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Biomedical subjects

M M Goodsitt

Publications and source records attributed to M M Goodsitt.

49 records · Page 3Linked to original sources
PubMed1987

Digital simulation of pulsed ultrasonic waveforms.

When modeling or simulating an ultrasonic pulse-echo system it is necessary to know the transducer waveforms that are the input to the system. In general, accurate transducer modeling is complex and waveform calculation is computationally intensive. Because of this, investigators often assume these waveforms to be simple sinusoids, modulated by Gaussian or exponential envelopes. However, these latter type pulses do not properly represent the complex response of modern piezoelectric transducers. In this paper, a simple set of equations is presented which can approximate the behavior of a number of common transducer configurations. In the first step of the procedure, a simple but accurate model is employed to calculate the step responses of quarter-wave-matched and backed piezoelectric transducers, assuming open circuit conditions. Effects of electrical terminations and transmit/receive bandwidth limitations are accounted for, approximately, by cascaded filtering. Emitted pressure waveforms and echo voltage waveforms synthesized by this simple procedure are very similar to measured waveforms from real transducers. Under most conditions, the method is only an approximation because the model erroneously assumes isolation between the electrical and acoustic networks. However, under many conditions the model is sufficiently accurate to predict actual transducer performance.

Computer Simulation↗
PubMed1986

Radiation dose reduction during hysterosalpingography: an application of scanning-beam digital radiography.

Hysterosalpingography was performed in 31 patients by means of a low-dose scanning-beam digital radiographic system. The technique permits adequate evaluation of gynecologic abnormalities while allowing significant reduction in radiation: 2.4-mR (6.1 X 10(-7) C/kg) exposure to the skin and 0.7-mrad (7 X 10(-6) Gy) mean dose to the ovaries per image obtained. Sixteen patients demonstrated readily recognizable and documented abnormalities, corroborated by laparoscopy, laparotomy, or other supportive evidence.

Adolescent↗
PubMed1985

Digital subtraction angiography systems: assessing performance with phantoms.

A solid, acrylic phantom was developed to assess the iodine perceptibility of three digital subtraction angiography (DSA) systems, including one using a recursive filter technique. Three phantoms, designed to mimic flow of iodinated boluses through blood vessels, were used. Each contained four triangular boluses of different widths and of a specific iodine concentration. Motion, required to test recursively filtered DSA systems, was simulated by placing the phantoms on a motorized cart. The phantoms were also used to test flow curve generation in applicable systems. Intersystem differences in perceptibility were attributed to differences in system noise, system resolution, and dynamic range. Flow curves produced with the phantoms were similar to those obtained in patient studies.

Angiography↗
PubMed1985

Quantitative tests of a three-dimensional gray scale texture model.

A three-dimensional model for gray scale texture in ultrasound B-mode images has been extended to enable absolute quantitative predictions of echo signal levels and texture characteristics. The quantitative aspects of the model are tested with a phantom in which the ultrasonic scattering properties as well as the ultrasonic attenuation coefficient and the speed of sound are known as functions of frequency. Good agreement between theoretical predictions and experimental results was found in the overall brightness of B-mode images, in pixel value histograms, and in an autocorrelation function analysis of images. Passing quantitative tests is additional evidence that the model is a reliable tool for computer simulations involving many important facets of ultrasound B-mode imaging and tissue characterization.

Mathematics↗
PubMed1984

Angular distribution of scattered ultrasound from a single steel sphere in agar gelatin: a comparison between theory and experiment.

Experimental results for the angular distribution of scattered ultrasound in water from a 0.635 mm diameter steel sphere embedded in agar were obtained for interrogating frequencies of 1.0, 2.25, 3.5 and 5.0 MHz. The experimental results compared favorably with theoretical predictions based on the work of Faran. The results for both theory and experiment are presented in the form of the Differential Scattering Cross Section (DSC) for scattering angles from 170 degrees to 44 degrees. The implications of this study on calculating the expected scattering behavior of gelatin based ultrasound phantoms are briefly discussed.

Acoustics↗
PubMed1983

A three dimensional model for generating the texture in B-scan ultrasound images.

A three-dimensional model for production of gray scale texture in ultrasound B-mode images is described. The model computes time-dependent echo signals resulting from scattering of acoustic pulses by particles randomly distributed in an attenuating medium and transforms these signals into a gray scale image. Specific transducer and pulser-receiver characteristics are accounted for, as well as the three-dimensional nature of the problem, without loss of computational efficiency. The model generates texture that closely corresponds to that found experimentally in ultrasound images of tissue-mimicking phantoms. The dependence of the texture upon the depth of the region that was scanned and on the characteristics of the transducer-receiver system were clearly demonstrated. Good agreement between theory and experiment was found for the texture in phantoms containing simulated spherical low-scatter tumors.

Humans↗
PubMed1979

An automated ultrasound transducer beam profiling system.

An automatic, three-dimensional, ultrasound beam profiling system was developed and incorporated into a radiotherapy planning minicomputer system with few modifications and at minimal cost. This profiler was invaluable in assessing the characteristics of beams emitted by ultrasound transducers.

Humans↗
PubMed1977

Digital K-edge subtraction radiography.

K-edge subtraction images have been produced using a digital video image processor. Images formed by three filtered x-ray beams are detected by an image intensifier-Plumbicon system, digitilized, and combined in real time to produce bone- and tissue-free K-edge subtraction images of iodinated structures. Preliminary studies of rhesus monkey cranial, spinal, and abdominal structures are compared with those of conventional radiography.

Animals↗
PubMedDate not supplied

Fatty replacement of spinal bone marrow due to radiation: demonstration by dual energy quantitative CT and MR imaging.

Dual energy CT and quantitative magnetic resonance (MR) imaging were used to evaluate marrow changes due to radiation. The bright signal intensity seen on MR was shown by the two quantitative techniques to be due to a threefold increase in the marrow fat content compared with nonradiated levels and to a normal control. Fat estimates by MR and dual energy CT were in excellent agreement. Single energy CT overestimates the amount of bone loss in the radiation field. Dual energy CT and quantitative MR can be used to correct this error.

Adipose Tissue↗
PubMedDate not supplied

Precision in quantitative CT: impact of x-ray dose and matrix size.

A study was performed to determine whether recommended technique factors for postprocessing dual-energy (DE) quantitative computed tomography are optimum in terms of precision and x-ray dose. In particular, possible dose reduction as a result of an upgrade of the CT scanner to more efficient detectors was explored. Series of images of an anthropomorphic phantom containing a human vertebra, a tissue-simulating lumbar simulator with various marrow inserts, and a polyethylene cylinder were generated. Recommended DE x-ray technique factors as well as factors resulting in about two times, one-half, and one-fourth the x-ray dose were employed. The effects of reconstruction with different matrix sizes was studied. Standard deviations of the CT numbers within regions of interest in individual images (noise) and standard deviations of mean CT numbers, single-energy (SE), and DE measurements for series of images (reproducibilities) were computed. It was found that the low-energy component of the DE technique was optimum, but the high-energy component could be reduced by a factor of 2 with negligible loss in precision. This translates into a dose reduction of 36% relative to the recommended DE technique. Vertebral inhomogeneities were responsible for more than 65% of the standard deviations in individual images of the vertebra even at the lowest doses. For all of the techniques, the noise in images of all objects decreased as the x-ray dose increased and as the matrix size decreased. Reproducibility of mean values, however, did not necessarily improve, and aberrant results such as improvement in reproducibility with a reduction in dose were sometimes observed. It is hypothesized that this may be due to variations in the actual kVp for each image in a series.

Absorptiometry, Photon↗
PubMedDate not supplied

Evaluation of a new set of calibration standards for the measurement of fat content via DPA and DXA.

A simulation study was performed to evaluate a new set of calibration standards for estimating the fat content of the body via dual-photon absorptiometry (DPA) and dual-energy x-ray absorptiometry (DXA). The standards, proposed by Nord and Payne [presented at the 2nd meeting of The Bath Conference on Bone Mineral Measurement (1990)] consist of stearic acid (100% fat) and 0.6% NaCl in water (100% lean). They were compared with other standards consisting of average composition adipose/muscle tissues and fatty adipose/lean muscle tissues. Source and detector properties of a Gd-153 DPA system and three commercial DXA systems were modeled. For each system and calibration set, rms errors in the calculated fat contents of simulated tissues having fat mass percentages that ranged from about 4%-44% and thicknesses that ranged from 5-20 cm were determined. Beam hardening errors for the systems were evaluated as was a calibration technique employed by one of the manufacturers to correct for such errors. In general, the smallest rms errors (2% or less when the calibration standards and tissues were of equal thickness) were obtained with the average adipose/muscle standards. Equivalent results were obtained with standards consisting of stearic acid and 0.8% NaCl. The latter is a higher salt content than proposed by Nord and Payne and results from differences in the x-ray attenuation coefficients that were employed in calculating the fat equivalence of water. Other, more convenient standards, such as lucite and water may be employed by using appropriate fat equivalences (approximately 69% for lucite and approximately 10% for water). Beam hardening errors for the DXA systems are considerable, and the simulated correction technique was shown to be effective.

Absorptiometry, Photon↗