Multiresolution analysis of intravascular ultrasound harmonic signals to image pre-rupture plaques

The pursuit of a definitive method of plaque diagnosis continues as there is an unmet need for clinical identification of vulnerable plaque before they rupture. Despite the efforts of current leading technologies like 3D volumetric analysis, wavelet analysis and virtual histology in imaging vulnerable plaque, these are not considered definitive due to their lack of identification of plaques likely to rupture, inability to differentiate vulnerable from stable plaque characteristics and primarily, the inability to image at high resolution. There is a need for a higher resolution IVUS device and a method to characterize the thin cap fibroatheromas (TCFA) before they rupture causing an acute coronary event. The objective is the early detection of vulnerable plaque by multiresolution analysis (MRA) of IVUS radiofrequency (RF) signals from harmonic imaging. Broadband high resolution (~19 ?m) focused polymer transducers were fabricated. Fundamental (at 20 MHz and 40 MHz) and Harmonic signals (at 40 MHz and 80 MHz) from the tissue were obtained in one scan line using a previously established pulse inversion technique with 60% bandwidth Gaussian pulses. Multiresolution analysis was carried out by obtaining the wavelet coefficients with forward wavelet transform for fundamental and harmonic signals. Daubechies 4 wavelet filter was used to resolve components as close as 24 ?m. Fundamental and harmonic signals were analyzed at different resolutions to find an appropriate scale. Circumferential images of the coronary artery generated by inverse wavelet transform of wavelet coefficients from scales 4 to 8 were compared. Multiresolution analysis of the RF signals reveal that the fundamental and harmonic cross sectional images can be viewed at various scales, each scale offering unique diagnostic information. Harmonic signals identify tissue components not seen in fundamental at 20 MHz and 40 MHz. MRA of harmonic signals leads to identification of plaque components at multiple freq- - uencies providing additional diagnostic information. This technique may lead to an early detection of plaque, thereby reducing the incidents of acute myocardial infarctions (AMI).