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Biomedical subjects

F H Fahey

Publications and source records attributed to F H Fahey.

28 records · Page 2Linked to original sources
PubMed1987

99mTc-glucoheptonate for quantitation of differential renal function.

Differential renal function was calculated by using 99mTc-glucoheptonate (Tc-GH) in 51 patients. Computer-acquired background-corrected individual renal function was calculated by using both the 1-3-min uptake counts and the 2-4-hr delayed static counts. The degree of correlation between the two was high (r = .96). An equally high correlation was noted in 16 children who were 12 years old or younger, in 15 patients with renal size disparity greater than 60/40%, and in six patients with abnormal creatinine clearances. Ten patients had a 30-min dynamic 99mTc-DTPA study followed immediately by the injection of Tc-GH and acquisition of delayed static images 2-4 hr later. A high degree of correlation (r = .99) was seen between the 1-3-min differential function obtained by using Tc-DTPA and the 2-4-hr delayed differential function obtained by using Tc-GH. This study shows that Tc-GH is a clinically useful and valid tool for calculation of differential renal function and that Tc-GH combines many of the best aspects of Tc-DTPA and Tc-DMSA.

Adolescent↗
PubMed1987

Hepatic visualization on iodine-131 whole-body thyroid cancer scans.

This study examines the frequency and significance of diffuse liver uptake on 131I whole-body thyroid cancer scans. Sixty whole-body scans on 27 patients with differentiated thyroid cancer were reviewed. Liver uptake was quantitated on another 21 studies (16 patients). Diffuse hepatic uptake was seen in 44% of patients and 35% of all the studies. It correlated best with the 131I dose administered (r = 0.733) and the product of the 131I percent radioactive iodine uptake (RAIU) and administered dose (r = 0.656), less well with the serum 131I protein bound iodine (r = 0.494) and the RAIU. This study demonstrates that liver visualization is more common than generally appreciated and is related to the 131I dose and indices of thyroid function although other factors may also play a role in liver visualization.

Adenocarcinoma↗
PubMed1986

Impact of radiocontaminants in commercially available iodine-123: dosimetric evaluation.

Iodine-123 (123I) is considered by some to be the radionuclide of choice for thyroid scintigraphy because of its ideal physical and biological characteristics and low radiation absorbed dose to the thyroid. However, commercially available 123I (p,2n) and (p,5n) have radiocontaminants. The MIRD formalism was used to estimate the absorbed dose to the thyroid for various age groups receiving recommended administered activities at the time of delivery and at two half-lives assuming radiocontamination levels specified by the suppliers. The calculations demonstrate that an 131I uptake with a technetium-99m scan at the time of delivery results in less absorbed dose to the thyroid than an 123I (p,2n) scan and uptake. At two half-lives the absorbed dose triples and becomes equivalent to the dose from an 131I scan. The absorbed dose from an 123I (p,5n) scan at two half-lives is higher than that of an 123I (p,2n) scan at the time of delivery. Iodine-123 capsules should not be decayed down in order to obtain a recommended pediatric administered activity. There appears to be no dosimetric advantage of commercially available 123I for thyroid scintigraphy for adults or most children.

Adolescent↗
PubMed1985

Thallium/technetium functional imaging of the thyroid and parathyroid. A case report.

This case report demonstrates the usefulness and limitations of technetium/thallium scintigraphy in the diagnosis of parathyroid hyperplasia. In addition, discordant thyroid tracer uptake (Tc-99m but not TI-201) due to colloid cysts is described. Another perspective in the controversy over which radiopharmaceutical, Tc-99m or TI-201, should be injected first also is presented.

Aged↗
PubMed1981

Choosing populations to study the health effects of low-dose ionizing radiation.

In January 1978, the United States Congress requested information about the utility of additional epidemiologic studies for quantifying the health effects of low-dose ionizing radiation. In our judgment, no single population can be recommended for study on purely scientific grounds, since the largest group offers only a small chance to obtain a definitive result. On the other hand, if social pressures and regulatory agencies mandate that such studies be attempted, we would recommend prospective cohort studies of occupational populations. We propose that a national worker registry be developed using ionizing radiation as the prototype for studying other occupational exposures. The problems related to studying low-level radiation are not unique, but apply equally to investigations dealing with a great variety of toxic agents. A national plan for collecting information on workers' exposure and health could provide a cost-efficient means to answer public health questions posed by the Congress, scientists and the public.

Adult↗
PubMedDate not supplied

Digital image processing of radiation therapy portal films.

Digital image processing has the potential to enhance and improve several functions of a modern radiation oncology department. These functions may include improving perception of information for low contrast films, electronic transfer of images to remote facilities and back, and reducing storage space requirements for archiving once treatment is finished. This paper gives an overview of the digitization process and of image processing fundamentals. The clinical evaluation of digitized portal films is also discussed. The authors conclude that digitizing low contrast radiation therapy portal films is feasible with present technology and will produce images acceptable for routine clinical use in most instances. The role of image enhancement is less well established and remains investigational.

Humans↗
PubMedDate not supplied

Evaluation of brain activity in FDG PET studies.

PURPOSE: A tool (Gemini) was developed for quantifying regions of interest (ROIs) in registered MR and PET data. Its use was validated through phantom and simulated studies. METHOD: Hot spheres were imaged in a phantom (3:1 and 5:1 target-to-nontarget ratios). The computerized 3D Hoffman brain phantom was used to simulate PET studies. Spherical local activity features of two diameters (4 and 10 mm) and five intensities (5, 15, 25, 50, and 100% increase over gray matter) were added to the data in the thalamus and Brodmann area 37. The data were reprojected into sinograms and blurred with a 7 mm kernel. Poisson noise was added, and the sinograms were then reconstructed and analyzed using both SPM96 and Gemini spherical ROIs. RESULTS: Based on phantom and simulated data, the 95th percentile of intensity within a Gemini ROI afforded a reasonable joint optimization of variance (reliability) and accuracy (validity). SPM96 and Gemini results were similar for the larger (10 mm) feature, but in this application, Gemini was more sensitive than SPM96 for the small feature (4 mm). CONCLUSION: Gemini, a tool for display and measurement of spherical ROIs in registered PET and MR data, is precise and accurate for testing hypotheses of differences in localized brain activity, comparing favorably with SPM96.

Brain↗
PubMedDate not supplied

Energy resolution in a high-pressure gas scintillation proportional chamber.

A high-pressure gas scintillation proportional chamber has been designed and constructed to image x and gamma rays for medical applications. The chamber contains 4 atm of pure xenon. Ultraviolet light emitted from excited xenon atoms within the detector is collected by a hexagonal array of seven UV-sensitive photomultiplier tubes, which in turn are separated from the pressurized gas by 1-cm-thick fused-silica windows. A model was used to predict the energy resolution of the device as a function of fill-gas pressure, voltage within the detector, and light-collection efficiency. The energy resolution improved with increasing scintillation region voltage from 17% full width at half maximum (FWHM) at 1.9 kV to 10% FWHM at 3.0 kV for 59.5-keV photons; once above 1.5 kV, there was no improvement with increasing drift voltage. The addition of the signals from the peripheral phototubes to that of the center phototube did not substantially improve the energy resolution of the device. This was because the noise that was present yielded a high correlation between the phototubes; when this noise was incorporated into the model, the energy resolution of the multiphototube system was accurately estimated. The energy resolution of the gas scintillation proportional chamber was found to be superior to the sodium iodide Anger camera at 59.5 keV by a factor of 2. Further improvement can be obtained by increasing the scintillation region voltage and by increasing the light-collection efficiency by moving the scintillation region closer to the phototubes.

Gamma Rays↗
PubMedDate not supplied

Detection efficiency of a high-pressure gas scintillation proportional chamber.

The detection efficiency of a high-pressure, gas scintillation proportional chamber (GSPC), designed for medical imaging in the 30-150 keV energy range, has been investigated through measurement and Monte Carlo simulation. Measurements were conducted on a GSPC containing 4 atm of pure xenon separated from a hexagonal array of seven ultraviolet-sensitive photomultiplier tubes by 1.27-cm-thick fused-silica windows. Experimental measurements of the photopeak efficiency, fluorescence escape efficiency, and the energy collection efficiency were obtained. Results were also obtained for different photon energies and different values of temporal resolution. The measurements were compared with the results obtained from a Monte Carlo simulation designed specifically for investigating the imaging of low-energy photons (below 150 keV) with a gas-filled detector. The simulation was used to estimate photopeak efficiency, fluorescence escape efficiency, photopeak-to-fluorescence escape peak ratio, quantum interaction efficiency, energy collection efficiency, and local energy collection efficiency. The photopeak efficiency of the GSPC relative to that of a 3-in. (7.62-cm)-thick sodium iodide crystal was measured to be 0.284 +/- 0.001 at 60 keV and 0.057 +/- 0.001 at 140 keV. Of the 60-keV photons incident upon the detector, 70% +/- 4% interacted in the detector, with 28% +/- 1% being in the photopeak, as estimated both by experimentation and through the simulation. The maximum energy collection efficiency was found to be 65% at 60 keV, with 46% being deposited within 0.2 cm of the initial photon interaction. The information gained from this study is being used to design an optimized detector for use in specialized nuclear medicine studies.

Biophysical Phenomena↗