Biomedical subjects

D A Bassano

Publications and source records attributed to D A Bassano.

15 recordsLinked to original sources

PubMed1992

Imaging of the human torso using cone-beam transmission CT implemented on a rotating gamma camera.

Radionuclide transmission CT generated on a rotating gamma camera can improve SPECT imaging by providing attenuation maps for attenuation compensation and for anatomical correlation. This paper demonstrates the feasibility and high quality of cone-beam transmission CT (CB-CT) of human subjects, in comparison to conventional parallel-ray CT, and evaluates some possible imaging protocols. Two CB-CT implementation modes, with a cone-beam collimator and without any collimator, were evaluated. Three human subjects of different dimensions were imaged. For the two smaller subjects, the CB-CT images were dramatically superior, in terms of noise and resolution, to those obtained with a parallel-ray geometry. The image noise was less by a factor of 6. CB-CT linear attenuation coefficients were found to be in close agreement with published values for various tissues. For the largest subject, image truncation produced a ring artifact at the edge, but inside the artifact, the image quality was still very good. Cone-beam images obtained without any collimator were acceptable, but photon scatter degraded the image contrast.

Body Height↗

PubMed1991

Pitfalls in dose calculation using a commercial treatment planning computer for Clinac-4 4MV x-ray beam.

Dose calculations on a commercial treatment planning computer based on the storage of profile data along a principal axis for Clinac-4 4MV x-ray can lead to significant error in calculated dose in the corners of a large field. These errors are due to the unique nature of the lead flattening filter on Cl-4. A method is suggested to remedy this problem by storing profile data along a diagonal of a large field.

Humans↗

PubMed1991

Cone-beam transmission computed tomography for nonuniform attenuation compensation of SPECT images.

This paper develops and tests cone-beam transmission computed tomography (CB-CT) for attenuation compensation of SPECT images. CB-CT was implemented on a rotating gamma camera with a point source (1-2 mCi) of 99mTc, and a light-weight aluminum source holder. A cone-beam collimator may be used but is not required. Since the point source is either located at the collimator focal point, or the camera is uncollimated, CB-CT has excellent sensitivity (at least 150 times that of a parallel-hole, high-resolution collimator). The predicted resolution is equal to the intrinsic gamma camera resolution (3-4 mm), which is much higher than for a high-resolution, parallel-hole collimator (10-20 mm). In the present study, CB-CT provided low noise, high-resolution attenuation maps for use in a nonuniform attenuation-weighted backprojection algorithm. The attenuation compensation accuracy was tested using basic geometries of line sources and nonuniform density models. For the appropriate scaling of the attenuation map, the attenuation compensation was accurate and removed the SPECT image distortion associated with nonuniform attenuation. Attenuation maps acquired either with cone beam collimator or without any collimator were both successful. Using CB-CT, SPECT can thus be made much more accurate without adding unduly to the imaging time, complexity, or cost.

Algorithms↗

PubMed1990

Dosimetry of I-125 seeds implanted on the surface of a cavity.

Dosimetry of a new implant technique to treat brain tumors is presented. High grade gliomas or astrocytomas are surgically removed, and radioactive I-125 seeds are implanted on the surface of the cavity. A computational model is presented to determine the number of seeds and the activity of the seeds for a given dose and cavity size.

Astrocytoma↗

PubMed1988

Vertebral mineralization after parathyroidectomy: measurement by quantitative CT.

Quantitative CT has been used to document abnormally low levels of vertebral bone mineral in hyperparathyroid states. No one has yet reported an improvement in vertebral bone mineral concentration after parathyroidectomy. Quantitative CT was used to measure mineralization of lumbar vertebral bodies in five women with primary hyperparathyroidism, at the time of surgical resection of a parathyroid adenoma and again 4 months after surgery. Four of the patients had increased vertebral mineralization after 4 months; the increase for the entire group (13%) was statistically significant. In one patient, examined for a third time 8 months after surgery, a continuing increase in vertebral bone mineral concentration was seen. A final examination, obtained 20-33 months after surgery, revealed that in every patient the bone mineral concentration was lower than on the first postoperative study and in some cases was less than the original preoperative measurement. We conclude that a temporary increase in vertebral trabecular mineralization occurs after parathyroidectomy for primary hyperparathyroidism. During the following 3 years, however, this increase is not sustained.

Adult↗

PubMed1986

Bone mineral measurement in the human spine using computed tomography.

A new method to measure bone mineral mass and density in human vertebrae was developed and clinically implemented. Using single-energy CT in the lumbar spine, it is possible to measure trabecular and cortical bone mineral mass regardless of the amount of soft tissue "background" present. Although the method is sensitive to the fat that resides in the marrow space of the vertebral body, an estimate of fat content can be incorporated into the calculations. We present and demonstrate the conceptual model upon which the method rests, and show that the results derived from its clinical use are highly correlated with those obtained from the conventional method of determining bone mineral concentration.

Adipose Tissue↗

PubMed1979

Effects of phenobarbital on taste aversion induced by X-radiation.

The effects of phenobarbital on taste aversion induced by X-radiation were examined. Rats were adapted to a 23 hr 50 min water deprivation schedule. On the Treatment Day animals were given a novel 0.125% Na saccharin solution during the 10 min drinking session and were then exposed to 100 rads of X-radiation. The saccharin solution was presented again on six subsequent Test Days. Phenobarbital in doses of 20, 40, 60 and 80 mg/kg was administered 15 min prior to drinking on the first Test Day. Results demonstrate that phenobarbital in all doses tested has a significant attenuating effect on radiation induced taste aversion.

Animals↗

PubMed1978

Protocol for a computed tomography scanner performance repository.

An argument is presented for organization of a Computed Tomography Scanner Performance Repository. Performance data on CT scanners would be distributed in statistical form to the radiological community. A Protocol is presented for the uniform collection of data. Results of exposure, resolution and visibility measurements made by the authors are presented for the EMI 5005/U, Pfizer 0200 FS and General Electric CT/T scanners.

Humans↗

PubMed1978

Computed tomography of the lung.

Preliminary work has shown that normal lungs have predictable CT patterns and density ranges. In emphysema, there are irregular zones of extremely low density as well as an overall low mean density. CT appears to have considerable potential for early detection of pulmonary emphysema and characterization of the degree of involvement. CT can also be useful in the study of physiological phenomena such as regional blood flow.

Adolescent↗

PubMed1977

Physical, performance, and dosimetric characteristics of the delta-Scan 50 whole-body/brain scanner.

The delta-Scan 50 computed tomographic (CT) scanner has the ability to determine x-ray attenuation coefficients with a precision ranging from 0.3 to 2.6% depending upon such factors as patient size and scan diameter. Resolution is 20-80% greater than the pixel width, with values ranging from 1.2 to 2.1 mm. The collimating system determines certain characteristics of the image and affects the dose to the patient: doses for typical procedures are on the order of 1 rad, and gonadal doses are in the millirad range. Potential improvements are discussed.

Brain Diseases↗

PubMedDate not supplied

Lung density effect on 125I dose distribution.

Perturbations in 125I implant dose distribution due to lung tissue variations have been investigated. Dose correction factors for a point source, a planar, and a volume implant have been calculated using a model which accounts for the changes in primary photon attenuation and in buildup factor when the medium is lung rather than water. Results of our calculation show that the change in dose is about 9% and 20% in the core and the periphery, respectively, of a representative implanted volume whose density is 0.25 relative to water.

Brachytherapy↗

PubMedDate not supplied

Dose distribution for 125I implants due to anisotropic radiation emission and unknown seed orientation.

Variations in dose distribution due to anisotropic radiation emission around 125I seeds and a lack of knowledge about the orientation of the implanted seeds have been investigated. Upper and lower bounds for dose distributions have been calculated for planar implants using the experimentally determined angular dose distribution around a typical 125I seed. Results of our study suggest that significant dose variations in the center and the periphery of the implanted area are possible.

Brachytherapy↗

PubMedDate not supplied

Comparison of absorbed dose in bone substitute material and water using ionization measurements.

Absorbed dose in a liquid substitute for bone has been compared with absorbed dose in water for 9-, 12-, and 15-MeV electron beams using ionization chamber measurements. The ionization readings were converted to dose using collisional mass stopping power ratios. The collisional mass stopping powers for the liquid substitute of bone were calculated using the Monte Carlo Code PEGS4. The results of our study show that there is an increase in dose in the liquid bone substitute compared to water at shallow depths. The maximum increase in dose was 5%, 4%, and 2% at depths of 1.2, 1.5, and 2.0 cm, respectively, for 9-, 12-, and 15-MeV electrons. The density of the liquid bone substitute was 1360 kg/m3 and the effective atomic number was 11.

Bone and Bones↗

PubMedDate not supplied

Corner transmission in several linear accelerator photon beams.

Maximum x-ray field sizes on many linear accelerators are obtained only with truncated corners. Transmissions through the corners of such fields has been measured utilizing film and ion chamber dosimetry for a number of accelerators. Transmissions are found to be significantly larger than for the movable jaws.

Humans↗

PubMedDate not supplied

Detection nonuniformity measurements and corrections for cone beam transmission CT on a gamma camera.

Cone beam transmission CT (CB-CT) improves SPECT imaging by providing high-quality attenuation maps for attenuation compensation and for correlated SPECT and CT imaging. The present work measures the detection nonuniformity for CB-CT implemented with a gamma camera, and applies nonuniformity corrections to make CB-CT more uniform and accurate. Two cone beam collimators were investigated, as well as the uncollimated cone beam geometry, using both uniformity images and CB-CT reconstructions of a uniform circular cylinder. Uniformity images were acquired as a function of point source position relative to the nominal focal point. The uniformity images for both collimators were highly nonuniform, with some regions differing by more than 15% from the average image counts per pixel, indicating that the holes do not focus to the same point. The most uniform images were obtained with the point source located at or near the nominal focal point. Radiographs estimated the misfocusing of the holes to be about 0.6 degrees in some regions. There were no indications that the hole size was nonuniform. The CB-CT reconstructions of data acquired with collimator showed no obvious signs of image artifact from the detection nonuniformities. However, low-noise simulated data with well-localized detection defects produced readily-apparent circular artifacts. The nonuniformity correction was accurate and easy to apply, and should be used whenever quantitative accuracy is required. The uniformity images acquired without collimator lacked the collimator-produced nonuniformities, but had decreased counts near the detector edge. The decrease was predictable, using simple geometric considerations. Uniform cylinder reconstructions of "without collimator" data showed a corresponding decrease in center density relative to the edge (edge-to-center ratio = 1.25), which was improved by the nonuniformity correction (ratio = 0.21). Accurate CB-CT without collimator will require further correction for photon scatter.

Gamma Cameras↗