Potential advantage of flash echocardiography for digital subtraction of B-mode images acquired during myocardial contrast echocardiography

Optimal assessment of myocardial perfusion with contrast echocardiography b y using B-mode imaging often requires image alignment and background subtra ction, which are time consuming and need extensive expertise. Flash echocar diography Is a new technique in which primary images are gated to the elect rocardiogram and secondary Images are obtained by transmitting ultrasound p ulses in rapid succession after each primary image. Myocardial opacificatio n is seen in the primary image and not in the secondary images because of u ltrasound-induced bubble destruction. Because the interval between the prim ary and first few secondary images is very short, cardiac motion between th ese images should be minimal. Therefore we hypothesized that 1 or more seco ndary images could be subtracted from the primary image without the need fo r image alignment. The ability of ultrasound to destroy microbubbles was as sessed by varying the sampling rate, line density, and mechanical, index in 6 open-chest dogs. The degree of translation between images was quantified in the x and y directions with the use of computer cross-correlation. At s ampling rates of 158 Hz or less and a mechanical index of more than 0.6, vi deointensity rapidly declined to baseline levels by 25 ms. Significant tran slation between images was noted only at intervals of more than 112 ms. It Is concluded that flash echocardiography can be used for digital subtractio n of baseline from contrast-enhanced B-mode images without image alignment. Background subtraction is therefore feasible on-line, potentially eliminat ing the need for off-line image processing in the future.