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Biomedical subjects

E C Gregg

Publications and source records attributed to E C Gregg.

12 recordsLinked to original sources
PubMed1979

Effect of low dose rate radiation on cell growth kinetics.

Experimental determinations were made of cell number as a function of time for two strains of L5178Y mammalian cells maintained continuously in various environments of radiation. One strain possessed a shoulder in its dose response curve whereas the other did not. Neither strain showed any significant difference in growth rate for interdivision doses on the order of the median lethal dose or less delivered continuously at a low dose rate or pulsed every 4 h at a high instantaneous dose rate. It was also shown that large numbers of dead cells have little effect on growth rate and that these dead cells last as discrete entities for many days. A simple theory of growth rate in the presence of radiation is presented, and the agreement with the observations implies that there is no effect of any sublethal low dose rate radiation received in one generation on the growth rate or radiation sensitivity of the succeeding generation. Further analysis of the data also showed that for the no-shoulder cells at 37 degrees C, tritiated water had a relative biological effect close to unity for cell sterilization.

Animals↗
PubMed1979

Risks of exposure to X-rays in patients undergoing long-term treatment for scoliosis.

Thirteen healthy teenage girls with idiopathic adolescent scoliosis were studied using multiple thermoluminescent dosimeters while undergoing standard diagnostic roentgenograms. Average organ doses for each anteroposterior and lateral examination were calculated for bone marrow, gastrointestinal tract, lungs, breast tissue, and gonads. Given an average of twenty-two roentgenograms over a three-year Milwaukee brace-treatment program, the increase in organ carcinogenic risk due to x-ray radiation ranged from 3.4 to fifteen per million (1.3 per cent to 7.5 per cent), except for breast tissue which increased from 140 to 290 per million (110 per cent). Using posteroanterior rather than anteroposterior exposures reduced the increased risk to 5.3 per million (3.8 per cent). The genetic risks of scoliosis roentgenographic studies were considered to be negligible, especially with gonadal shielding and infrequent roentgenograms made every three to four months. Good technique and judicious ordering of roentgenograms added significantly to the safety of the patient.

Bone Marrow↗
PubMed1977

Radiation risks with diagnostic x-rays.

Calculations are presented which correlate the risk of carcinogenesis with various diagnostic radiological procedures. Even though "worst case" conditions are assumed, such as a linear non-threshold dose-response relationship, most of the radiographic procedures appeared to be quite conservative in terms of carcinogenic risk. This was not true, however, for mammography of younger women.

Adult↗
PubMed1977

Subtraction radiography: techniques and limitations.

Subtraction radiography permits the use of 7-10 times less contrast material than is required without subtraction techniques. The first-order, second-order, and composite mask techniques are described and evaluated. While the second-order technique gives more complete cancellation of common structures, the more commonly used first-order technique was found to be adequate for most clinical uses. The smallest change in contrast which can be detected using subtraction radiography is limited by inherent background film noise in the original radiographs and not by statistical fluctuations in the x-ray quanta.

Subtraction Technique↗
PubMedDate not supplied

An analysis of the value of additional diagnostic procedures.

When several diagnostic procedures are performed on a patient, the probability of his having or not having a specific ailment will change as the result of each procedure is known. This paper describes how such a change is readily calculated using Bayes' theorem. Information theory is also used to find the increment in information from each successive test. Numerical estimates are made using data pertinent to lung X-ray examinations. Finally, some implications for diagnostic examinations in general are drawn.

Bayes Theorem↗
PubMedDate not supplied

Designing a wax phantom to simulate a flat tumor with diffuse edges.

A suitable was phantom was designed for evaluating various film techniques used in subtraction radiography. Holes are drilled in a slab of wax and filled with various concentrations of iodinated wax, producing disk-shaped regions with diffuse borders. The technical details of construction and a representative application are described.

Models, Structural↗
PubMedDate not supplied

Radiographic quality, tube potential, and patient dose.

Measurements were made to determine if there was an optimal kVp that would maximize radiographic contrast for various materials while minimizing average patient dose. Radiographs were made of a 17-cm-thick plexiglass phantom (to simulate a typical abdomen) with added regions of plexiglass, hydroxyapatite, and iodine with peak kilovoltages from 40 to 150 kVp and 2 mm A1 added filtration. Radiographs were also made of a 4-cm-thick plexiglass phantom to simulate a typical breast, with added regions of plexiglass, hydroxyapatite, and fat at a peak kilovoltage from 35 to 100 kVp and with 1 mm added filtration. For the thicker phantom it was found that the contrast per average absorbed dose for the added plexiglass, hydroxyapatite, and iodine increased by about 3, 2, and 0.4, respectively, when going from 50 to 150 kVp. Contrast was measured relative to a reference region on the phantom. Similar data for the thinner phantom showed an increase of about 35% in contrast per average absorbed dose for plexiglass and fat but a decrease by about 30% for hydroxyapatite as the kVp changes from 35 to 100 kVp.

Humans↗