5 sonuçlar
Arama Sonuçları
Listeleniyor 1 - 5 / 5
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 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.
