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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 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.Yayın Forward-looking IVUS imaging using an annular-ring CMUT array(IEEE, 2005) Değertekin, Fahrettin Levent; Karaman, Mustafa; Güldiken, Rasim OytunA 64-element, 1.15mm diameter annular-ring CMUT array was characterized and used for forward-looking IVUS imaging tests. The array was manufactured using low temperature processes suitable for CMOS electronics integration on a single chip. The 43×140µm2 array element has suitable view angle for forward looking imaging around 15MHz center frequency and pulse-echo measurements show nearly 100% fractional bandwidth around 17MHz. For imaging and SNR measurements, RF A-scan data sets from various targets were collected using an interconnect scheme forming a 32-element array configuration. The results demonstrate that annular-ring CMUT arrays fabricated with CMOS compatible processes are capable of forward-looking IVUS imaging.Yayın A lumped circuit model for the radiation impedance of a 2D CMUT array element(IEEE, 2005) Bozkurt, Ayhan; Karaman, MustafaElements of a 2D array used for 3D acoustic imaging have dimensions smaller than half of the acoustic wavelength due to the Nyquist criteria for spatial sampling. Therefore, analyses involving circuit models for the array elements have to account for the reactive part of the radiation impedance of the array element. In this paper, we introduce a lumped circuit model for the complex radiation impedance of a 2D CMUT array element. Using the finite element method (FEM) we first show that the radiation impedance of the array element is identical to that of a plane piston transducer of comparable dimensions. Then, we show that the complex radiation impedance of the 2D array element can be represented by a simple resonant circuit placed parallel to the real radiation impedance in the Mason's equivalent circuit. The component values of the reactive lumped elements forming the resonant circuit were determined by fitting the impedance of overall equivalent circuit to the FEM results using the Nelder-Mead minimization algorithm.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 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 Dual electrode capacitive micromachined ultrasonic transducer array for 1-D intracardiac echocardiography (ICE)(American Society of Mechanical Engineers (ASME), 2007) Güldiken, Rasim Oytun; Zahorian, Jaime S.; Karaman, Mustafa; Değertekin, Fahrettin LeventWe designed and fabricated a 64 element 1-D linear dual electrode Capacitive Micromachined Ultrasonic Transducer (CMUT) array operating at 9.5 MHz for Intracardiac Echocardiography (ICE). The dual electrode CMUT structure increases the overall sensitivity by 12.6dB (6.2dB in receive sensitivity; 6.4dB in output pressure) when compared to optimized single electrode CMUT. We report peak output pressure of 2.3MPa on the CMUT surface when 170V AC and 180V DC is applied. This significant performance increase makes the CMUT more competitive with their piezoelectric counterparts.Yayın Micromachined capacitive transducer arrays for intravascular ultrasound(SPIE, 2005) Değertekin, Fahrettin Levent; Güldiken, Rasim Oytun; Karaman, MustafaIntravascular ultrasound (IVUS) imaging has become an essential imaging modality for the effective diagnosis and treatment of cardiovascular diseases during the past decade enabled by innovative applications of piezoelectric transducer technology. The limitations in the manufacture and performance of the same piezoelectric transducers have also impeded the improvement of IVUS for emerging clinically important applications such as forward viewing arrays for guiding interventions and high resolution imaging of arterial structure such as vulnerable plaque and fibrous cap, and also implementation of techniques such as harmonic imaging of the tissue and of the contrast agents. Capacitive micromachined ultrasonic transducer (CMUT) technology shows great potential for transforming IVUS not only to satisfy these clinical needs but also to open up possibilities for low-cost imaging devices integrated to therapeutic tools. We have developed manufacturing processes with a maximum process temperature of 250°C to build CMUTs on the same silicon chip with integrated electronics. Using these processes we fabricated CMUT arrays suitable for forward viewing IVUS in the 10-20MHz range. We characterized these array elements in terms of pulse-echo response, radiation pattern measurements and demonstrated its volumetric imaging capabilities on various imaging targets.
