Li W, van der Steen A F, Lancee C T, Honkoop J, Gussenhoven E J, Bom N
Erasmus University Rotterdam, The Netherlands.
Ultrasound Med Biol. 1996;22(5):583-90. doi: 10.1016/0301-5629(96)00023-3.
One limitation encountered using high frequency intravascular ultrasound (IVUS) is the echogenicity of blood, which increases dramatically at frequencies of 20-40 MHz. Because of the higher velocity of moving blood particles, the echo pattern of flowing blood shows more variations in time than that of the wall. To investigate the time-varying characteristics of the blood scattering measurements were performed on the radiofrequency (RF) data collected in vivo from five pig experiments. After positioning the echo catheter inside the iliac artery, an M-mode sequence of 30 RF traces was acquired at a high pulse repetition rate (5 kHz). The RF correlation time was measured on the regions of blood and the arterial wall. Two processing techniques, temporal averaging and correlation, were tested for suppression of the blood echo intensity. The correlation time Tc measured in the blood region was approximately 1 ms, which was shorter than that measured in the wall region (Tc >> 6 ms). The correlation values calculated in a small window showed a large variation in the blood region while the wall region produced a constant high output. After processing eight consecutive RF traces (delta T = 200 microseconds), the temporal averaging method results in a 50% intensity reduction in the blood region. Using the correlation output as a weighting function, the blood echo intensity can be further reduced to only 10% of its original value. Application of the RF correlation processing to a cross-sectional image data demonstrates the feasibility of this technique to remove most of the blood echoes and enhance the image contrast of the luminal interface.
使用高频血管内超声（IVUS）时遇到的一个限制是血液的回声性，在20 - 40兆赫兹频率下其回声性会急剧增加。由于流动血液颗粒的速度较高，流动血液的回波模式在时间上的变化比血管壁的回波模式更多。为了研究血液散射的时变特性，对从五个猪实验体内采集的射频（RF）数据进行了测量。将回波导管置于髂动脉内后，以高脉冲重复频率（5千赫兹）采集了30条RF迹线的M型序列。在血液区域和动脉壁区域测量了RF相关时间。测试了两种处理技术，即时间平均和相关，以抑制血液回波强度。在血液区域测量的相关时间Tc约为1毫秒，比在血管壁区域测量的相关时间短（Tc >> 6毫秒）。在一个小窗口中计算的相关值在血液区域显示出很大变化，而血管壁区域产生恒定的高输出。在处理八条连续的RF迹线（时间间隔ΔT = 200微秒）后，时间平均方法使血液区域的强度降低了50%。使用相关输出作为加权函数，血液回波强度可进一步降低至其原始值的仅10%。将RF相关处理应用于横截面图像数据证明了该技术去除大部分血液回波并增强管腔界面图像对比度的可行性。
