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Yayın An Analog beamformer for integrated high-frequency medical ultrasound imaging(IEEE, 2011) Gürün, Gökçe; Zahorian, Jaime; Tekeş, Coşkun; Karaman, Mustafa; Hasler, Paul E.; Değertekin, Fahrettin LeventWe designed and fabricated a dynamic receive beamforming integrated circuit (IC) in 0.35-mu m CMOS technology. This beamformer is suitable for integration with an ultrasound annular array for high-frequency (30-50 MHz) intravascular ultrasound (IVUS) imaging. The beamformer IC is capable of buffering, delaying and preamplification for 8 receive channels. We explored an analog delay cell based on a currentmode first-order all-pass filter, which is used as the basic building block to form an analog dynamic delay line. We also explored a bandwidth enhancement method on the delay cell that improved the overall bandwidth of the delay line by a factor of 6. Each delay cell consumes 2.1 mW of power and is capable of generating a tunable delay between 1.75 ns to 2.5 ns, enabling dynamic receive beamforming over a focal range from 1.4 mm to 2 mm. We successfully integrated the fabricated beamformer IC with an 8-element annular array. Our experimental test results demonstrated the desired buffering, preamplification and delaying capabilities of the beamformer.Yayın An analog integrated circuit beamformer for high-frequency medical ultrasound imaging(IEEE-INST Electrical Electronics Engineers Inc, 2012-10) Gürün, Gökçe; Zahorian, Jaime S.; Şişman, Alper; Karaman, Mustafa; Hasler, Paul E.; Değertekin, Fahrettin LeventWe designed and fabricated a dynamic receive beamformer integrated circuit (IC) in 0.35-mu m CMOS technology. This beamformer IC is suitable for integration with an annular array transducer for high-frequency (30-50 MHz) intravascular ultrasound (IVUS) imaging. The beamformer IC consists of receive preamplifiers, an analog dynamic delay-and-sum beamformer, and buffers for 8 receive channels. To form an analog dynamic delay line we designed an analog delay cell based on the current-mode first-order all-pass filter topology, as the basic building block. To increase the bandwidth of the delay cell, we explored an enhancement technique on the current mirrors. This technique improved the overall bandwidth of the delay line by a factor of 6. Each delay cell consumes 2.1-mW of power and is capable of generating a tunable time delay between 1.75 ns to 2.5 ns. We successfully integrated the fabricated beamformer IC with an 8-element annular array. Experimental test results demonstrated the desired buffering, preamplification and delaying capabilities of the beamformer.Yayın An annular CMUT array beamforming system for high-frequency side looking IVUS imaging(2010) Satır, Sarp; Gürün, Gökçe; Zahorian, Jaime S.; Karaman, Mustafa; Hasler, Paul E.; Değertekin, Fahrettin LeventA CMUT annular array system for Side-Looking Intravascular Ultrasound (SL-IVUS) with fixed transmit and dynamic receive focusing capabilities has been developed. The system was experimentally characterized and validated through analytical models that simulate the beamformed transducer behavior. An 840 m diameter, 35MHz array was fabricated, characterized, and used in experiments. The array consists of curved 18m by 60m CMUT membranes that form 8 ring transducer elements with approximately equal areas. The beamforming system uses an IC chip consisting of 8 transimpedance amplifiers and delay elements for receive beamforming with adjustable delays between 2ns and 4ns, that are constant up to 50 MHz with close to unity gain. Transmit focusing is implemented with an FPGA controlled, high voltage pulser board that can generate adjustable electrical pulses with delays as small as 2ns. The system is characterized by measuring the radiation patterns of individual CMUT annular array elements as well as the unfocused and fixed transmit focused arrays. The results show predicted behavior including acoustic crosstalk effects at certain frequencies. For transmit-receive beamforming characterization, a 25m gold wire was imaged using 4 beamformed transmit elements and 4 beamformed receive elements with different delay values. The results show improved lateral resolution and lower side lobes with proper beamforming.Yayın Evaluation of CMUT annular arrays for side-looking IVUS(IEEE, 2009) Şişman, Alper; Zahorian, Jaime S.; Gürün, Gökçe; Karaman, Mustafa; Balantekin, Müjdat; Değertekin, Fahrettin Levent; Hasler, Paul E.Side-looking (SL) IVUS probes are extensively used for management of cardiovascular diseases. Currently SL-IVUS imaging probes use either a single rotating transducer element or solid-state arrays. Probes with single rotating piezoelectric transducer have simple front-end, but have fixed focused operation, and suffers from motion artifacts. Solid-state SL-IVUS imaging probes use piezoelectric transducer arrays and electronic beam-forming. Synthetic phased array processing of signals detected with small-sized elements in these arrays limits the SNR achievable with these probes. In this study, we explore a new SL-IVUS probe architecture employing rotating phased annular CMUT arrays. We tested and compared imaging performance of the existing and proposed probe configurations through simulated point spread functions. We also two fabricated sample annular array designs operating at 20-MHz and 50-MHz. Our experimental measurements on the 20-MHz array in oil shows 105% fractional bandwidth. The 50-MHz array with parylene coating shows approximately 40% fractional bandwidth measured in water. We also present imaging results acquired from wire-targets to test the experimental point-spread functions.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 Front-end CMOS electronics for monolithic integration with CMUT arrays: Circuit design and initial experimental results(2008) Gürün, Gökçe; Qureshi, Muhammad Shakeel; Balantekin, Müjdat; Güldiken, Rasim Oytun; Zahorian, Jaime S.; Peng, Shengyu; Basu, Arindam; Karaman, Mustafa; Hasler, Paul E.; Değertekin, Fahrettin LeventThis paper discusses design of CMOS-ASICs for monolithic integration of CMUT arrays by post-CMOS fabrication. We describe design strategies for monolithic integration and demonstrate the advantages of CMUT-on-CMOS approach. On the same wafer, separate sets of IC cells are designed to interface different types of CMUT arrays for IVUS and ICE applications. Circuit topologies include resistive feedback transimpedance amplifiers on the receiver side, along with multiplexers and buffers. Gains and bandwidths of receiving amplifiers are optimized separately to fit different array specifications such as number of elements, element size and operation bandwidth. To drive CMUTs a high voltage pulser array is designed in the same 3.3V unmodified CMOS technology by combining existing technological layers in an unconventional way. CMUT arrays are then built on top of the custom made 8" wafer containing these circuits fabricated in a 0.35µm standard CMOS process. We present initial characterization of the CMO electronics and pulse-echo measurements obtained post-CMOS fabricated CMUT elements.Yayın A tunable analog delay element for high-frequency dynamic beamforming(IEEE, 2009) Gürün, Gökçe; Şişman, Alper; Zahorian, Jaime S.; Satır, Sarp; Karaman, Mustafa; Hasler, Paul E.; Değertekin, Fahrettin LeventImplementing beamforming for high frequency arrays is challenging because of the accurate delay requirements at high frequencies. High frequency digital beamforming is not suitable for catheter based applications as a large number of cables is required between the array and the external beamformer. A possible solution is to perform analog beamforming on an integrated circuit adjacent or monolithically integrated to the imaging array. In this study, we introduce an improved voltage in voltage out low pass filter as an analog delay cell for high frequency dynamic beamformers. This circuit can generate three times more delay with a given bandwidth when compared to conventional low pass filters. Delay of the circuit is tunable and the gain of the cell is inherently very close to unity. The proposed delay cell operates single ended and therefore is more suitable for CMUT operation which generates single ended output. We designed a test beamformer for a 30MHz, equal area, annular array with 100% bandwidth using the proposed delay cell and the unit-delay focusing architecture. Required delays are implemented using a delay line made up of improved delay elements with tunable delays. To demonstrate functionality we designed and fabricated a custom front-end IC in a 0.5µm standard CMOS process. The IC chip consists of 8 transimpedance amplifiers, voltage-to-current converters, the analog dynamic beamformer, and two buffers. We present results of preliminary imaging experiments that demonstrate the focusing capability.
