Estimation of Regional Myocardial Blood Flow by Trans Venous Micro-bubble and Two Dimensional Low Frequency Doppler

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To utilize non-linear character of micro-bubbles for ultrasonic visualization of tissue perfusion, fundamental characters of micro-bubbles were studied on Albunex, SHU508A,QW3600 and F-04E (PVC-AN). Radio-frequency (RF) signals of backscatter from micro-bubbles or/and Doppler signal were digitized with 12bit A/D converter. Power spectra of RF and Doppler shift were calculated. B-mode scan with 2.5 and 3.5MHz scanner or doppler sampling with 2.0 and 2.5MHz probe and variable pulse repetition rates were performed. Decay of power spectra and fundamental/second harmonic ratio were observed. Digitized RF signal were Hilbert transformed with Fourier transformation and frequency band-pass filtering to carrier (fundamental) and 2nd harmonic. From B-mode image representing regional amplitude of back scatter obtained with Hilbelt transform, the region of micro-bubble was selected. The amplitude of back scatter in dB was exponentially decreased with continuous scan. The decay of backscatter was the largest in Albunex under 2.5MHz scan. SHU508A and F-04E showed similar exponential decay with smaller velocity. In all micro-bubbles, the absolute backscatter and the ratio of the second harmonic/fundamental (.186 to .371) were larger in 2.5MHz than in 3.5MHz. The decay was also larger in 2.5MHz. QW3600 showed quite slow decay of backscatter with durability to ultrasound exposure, compared to the other three bubbles. The decay of carrier frequency and 2nd harmonic was not identical in Albunex under 2.5MHz.