为7 dB（敏感性：96%；特异性：83%）。使用比最佳阈值高2 dB的强度阈值会使真正HITS的排除率分别增加8%和14%。
使用高于最佳阈值的强度阈值进行栓子检测会减少HITS计数。选择阈值取决于用于测量信号强度的方法类型。为使临床试验更具可比性，需要统一的阈值标准以及不同多普勒设备之间的比较研究。
