Solid-state arrays and beamformers for side-looking intravascular ultrasonic imaging

Current solid-state intravascular ultrasound (IVUS) devices use a one-dimensional(1-D) rectangular array wrapped around the cylindrical catheter. Beamforming inthese devices is limited to synthetic phased array processing, and the image quality isdegraded by low signal to noise ratio (SNR) and lack of focusing in elevation. Wepropose new solid-state reconfigurable cylindrical array configurations, based onnon-uniform aperture sampling, enabling realization of low-cost integrated phasedarray beamformers based on the latest IC and transducer integration techniques. Weemployed non-uniform (Fresnel) aperture sampling with identical differential delaysbetween adjacent elements to reduce dynamic beamformer complexity. For thispurpose, the angles of the element boundaries and centers are determined byequalizing path difference of neighboring elements. For Side Looking-IVUS (SLIVUS),the image plane is scanned through stepping the active aperture, and theactive array must be reformed in each step. Fresnel sampled ring array leads to asimplified phased array beamformer with N/2 identical differential delays. The samelogic applies to a two-dimensional (2-D) array with NL×NE-elements over acylindrical patch. We compared the proposed and existing array designs throughnumerical point spread function (PSF) simulations. The uniform and Fresnel sampled1-D ring arrays perform similarly in terms of beam quality while the latter improvesimage SNR by a factor of ?NL due to synthetic vs full phased array processing. TheFresnel sampled 2-D array performs dramatically better in elevation compared to 1-Dring array. The additional contribution of 2-D array on image quality is high SNRproduced by phased array beamforming. The proposed Fresnel sampling ofcylindrical aperture simplifies phased array beamformer by halving the requireddelay element count and transforms the complex 2-D beamformer into a separablebeamformer that requires simple 1-D beamformers. The resulting 1-D and 2-D SLIVUSarray configurations could be realizable using monolithic integration of theanalog beamformers with transducer arrays.