Integrated Multi-frequency Intravascular Ultrasound and Photoacoustic Imaging

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The majority (50-60%) of sudden cardiac deaths are the result of acute intracoronary thrombosis arising from what are frequently referred to as vulnerable plaques. Angiography, the gold standard in interventional coronary artery lumen imaging, is well suited to identifying flow-limiting lesions but it is now recognized that a significant proportion of ensuing cardiac events resulting in fatalities arise from vulnerable plaques that do not have significant stenosis. There is therefore an intense interest in developing imaging methods to identify these lesions with the objective of improving guidance for interventional procedures (e.g. stent placements). Intravascular imaging has the potential to detect vulnerable plaque if methods can be devised to detect 1) the thin fibrous cap at the surface of these dangerous lesions and 2) the underlying thrombogenic lippid pools that are thought to play a major role in rupture and vessel blockage. We plan to create a catheter based imaging approach that is designed to detect and quantify both of these features. Our technical expertise in the areas of micro-ultrasound arrays, photoacoustics, and intravascular ultrasound (IVUS) transducers will be the basis for the new intravascular technologies proposed here. The specific objectives of this research are to: 1) develop a bidirectional 2 frequency catheter based ultrasound probe in which the transducer is optimized for detection of thin fibrous caps in the 60 to 100 MHz range, 2) combine the dual frequency IVUS probe with appropriate optical fibre technology for the delivery of pulsed or modulated continuous wave laser energy in the near infrared region of the spectrum to perform photoacoustic imaging of lipids, and 3) quantify ultrasound and laser beam distributions and perform studies of device performance in phantoms, ex vivo coronary artery samples, and in vivo in animal models. The novelty in this project is high in that multi-frequency IVUS catheters have not previously been integrated into intravascular imaging systems much less combined with photoacoustics. This new technology would thus be well positioned to guide interventions and assist in critical decision making regarding the risk associated with vulnerable plaque.