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

为了利用微泡的非线性特征用于组织血流灌注的超声可视化，研究了Albunex、SHU508A、QW3600和F-04E(PVC-AN)上微泡的基本特征。利用12位A/D转换器对微泡后向散射的射频信号或/和多普勒信号进行数字化处理。计算了射频功率谱和多普勒频移。采用2.5 Mhz和3.5 Mhz扫描仪进行B型扫描，或采用2.0 Mhz和2.5 Mhz探头、可变脉冲重复频率的多谱勒采样。观察到功率谱和基波/二次谐波比的衰减。数字化射频信号经过傅里叶变换和带通滤波，得到载波(基波)和二次谐波的Hilbert变换。从代表后向散射区域幅度的B-型图像中，选择微气泡区域。后向散射的幅度(以分贝为单位)随扫描时间的延长呈指数下降。在2.5 MHz扫描下，Albunex的后向散射衰减最大。SHU508A和F-04E表现出相似的指数衰减，但速度较小。在所有微泡中，2.5 MHz的绝对后向散射和二次谐波/基波的比值(0.186~0.371)大于3.5 MHz。在2.5 MHz，衰减也更大。与其他三个气泡相比，QW3600显示出非常缓慢的后向散射衰减，具有对超声波暴露的耐久性。在2.5 MHz以下，Albunex的载频和二次谐波的衰减不一致。

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.