Abstract
The study “Longitudinal changes in cerebral blood flow velocities in different clinical courses of migraine” by Lee et al., 2016 (1) used transcranial Doppler (TCD) for assessments of the cerebral blood flow velocities (CBFV). But TCD devices (e.g. Pioneer TC 8080 ultrasound device, Nicolet Vascular, Madison, WI, USA) measure a Doppler frequency shift. Together with the cosine of the insonation angle α (between ultrasound beam and direction of blood flow) the cerebral blood flow velocity (CBFV) can be calculated.
The insonation angle α cannot be measured with TCD, therefore for correct CBFV assessments the TCD is not suitable. As a sonographer experiences every day, small changes of the insonation angle (e.g. change of hand-held TCD probe) will considerably change the resulting CBFV.
Comparisons of CBFV at baseline and follow-up are only valid with the same insonation angle. This can be achieved by the use of Transcranial Color Doppler (TCCD) or a TCD probe holding device.
The reported changes in CBFV in the study of Lee et al., 2016 (1) are most probably caused by different angles of insonation and not by different clinical courses of migraine. Other studies reporting different CBFV in the migraine course (2,3) were also not considering this methodical restriction of TCD-based CBFV assessment.
Footnotes
Declaration of conflicting interests
The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author received no financial support for the research, authorship, and/or publication of this article.