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Yayın Co-array optimization of CMUT arrays for forward-looking IVUS(IEEE, 2009-09) Tekeş, Coşkun; Karaman, Mustafa; Değertekin, Fahrettin LeventThe ring annular array structure is a preferred configuration for implementing Forward-Looking IVUS (FLIVUS) catheters as it allows for volumetric imaging as well as use of a guidewire at the center. CMUT technology is promising for these arrays especially with the flexibility of locating array elements on the circular donut area efficiently. To take advantage of this flexibility, in this study, we introduce a new co-array sampling strategy that improves imaging performance while keeping the number of firings at a level suitable for real-time imaging. The presented co-array sampling strategy is based on the idea of adjusting the element density of the co-array rings in radial direction to suppress side lobes. In non-uniform sampling of the co-array with a given number of firings, the inter-element distances are adjusted both in radial and angular direction from inner ring to outer ring to fit a given apodization function. To test the imaging performance, we performed numerical simulations of the co-array with non-uniform sampling fitting to the raised-cosine apodization. The simulation results shows that sidelobe level can be reduced more than 10 dB by using non-uniform co-array sampling. This approach does use uniform weighting of all Tx and Rx elements in beamforming, and hence does not cause any SNR loss for apodization.Yayın Dual-annular-ring CMUT array for forward-looking IVUS imaging(IEEE, 2006) Güldiken, Rasim Oytun; Zahorian, Jaime; Balantekin, Müjdat; Değertekin, Fahrettin Levent; Tekeş, Coşkun; Şişman, Alper; Karaman, MustafaWe investigate a dual-annular-ring CMUT array configuration for forward-looking intravascular ultrasound (FL-IVUS) imaging. The array consists of separate, concentric transmit and receive ring arrays built on the same silicon substrate. This configuration has the potential for independent optimization of each array and uses the silicon area more effectively without any particular drawback. We designed and fabricated a 1mm diameter test array which consists of 24 transmit and 32 receive elements. We investigated synthetic phased array beamforming with a non-redundant subset (if transmit-receive element pairs of the dual-annular-ring array. For imaging experiments, we designed and constructed a programmable FPGA-based data acquisition and phased array beamforming system. Pulse-echo measurements along with imaging simulations suggest that dual-ring-annular array should provide performance suitable for real-time FLAVUS applications.Yayın Forward-looking IVUS imaging using a dual-annular ring CMUT array: Experimental results(IEEE, 2007) Güldiken, Rasim Oytun; Zahorian, Jaime S.; Gürün, Gökçe; Qureshi, Muhammad Shakeel; Balantekin, Müjdat; Tekeş, Coşkun; Hasler, Paul E.; Karaman, Mustafa; Carlier, Stephane; Değertekin, Fahrettin LeventThis paper presents the experimental results on forward-looking Intravascular ultrasound (FL-IVUS) using dual-annular-ring CMUT arrays. The array has a diameter of 1mm including bondpads which consists of separate, concentric 24 transmit and 32 receive ring arrays built on the same silicon substrate. This configuration has the potential for Independent optimization of each array and uses the silicon area more effectively without any drawback. For imaging experiments, we designed and constructed a custom integrated circuit using a standard 0.5 mu m CMOS process for data acquisition. A sample pulse-echo signal received from the oil-air Interface (plane reflector) at 6mm had a center frequency of 11MHz with 95% fractional 6-dB bandwidth. The measured SNR of the echo was 24 dB with no averaging. B-scan image of a wire-phantom was generated to test the resolution.Yayın Annular CMUT arrays for side looking intravascular ultrasound imaging(IEEE, 2007) Zahorian, Jaime; Güldiken, Rasim Oytun; Gürün, Gökçe; Qureshi, Muhammad Shakeel; Balantekin, Müjdat; Değertekin, Fahrettin Levent; Carlier, Stephane; Şişman, Alper; Karaman, MustafaAlthough side looking intravascular ultrasound (SL-IVUS) imaging systems using single element piezoelectric transducers set the resolution standard in the assessment of the extent of coronary artery disease, improvements in transducer performance are needed to perform harmonic imaging and high resolution imaging of vulnerable plaque. With their small channel count; annular arrays exploiting the inherent broad bandwidth of CMUTs and electronic focusing capability of integrated electronics provide a path for desired SL-IVUS imaging catheters. In this paper, we first describe the design, low temperature fabrication of an 8401 mu m diameter, 8 element CMUT annular array. Testing of the individual elements in oil shows a uniform device behavior with 100% fractional bandwidth around 20MHz without including the effects of attenuation and diffraction. We also present linear scan imaging results obtained on wire targets in oil, tissue and tissue mimicking phantoms using both unfocused and dynamically focused transducers. The results for axial and lateral resolution are in agreement predicted by the simulations and show the feasibility of this approach for high resolution SL-IVUS imaging.
