IEEE transactions on ultrasonics, ferroelectrics, and frequency control
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IEEE Trans Ultrason Ferroelectr Freq Control · Oct 2006
Intravascular ultrasound tissue harmonic imaging in vivo.
Tissue harmonic imaging (THI) has been shown to increase image quality of medical ultrasound in the frequency range from 2 to 10 MHz and might, therefore, also be used to improve image quality in intravascular ultrasound (IVUS). In this study we constructed a prototype IVUS system that could operate in both fundamental frequency and second harmonic imaging modes. This system uses a conventional, continuously rotating, single-element IVUS catheter and was operated in fundamental 20 MHz, fundamental 40 MHz, and harmonic 40 MHz modes (transmit 20 MHz, receive 40 MHz). ⋯ Acquisitions of fundamental 20 and 40 MHz and second harmonic acquisitions resulted in cross sections of the phantom and a rabbit aorta. The harmonic results of the imaging experiments showed the feasibility of intravascular THI with a conventional IVUS catheter both in a phantom and in vivo. The harmonic acquisitions also showed the potential of THI to reduce image artifacts compared to fundamental imaging.
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IEEE Trans Ultrason Ferroelectr Freq Control · Jun 2006
Novel transmit aperture for very large depth of focus in medical ultrasound B-scan.
Obtaining high quality ultrasound images at high frame rates has great medical importance, especially in applications in which tissue motion is significant (e.g., the beating heart). Dynamic focus and dynamic aperture can improve image quality significantly, and they have been implemented on the receive beam in state-of-the-art medical ultrasound systems. ⋯ Thus uniform sensitivity and uniform point spread function can be achieved over a very large depth without reducing the frame rate. Numerical simulations validate our theoretical analysis and demonstrate significant promises of the new technique.
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IEEE Trans Ultrason Ferroelectr Freq Control · Feb 2006
Annular-ring CMUT arrays for forward-looking IVUS: transducer characterization and imaging.
In this study, a 64-element, 1.15-mm diameter annular-ring capacitive micromachined ultrasonic transducer (CMUT) array was characterized and used for forward-looking intravascular ultrasound (IVUS) imaging tests. The array was manufactured using low-temperature processes suitable for CMOS electronics integration on a single chip. The measured radiation pattern of a 43 X 140-microm2 array element depicts a 40 degrees view angle for forward-looking imaging around a 15-MHz center frequency in agreement with theoretical models. ⋯ 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. An experimental point spread function was obtained and compared with simulated and theoretical array responses, showing good agreement. Therefore, this study demonstrates that annular-ring CMUT arrays fabricated with CMOS-compatible processes are capable of forward-looking IVUS imaging, and the developed modeling tools can be used to design improved IVUS imaging arrays.
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IEEE Trans Ultrason Ferroelectr Freq Control · Feb 2006
High-frequency ultrasound annular array imaging. Part II: digital beamformer design and imaging.
This is the second part of a two-paper series reporting a recent effort in the development of a high-frequency annular array ultrasound imaging system. In this paper an imaging system composed of a six-element, 43 MHz annular array transducer, a six-channel analog front-end, a field programmable gate array (FPGA)-based beamformer, and a digital signal processor (DSP) microprocessor-based scan converter will be described. A computer is used as the interface for image display. ⋯ The image from a wire phantom obtained with the imaging system was compared to that from a prototype ultrasonic backscatter microscope with a 45 MHz single-element transducer. The improved lateral resolution and depth of field from the wire phantom image were observed. Images from an excised rabbit eye sample also were obtained, and fine anatomical structures were discerned.
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IEEE Trans Ultrason Ferroelectr Freq Control · Dec 2005
LetterTransducer for harmonic intravascular ultrasound imaging.
A recent study has shown the feasibility of tissue harmonic imaging (THI) using an intravascular ultrasound (IVUS) transducer. This correspondence describes the design, fabrication, and characterization of a THI-optimized piezoelectric transducer with oval aperture of 0.75 mm by 1 mm. ⋯ The Krimholtz-Leedom-Matthaei (KLM) model was used to iteratively find optimal material properties of the different layers. The transducer characterization showed -6 dB fractional bandwidths of 30% and 25%, and two-way insertion losses of -20 dB and -36 dB, respectively.