Methodological parameters influence the detection of right-to-left shunts by contrast transcranial Doppler ultrasonography

Background and Purpose-Contrast transcranial Doppler ultrasonography is a n ew method to detect intracardiac right-to-left shunts, such as the patent f oramen ovale. However, the methodology of the procedure varies considerably among investigators. This study was undertaken to assess the influence of methodological parameters on the results of the contrast transcranial Doppl er examination in the detection of right-to-left shunts. Methods-A total of 72 patients (mean age, 58.2+/-14.7 years) had a contrast transcranial Doppler ultrasonography examination. To study the influence o f methodological factors, patients with evidence of a right-to-left shunt u nderwent repeated examinations with modified procedures. Parameters under i nvestigation were the timing of the Valsalva maneuver, the dose of the cont rast medium, and the patient's posture during the examination. Results-The median contrast signal count was 58.5 and 48.0 (P<0.001) and th e median latency of the first intracranially detected contrast signal was 1 2.5 and 8.5 seconds (P=0.05) when the Valsalva maneuver was performed 5 and 0 seconds after the start of the injection, respectively. Reducing the con trast medium dose from 10 to 5, 2.5, and 1.2 mt resulted in a decline of th e median signal count from 54.5 to 28.5, 20.5, and 12.0 (P<0.01), respectiv ely, while the latency of the first contrast signal increased from 13.3 to 14.0, 14.6, and 15.0 seconds (P<0.05). The sitting position also produced a lower signal count than the supine position (P<0.02). Conclusions-This study demonstrates that several essential methodological p arameters influence the results of the contrast transcranial Doppler ultras onography examination. Therefore, it is necessary to standardize the proced ure to permit comparable quantitative assessments of the shunt volume. The findings of the present study suggest that 10 mi, of contrast medium be inj ected with the patient in the supine position and that the Valsalva maneuve r be performed 5 seconds after the start of the injection.