Biomedical subjects

K Ulin

Publications and source records attributed to K Ulin.

5 recordsLinked to original sources

PubMed1986

Photon activation analysis as a new technique for body composition studies.

A study was undertaken to demonstrate the usefulness of the recently developed photon activation analysis (PAA) technique for in vivo body composition studies. PAA can be used for direct measurement of total-body oxygen, nitrogen, and carbon. Sequential measurements were made on rats fed diets of 0%, 4.2%, or 20% protein for 6 1/2 wk, and significant changes in body composition were noted. In addition, rats of different ages, strains, nutritional states, and degrees of obesity were included in a comparison of PAA results in vivo with results from chemical analysis after sacrifice of the animals. High positive correlations were found between PAA measurements of carbon and chemical analysis measurements of fat and between PAA measurements of oxygen and chemical analysis measurements of total-body water. A low positive correlation was found between PAA measurements of nitrogen and chemical analysis measurements of protein.

Activation Analysis↗

PubMedDate not supplied

Measurement of total-body oxygen, nitrogen, and carbon in vivo by photon activation analysis.

A method has been developed to measure total-body oxygen, nitrogen, and carbon in vivo using the x-ray beam of a 45-MV betatron and a whole-body counter. Following x-ray irradiation of living tissue, the positron emitting activation products 15O, 11C, and 13N are produced. The decay of these radionuclides has been measured in both phantoms and animals, and a computer curve-fitting algorithm used to resolve the decay curve into separate contributions from 15O, 11C, and 13N. The decay curve was corrected for interfering activity from 30P, 38K, and 34mCl, and in the case of live animals, also corrected for a substantial fraction of 11C lost through exhalation. Activation uniformity profiles have been measured for phantoms up to 30 cm in thickness. With a radiation dose of 20 cGy, total-body O, N, and C were measured in dead rats with estimated accuracies of +/- 1.4%, +/- 4.5%, and +/- 1.5% [1 standard deviation (SD)], respectively. With a radiation dose of 40 cGy, total-body O, N, and C were measured in living rats with estimated accuracies of +/- 1.4%, +/- 6.9%, and +/- 1.5% (1 SD), respectively. It is anticipated that total-body O, N, and C similarly could be measured in human subjects with a radiation dose of 1-2 cGy and with accuracies comparable to those obtained in rats. Although most of the measurements were made using a beam energy of 45 MV, we have shown that useful results may be achievable with a beam energy as low as 25 MV. This accurate, convenient, and safe technique for total-body O, C, and N measurement should have applications in the study of nutritional status in health and disease, both in human subjects and in animals.

Activation Analysis↗

PubMedDate not supplied

Improved "nonisolated-sensor" solid polystyrene calorimeter.

A "nonisolated-sensor" solid polystyrene calorimeter is described which permits absorbed dose measurements with precision of less than 0.3% (standard error of the mean). The accuracy for obtaining absolute absorbed dose was estimated by comparisons with cavity ionization measurements. The calculation of absorbed dose with ionization chambers was carried out based upon the TG-21 AAPM dosimetry protocol. Measurements in a 60Co gamma-ray field with three different polystyrene parallel-plate ion chambers in a polystyrene phantom did not differ by more than 1.5% from that obtained with the polystyrene calorimeter. Measurements taken over a period of 247 days are compared with the expected values on the basis of the decay 60Co. The calorimeter system, with its capability of acquiring, printing, storing, plotting, and analyzing the data by computer, is described.

Calorimetry↗

PubMedDate not supplied

A dose homogeneity index for evaluating 192Ir interstitial breast implants.

To evaluate and optimize dose homogeneity of 192Ir interstitial breast implants, we define a quantity, the dose homogeneity index (DHI), as follows: DHI = [V(TDR)--V(HDR)]/V(TDR), where V(TDR) denotes the total treatment volume enclosed by the prescribed treatment dose rate (TDR) and V(HDR) denotes the volume enclosed by high-dose rate (HDR), which is 1.5 X TDR or greater. We have used the DHI to examine and compare 192Ir double-plane implants of various sizes planned by the Memorial system or the Tufts system. Criteria have been suggested for the number of planes required for implants in a given treatment volume. Anderson's volume-dose histogram with inverse square suppression is adopted for illustration.

Brachytherapy↗

PubMedDate not supplied

An isodose shift technique for obliquely incident electron beams.

It is well known that when an electron beam is incident obliquely on the surface of a phantom, the depth dose curve measured normal to the surface is shifted toward the surface. Based on geometrical arguments alone, the depth of the nth isodose line for an electron beam incident at an angle theta should be equal to the product of cos theta and the depth of the nth isodose line at normal incidence. This method, however, ignores the effects of scatter and can lead to significant errors in isodose placement for beams at large angles of incidence. A semi-empirical functional relationship and a table of isodose shift factors have been developed with which one may easily calculate the depth of any isodose line for beams at incident angles of 0 degrees to 60 degrees. The isodose shift factors are tabulated in terms of beam energy (6-22 MeV) and isodose line (10%-90%) and are shown to be relatively independent of beam size and incident angle for angles less than 60 degrees. Extensive measurements have been made on a Varian Clinac 2500 linear accelerator with a parallel-plate chamber and polystyrene phantom. The dependence of the chamber response on beam angulation has been checked, and the scaling factor of the polystyrene phantom has been determined to be equal to 1.00.

Electrons↗