Pulsed photoacoustic Doppler flow measurements in blood-mimicking phantoms
Pulsed photoacoustic Doppler flow measurements in blood-mimicking phantoms
复制标题
模拟血液模型中的脉冲光声多普勒血流测量
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
P. Beard
中科院分区：
文献类型：
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作者：
J. Brunker;P. Beard
利用脉冲光声多普勒技术进行血流空间分辨测量的可行性进行了探讨。多普勒时移通过交叉相关的光声波形内产生的血液模拟体模使用对激光脉冲。使用聚焦或平面PZT超声换能器检测光声波。对于每次流量测量，收集了一系列100个波形对。以前的数据处理方法涉及拒绝相关性差的波形对;然后从选定的速度测量分布中提取模态速度值和标准偏差。然而，这种方法中使用的数据选择标准在某种程度上是任意的。一个新的数据分析协议，其中涉及平均的100个互相关函数，从而使用所有的测量数据，已被设计，以防止排除离群值。这种更严格的方法已被证明是有效的量化的线性运动的微米级的吸收器上的醋酸酯片移动的速度在0.14至1.25 ms-1的范围内。实验参数，如激光脉冲和传感器的频率响应之间的时间间隔，进行了评估，在它们的精度，分辨率和可测量的速度范围的影响。该技术随后被应用到流体幻影流动速率小于5沿着一个光学透明管。初步结果描述了三种不同的酚醛树脂微球悬浮液，也为全血。即使在非最佳条件下使用低频换能器和低脉冲重复频率也能获得速度信息。脉冲激励而不是连续波激励的显著优点是可以进行空间分辨的速度测量。这提供了在微循环内绘制血流的前景，从而提供了对肿瘤灌注和以血流状态异常为特征的其他病理的了解。
The feasibility of making spatially resolved measurements of blood flow using pulsed photoacoustic Doppler techniques has been explored. Doppler time shifts were quantified via cross-correlation of pairs of photoacoustic waveforms generated within a blood-simulating phantom using pairs of laser light pulses. The photoacoustic waves were detected using a focussed or planar PZT ultrasound transducer. For each flow measurement, a series of 100 waveform pairs was collected. Previous data processing methods involved rejection of poorly correlated waveform pairs; the modal velocity value and standard deviation were then extracted from the selected distribution of velocity measurements. However, the data selection criteria used in this approach is to some extent arbitrary. A new data analysis protocol, which involves averaging the 100 cross-correlation functions and thus uses all of the measured data, has been designed in order to prevent exclusion of outliers. This more rigorous approach has proved effective for quantifying the linear motion of micron-scale absorbers imprinted on an acetate sheet moving with velocities in the range 0.14 to 1.25 ms-1. Experimental parameters, such as the time separation between the laser pulses and the transducer frequency response, were evaluated in terms of their effect on the accuracy, resolution and range of measurable velocities. The technique was subsequently applied to fluid phantoms flowing at rates less than 5 mms-1 along an optically transparent tube. Preliminary results are described for three different suspensions of phenolic resin microspheres, and also for whole blood. Velocity information was obtained even under non-optimal conditions using a low frequency transducer and a low pulse repetition frequency. The distinguishing advantage of pulsed rather than continuous-wave excitation is that spatially resolved velocity measurements can be made. This offers the prospect of mapping flow within the microcirculation and thus providing insights into the perfusion of tumours and other pathologies characterised by abnormalities in flow status.