The effects of temporal bone on transcranial Doppler ultrasound beam shape

A knowledge of beam shape is desirable for many Doppler ultrasound applications, and is especially important for transcranial Doppler recordings where the beam may undergo significant distortion by the skull. Although it may not be possible to determine the precise beam shape for individual cases due to variations in the physical characteristics of the media in the beam path, information about the range of beam shapes that are likely to arise for in vivo recordings from the middle cerebral artery may in future allow limits of uncertainty to be derived, and may even allow partial correction in some cases. In order to assess the potential intersubject variation in beam sensitivity across the middle cerebral artery, the beam shapes generated by four commercial Transcranial Doppler transducers and the effects on beam shape of four different samples of temporal bone were investigated. The results demonstrate that there seems to be relatively little difference in the beam shapes of commercial transducers, but that the distortion effects of temporal bone are variable and unpredictable.