Browsing by Author "Kumru, Y."
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Item Open Access Coded divergent waves for fast ultrasonic imaging: Optimization and comparative performance analysis(Cornell University, 2021-04-21) Kumru, Y.; Köymen, HayrettinIn this paper, we present the optimal use of coded signals in diverging wave transmission for fast ultrasonic imaging. The performance of coded imaging with diverging waves, quantified by SNR, CNR, speckle power and target signal strength, is optimized in terms of code length, wave profile, aperture size and field of view. We obtained one frame in 200 microseconds using coded diverging wave transmission, equivalent to very high 5000 frames/s rate, where the imaging depth is 7.5 cm. The performances of coded diverging wave transmission and conventional single focused phased array imaging are compared on a single frame basis. Complementary Golay sequences with code lengths ranging from 2 to 10 bits are used to code the signal. The signal strength and SNR obtained using synthetic transmit aperture and conventional single focused phased array imaging techniques, respectively, are used as reference in the performance analysis. We present a method to determine the optimum diverging wave profile to maximize the SNR across the entire viewing sector, which matches the received signal strength distribution to that of synthetic transmit aperture imaging. Optimum diverging wave profiles are determined for different sector angles and for different array apertures. For 90° sector, the SNR of 8-bit coded signal with optimized diverging wave profile is higher than that of conventional single focused phased array imaging at all depths and regions except the focal region, where it is 2-8 dB lower.Item Open Access Signal-to-noise ratio of diverging waves in multiscattering media: Effects of signal duration and divergence angle(AIP Publishing, 2022-01-18) Kumru, Y.; Köymen, HayrettinIn this paper, SNR maximization in coded diverging waves is studied, and experimental verification of the results is presented. Complementary Golay sequences and binary phase shift keying modulation are used to code the transmitted signal. The SNR in speckle and pin targets is maximized with respect to chip signal length. The maximum SNR is obtained in diverging wave transmission when the chip signal is as short a duration as the array permits. We determined the optimum diverging wave profile to confine the transmitted ultrasound energy in the imaging sector. The optimized profile also contributes to the SNR maximization. The SNR performances of the optimized coded diverging wave and conventional single-focused phased array imaging are compared on a single frame basis. The SNR of the optimized coded diverging wave is higher than that of the conventional single-focused phased array imaging at all depths and regions.Item Open Access Ultrasonic array characterization in multiscattering and attenuating media using pin targets(Cornell University, 2021-05-31) Kumru, Y.; Köymen, HayrettinThis paper presents an approach to characterize ultrasonic imaging arrays using pin targets in commercial test phantoms. We used a 128-element phased array transducer operating at 7.5 MHz with a fractional bandwidth of %70. We also used a tissue-mimicking phantom in the measurements. This phantom consists of pin targets with a 50 𝝁𝒎 diameter. We excited the transducer with pulsed and coded signals. We used Complementary Golay Sequences to code the transmitted signal and Binary Phase Shift Keying for modulation. We characterized the transducer array by using the transfer function, line spread function, range resolution, and beam width in an attenuating and scattering medium. We showed that the pin targets, which are very thin compared to the diffractionlimited focus of the transducer array, are suitable for the transducer characterization under weak reflected signal conditions.