Stimulated Acoustic Emission Detected by Transcranial Color Doppler Ultrasound

Abstract

Background and Purpose —Experimental and clinical data suggest that insonation of echo-contrast agents with high acoustical power produces disintegration of microbubbles, resulting in a pseudo-Doppler phenomenon called stimulated acoustic emission (SAE). The purpose of this study was to investigate whether SAE might be detected by transcranial color Doppler imaging and whether 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 detected by velocity-coded color Doppler and power Doppler recordings. Transcranial color as well as power Doppler investigations were performed in 10 healthy 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 mosaic of color Doppler pixels ranging over the full color scale. Apparent velocity information and spatial distribution of SAE signals changed from image frame to image frame. In the experimental model, the intensity of SAE signals 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 stronger and more rapid disintegration. In humans, SAE signals were clearly detected in cerebral tissue regions. The intensity of SAE signals in those regions (eg, temporal cortex, 3.7±1.2 dB) was ≈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 detectable by transcranial color and power Doppler sonography. Signals due to SAE might represent tissue perfusion, thereby providing a method for imaging flow with transcranial ultrasound.