Application of interhemispheric index for transcranial Doppler sonography velocity measurements and evaluation of recording time

BACKGROUND AND PURPOSE: To validate the reliability of transcranial Doppler sonography velocity measurements in clinical settings, assessment of the reproducibility of repeated bilateral simultaneous measurements and the optimal recording time is needed. Our hypothesis was that interhemispheric indices would prove more valid than the absolute velocity measurements usually applied. The potential interference between ultrasound beams in bilateral samplings also needs evaluation.

METHODS: Thirty healthy volunteers were studied at rest within hours or with a 2-month interval between measurements. Absolute blood flow velocities and side-to-side indices between velocities obtained in the middle cerebral arteries were measured over a 30-second period by two independent examiners. The correlation coefficient (r) and the coefficients of variation of the difference between either absolute velocities (CV) or indices (CVi) were calculated. The beat-to-beat variation of the diastolic, systolic, and mean velocities was also recorded. For evaluation of ultrasound beam interference, measurements were performed with and without one probe unplugged.

RESULTS: In the interobserver study in which measurements were repeated within hours, r = .92, CV = 8.8%, and CVi = 4.1%. In the intraobserver study in which measurements were repeated with a 2-month interval, r = .8, CV = 13.0%, and CVi = 7.3%. A recording time of 30 seconds reduced CVi to 2.6%, whereas for absolute velocities 5-second recordings produced an acceptable variation. There was no significant interference between bilaterally placed probes.

CONCLUSIONS: The introduction of interhemispheric indices improve interobserver and intraobserver reproducibility by approximately 50%. We recommend use of the index in clinical settings in which unilateral velocity changes are expected. For measurement of an interhemispheric index, a recording time of 30 seconds is recommended, whereas 5-second measurement periods yield a sufficient estimate of absolute velocities.