使用经颅多普勒超声比较1兆赫兹和2兆赫兹探头在微栓子检测中的应用

Droste Dirk W, Lerner Thomas, Dittrich Ralf, Ritter Martin, Ringelstein E Bernd

Department of Neurology, University of Münster, Germany.

Neurol Res. 2005 Jul;27(5):471-6. doi: 10.1179/016164105X15695.

OBJECTIVES

Clinically silent microembolic signals (MES) can be detected by transcranial Doppler sonography (TCD). There is theoretical evidence that lower ultrasound emission frequencies may lead to a higher signal intensity and thus sensitivity to detect MES. We compared a 1-MHz probe with a 2-MHz probe regarding sensitivity in the detection of MES. Moreover, embolus detection by transcranial Doppler ultrasound is very time consuming and semi-automated detection is mandatory. Therefore, we studied an on-line algorithm using the bi-gate technique and the two transmission frequencies.

METHODS

After defining detection thresholds of > or = 12 dB (1 MHz) and > or = 10 dB (2 MHz) with eight normal subjects as MES-negative controls, taking into account natural fluctuations of the Doppler spectrum, we studied 36 patients with ischaemic events and five asymptomatic patients with incidental embolic sources. All patients subsequently underwent a 1-hour unilateral embolus detection from the middle cerebral artery (MCA) or the posterior cerebral artery (PCA), respectively, using 1 and 2 MHz for 30 minutes each in a randomized order. The software algorithm was compared with a blinded off-line analysis by an experienced observer as a gold standard.

RESULTS

The investigator detected 198 MES (range 0-41 MES) in the recordings of 29 patients out of the 41 patients using the 1-MHz probe and 101 MES (range 0-32 MES) in the recordings of 14 patients using the 2-MHz probe (p = 0.0007). Sensitivity of the software to detect MES confirmed by the investigator was 31% using 1 MHz and 41% using 2 MHz. The positive predictive value was 6 and 30%, respectively.

DISCUSSION

The sensitivity and positive predictive values of the automated algorithm to detect MES were unacceptably low for clinical practice with both frequencies. The use of 1 MHz instead of 2 MHz may, however, be useful when evaluating the recordings off-line by an experienced blinded observer.

目的

经颅多普勒超声检查（TCD）可检测到临床上无症状的微栓塞信号（MES）。理论证据表明，较低的超声发射频率可能会导致更高的信号强度，从而提高检测MES的灵敏度。我们比较了1兆赫探头和2兆赫探头在检测MES方面的灵敏度。此外，经颅多普勒超声检测栓子非常耗时，半自动检测是必需的。因此，我们研究了一种使用双门技术和两种发射频率的在线算法。

方法

以8名正常受试者作为MES阴性对照，在考虑多普勒频谱自然波动的情况下，定义检测阈值为≥12分贝（1兆赫）和≥10分贝（2兆赫），我们研究了36例缺血性事件患者和5例有无症状栓子来源的患者。随后，所有患者分别从中脑动脉（MCA）或大脑后动脉（PCA）进行1小时的单侧栓子检测，以随机顺序分别使用1兆赫和2兆赫各30分钟。将软件算法与由经验丰富的观察者进行的盲法离线分析作为金标准进行比较。

结果

在41例患者中，研究者使用1兆赫探头在29例患者的记录中检测到198个MES（范围为0 - 41个MES），使用2兆赫探头在14例患者的记录中检测到101个MES（范围为0 - 32个MES）（p = 0.0007）。研究者确认软件检测MES的灵敏度在使用1兆赫时为31%，使用2兆赫时为41%。阳性预测值分别为6%和30%。