Cullinane M, Markus H S
Department of Clinical Neuroscience, St George's Hospital Medical School, London, UK.
Ultrasound Med Biol. 2001 Jun;27(6):795-800. doi: 10.1016/s0301-5629(01)00369-6.
A 1 MHz transducer for use with transcranial Doppler ultrasound may improve the intensity and therefore the detection of embolic signals (ES) and may also reduce the number of absent acoustic windows. A series of studies was performed to investigate its potential benefits. Firstly, ES were detected using a 1 MHz and a 2 MHz transducer both in vitro and in vivo. Secondly, the time taken to identify 100 middle cerebral arteries (MCA) was recorded for both transducers and the best Doppler signal obtained was reviewed off-line and graded for quality. ES were more intense when detected with the 1 MHz compared with the 2 MHz transducer, both in vitro (p <.0001) and in vivo (p <.0001). Of the 100 MCAs studied, 81 had acoustic windows identified with both transducers. The number of acoustic windows detected with one transducer but not the other was the same for both transducers (n = 3). The time taken to identify the MCA was longer with the 1 MHz transducer (p <.0001) and the quality of the signal achieved was poorer (p <.0001). In conclusion, the 1 MHz transducer improved embolic signal intensity but the overall quality of the flow spectrum obtained was poorer with the 1 MHz than with the 2 MHz transducer. A lower frequency transducer of 1 MHz or possibly 1.5 MHz with transcranial Doppler ultrasound may improve the application of embolic signal detection but may not improve the signal for routine measurement of flow velocities.
用于经颅多普勒超声的1兆赫换能器可能会提高强度，从而改善对栓塞信号（ES）的检测，并且还可能减少无回声窗的数量。进行了一系列研究以调查其潜在益处。首先，在体外和体内分别使用1兆赫和2兆赫的换能器检测栓塞信号。其次，记录两个换能器识别100条大脑中动脉（MCA）所需的时间，并离线查看获得的最佳多普勒信号并对其质量进行分级。与2兆赫换能器相比，使用1兆赫换能器检测到的栓塞信号在体外（p <.0001）和体内（p <.0001）时更强。在所研究的100条MCA中，81条通过两个换能器都识别出了声学窗。两个换能器中，仅用一个换能器检测到而另一个未检测到的声学窗数量相同（n = 3）。使用1兆赫换能器识别MCA所需的时间更长（p <.0001），并且获得的信号质量更差（p <.0001）。总之，1兆赫换能器提高了栓塞信号强度，但与2兆赫换能器相比，使用1兆赫换能器获得的血流频谱的整体质量较差。经颅多普勒超声使用1兆赫或可能1.5兆赫的较低频率换能器可能会改善栓塞信号检测的应用，但可能不会改善用于常规流速测量的信号。
