Objective: Novel applications of transcranial Doppler (TCD) ultrasonography, such as the assessment of cerebral vessel narrowing/occlusion or the non-invasive estimation of intracranial pressure (ICP), require high-quality maximal flow velocity waveforms. However, due to the low signal-to-noise ratio of TCD spectrograms, measuring the maximal flow velocity is challenging. In this work, we propose a calibration-free algorithm for estimating maximal flow velocities from TCD spectrograms and present a pertaining beat-by-beat signal quality index. Methods: Our algorithm performs multiple binary segmentations of the TCD spectrogram and then extracts the pertaining envelopes (maximal flow velocity waveforms) via an edge-following step that incorporates physiological constraints. The candidate maximal flow velocity waveform with the highest signal quality index is finally selected. Results: We evaluated the algorithm on 32 TCD recordings from the middle cerebral and internal carotid arteries in 6 healthy and 12 neurocritical care patients. Compared to manual spectrogram tracings, we obtained a relative error of −1.5%, when considering the whole waveform, and a relative error of −3.3% for the peak systolic velocity. Conclusion: The feedback loop between the signal quality assessment and the binary segmentation yields a robust algorithm for maximal flow velocity estimation. Clinical Impact: The algorithm has already been used in our ICP estimation pipeline. By making the code and the data publicly available, we hope that the algorithm will be a useful building block for the development of novel TCD applications that require high-quality flow velocity waveforms.

中文翻译：

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经颅多普勒回波自适应最大血流速度估计

目的：经颅多普勒 (TCD) 超声的新应用，例如脑血管狭窄/闭塞的评估或颅内压 (ICP) 的无创估计，需要高质量的最大流速波形。然而，由于 TCD 谱图的低信噪比，测量最大流速具有挑战性。在这项工作中，我们提出了一种无需校准的算法，用于从 TCD 谱图估计最大流速，并提供相关的逐搏信号质量指数。方法：我们的算法对 TCD 频谱图执行多个二进制分割，然后通过结合生理约束的边缘跟踪步骤提取相关包络（最大流速波形）。最后选择信号质量指标最高的候选最大流速波形。结果：我们评估了 6 名健康和 12 名神经重症监护患者大脑中动脉和颈内动脉的 32 次 TCD 记录的算法。与手动频谱图追踪相比，考虑到整个波形时，我们获得了 -1.5% 的相对误差，以及峰值收缩速度的相对误差为 -3.3%。结论：信号质量评估和二元分割之间的反馈回路产生了用于最大流速估计的稳健算法。临床影响：该算法已用于我们的 ICP 估计管道。通过公开代码和数据，