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Biomedical subjects

J F Valley

Publications and source records attributed to J F Valley.

33 records · Page 2Linked to original sources
PubMed1991

Influence of anode and filter material on image quality and glandular dose for screen-film mammography.

The influence of anode and filter materials on the performance (image quality and dose) of a mammography system is investigated. The image quality is evaluated with the image quality index method. A computer simulation has been developed to calculate the physical parameters of the image quality index (contrast, resolution and noise) as well as the mean glandular dose. The calculations take into account the successive steps of the process: x-ray production, filtration, interaction with the test object, anti-scatter grid, interaction with the image detector (screen-film system). An excellent correlation is obtained between the results predicted by the model and those of experimental measurements, suggesting that the model may be used for the prediction of the performance of mammographic equipment. The experimental conclusions are confirmed: the use of a tungsten anode with a rhodium filter allows a dose reduction without a significant degradation of image quality. The computer program can also be used to simulate the influence of factors which are difficult to combine in practice, e.g., various anode and filter materials, monoenergetic x-rays, etc.

Electrodes↗
PubMed1986

[Large breasts, small breasts; which mammographic technic?].

The variation of dose and image quality parameters in the voltage range 25...33 kV have been studied on 3 mammographic phantoms simulating thin, average and thick breasts respectively. The global image quality has been objectively evaluated by an image quality index. The average glandular dose has been chosen as relevant indicator of risk. The study shows that the surface dose and the midplane dose are not suitable indicators of risk if the breast thickness is variable. For all phantoms, the deterioration of image quality with voltage increase was found to be relatively less important than the decrease of the average glandular dose. Consequently, the following optimum voltages are proposed: 28-29 kV for thin breasts, 29-30 kV for average breasts and 33-35 kV for thick ones. The study showed that breast thickness variation is not suitably compensated by the automatic exposure devices currently available.

Breast↗
PubMed1985

Objective assessment of mammography systems. Part I: Method.

The authors have developed an experimental method for simultaneous determination of dose and image parameters in mammography. A global and objective quality concept, the image quality index, is proposed and its reliability demonstrated by tests of reproducibility. Objective quality tests and subjective evaluation by radiologists showed good correlation.

Evaluation Studies as Topic↗
PubMed1985

Objective assessment of mammography systems. Part II: Implementation.

A quality control program for mammography units was carried out, based on objective tests of image quality and dose. Results are reported for 31 units, including correlation between various parameters. Satisfactory results were obtained in the case of 21 installations; for the other 10, comparison between measured quality parameters and those of the reference system suggested ways in which quality might be improved.

Female↗
PubMed1981

[Technic of curietherapy in the management of prostatic cancers].

With one or serveral charges of 137 Cs placed in an ordinary indwelling catheter, one can deliver to the prostate a radiation dose in 24 hours equivalent to the same dose which could be produced by 226 Ra in five days, or 60 Co in 6 to 7 weeks using the usual methods. 10 patients in whom a carcinoma of the prostate was discovered during adenomectomy (hidden Ca, stage A) have been treated in this way with hardly any immediate disadvantages.

Catheters, Indwelling↗
PubMed1979

Application of the thermoluminescent dosimetry to a pion beam.

The thermoluminescent dosimetry is currently applied to radiation therapy in order to measure dose distributions on phantoms or to control the dose in vivo for special procedures or critical organs. The application of this method to the SIN's (Switzerland) pion beam has been studied. Measurements have been made on the following thermoluminescent materials: 7LiF, 6LiF, Li(nat)F, Li2B4O7, CaF2 : Mn, and CaF2 : Dy. Except for the last one a reduction (10%) of the sensitivity of the phosphors has been observed in the peak relative to the plateau region. An increase of the 6LiF sensitivity relative to that of 7LiF has been pointed out due to the neutron background through the (n, alpha) reaction on 6Li. Glow curves of the LiF phosphors have been measured. A reduction (5%) of the intensities of peak 3 and 4 relative to peak 5 has been observed for irradiation in the peak region. This effect however can't be used in order to localize the dosimeter in the beam because the intensity of the thermoluminescence peaks shows a larger variability in a batch of dosimeters.

Elementary Particles↗
PubMedDate not supplied

Using 80 kVp versus 120 kVp in perfusion CT measurement of regional cerebral blood flow.

Perfusion CT studies of regional cerebral blood flow (rCBF), involving sequential acquisition of cerebral CT sections during IV contrast material administration, have classically been reported to be achieved at 120 kVp. We hypothesized that using 80 kVp should result in the same image quality while significantly lowering the patient's radiation dose, and we evaluated this assumption. In five patients undergoing cerebral CT survey, one section level was imaged at 120 kVp and 80 kVp, before and after IV administration of iodinated contrast material. These four cerebral CT sections obtained in each patient were analyzed with special interest to contrast, noise, and radiation dose. Contrast enhancement at 80 kVp is significantly increased (P < .001), as well as contrast between gray matter and white matter after contrast enhancement (P < .001). Mean noise at 80 kVp is not statistically different (P = .042). Finally, performance of perfusion CT studies at 80 kVp, keeping mAs constant, lowers the radiation dose by a factor of 2.8. We, thus, conclude that 80 kVp acquisition of perfusion CT studies of rCBF will result in increased contrast enhancement and should improve rCBF analysis, with a reduced patient's irradiation.

Brain↗