Abstract
Response: We have read with interest the comments by Dr Syme regarding our recent study investigating the potential association of knock-type-Doppler signal (KTDS) with the vessel affected by ischemia and the presence of microvascular ischemia on brain MRI.1 Dr Syme has made some provocative observations that we would like to address. First, we did not use DWL-Compumedics Transcranial Doppler (TCD) machines. This type of a TCD unit was previously used to detect knock signals in the original case reports by Dr Syme.2,3 We believe that case reports do not offer any solid evidence to choose one TCD make over the other. In fact, for the knock signal to be truly generalizable, it has to be detected by all commercially available TCD devices because they share the same carrying frequency. Second, Dr Syme pointed out that the filter we used for KTDS detection (100 Hz) was too high, and therefore many signals may have been missed because of the high-pass filter setting. Filters …
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