Goertz David E, Frijlink Martijn E, de Jong Nico, van der Steen Antonius F W
Biomedical Engineering Department, Erasmus Medical Centre, Rotterdam, The Netherlands.
Ultrasound Med Biol. 2006 Apr;32(4):491-502. doi: 10.1016/j.ultrasmedbio.2006.01.001.
Nonlinear contrast agent imaging with intravascular ultrasound (IVUS) is investigated using a prototype IVUS system and an experimental small bubble contrast agent. The IVUS system employed a mechanically scanned single element transducer and was operated at a 20 MHz transmit frequency (F20) for second harmonic imaging (H40), and at a 40 MHz transmit frequency (F40) for subharmonic imaging (SH20). Characterization experiments were performed with agent and tissue phantom signals acquired during transducer rotation. The suppression of transmit frequency tissue signals was achieved using a combination of pulse-inversion and bandpass filtering. H40 was found to improve the contrast-to-tissue signal ratio (CTR) by up to 22 dB relative to F20, but suffered from tissue propagation harmonics at higher pressures (>0.3 MPa). SH20 was also shown to be possible at a range of pressures (approximately 0.25 to 1.8 MPa), with tissue signals suppressed to near the noise floor. Coronary phantom experiments demonstrated the detection of agent in 1 mm diameter vessels outside a larger 4 mm diameter vessel in which the IVUS catheter was situated. These results suggest the feasibility of harmonic IVUS contrast imaging, which may have applications in coronary lumen boundary detection and vasa vasorum imaging.
使用原型血管内超声（IVUS）系统和实验性小气泡造影剂对血管内超声的非线性造影剂成像进行了研究。该IVUS系统采用机械扫描单元素换能器，在20 MHz发射频率（F20）下进行二次谐波成像（H40），在40 MHz发射频率（F40）下进行亚谐波成像（SH20）。在换能器旋转过程中采集造影剂和组织体模信号进行表征实验。通过脉冲反转和带通滤波相结合的方式实现了发射频率组织信号的抑制。相对于F20，发现H40可将对比组织信号比（CTR）提高多达22 dB，但在较高压力（>0.3 MPa）下会受到组织传播谐波的影响。在一系列压力（约0.25至1.8 MPa）下也显示出SH20是可行的，组织信号被抑制到接近本底噪声水平。冠状动脉体模实验证明了在IVUS导管所在的4 mm直径较大血管外1 mm直径血管中检测到造影剂。这些结果表明谐波IVUS造影成像的可行性，其可能在冠状动脉腔边界检测和血管滋养管成像中具有应用价值。
