Influence of temporal insonation window quality on the assessment of cerebral autoregulation with transcranial Doppler sonography.
Cerebral autoregulation can be assessed quickly and noninvasively using transcranial Doppler sonography (TCD). A poor transtemporal insonation window is a common limitation in TCD examinations. The effects of insonation quality on TCD autoregulation measurements have never been investigated. We developed two methods to quantitatively measure insonation quality. We also validated a model to artificially worsen the insonation window. This involves inserting a thin aluminium foil between the TCD probe and the skin. Forty-six healthy volunteers underwent TCD examination before and after artificial reduction of the transtemporal insonation quality. Two autoregulation parameters, the phase difference (PD) and a cross-correlation coefficient (Mx), were calculated from the recordings. The aluminium foil model realistically simulates poor insonation conditions, producing a decrease in the signal power from 36.4 +/- 2.8 dB to 32.0 +/- 1.5 dB. In corrupted insonation windows, the PD is artificially low (native: 34.2 +/- 9.3 degrees , corrupted: 29.9 +/- 9.7 degrees , p = 0.002), but the Mx is not significantly different. Insonation quality may introduce a systematic bias of clinically relevant magnitude into TCD-based cerebral autoregulation studies. This must be considered when studies of elderly patients are planned. This article discusses strategies to account for this bias.
Lorenz
Matthias W
MW
Department of Neurology, Johann Wolfgang Goethe University, Frankfurt am Main, Germany. matthias.lorenz@em.uni-frankfurt.de
Gonzalez
Marilen
M
Lienerth
Christian
C
Loesel
Nadine
N
Thoelen
Nina
N
Sitzer
Matthias
M
D000328:Adult; D000465:Algorithms; D000535:Aluminum; D002536:Cerebral Arteries / Q000000981:diagnostic imaging; D003627:Data Interpretation, Statistical; D006706:Homeostasis; D006801:Humans; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013701:Temporal Bone / Q000033:anatomy & histology*; D017585:Ultrasonography, Doppler, Transcranial / Q000295:instrumentation / Q000379:methods*
D000535:Aluminum