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Biomedical subjects

M L Freeman

Publications and source records attributed to M L Freeman.

At least 109 records · Page 6Linked to original sources
PubMed1984

An acidic extracellular environment reduces the fixation of radiation damage.

Chinese hamster ovary cells in exponential growth were irradiated with gamma or X rays in an acidic or alkaline extracellular environment. Incubation in acid medium during or after irradiation reduced the degree of fixation of potentially lethal lesions. Fixation and repair of acid-modified damage occurred with a halftime of 9 to 10 min. The rate of repair of sublethal damage was unaffected by hydrogen ion concentration and progressed with a half-time of 30 min. An acid environment modified only survival of exponentially growing cells; unfed plateau-phase cultures were unaffected.

Animals↗
PubMed1983

The use of radionuclide retinal scintigraphy for the assessment of retinopathy in diabetes mellitus.

A computerized radiotracer technique for the detection of loss of retinal vascular integrity secondary to diabetes is presented. Radionuclide retinal scintigraphy with Technetium-99m DTPA was performed on 40 insulin-dependent diabetics and 10 nondiabetics. A ratio of eye to brain activity was used to eliminate errors associated with absolute counting. Ratios were found to be significantly higher in diabetics, especially those with active neovascularization. This technique may prove useful in the assessment and staging of eyes prone to retinopathy.

Adult↗
PubMed1983

The repair of sublethal damage in diploid human fibroblasts: a comparison between human and rodent cell lines.

Two diploid cell lines of human origin were irradiated in vitro. Repair of sublethal damage was observed in both lines when they were exposed to a single gamma-ray dose and incubated at 37 degrees C prior to receiving a graded second dose. In addition cells were irradiated at a low dose rate (56 or 76 rad/hr) and survival was compared to that after an acute exposure. A dose-rate effect was demonstrated. Sublethal damage repair was also studied using CHO or V-79 Chinese hamster cells, and the data suggest that the degree of repair is similar in human and rodent cell lines at photon doses up to 500 rad. The repair of sublethal damage can be a significant factor in the survival of human cells in vitro for fractionated doses.

Animals↗
PubMed1982

Time--domain analysis in gated cardiac blood pool studies.

A technique is presented for producing functional images derived from equilibrium gated blood pool studies as a means of diagnosing cardiac disease. These functional images are based on characteristics associated with the time variation of the count rate (the time domain) at each point of the image matrix rather than on the Fourier transform of the time-activity curve (the frequency domain) which has gained recent attention. As examples of this method, we present images which display the statistical variance of the time-activity curve at each pixel, corrected for the expected contribution due to random statistical fluctuation, and images which display the time at which each pixel reaches its minimum count value. Variance and time-to-minimum images are comparable to Fourier amplitude and phase images, respectively, and have been found to be useful in facilitating the diagnosis of wall motion abnormalities. A major advantage of time-domain analysis is the wide variety of features of potential clinical significance which may be investigated.

Fourier Analysis↗
PubMed1982

Studies with encapsulated 125I sources. I. Apparatus and dosimetry for determination of relative biological effectiveness.

Apparatus and dosimetry techniques have been developed which make possible studies of the biological effects of radiation from encapsulated 125I sources at clinically relevant dose rates using mammalian cells attached to culture dishes. The variation of dose rate from 125I photons as a function of distance from the interface between different materials was investigated. A polystyrene substrate changes the mean dose rate in attached cells by about 21%, depending on cell thickness. To reduce dosimetry uncertainty caused by this effect, special petri dishes were made from polyvinylidene fluoride, which changes the mean dose in attached cells by only 10%. Chinese hamster ovary cells attached to these dishes were cultured in incubators which contained 125I and 137Cs sources, allowing the effects of various dose rates (.005 to 0.80 Gy/hr) of radiation from the two isotopes to be compared. The relative dose rates from these low- and high-energy photons were measured with an accuracy of +/- 7% or better using an air-equivalent ionization chamber designed to resemble one of our special petri dishes. Calculations of dose rates from 125I give values within 4% of the measured dose rates used to determine the relative biological effectiveness of 125I photons.

Animals↗
PubMed1982

Studies with encapsulated 125I sources. II. Determination of the relative biological effectiveness using cultured mammalian cells.

Chinese hamster ovary (CHO) cells, in either exponential growth or unfed plateau phase were exposed to graded doses of radiation from Iodine-125 or from Cesium-137 at various dose-rates and the cells were assayed for reproductive integrity. From the patterns of cell survival obtained, the relative biological effectiveness (RBE) of the emission from 125I was determined relative to 137Cs. The RBE determined using cells in exponential growth was found to have a value of about 1.2, which was independent of the level of cell survival and did not vary over the dose-rate range from 7.5 to 53 cGy/hr. Using plateau phase cells the RBE has a constant value of about 1.3 between 13 to 46 cGy/hr, but is closer to 2.0 at lower dose-rates of 5 to 7 cGy/hr.

Animals↗
PubMed1977

Effect of pH on hyperthermic cell survival.

Chinese hamster ovary cells incubated with various concentrations of CO2, to obtain extracellular pH values in the range of 6.40-7.85, were heated at 45.5C for 5, 10, or 20 minutes. Thermal sensitivity increased sharply from pH 7.35 to 6.65 (i.e., survival decreased from 1 X 10(-2) to 3 X 10(-5) for 20 minutes of heating), but remained constant from pH 7.35 to 7.85. The enhanced thermal sensitivity at pH values below pth 7.35 suggested that tumors should be preferentially destroyed by heat relative to normal tissue, since reports indicated that tumors were more acidic than the surrounding normal tissue.

Cell Survival↗