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Yayın Phased subarray imaging for low-cost, wideband coherent array imaging(IEEE, 2003) Johnson, Jeremy A.; Oralkan, Ömer; Ergün, Arif Sanlı; Demirci, Utkan; Karaman, Mustafa; Khuri-Yakub, Butrus ThomasThe front-end hardware complexity of conventional full phased array (FPA) imaging is proportional to the number of array elements. Phased subarray (PSA) imaging has been proposed as a method of reducing the hardware complexity-and therefore system cost and size-while achieving near-FPA image quality. A new method is presented for designing the subarray-dependent interpolation filters suitable for wideband PSA imaging. The method was tested experimentally using pulse-echo data of a wire target phantom acquired using a 3.2-cm. 128-element capacitive micromachined ultrasonic transducer (CMUT) array with 85% fractional bandwidth at 3 MHz. A specific PSA configuration using seven 32-element subarrays was compared to FPA imaging, representing a 4-fold reduction in front-end hardware complexity and a 43% decrease in frame rate. For targets near the fixed transmit focal distance, the mean 6-dB lateral resolution was identical to that of FPA, the axial resolution improved by 4%, and the SNR decreased by 5 dB. Measurements were repeated for 10 different PSA configurations with subarray sizes ranging from 4 to 60. The lateral and axial resolutions did not vary significantly with subarray size; both the SNR and contrast-to-noise ratio (CNR) improved with increased subarray size.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 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 An endoscopie imaging system based on a two-dimensional CMUT array: real-time imaging results(IEEE, 2005) Wygant, Ira O.; Zhuang, Xuefeng; Yeh, David T.; Vaithilingam, Srikant; Nikoozadeh, Amin; Oralkan, Ömer; Ergün, Arif Sanlı; Karaman, Mustafa; Khuri-Yakub, Butrus ThomasReal-time catheter-based ultrasound imaging tools are needed for diagnosis and image-guided procedures. The continued development of these tools is partially limited by the difficulty of fabricating two-dimensional array geometries of piezoelectric transducers. Using capacitive micromachined ultrasonic transducer (CMUT) technology, transducer arrays with widely varying geometries, high frequencies, and wide bandwidths can be fabricated. A volumetric ultrasound imaging system based on a two-dimensional, 16×l6-element, CMUT array is presented. Transducer arrays with operating frequencies ranging from 3 MHz to 7.5 MHz were fabricated for this system. The transducer array including DC bias pads measures 4 mm by 4.7 mm. The transducer elements are connected to flip-chip bond pads on the array back side with 400-?m long through-wafer interconnects. The array is flip-chip bonded to a custom-designed integrated circuit (IC) that comprises the front-end electronics. Integrating the front-end electronics with the transducer array reduces the effects of cable capacitance on the transducer's performance and provides a compact means of connecting to the transducer elements. The front-end IC provides a 27-V pulser and 10-MHz bandwidth amplifier for each element of the array. An FPGA-based data acquisition system is used for control and data acquisition. Output pressure of 230 kPa was measured for the integrated device. A receive sensitivity of 125 mV/kPa was measured at the output of the amplifier. Amplifier output noise at 5 Mhz is 112 nV/?Hz. Volumetric images of a wire phantom and vessel phantom are presented. Volumetric data for a wire phantom was acquired in real-time at 30 frames per second.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 Üç boyutlu akustik görüntüleme için ön alıcı-verici tümdevre(IEEE, 2004) Çiçek, İhsan; Bozkurt, Ayhan; Karaman, MustafaTıbbi ultrasonik görüntüleme sistemleri, genel olarak bir çevirici elemanı ve akustik işaretin üretilip algılanmasından sorumlu elektronik oluşmaktadır. Tek boyutlu dönüştürücü dizileriyle, incelenmekte olan ortamın iki boyutlu kesit görüntüsü elde edilmektedir. Dönüştürücü teknolojisindeki son gelişmelerle, iki boyutlu dönüştürücü dizilerinin üretimi gerçekleştirilmiş, böylece üç boyutlu (hacimsel) görüntüleme yapılması mümkün olmuştur[1,2]. Ancak, özellikle Nyquist kriteri, dönüştürücü elemanların boyutlarını sınırladığı için, eleman boyutları oldukça küçülmüştür; bu da algılanan işareti oldukça zayıflatmaktadır. Bu nedenle, kabul edilebilir nitelikteki görüntülerin alınabilmesi için, alıcı-verici elektroniğinin iyileştirilmesi gerekmektedir. Bu çalışmada, iki boyutlu akustik çeviriciler için CMOS tabanlı ön alıcı-verici devresinin tasarımı gerçekleştirilmiştir. Devre, temel olarak, bir yüksek gerilim darbe üretici, alıcı-verici anahtarı, düşük gürültülü ön yükseltici ve dönüştürücü elemanın bağlantı dolgulamasından oluşmaktadır.Yayın Volumetric imaging using fan-beam scanning with reduced redundancy 2D arrays(IEEE, 2006) Wygant, Ira; Karaman, Mustafa; Oralkan, Ömer; Khuri-Yakub, Butrus ThomasPhased array processing with a fully populated 2D array produces the best image quality but requires excessive number of active parallel front-end channels. Here we explore four array designs with reduced redundancy in spatial frequency contents. To minimize the number of firings we employ fan-beam processing, where ID arrays are used to insonify 2D planar slices of the volume at successive firing events; echo signals are collected by the receive array elements. The array designs are compared based on simulated point spread functions, frame rate, motion susceptibility, and signal-to-noise ratio.Yayın Volumetric imaging using 2D capacitive micromachined ultrasonic transducer arrays (CMUTs): Initial results(IEEE, 2002) Oralkan, Ömer; Ergün, Arif Sanlı; Cheng, Ching-Hsiang; Johnson, Jeremy A.; Karaman, Mustafa; Lee, Thomas H.; Khuri-Yakub, Butrus ThomasThis paper presents the first volumetric images obtained using a 2D CMUT array with through-wafer via interconnects. An 8×16-element portion of a 32×64-element array flip-chip bonded onto a glass fanout chip was used in the experiments. This study experimentally demonstrates that 2D CMUT arrays can be fabricated with high yield using silicon micromachining processes, individual electrical connections can be provided using through-wafer interconnects, and the flip-chip bonding technique can be used to integrate the dense 2D arrays with electronic circuits for practical imaging applications.Yayın An integrated circuit with transmit beamforming and parallel receive channels for 3D ultrasound imaging: testing and characterization(IEEE, 2007) Wygant, Ira O.; Jamal, Nafis S.; Lee, Hyunjoo J.; Nikoozadeh, Amin; Zhuang, Xuefeng; Oralkan, Ömer; Ergün, Arif Sanlı; Karaman, Mustafa; Khuri-Yakub, Butrus ThomasThe cost and complexity of medical ultrasound imaging systems can be reduced by integrating the transducer array with an integrated circuit (IC). By incorporating some of the system's front-end electronics into an IC, bulky cables and costly system electronics can be eliminated. Here we present an IC for 3D intracavital imaging that requires few electrical connections but uses a large fraction of a 16x16-element 2D transducer array to transmit focused ultrasound. To simplify the receive and data acquisition electronics, only the 32 elements along the array diagonals are used as receivers. The IC provides a preamplifier for each receiving element. Each of the 224 transmitting elements is provided an 8-bit shift register, a comparator, and a 25-V pulser. To transmit, a global counter is incremented from 1 to 224; each pulser fires when its stored register value is equal to the global count value. Electrical testing of the fabricated IC shows that it works as designed. The IC was flip-chip bonded to a two-dimensional capacitive micromachined ultrasonic transducer (CMUT) array. A two-dimensional image of a wire target phantom was acquired.
