Search PubMed⌕ Search

Biomedical subjects

T F Budinger

Publications and source records attributed to T F Budinger.

At least 127 records · Page 7Linked to original sources
PubMed1975

Analytical study of a high-resolution positron ring detector system for transaxial reconstruction tomography.

This paper presents an analytical study of a high-resolution positron ring detector system for transaxial reconstruction tomography. Our goal is a combination of good spatial resolution, high sensitivity, rejection of scattered photons, variable section thickness, and the minimization of the number of photomultipliers and coincidence circuits. A circular ring of 288 NaI(Tl) crystals 0.8 cm wide should provide a resolution of 4--7 mm FWHM over a circular region 30 cm in diameter. Coded light pipes permit readout using only 72 photomultipliers and 12 coincidence circuits. With properly designed shielding and an energy resolution of 30% FWHM, a positron activity of 200 muCi per axial centimeter in a 20-cm-diam cylinder of tissue should provide approximately 7,000 events/sex from a 2-cm-thick transaxial section (including a 5% accidental coincident background and a 26% scattered coincident background). This rate is adequate for both static and dynamic imaging. The device can operate at two to three times higher event rates with increased backgrounds.

Elementary Particles↗
PubMed1973

Biological effects due to single accelerated heavy particles and the problems of nervous system exposure in space.

The use of accelerated nitrogen and oxygen nuclei with 270 MeV nucleon-1 at the Berkeley Bevatron allowed a beginning to be made of systematic studies of the effects of heavy particles in multicellular organisms. Initial studies will be briefly reviewed. Individual nitrogen particles produced definite light flashes, streaks and interrupted streaks when they crossed light-sensitive parts of the human retina. The possible hazard from primary heavy galactic cosmic ray particles on long-term space flights are discussed, with special attention to the nervous system.

Animals↗
PubMed1971

Visual phenomena noted by human subjects on exposure to neutrons of energies less than 25 million electron volts.

Six subjects reported multiple starlike flashes and short streaks on exposure to neutrons of energies up to 25 million electron volts. The probable mechanism is interaction with the retinal rods by proton recoils and by alpha particles released from neutron reactions with carbon and oxygen. These observations are similar to light flashes and streaks seen by astronauts who are exposed to high-energy cosmic rays on translunar flight.

Alpha Particles↗
PubMedDate not supplied

Perspectives on imaging modalities.

In the comparison of various techniques it is important to analyze what is known about the physical possibilities of a particular technique for making a specific measurement. X-ray CT, ultrasound, and emission methods with radionuclides do not measure chemical composition. NMR can uniquely measure chemical composition. Unfortunately in the measurement of chemical composition, NMR is insensitive, thus large volumes of tissue must be selected by the NMR spectroscopic experiment for a reliable measurement. Measurements that rely on tissue physical differences to detect surfaces and motion include rapid x-ray imaging and ultrasound. For these reasons they have some attributes for particular types of studies that are superior to emission tomography and NMR. However, in the past few years, improvements in the NMR technology have led to the ability to acquire images representing only 30 sec of time in 3-dimensional studies of the beating human heart. It was believed until recently that anatomical resolution of PET was so poor that other imaging modalities would have to be used to delineate the specific region from which the PET information was coming, particularly in studies of the brain. However, in the past year it has been demonstrated that PET can acquire high resolution images of the CNS cortical ribbon at 2.5 mm or better.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnostic Imaging↗
PubMedDate not supplied

Dynamic PET data analysis.

A general method for estimating the precision of parameters resulting from the use of various experimental designs (rate of injection and rate of tomographic data collection) in emission tomography studies is proposed. The sensitivity matrix of the study model and an estimate of the statistical uncertainty of the tomographic data are used to compute the covariance matrix of the parameters. The determinant of this covariance matrix (proportional to the total volume of uncertainty of the model parameters) serves as a criterion to be minimized. The method is applied to a three-compartment, three-transfer rate constant for glucose metabolism using dynamic positron emission tomography, and a comparison of various current protocols is made with simulated data. The results show that higher rates of injection and higher rates of tomographic data collection at early times lead to smaller statistical uncertainties for the estimates of rate constants. However, for the range of rate constants encountered in practice, differences are insignificant when an initial scan duration less than 30 s is used, without regarding the injection duration.

Deoxyglucose↗
PubMedDate not supplied

Differentiation of cerebral radiation necrosis from tumor recurrence by [18F]FDG and 82Rb positron emission tomography.

Nine radiation-treated brain tumor patients were studied by positron emission tomography (PET) in an attempt to differentiate tumor recurrence from radiation necrosis. Rubidium-82 was used to define the region of absent or disturbed blood-brain barrier and [18F]2-fluoro-2-deoxy-D-glucose ([18F]FDG) was used to evaluate the metabolic state of the brain. By comparing glucose utilization in the pathologic region with utilization in the adjacent tissue, a diagnosis of recurrent tumor (increased [18F]FDG accumulation) or necrosis (decreased FDG accumulation) was made. In the seven patients who underwent surgery the PET diagnosis was confirmed by histologic examination of resected tissue. The two patients who did not undergo surgery have had a clinical course consistent with the PET diagnosis of necrosis. Dynamic 82Rb imaging showed that the rate of 82Rb accumulation was greater in tumor than in normal brain. However, this finding alone did not differentiate tumor from necrosis, as some necrotic tissue also showed high rates of 82Rb accumulation, and washout kinetics were similarly nonspecific. The differentiation of radiation necrosis from tumor recurrence is reliably achieved by [18F]FDG PET examination and is aided by information obtained from a 82Rb PET study done immediately prior to the [18F]FDG injection.

Brain↗
PubMedDate not supplied

Physiological effects of fast oscillating magnetic field gradients.

To evaluate the physiological thresholds of neuromuscular stimulation relevant to very fast NMR imaging studies that use gradient switching at frequencies of 1-2 kHz and a maximum magnetic field of up to 10 mT, a series of studies were done with human volunteers using an experimental echo planar gradient coil set. The threshold for induction of localized and momentary sensations in the human back and abdomen for 10 subjects is 60 T/s for sinusoidally oscillating magnetic fields at 1.27 kHz. The threshold relates to an E field of 6 V/m and is shown to vary with number of oscillations and frequency in accord with theory. Using a simple model of E field induction, the threshold for stimulation of cardiac electrical events should be greater than 4 times this value.

Abdomen↗