Stimulated acoustic emission detected by transcranial color Doppler ultrasound - A contrast-specific phenomenon useful for the detection of cerebral tissue perfusion

Background and Purpose-Experimental and clinical data suggest that insonati on of echo-contrast agents with high acoustical power produces disintegrati on of microbubbles, resulting in a pseudo-Doppler phenomenon called stimula ted acoustic emission (SAE). The purpose of this study was to investigate w hether SAE might be detected by transcranial color Doppler imaging and whet her these signals might be used for cerebral tissue perfusion measurements. Methods-Nonmoving microbubbles (SHU 563 A) were insonated in vitro through the temporal parts of a human cadaver skull, and contrast signals were dete cted by velocity-coded color Doppler and power Doppler recordings. Transcra nial color as well as power Doppler investigations were performed in 10 hea lthy volunteers with the echo-contrast agent Levovist (SHU 508 A). Results-Color Doppler signals indicating SAE were observed in vitro and in transcranial human investigations. These signals were characterized by a mo saic of color Doppler pixels ranging over the full color scale. Apparent ve locity information and spatial distribution of SAE signals changed from ima ge frame to image frame. In the experimental model, the intensity of SAE si gnals decreased exponentially over time. With an increase of acoustic power , there was a significant increase of the maximum signal intensity (P<0.01) and a significantly shortened signal duration (P<0.01), consistent with st ronger and more rapid disintegration. In humans, SAE signals were clearly d etected in cerebral tissue regions. The intensity of SAE signals in those r egions (eg, temporal cortex, 3.7+/-1.2 dB) was approximate to 8 times lower than the signal enhancement in the major cerebral arteries (eg, in the MCA , 29.5+/-5.6). Conclusions-Echo-contrast specific color Doppler signals known as SAE are d etectable by transcranial color and power Doppler sonography. Signals due t o SAE might represent tissue perfusion, thereby providing a method for imag ing flow with transcranial ultrasound.