An array transmitter for dual-frequency contrast enhanced intravascular ultrasound imaging

Recent studies suggests that contrast ultrasound for molecular imaging or vasa vasorum (VV) assessment may be promising in identification of vulnerable plaques. However, conventional intravascular ultrasound (IVUS) transducers with frequency of 15 MHz – 60 MHz are not optimized for imaging with micro bubble contrast agents due to the ineffective micro bubble excitation at high frequencies and poor signal separation from tissue. This paper presents design and fabrication of a lateral mode transducer array with center frequency of 2 MHz for contrast enhanced IVUS (CE-IVUS) imaging, which can generate sufficient pressure to excite microbubbles more effectively and therefore could be used for dual-frequency microbubble superharmonic imaging, or ‘acoustic angiography’. Several commercial transducers with central frequency of 15 MHz, 20 MHz and 25 MHz were used as receivers to receive the contrast signal. In the contrast testing, the high frequency echo of the nonlinear response from microbubbles in a micro-tube with diameter of 0.2 mm was detected. The maximum contrast to noise ratio was 12.2 dB. The results show that superharmonic signals (over 9
^th
harmonic) can be received; suggesting good resolution and signal separation in contrast enhanced IVUS imaging.