Detection of Contrast Agents: Plane Wave Versus Focused Transmission

Ultrasound contrast agent (UCA) imaging provides a cost-effective diagnostic tool to assess tissue perfusion and vascular pathologies. However, excessive transmission (TX) levels may negatively impact both uniform diffusion and survival rates of contrast agents, limiting their density and thus their echogenicity. Contrast detection methods with both high sensitivity and low-contrast destruction rate are thus essential to maintain diagnostic capabilities. Plane-wave TX with a high number of compounding angles has been suggested to produce good quality images at pressure levels that do not destroy UCA. In this paper, we performed a quantitative evaluation of detection efficacy of flowing UCA with either traditional focused scanning or ultrafast plane-wave imaging. Amplitude modulation (AM) at nondestructive pressure levels was implemented in the ULA-OP ultrasound research platform. The influence of the number of compounding angles, peak-negative pressure, and flow speed on the final image quality was investigated. Results show that the images obtained by compounding multiple angled plane waves offer a greater contrast (up to a 12-dB increase) with respect to focused AM. This increase is attributed mainly to noise reduction caused by the coherent summation in the compounding step. Additionally, we show that highly sensitive detection is already achieved with a limited compounding number (N