Visualizing carotid artery plaque by ultrasound is not a perfect test, as it does not reveal whether the plaque is of the kind that has a greater chance of embolization, unless it is clearly ulcerating, heterogeneous, and of high grade. There are a couple techniques that can indicate whether the plaque is “vulnerable” to embolism, including detecting microvessels that penetrate the plaque and spotting the molecular signatures of plaques that commonly break off. Both use microbubbles as contrast agents that are detected using intravascular ultrasound, but traditional ultrasound still does a poor job of it.
Researchers from North Carolina State University and the University of North Carolina at Chapel Hill have just reported the development of a dual-frequency intravascular ultrasound that is significantly better at spotting microbubbles passing by. So far the researchers tested the device in laboratory experiments and are planning on moving forward with pre-clinical studies that will set the stage for testing the technology on humans.
Some details from the study abstract:
Current intravascular ultrasound (IVUS) probes are not optimized for contrast detection because of their design for high-frequency fundamental-mode imaging. However, data from transcutaneous contrast imaging suggests the possibility of utilizing contrast ultrasound for molecular imaging or vasa vasorum assessment to further elucidate atherosclerotic plaque deposition. This paper presents the design, fabrication, and characterization of a small-aperture (0.6 × 3 mm) IVUS probe optimized for high-frequency contrast imaging. The design utilizes a dual-frequency (6.5 MHz/30 MHz) transducer arrangement for exciting microbubbles at low frequencies (near their resonance) and detecting their broadband harmonics at high frequencies, minimizing detected tissue backscatter. The prototype probe is able to generate nonlinear microbubble response with more than 1.2 MPa of rarefractional pressure (mechanical index: 0.48) at 6.5 MHz, and is also able to detect microbubble response with a broadband receiving element (center frequency: 30 MHz, −6-dB fractional bandwidth: 58.6%). Nonlinear super-harmonics from microbubbles flowing through a 200-µm-diameter micro-tube were clearly detected with a signal-to-noise ratio higher than 12 dB. Preliminary phantom imaging at the fundamental frequency (30 MHz) and dual-frequency super-harmonic imaging results suggest the promise of small aperture, dual-frequency IVUS transducers for contrast-enhanced IVUS imaging.
Study in IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control: A Preliminary Engineering Design of Intravascular Dual-Frequency Transducers for Contrast-Enhanced Acoustic Angiography and Molecular Imaging…