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Harmonic intravascular ultrasound

The goal of this project is to investigate the inherent benefits of THI in IVUS applications over fundamental IVUS.

Researchers: Marcia Emmer, David Maresca, Robert Beurskens, Nico de Jong, Ton van der Steen

Background:
Arising from the use of contrast agents it was discovered recently that the nonlinear properties of tissue could be used very well for imaging. During nonlinear propagation, sound fields are generated at integer multiples of the transmitted frequency. Tissue Harmonic Imaging (THI) has been shown to increase the image quality of ultrasound images in conventional echocardiography, due in large part to the reduced effects of phase aberration, reverberation and sidelobe artefacts. Furthermore, the nonlinear properties of ultrasound are material-dependent. This might give potential for tissue characterization. Feasibility studies showed the possibility to generate and image second harmonic signals at higher frequencies (20 MHz) with ultrasound biomicroscopy and Intravascular Ultrasound (IVUS) systems.

Aim:
The goal of this subproject is to investigate the inherent benefits of THI in IVUS applications over fundamental IVUS.

Methodology:
An experimental set up has been constructed and in vitro and in vivo experiments have been done. The fundamental beam at 20 and 40 MHz has been compared with the second harmonic beam of 40 MHz of several transducers, both PVDF and PZT transducers. Situations where higly reflective stents degrade ultrasound images have been imaged in both fundamental and harmonic modes. In vivo experiments have been performed with conventional single element rotating IVUS catheters.

Results:
Beam profiles show that second harmonic imaging improve the beam width and reduce the acoustic energy of side lobes and in the near field, compared to the fundamental beam. We also showed that THI can improve ultrasound imaging at IVUS frequencies in situations where a stent is involved. Another study showed the feasibility of THI with a conventional IVUS catheter in vivo.

Publications:
M.E. Frijlink, D.E. Goertz, F.S. Foster and A.F.W.van der Steen, ‘High Frequency Harmonic Imaging in Presence of Intravascular Stents’. Transactions of IEEE Ultrasonics 2003, pp.208-211.

Illustrations: