The demographics of the stroke population consist mainly of elderly patients. Transcranial Doppler is an effective method for intracranial flow detection, but can be limited due to the poor temporal window (PTW), which is frequent in the elderly. Therefore, we investigated whether the low frequency 1.6-MHz probe can be useful to improve flow detection for PTW.

All 201 participants had a history of transient ischemic attack or minor ischemic stroke. Firstly, we analyzed the success rate of recording intracranial blood flow via temporal window by using 2.0-MHz (high frequency, HF) and 1.6-MHz (low frequency, LF) probes for a maximum of 10 minutes. Secondly, mean flow velocity (MFV) and pulsatile index (PI) of insonated spectrum of 25 patients with good temporal window were compared between the two probes.

Results: Seventy-eight patients were female and the mean age was 64.1±12.4 years. Among 402 windows, 125 (31.1%) were undetected when using the 2.0-MHz probe. Fifty-five patients were detected for the spectrum by the 1.6-MHz probe. However, 70 (17.4%) still remained as PTW. Between the two probes, there were no significant differences of variables from the middle cerebral arteries as below,

Below is Flow spectrum at the same location between 1.6 MHz (A) and 2 MHz (B) probes. Compared to the conventional probes, the 1.6 MHz probe appears to have a higher gain at the same location.

Conclusion: 1.6- MHz probe was feasible to Improve flow detection for PTW which expand the TCD clinical application

Reference: Feasibility of 1.6-MHz Probe for Detection of Cerebral Blood Flow in the Poor Temporal Window.Korean Neurol Assoc 32(1):8-13, 2014