-
[show abstract]
[hide abstract]
ABSTRACT: High-frequency (HF) ultrasound imaging has been shown to be useful for non-invasively imaging anatomical structures of the eye and small animals in biological and pharmaceutical research, achieving superior spatial resolution. Cardiovascular research utilizing mice requires not only realtime B-scan imaging, but also ultrasound Doppler to evaluate both anatomy and blood flow of the mouse heart. This paper reports the development of an HF ultrasound duplex imaging system capable of both B-mode imaging and Doppler flow measurements, using a 64-element linear array. The system included an HF pulsed-wave Doppler module, a 32-channel HF B-mode imaging module, a PC with a 200 MS/s 14-bit A/D card, and real-time Lab View software. A 50 dB SNR and a depth of penetration of larger than 12 mm were achieved using a 35-MHz linear array with 50 μm pitch. The two-way beam widths were determined to be 165 to 260 μm and the clutter-energy-to-total-energy ratio (CTR) were 9.1 to 12 dB when the array was electronically focused at different focal points at depths from 4.8 to 9.6 mm. The system is capable of acquiring real-time B-mode images at a rate greater than 400 frames per second (fps) for a 4.8 × 13 mm field of view, using a 30 MHz 64-element linear array with 100 μm pitch. Sample in vivo cardiac high frame rate images and duplex images of mouse hearts are shown to assess its current imaging capability and performance for small animals.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 08/2010; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: For real-time visualization of the mouse heart (6 to 13 beats per second), a back-end processing system involving high-speed signal processing functions to form and display images has been developed. This back-end system was designed with new signal processing algorithms to achieve a frame rate of more than 400 images per second. These algorithms were implemented in a simple and cost-effective manner with a single field-programmable gate array (FPGA) and software programs written in C++. The operating speed of the back-end system was investigated by recording the time required for transferring an image to a personal computer. Experimental results showed that the back-end system is capable of producing 433 images per second. To evaluate the imaging performance of the back-end system, a complete imaging system was built. This imaging system, which consisted of a recently reported highspeed mechanical sector scanner assembled with the back-end system, was tested by imaging a wire phantom, a pig eye (in vitro), and a mouse heart (in vivo). It was shown that this system is capable of providing high spatial resolution images with fast temporal resolution.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 08/2009; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have recently presented a new method to suppress side lobes and clutter in ultrasound imaging called dual apodization with cross-correlation (DAX). However, due to the random nature of speckle, artifactual black spots may arise with DAX-processed images. In this paper, we present one possible solution, called dynamic DAX, to reduce these black spots. We also evaluate the robustness of dynamic DAX in the presence of phase aberration and noise. Simulation results using a 5 MHz, 128-element linear array are presented using dynamic DAX with aberrator strengths ranging from 25 ns root-mean-square (RMS) to 45 ns RMS and correlation lengths of 3 mm and 5 mm. When simulating a 3 mm diameter anechoic cyst, at least 100% improvement in the contrast-to-noise ratio (CNR) compared with standard beamforming is seen using dynamic DAX, except in the most severe case. Layers of pig skin, fat, and muscle were used as experimental aberrators. Simulation and experimental results are also presented using dynamic DAX in the presence of noise. With a system signal-to-noise ratio (SNR) of at least 15 dB, we have a CNR improvement of more than 100% compared with standard beamforming. This work shows that dynamic DAX is able to improve the contrast-to-noise ratio reliably in the presence of phase aberration and noise.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 03/2009; 56(2):291-303. · 1.80 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Very large element counts (16,000-65,000) are required for 2-D arrays for 3-D rectilinear imaging. The difficulties in fabricating and interconnecting 2-D arrays with a large number of elements (>5,000) have limited the development of suitable transducers for 3-D rectilinear imaging. In this paper, we propose an alternative solution to this problem by using a dual-layer transducer array design. This design consists of 2 perpendicular 1-D arrays for clinical 3-D imaging of targets near the transducer. These targets include the breast, carotid artery, and musculoskeletal system. This transducer design reduces the fabrication complexity and the channel count, making 3-D rectilinear imaging more realizable. With this design, an effective N times N 2-D array can be developed using only N transmitters and N receivers. This benefit becomes very significant when N becomes greater than 128, for example. To demonstrate feasibility, we constructed a 4 times 4 cm prototype dual-layer array. The transmit array uses diced PZT-5H elements, and the receive array is a single sheet of un-diced P[VDF-TrFE] copolymer. The receive elements are defined by the copper traces on the flexible interconnect circuit. The measured -6 dB fractional bandwidth was 80% with a center frequency of 4.8 MHz. At 5 MHz, the nearest neighbor crosstalk of the PZT array and PVDF array was -30.4 plusmn 3.1 dB and -28.8 plusmn 3.7 dB, respectively. This dual-layer transducer was interfaced with an Ultrasonix Sonix RP system, and a synthetic aperture 3-D data set was acquired. We then performed offline 3-D beamforming to obtain volumes of nylon wire targets. The theoretical lateral beamwidth was 0.52 mm compared with measured beamwidths of 0.65 mm and 0.67 mm in azimuth and elevation, respectively. Then, 3-D images of an 8 mm diameter anechoic cyst phantom were also acquired.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 02/2009; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Very large element counts (16,000-65,000) are required for 2-D arrays for 3-D rectilinear imaging. The difficulties in fabricating and interconnecting 2-D arrays with a large number of elements (>5,000) have limited the development of suitable transducers for 3-D rectilinear imaging. In this paper, we propose an alternative solution to this problem by using a dual-layer transducer array design. This design consists of 2 perpendicular 1-D arrays for clinical 3-D imaging of targets near the transducer. These targets include the breast, carotid artery, and musculoskeletal system. This transducer design reduces the fabrication complexity and the channel count, making 3-D rectilinear imaging more realizable. With this design, an effective N x N 2-D array can be developed using only N transmitters and N receivers. This benefit becomes very significant when N becomes greater than 128, for example. To demonstrate feasibility, we constructed a 4 x 4 cm prototype dual-layer array. The transmit array uses diced PZT-5H elements, and the receive array is a single sheet of undiced P[VDF-TrFE] copolymer. The receive elements are defined by the copper traces on the flexible interconnect circuit. The measured -6 dB fractional bandwidth was 80% with a center frequency of 4.8 MHz. At 5 MHz, the nearest neighbor crosstalk of the PZT array and PVDF array was -30.4 +/- 3.1 dB and -28.8 +/- 3.7 dB, respectively. This dual-layer transducer was interfaced with an Ultrasonix Sonix RP system, and a synthetic aperture 3-D data set was acquired. We then performed offline 3-D beamforming to obtain volumes of nylon wire targets. The theoretical lateral beamwidth was 0.52 mm compared with measured beamwidths of 0.65 mm and 0.67 mm in azimuth and elevation, respectively. Then, 3-D images of an 8 mm diameter anechoic cyst phantom were also acquired.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 01/2009; 56(1):204-12. · 1.80 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, we report recent progress that has been made in the development of a high frame rate duplex HF ultrasound system with both B-scan imaging and Doppler flow measurements. A 32-channel HF analog beamformer module with transmitting focusing and dynamic focusing on reception was implemented. High-speed timing circuits were used to achieve high imaging frame rate by reducing the acquisition overhead. Therefore, the frame rate of the system relies only on the field of view. The system also included a 64-channel analog front-end pulser/receiver, a HF pulsed-wave (PW) Doppler module, a PC with a 200 MS/s 14-bit PCI A/D card and real-time Labview software for data acquisition and image display. A wire phantom used to evaluate the resolution of the system. High frame rate B-scan images of mouse hearts have been obtained, as well as the PW Doppler blood flow velocity profiles at the specified location. The system is able to acquire real-time B-mode images at a rate greater than 400 frames per second in a 4.8 times 13 mm field of view. In vivo mouse experiment results show a promising future of this system in small animal research. The system will be expanded to support future arrays with more elements.
Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
-
[show abstract]
[hide abstract]
ABSTRACT: Under mechanical compression, tissue movements are inherently three-dimensional. 2-D strain imaging can suffer from decorrelation noise caused by out-of-plane tissue movement in elevation. With 3-D strain imaging, all tissue movements can be estimated and compensated, hence minimizing out-of-plane decorrelation noise. Promising 3-D strain imaging results have been shown using 1-D arrays with mechanical translation in elevation. However, the relatively large slice thickness and mechanical translation can degrade image quality. Using 2-D arrays, a better elevational resolution can be achieved with elevational focusing Furthermore, scanning with 2-D arrays is done electronically, which eliminates the need for mechanical translation. In this paper, we present our initial 3-D strain images of gelatin/agar phantoms using a 4 cm x 4 cm ultrasonic sparse rectilinear 2-D array operating at 5 MHz.
Ultrasonics Symposium, 2007. IEEE; 11/2007
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents a recently developed backend processing system for high-frequency high-frame rate ultrasound B-mode imaging, which is responsible for extracting clinically useful information from acquired echo signals and displaying the information on a monitor in real time. The system is capable of producing up to 400 images per second with minimal signal processing error for real-time display. With this capability, the system can be used for cardiac imaging of the mouse where the heart rate is 5-10 beats per second. The backend processing system was implemented by using a single FPGA (Stratix EP1S60F1020C6, Altera Corporation, San Jose, CA) and software programs written by C++. Its performances were evaluated by wire phantom, in vitro pig eye, and in vivo mouse heart imaging tests. Experimental results demonstrate that the implemented system is capable of acquiring up to 400 images per second of which an image size is 256 by 256 pixels and providing the -6 dB axial and lateral resolutions of 48 mum and 103 mum, respectively. In addition, it is shown that the image display rate of the system is currently 95 images per second due to the limitation of a monitor's capability although one thousand consecutive images can be stored in a hard disk of a personal computer.
Ultrasonics Symposium, 2007. IEEE; 11/2007
-
[show abstract]
[hide abstract]
ABSTRACT: High-frequency (HF) ultrasound imaging has been shown to be useful for imaging anatomical structures of the eye and small animals in biological and pharmaceutical research, achieving good spatial resolution at an affordable price. Cardiovascular research utilizing mice requires not only real-time B-scan imaging, but also ultrasound Doppler to evaluate both movements and blood flow of the mouse heart. In this paper, we report the development of the first real-time duplex HF ultrasound system with both B-scan imaging and Doppler imaging, using a 30 MHz 64-element linear array. The system included a HF pulsed-wave Doppler module, a 16-channel HF analog beamformer module, a PC with a 200 MS/s 14-bit PCI A/D card, and real-time Labview software. Both a wire phantom and a micro flow phantom were used to evaluate system performance. The system has a lateral resolution better than 160 urn and is capable of measuring motion velocity as low as 0.1 mm/s and as high as 1 m/s. B-scan images of excised rabbit eyes have been achieved, as well as clear blood flow velocity profiles in mouse superficial vessels with diameters of 200 mum and major aortas. The system is able to acquire real-time B-mode and Doppler images. The system will also have the capability of acquiring 400 B-mode images per second. In vivo zebrafish and mouse experiment results show a promising future of this system in small animal research.
Ultrasonics Symposium, 2007. IEEE; 11/2007
-
[show abstract]
[hide abstract]
ABSTRACT: This paper proposes a novel design of envelope detectors capable of supporting a small animal cardiac imaging system requiring a temporal resolution of more than 150 frames per second. The proposed envelope detector adopts the quadrature demodulation and the look-up table (LUT) method to compute the magnitude of the complex baseband components of received echo signals. Because the direct use of the LUT method for a square root function is not feasible due to a large memory size, this paper presents a new LUT strategy dramatically reducing its size by using binary logarithmic number system (BLNS). Due to the nature of BLNS, the proposed design does not require an individual LOG-compression functional block. In the implementation using a field programmable gate array (FPGA), a total of 166.56 Kbytes memories were used for computing the magnitude of 16-bit in-phase and quadrature components instead of 4 Gbytes in the case of the direct use of the LUT method. The experimental results show that the proposed envelope detector is capable of generating LOG- compressed envelope data at every clock cycle after 32 clock cycle latency, and its maximum error is less than 0.5 (i.e., within the rounding error), compared with the arithmetic results of square root function and LOG compression.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 10/2007; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report the development of a high-frequency (30-50 MHz), real-time ultrasonic imaging system for cardiac imaging in mice. This system is capable of producing images at 130 frames per second (fps) with a spatial resolution of less than 50 mum. A novel mechanical sector probe was developed that utilizes a magnetic drive mechanism and custom-built servo controller for high speed and accuracy. Additionally, a very light-weight (< 0.28 g), single-element transducer was constructed and used to reduce the mass load on the motor. The imaging electronics were triggered according to the angular position of the transducer in order to compensate for the varying speed of the sector motor. This strategy ensured the production of equally spaced scan lines with minimal jitter. Wire phantom testing showed that the system axial and lateral resolutions wore 48 mum and 72 mum, respectively. In vivo experiments showed that high-frequency ultrasonic imaging at 130 fps is capable of showing a detailed depiction of a beating mouse heart.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 09/2007; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A design of a low-cost bipolar pulse generator for high-frequency (HF) ultrasound applications is presented. The pulse generator can produce N cycle (1-255 cycles) bipolar pulses with center frequency over 60 MHz. The measured pulse amplitude was over 160 Vpp, and the pulse ringing was less than 0.3 Vpp (i.e., signal-to-ring ratio is 55 dB). The pulser can be used in high-frequency ultrasound Doppler and B-mode imaging applications with arrays
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 03/2007; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Small animals, especially mice, have become widely used models for studies of genes and human diseases. For cardiac imaging in mice, whose hearts beat at a rate higher than 300 beats per minute, the spatial and temporal resolution of current clinical ultrasonic scanners are far from ideal and simply inadequate for such applications. In this research, a real-time high frequency (30-50 MHz) ultrasound imaging system was developed with a frame rate of 130 frames per second (fps) and spatial resolution of 50 microns for cardiac applications in small animals. The mechanical scanning of the device was provided by a sector scanner using a magnetic drive mechanism and a digital servo controller for high speed and accuracy. A very light-weight (< 0.28 g), single element, focused transducer was specially designed and constructed to reduce the motor load and achieve high frame rates. To ensure equally spaced scan lines and minimize jitters, the imaging electronics were triggered according to the angular position of the transducer to compensate for the varying speed of the sector motor. In vivo experiments on adult mice and mouse embryos showed that real time ultrasound imaging at a frame rate of 130 fps could demonstrate detailed depiction of cardiac function with adequate spatial resolution, which allows researchers to examine and monitor small animal cardiac function
Ultrasonics Symposium, 2006. IEEE; 11/2006
-
[show abstract]
[hide abstract]
ABSTRACT: A two-dimensional (2-D) array of 256 times 256 = 65,536 elements, with total area 4 times 4 = 16 cm<sup>2</sup>, serves as a flexible platform for developing acquisition schemes for 3-D rectilinear ultrasound imaging at 10 MHz using synthetic aperture techniques. This innovative system combines a simplified interconnect scheme and synthetic aperture techniques with a 2-D array for 3-D imaging. A row-column addressing scheme is used to access different elements for different transmit events. This addressing scheme is achieved through a simple interconnect, consisting of one top, one bottom single-layer, flex circuits that, compared to multilayer flex circuits, are simpler to design, cheaper to manufacture, and thinner so their effect on the acoustic response is minimized. We present three designs that prioritize different design objectives: volume acquisition time, resolution, and sensitivity, while maintaining acceptable figures for the other design objectives. For example, one design overlooks time-acquisition requirements, assumes good noise conditions, and optimizes for resolution, achieving -6 dB and -20 dB beamwidths of less than 0.2 and 0.5 mm, respectively, for an F/2 aperture. Another design can acquire an entire volume in 256 transmit events, with -6 dB and -20 dB beamwidths in the order of 0.4 and 0.8 mm, respectively
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 06/2006; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A real-time digital beamformer for high-frequency ( >20 MHz) linear ultrasonic arrays has been developed. The system can handle up to 64-element linear array transducers and excite 16 channels and receive simultaneously at 100 MHz sampling frequency with 8-bit precision. Radio frequency (RF) signals are digitized, delayed, and summed through a real-time digital beamformer, which is implanted using a field programmable gate array (FPGA). Using fractional delay filters, fine delays as small as 2 ns can be implemented. A frame rate of 30 frames per second is achieved. Wire phantom (20 μm tungsten) images were obtained and -6 dB axial and lateral widths were measured. The results showed that, using a 30 MHz, 48-element array with a pitch of 100 μm produced a -6 dB width of 68 μm in the axial and 370 μm in the lateral direction at 6.4 mm range. Images from an excised rabbit eye sample also were acquired, and fine anatomical structures, such as the cornea and lens, were resolved.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 03/2006; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have developed two digital beamformers for eye imaging using 30-50 MHz transducer arrays: a 6-channel digital beamformer for a six-ring annular array ultrasound transducer (43 MHz) and a 16-channel digital beamformer for a linear array ultrasound transducer (30 MHz) of 48-64 elements. The hardware allows the flexibility for multiple transmit focusing, dynamic receive focusing, amplitude apodization, and dynamic aperture control. Individual channel delays are applied using a combination of coarse and fine delays. The coarse delays are integer multiples of the clock periods achieved by using a FIFO structure, and the fine delays are applied with interpolation of a 4-tap fractional delay (FD) FIR filter. The dynamic receive focusing is implemented based on a state machine which updates delay values and the FD filter coefficients according to the depth of the echoes. The aperture apodization is set according to the focusing zone. Cross-sectional wire target images, using a 20 μm diameter wire, from both arrays are shown. The images of an excised pig eye clearly show the fine structures of the anterior segment, including cornea and lens.
Ultrasonics Symposium, 2004 IEEE; 09/2004
-
[show abstract]
[hide abstract]
ABSTRACT: In our continuing efforts to improve 3D rectilinear ultrasound, we present a new design using a simplified interconnect architecture, switching scheme, and synthetic aperture methods. The main benefit of this design is the interconnect, where an expensive multilayer flex circuit is no longer required. The interconnect uses a row-column addressing scheme to enable different groups of elements. Over multiple transmissions, this design is capable of essentially synthesizing a 256 × 256 = 65536-element, fully sampled 2D rectilinear array. Using a sparse synthetic transmit aperture, a column or several columns of elements are bussed together, so that a cylindrical wavefront is emitted into the field. In receive, the echoes from individual elements along a row are recorded by the system receive channels. Different columns and rows are selected in subsequent transmissions, and the echoes from these transmit events are then recorded to synthesize a fully sampled array. We have performed computer simulations of a 10 MHz, 256 × 256 2D synthetic array subaperture to determine the radiation pattern. For an F/2 aperture, the on-axis case (x,y,z) = (0,0,20) mm showed a narrow beam down to -52 dB. In the azimuth direction, on-axis lateral beamwidths at -6, -20, and -40 dB were 0.21 mm, 0.43 mm, and 0.87 mm, respectively. As a tradeoff, elevational on-axis beamwidths were wider, respectively 0.18 mm, 1.17 mm, and 7.82 mm for the same corresponding dB levels.
Ultrasonics Symposium, 2004 IEEE; 09/2004
-
[show abstract]
[hide abstract]
ABSTRACT: In previous work, we developed two generations of a real-time rectilinear volumetric scanner operating at 5 MHz for abdominal, breast, or vascular imaging using a Mills cross two-dimensional (2-D) array and a rectilinear periodic 2-D array. To improve spatial resolution performance and sensitivity, we developed a new design using 4:1 receive mode multiplexing. With 4:1 multiplexing, the new 65,000 element 2-D array has 4/spl times/256=1024 receivers so that 256 receivers can be used on any image line. The two major benefits of using receive mode multiplexing are an increase in receive sensitivity due to a greater number of receive elements, and a decrease in grating lobe and clutter levels due to increased receive element density. Theoretical simulations and analysis show an increase of about 13 dB in sensitivity compared to our previous work. With these encouraging results, a new 65,000 element 5-MHz, 2-D array having 1024 receivers and 169 transmitters was prototyped. In addition, the multiplexer and control circuitry were designed, built, and interfaced with both the transducer and volumetric scanner. Images of tissue-mimicking phantoms and in vivo targets were obtained. Using a spherical cyst phantom, experimental results showed a+12 dB improvement in signal-to-noise ratio and a+6 dB improvement in contrast compared to our previous work.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 03/2004; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In previous work, we developed two generations of a real-time rectilinear volumetric scanner operating at 5 MHz for abdominal, breast or vascular imaging using Mills cross 2-D array and rectilinear periodic 2-D array. To improve spatial resolution performance and sensitivity, we developed a new design using 4:1 receive mode multiplexing. With 4:1 multiplexing, the new 2-D array of 65,000 elements has 4 × 256 = 1024 receivers so that 256 receivers can be used on any image line. The two major benefits of using receive mode multiplexing include: (1) an increase in receive sensitivity due to the greater number of receive elements; and (2) an increase in receive element density which reduces grating lobe and clutter levels. Theoretical simulations and analysis show an increase of about 13 dB in sensitivity compared to our previous work. With these encouraging results, a new 65,000 element 5 MHz 2-D array having 1024 receivers and 169 transmitters was prototyped. In addition, multiplexer and control circuitry were designed, built, and interfaced with both the transducer and volumetric scanner. Images of tissue-mimicking phantoms and in vivo were obtained. Using a spherical cyst phantom, experimental results showed a +12 dB improvement in signal-to-noise ratio and a +6 dB improvement in contrast compared to our previous work.
Ultrasonics, 2003 IEEE Symposium on; 11/2003
-
[show abstract]
[hide abstract]
ABSTRACT: In patients who are obese or exhibit signs of pulmonary disease, standard transthoracic scanning may yield poor quality cardiac images. For these conditions, two-dimensional transesophageal echocardiography (TEE) is established as an essential diagnostic tool. Current techniques in transesophageal scanning, though, are limited by incomplete visualization of cardiac structures in close proximity to the transducer. Thus, we propose a 2D curvilinear array for 3D transesophageal echocardiography in order to widen the field of view and increase visualization close to the transducer face. In this project, a 440 channel 5 MHz two-dimensional array with a 12.6 mm aperture diameter on a flexible interconnect circuit has been molded to a 4 mm radius of curvature. A 75% element yield was achieved during fabrication and an average -6dB bandwidth of 30% was observed in pulse-echo tests. Using this transducer in conjunction with modifications to the beam former delay software and scan converter display software of the our 3D scanner, we obtained cylindrical real-time curvilinear volumetric scans of tissue phantoms, including a field of view of greater than 120 degrees in the curved, azimuth direction and 65 degrees phased array sector scans in the elevation direction. These images were achieved using a stepped subaperture across the cylindrical curvilinear direction of the transducer face and phased array sector scanning in the noncurved plane. In addition, real-time volume rendered images of a tissue mimicking phantom with holes ranging from 1 cm to less than 4 mm have been obtained. 3D color flow Doppler results have also been acquired. This configuration can theoretically achieve volumes displaying 180 degrees by 120 degrees. The transducer is also capable of obtaining images through a curvilinear stepped subaperture in azimuth in conjunction with a rectilinear stepped subaperture in elevation, further increasing the field of view close to the transducer face. Future work includes development of an array for adapting these modifications to a 6 mm diameter endoscope probe.
Ultrasonic Imaging 08/2003; 25(3):137-50. · 1.54 Impact Factor
