Combined intravascular ultrasound and photoacoustic imaging
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The primary focus of the work was to evaluate the capability of intravascular photoacoustic (IVPA) imaging in combination with intravascular ultrasound (IVUS) to detect and differentiate atherosclerotic plaques. The composition rather than structural narrowing of the arteries is a major indicator of the propensity of a vascular lesion to rupture. Consequently, intravascular imaging of these high-risk plaques is required to exactly determine the vulnerable plaque constituents for appropriate follow-up therapy. Our multi-modality imaging approach aims to utilize the high resolution structural assessment abilities of IVUS and the optical contrast of IVPA imaging and is capable of differentiating the lipid, fibrous and fibro-cellular components of an inflammatory lesion. To test the hypothesis, we developed an IVUS catheter based laboratory prototype of a combined IVUS/IVPA imaging system. The performance of the synergistic combination of IVUS and IVPA imaging was evaluated through tissue mimicking phantom studies. Further, to test the ability of the combined imaging to detect plaques, excised samples of an aorta were utilized from a specifically designed animal model of atherosclerosis. Ex-vivo IVPA imaging studies were performed using a 532 nm laser excitation to detect the lipids in the plaque. In addition, multi-wavelength spectroscopic IVPA imaging studies were evaluated to differentiate plaques. Finally, an ultrasound based temperature estimation method was utilized to demonstrate and confirm safety of IVPA imaging for clinical intravascular applications. Upon analysis of the results of our investigation, we believe that IVPA imaging offer numerous potential advantages when integrated with clinical IVUS imaging. The IVUS imaging system with integrated IVPA imaging capability could play a major role in interventional cardiology.