Biomedical subjects

R E Davidsen

Publications and source records attributed to R E Davidsen.

3 recordsLinked to original sources

PubMed1998

Progress in two-dimensional arrays for real-time volumetric imaging.

The design, fabrication, and evaluation of two dimensional array transducers for real-time volumetric imaging are described. The transducers we have previously described operated at frequencies below 3 MHz and were unwieldy to the operator because of the interconnect schemes used in connecting to the transducer handle. Several new transducers have been developed using new connection technology. A 40 x 40 = 1,600 element, 3.5 MHz array was fabricated with 256 transmit and 256 receive elements. A 60 x 60 = 3,600 element 5.0 MHz array was constructed with 248 transmit and 256 receive elements. An 80 x 80 = 6,400 element, 2.5 MHz array was fabricated with 256 transmit and 208receive elements. 2-D transducer arrays were also developed for volumetric scanning in an intra cardiac catheter, a 10 x 10 = 100 element 5.0 MHz forward-looking array and an 11 x 13 = 143 element 5.0 MHz side-scanning array. The-6dB fractional bandwidths for the different arrays varied from 50% to 63%, and the 50 omega insertion loss for all the transducers was about-64 dB. The transducers were used to generate real-time volumetric images in phantoms and in vivo using the Duke University real time volumetric imaging system, which is capable of generating multiple planes at any desired angle and depth within the pyramidal volume.

Cardiac Volume↗

PubMed1997

A two-dimensional array for B-mode and volumetric imaging with multiplexed electrostrictive elements.

A 2:1 multiplexed 2-D array has been developed that has a sparse element pattern designed for real time volumetric imaging and an alternate element pattern designed for B-mode imaging. For volumetric imaging, a small aperture was used to provide a wide transmit beam, allowing multiple beams to be received simultaneously. For B-mode imaging, a larger aperture with a more narrow transmit beam was used to improve image quality. Sparse random element patterns were evaluated by beamplot and cyst image simulations. Using the alternate element pattern for B-mode imaging, simulated cyst contrast was improved by 28%. The multiplexed transducer was fabricated using an electrostrictive material in which array elements were activated and deactivated by a dc bias field. The transducer had a 3.4 MHz center frequency with 46% bandwidth, which was consistent with KLM simulations. The high dielectric constant of the electrostrictive material resulted in an element clamped capacitance of 14.3 pF versus 2 pF for a convention PZT element. An output off isolation of -35 dB was measured for transmit and -61 dB for receive. The array was integrated with the volumetric scanner and used to make real time images of a cyst phantom. The images showed improved cyst contrast using the alternate aperture for B-mode imaging.

Image Processing, Computer-Assisted↗

PubMed1994

Two-dimensional random arrays for real time volumetric imaging.

Two-dimensional arrays are necessary for a variety of ultrasonic imaging techniques, including elevation focusing, 2-D phase aberration correction, and real time volumetric imaging. In order to reduce system cost and complexity, sparse 2-D arrays have been considered with element geometries selected ad hoc, by algorithm, or by random process. Two random sparse array geometries and a sparse array with a Mills cross receive pattern were simulated and compared to a fully sampled aperture with the same overall dimensions. The sparse arrays were designed to the constraints of the Duke University real time volumetric imaging system, which employs a wide transmit beam and receive mode parallel processing to increase image frame rate. Depth-of-field comparisons were made from simulated on-axis and off-axis beamplots at ranges from 30 to 160 mm for both coaxial and offset transmit and receive beams. A random array with Gaussian distribution of transmitters and uniform distribution of receivers was found to have better resolution and depth-of-field than both a Mills cross array and a random array with uniform distribution of both transmit and receive elements. The Gaussian random array was constructed and experimental system response measurements were made at several ranges. Comparisons of B-scan images of a tissue mimicking phantom show improvement in resolution and depth-of-field consistent with simulation results.

Ultrasonography↗