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Yayın Integrated ultrasonic imaging systems based on CMUT arrays: Recent progress(IEEE, 2004) Wygant, Ira O.; Zhuang, Xuefeng; Yeh, David T.; Nikoozadeh, Amin; Oralkan, Ömer; Ergün, Arif Sanlı; Karaman, Mustafa; Khuri-Yakub, Butrus ThomasThis paper describes the development of an ultrasonic imaging system based on a two-dimensional capacitive micromachined ultrasonic transducer (CMUT) array. The transducer array and front-end electronics are designed to fit in a 5-mm endoscopic channel. A custom-designed integrated circuit, which comprises the front-end electronics, will be connected with the transducer elements via through-wafer interconnects and flip-chip bonding. FPGA-based signal-processing hardware will provide real-time three-dimensional imaging. The imaging system is being developed to demonstrate a means of integrating the front-end electronics with the transducer array and to provide a clinically useful technology. Integration of the electronics can improve signal-to-noise ratio, reduce the number of cables connecting the imaging probe to a separate processing unit, and provide a means of connecting electronics to large two-dimensional transducer arrays. This paper describes the imaging system architecture and the progress we have made on implementing each of its components: a 16×16 CMUT array, custom-designed integrated circuits, a flip-chip bonding technique, and signal-processing hardware.Yayın CMUT-based volumetric ultrasonic imaging array design for forward looking ICE and IVUS applications(SPIE-Int Soc Optical Engineering, 2013) Tekeş, Coşkun; Zahorian, Jaime S.; Xu, Toby; Rashid, Muhammad Wasequr; Satır, Sarp; Gürün, Gökçe; Karaman, Mustafa; Hasler, Jennifer Olson; Değertekin, Fahrettin LeventDesigning a mechanically flexible catheter based volumetric ultrasonic imaging device for intravascular and intracardiac imaging is challenging due to small transducer area and limited number of cables. With a few parallel channels, synthetic phased array processing is necessary to acquire data from a large number of transducer elements. This increases the data collection time and hence reduces frame rate and causes artifacts due to tissue-transducer motion. Some of these drawbacks can be resolved by different array designs offered by CMUT-on-CMOS approach. We recently implemented a 2.1-mm diameter single chip 10 MHz dual ring CMUT-on-CMOS array for forward looking ICE with 64-transmit and 56-receive elements along with associated electronics. These volumetric arrays have the small element size required by high operating frequencies and achieve sub mm resolution, but the system would be susceptible to motion artifacts. To enable real time imaging with high SNR, we designed novel arrays consisting of multiple defocused annular rings for transmit aperture and a single ring receive array. The annular transmit rings are utilized to act as a high power element by focusing to a virtual ring shaped line behind the aperture. In this case, image reconstruction is performed by only receive beamforming, reducing total required firing steps from 896 to 14 with a trade-off in image resolution. The SNR of system is improved more than 5 dB for the same frequency and frame rate as compared to the dual ring array, which can be utilized to achieve the same resolution by increasing the operating frequency.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 Experimental study of dual-ring CMUT array optimization for forward-looking IVUS(IEEE, 2011) Tekeş, Coşkun; Zahorian, Jaime; Gürün, Gökçe; Satir, Sarp; Hochman, Michael; Xu, Toby; Rashid, Muhammad Wasequr; Değertekin, Fahrettin Levent; Karaman, MustafaForward-looking (FL) catheters have guiding and volumetric imaging capacities which are highly desirable for IVUS applications. Large channel and firing counts have to be reduced to enable 3-D real-time imaging and simplify front-end electronics. Recently, we have proposed an optimization procedure for dual ring FL arrays which is based on finding an optimal coarray set using the simulated annealing algorithm. The presented algorithm is based on finding a predefined number of optimal firing set which results in elimination of redundant spatial frequencies in the coarray. In this study, we present the experimental demonstration of the proposed method with fabricated single chip CMUT on CMOS system based FL dual ring arrays. The dual ring CMUT arrays were monolithically fabricated on top of CMOS chips which have 25-V pulsers and low-noise transimpedance amplifiers for each transmit and receive array elements. The fabricated CMUT arrays have 56 transmit and 48 receive elements operating at 12 MHz with a 1.4 mm outer diameter. To test the imaging performance of the optimal reduced set, we obtained a 512-element coarray set from the full 2688-element set. In the experiment, we used a phantom of 100-mu m aluminium wires immersed in oil tank. We have reconstructed both 2-D PSFs and B-scan images of wire targets. Experimental results demonstrate that the simulated annealing based optimal firing set achieves acceptable lateral and contrast resolution performances with 1/5 of the full set.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.Yayın A miniature real-time volumetric ultrasound imaging system(SPIE-Int Soc Optical Engineering, 2005) Wygant, Ira O.; Yeh, David T.; Zhuang, Xuefeng; Nikoozadeh, Amin; Oralkan, Ömer; Ergün, Arif Sanlı; Karaman, Mustafa; Khuri-Yakub, Butrus ThomasProgress made in the development of a miniature real-time volumetric ultrasound imaging system is presented. This system is targeted for use in a 5-mm endoscopic channel and will provide real-time, 30-mm deep, volumetric images. It is being developed as a clinically useful device, to demonstrate a means of integrating the front-end electronics with the transducer array, and to demonstrate the advantages of the capacitive micromachined ultrasonic transducer (CMUT) technology for medical imaging. Presented here is the progress made towards the initial implementation of this system, which is based on a two-dimensional, 16×16 CMUT array. Each CMUT element is 250 µm by 250 µm and has a 5-MHz center frequency. The elements are connected to bond pads on the back side of the array with 400-µm long through-wafer interconnects. The transducer array is flip-chip bonded to a custom-designed integrated circuit that comprises the front-end electronics. The result is that each transducer element is connected to a dedicated pulser and low-noise preamplifier. The pulser generates 25-V, 100-ns wide, unipolar pulses. The preamplifier has an approximate transimpedance gain of 500 k? and 3-dB bandwidth of 10 MHz. In the first implementation of the system, one element at a time can be selected for transmit and receive and thus synthetic aperture images can be generated. In future implementations, 16 channels will be active at a given time. These channels will connect to an FPGA-based data acquisition system for real-time image reconstruction.Yayın Beamforming and hardware design for a multichannel front-end integrated circuit for real-time 3D catheter-based ultrasonic imaging(SPIE-Int Soc Optical Engineering, 2006) Wygant, Ira O.; Karaman, Mustafa; Oralkan, Ömer; Khuri-Yakub, Butrus ThomasWe are working on integrating front-end electronics with the ultrasound transducer array for real-time 3D ultrasound imaging systems. We achieve this integration by flip-chip bonding a two-dimensional transducer array to an integrated circuit (IC) that comprises the front-end electronics. The front-end IC includes preamplifiers, multiplexers, and pulsers. We recently demonstrated a catheter-based real-time ultrasound imaging system based on a 16 x 16-element capacitive micromachined ultrasonic transducer (CMUT) array. The CMUT array is flip-chip bonded to a front-end IC that includes a pulser and preamplifier for each element of the array. To simplify the back-end processing and signal routing on the IC for this initial implementation, only a single array element is active at a time (classic synthetic aperture (CSA) imaging). Compared with classic phased array imaging (CPA), where multiple elements are used on transmit and receive, CSA imaging has reduced signal-to-noise ratio and prominent grating lobes. In this work, we evaluate three array designs for the next generation front-end IC. The designs assume there are 16 receive channels and that numerous transmit pulsers are provided by the IC. The designs presented are: plus-transmit x-receive, boundary-transmit x-receive with no common elements, and full-transmit x-receive with no common elements. Each design is compared with CSA and CPA imaging. We choose to implement an IC for the full-transmit x-receive with no common elements (FT-XR-NC) design for our next-generation catheter-based imaging system.
