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Biomedical subjects

G U Rao

Publications and source records attributed to G U Rao.

At least 19 recordsLinked to original sources
PubMed1991

Tissue doses in the upper gastrointestinal fluoroscopy examination.

A method was developed to estimate tissue doses from the upper gastrointestinal fluoroscopy examination. It involved measuring the technical parameters of the clinical examination, partitioning the dynamic examination into a set of discrete x-ray fields, and generating corresponding tissue does tables with an existing computer program. Knowledge of the radiation exposures associated with each of the fields enabled the calculation of tissue doses for the entire dynamic examination. In this limited sample (eight patients), fluoroscopy times ranged from 108 to 183 seconds. Radiation exposures ranged from 2.3 to 7.2 mC/kg (9.1-28 R), thyroid doses from 0.15 to 3.5 mGy (15-350 mrad), uterine doses from 0.16 to 1.0 mGy (16-100 mrad), lung doses from 0.90 to 4.2 mGy (90-420 mrad), and active bone marrow doses from 0.81 to 5.4 mGy (81-540 mrad).

Digestive System↗
PubMed1990

Predicting femoral neck strength from bone mineral data. A structural approach.

An interactive computer program was developed to derive femoral neck geometry from raw bone mineral image data for an estimate of hip strength using single plane engineering stress analysis. The program, which we call Hip Strength Analysis (HSA), was developed as an attempt to improve the predictive value of hip bone mineral data for osteoporosis fracture risk assessment. We report a series of experiments with an aluminum phantom and with cadaver femora, designed to test the accuracy of derived geometric measurements and strength estimates. Using data acquired with both Lunar DP3 (DPA) and Hologic QDR-1000 (x-ray) scanners, HSA computed femoral neck cross-sectional areas (CSA) and cross-sectional moments of inertia (CSMI) on an aluminum phantom were in excellent agreement with actual values (r greater than .99). Using Lunar DP3 data, CSA and CSMI measurements at mid-femoral necks of 22 cadaver specimens were in good general agreement with literature values. HSA computed cross-sectional properties of three of these specimens were compared with measurements derived from sequential CT cross-sectional images. Discrepancy between the two methods averaged less than 10% along the length of the femoral neck. Finally, breaking strengths of 20 of the femora were measured with a materials testing system, showing better agreement with HSA predicted strength (r = .89, percent standard of the estimate (%SEE) = 21%) than femoral neck bone mineral density (r = .79, %SEE = 28%).

Absorptiometry, Photon↗
PubMed1984

Regional cerebral blood flow measurements using stable xenon enhanced computed tomography: a theoretical and experimental evaluation.

Several theoretical and practical aspects of regional cerebral blood flow measurements using stable xenon gas and CT are discussed. It is shown that by comparing the enhancement at any time T1 with that at saturation or any other time T2, the need to use arbitrary means to bring the arterial concentration data and the CT enhancement data to the same system of measurement units can be eliminated. If CT is performed continuously during the washin phase, say at intervals of 1 min, least squares analysis of the enhancement data can be used to obtain the best possible estimates for the flow rate constant kappa and the saturation enhancement. However, if only a limited number of scans can be performed, as may be the case in human studies, it is also possible to get a good estimate of kappa from a knowledge of the ratio of the enhancement at any time T1 with that at any other time T2. Combinations of T1 = 2.0 min and T2 = 4.0 min, T1 = 1.0 min and T2 = 6.0 min, or T1 = 2.0 min and T2 = 5.0 min were found to be the most convenient. It is also shown that the end-tidal xenon concentration in the exhaled air can be accurately assessed indirectly by measuring the oxygen, CO2, and water vapor concentrations, thereby eliminating the need for more expensive methods involving the use of a mass spectrometer or a thermal conductivity gas analyzer.

Animals↗
PubMed1981

A comparison of carbon-fiber and aluminum front plates in rapid film changers.

The radiation transmission characteristics of 2-mm-thick aluminum front plates and 2-mm-thick carbon-fiber-reinforced plastic front plates for rapid film changers were compared. While the carbon-fiber plates were found to be intrinsically more radiolucent than the aluminum plates, the decrease in patient exposure with the carbon-fiber plates was only approximately 25%. No measurable differences in image quality were observed in carefully controlled experiments on the two types of front plates.

Aluminum↗
PubMed1979

Autoradiographic enhancement of mammograms. Investigation of a new dose reduction technique.

Autoradiographic image enhancement using thiourea labeled with 35S was investigated as a means of reducing dose in mammography. It was found that mammograms underexposed as much as tenfold can be autoradiographically intensified so that the enhanced image is comparable with a normal exposure. Limitations to routine use include cost, processing time, and disposal of radioactive solutions.

Breast Neoplasms↗
PubMed1977

Negative-mode soft-tissue xeroradiography.

Positive-mode xeroradiography is an excellent method of visualizing soft-tissue structures in mammography and other procedures; however, toner deletions over a large area may preclude adequate delineation of the soft tissues near high-density structures such as bone. Use of the negative mode in the development cycle provides excellent demonstration of the soft tissues without toner deletions and requires only about 70% of the exposure needed in the positive mode. Negative-mode images also exhibit greater changes in radiographic contrast than those observed with the positive mode. The extent of achilles tendon lacerations was shown particularly well by this technique.

Achilles Tendon↗
PubMed1976

Evaluation of xeroradiographic image quality.

A theory of edge enhancement has been developed to describe xeroradiographic images of linear step objects. The theory is shown to give an accurate description of the relationship between edge enhancement, subject contrast, radiation exposure, selenium charging potential and developer bias potential. An optimal transmitted x-ray exposure exists which gives the maximum edge enhancement. For low contrast structures, this same optimal exposure was found to yield the most acceptable images as judged subjectively. This finding has led to the successful application of automatic exposure termination in mammographic examinations using xeroradiography.

Mammography↗
PubMed1976

A circular test pattern for evaluating x-ray tube focal spots.

The design and use of a circular x-ray resolution test pattern is presented. This pattern is shown to yield equivalent focal spot dimensions equal to those obtained with the more commonly used star pattern. The advantage of using the circular pattern is that it obviates the necessity of positioning the pattern strictly along the x-ray beam central axis. A major source of experimental error in making focal spot measurements is therefore circumvented, especially in the case of x-ray tubes with a small target angle.

Mathematics↗
PubMed1975

Collimator misalignment in high energy therapy machines.

Measurements of the intensity distribution of a 60-Co beam revealed a significant field distortion caused by minor misalignment of the collimator assembly which was not detected by routine methods. Accurate monitoring of radiation intensity distribution and periodic visual inspection of collimators are suggested for early detection of this problem.

Absorptiometry, Photon↗