Kimberlee J. Kearfott

Evaluation of the performance characteristics of the PC 4600 positron emission tomograph.

The sensitivity, resolution, linearity, and count rate capability for the PC 4600 positron emission tomograph (PET), a neurological PET with five rings of 96 bismuth germanate crystals, are reported along with details of the design of this system. Phantom studies and preliminary human images demonstrate the clinical potential of this new instrument.

A new headholder for pet, ct, and nmr imaging

A new headholder was developed for patient restraint and repositioning during positron emission tomography (PET), CT, and nuclear magnetic resonance (NMR) imaging procedures. A customized form was produced for each patient by pouring polyurethane resin and catalyst between an injection-molded polystyrene shell and a protective latex sheet and placing the patients head in the form while the resin set. Excellent head restraint and repositioning was achieved when the headholder was used with a crossed-laser system. Repositioning accuracy was demonstrated by comparing transmission scans of the same patient obtained on different days and by comparing PET transmission scans with coplanar CT scans. No artifacts due to the headholder were apparent in CT, PET, and NMR images.

Characterization of the glow-peak fading properties of six common thermoluminescent materials.

The pre-irradiation and post-irradiation fading rates of the thermoluminescent glow peaks of six commonly used thermoluminescent dosimeters under controlled environmental conditions over approximately 30 d are examined. Glow peaks were fit to the first-order kinetics model using a computerized glow curve deconvolution program. Dosimeters studied were LiF:Mg,Ti, CaF(2):Dy, CaF(2):Tm, CaF(2):Mn, LiF:Mg,Cu,P, and CaSO(4):Dy. LiF:Mg,Ti and LiF:Mg,Cu,P experienced significant pre-irradiation fading. All types except CaF(2):Mn experienced post-irradiation fading. Ratios of glow-peak areas were fit to exponential decay functions when possible.

Preliminary experiences with 222Rn gas in Arizona homes

Results of a survey of 222Rn gas using four-day charcoal canister tests in 759 Arizona homes are reported. Although the study was not random with respect to population or land area, it was useful in identifying areas at risk and locating several homes having elevated indoor 222Rn air concentrations. Approximately 18% of the homes tested exceeded 150 Bq m-3 (4 pCi L-1), with 7% exceeding 300 Bq m-3 (8 pCi L-1). Several Arizona cities had larger fractions of homes exceeding 150 Bq m-3 (4 pCi L-1), such as Carefree and Cave Creek (23%), Paradise Valley (30%), Payson (33%), and Prescott (31%). The Granite Dells and Groom Creek areas of Prescott had in excess of 40-60% of the houses tested exceeding 150 Bq m-3 (4 pCi L-1). Elevated 222Rn concentrations were measured for a variety of home types having different construction materials. Private well water was identified as a potentially significant source of 222Rn gas in Prescott homes, with water from one well testing over 3.5 MBq m-3 (94,000 pCi L-1). A 222Rn concentration in air exceeding 410,000 Bq m-3 (11,000 pCi L-1) was measured using a four-day charcoal canister test in a house in Prescott which had a well opening into a living space. Additional measurements in this 150-m3 dwelling revealed a strikingly heterogeneous 222Rn concentration. The excessive 222Rn level in the dwelling was reduced to less than 190 Bq m-3 (5.2 pCi L-1) by sealing the well head with caulking and providing passive ventilation through a pipe.

Soil sample moisture content as a function of time during oven drying for gamma-ray spectroscopic measurements

In routine gamma-ray spectroscopic analyses of collected soil samples, procedure often calls to remove soil moisture by oven drying overnight at a temperature of 100iC [1]. Oven drying not only minimizes the gamma-ray self-attenuation of soil samples due to the absence of water during the gamma-ray spectroscopic analysis, but also allows for a straightforward calculation of the specific activity of radionuclides in soil, historically based on the sample dry weight. Because radon exhalation is strongly dependent on moisture [2,3], knowledge of the oven-drying time dependence of the soil moisture content, combined with radon exhalation measurements during oven drying and at room temperature for varying soil moisture contents, would allow conclusions to be made on how the oven-drying radon exhalation rate depends on soil moisture content. Determinations of the oven-drying radon exhalation from soil samples allow corrections to be made for the immediate laboratory gamma-ray spectroscopy of radionuclides in the natural uranium decay chain. This paper presents the results of soil moisture content measurements during oven drying and suggests useful empirical fits to the moisture data. ( 1999 Elsevier Science B.V. All rights reserved.

A review of conventional explosives detection using active neutron interrogation

Conventional explosives are relatively easy to obtain and may cause massive harm to people and property. There are several tools employed by law enforcement to detect explosives, but these can be subverted. Active neutron interrogation is a viable alternative to those techniques, and includes: fast neutron analysis, thermal neutron analysis, pulsed fast/thermal neutron analysis, neutron elastic scatter, and fast neutron radiography. These methods vary based on neutron energy and radiation detected. A thorough review of the principles behind, advantages, and disadvantages of the different types of active neutron interrogation is presented.

An improved in situ method for determining depth distributions of gamma-ray emitting radionuclides

Abstract In situ gamma-ray spectrometry determines the quantities of radionuclides in some medium with a portable detector. The main limitation of in situ gamma-ray spectrometry lies in determining the depth distribution of radionuclides. This limitation is addressed by developing an improved in situ method for determining the depth distributions of gamma-ray emitting radionuclides in large area sources. This paper implements a unique collimator design with conventional radiation detection equipment. Cylindrically symmetric collimators were fabricated to allow only those gamma-rays emitted from a selected range of polar angles (measured off the detector axis) to be detected. Positioned with its axis normal to surface of the media, each collimator enables the detection of gamma-rays emitted from a different range of polar angles and preferential depths. Previous in situ methods require a priori knowledge of the depth distribution shape. However, the absolute method presented in this paper determines the depth distribution as a histogram and does not rely on such assumptions. Other advantages over previous in situ methods are that this method only requires a single gamma-ray emission, provides more detailed depth information, and offers a superior ability for characterizing complex depth distributions. Collimated spectrometer measurements of buried area sources demonstrated the ability of the method to yield accurate depth information. Based on the results of actual measurements, this method increases the potential of in situ gamma-ray spectrometry as an independent characterization tool in situations with unknown radionuclide depth distributions.

Simulated annealing image reconstruction method for a pinhole aperture single photon emission computed tomograph (SPECT)

A series of computer experiments was performed to determine the relative performance of simulated annealing, quenched annealing, and a least-squares iterative technique for image reconstruction for single photon emission computed tomography (SPECT). The simulated SPECT geometry was of the pinhole aperture type, with 32 pinholes and 128 or 512 detectors. To test the robustness of the reconstruction techniques upon arbitrary geometries, a 360-detector geometry with a random pixel-detector-factor matrix was tested. Eight computer-simulated, 10-cm-diameter planar phantoms were used with 1961 2-mm(2) reconstruction bins and a range of 3000 to 50,000,000 detected photon counts. Reconstruction quality was measured by a normalized, squared error picture distance measure. Over a wide range of noise, the simulated annealing method had slightly better reconstruction quality than the iterative method, although requiring greater reconstruction time. Quenched annealing was faster than simulated annealing, with comparable reconstruction quality. Methods of efficiently controlling the simulated annealing algorithm are presented.

Quantitation of regional cerebral glucose metabolism

Kinetic analysis of 18F-labeled 2-fluoro-2-deoxy-D-glucose (2FDG) has been carried out in 28 studies on 25 subjects. The object of the analysis was to determine the practical problems of quantitation of glucose metabolic rate (GMR) using the Sokoloff model with 2FDG. We found that arterial and venous plasma concentration of 2FDG yielded equivalent values of the integrated plasma concentration (IPC*) and that one arterial or venous plasma sample at 30 min serves to predict IPC* to within +/- 7%. These observations suggest that quantitation is indeed possible in such subjects without using complex arterial or venous sampling procedures. The average values of K1, K2, and K3 are observed to be 0.14 +/- 0.08, 0.20 +/- 0.10, and 0.030 +/- 0.012 min-1. The data are consistent with a value of lumped constant of 0.4 and a considerable spread in global values of GMR (30%) in an unselected group of subjects.

Preliminary imaging results with 18f-2-fluoro-2-deoxy-D-glucose

Transverse section imaging with 18F-2-fluoro-2-deoxy-D-glucose (2FDG) is of considerable interest because quantitative values of regional glucose metabolism may be obtained. We present preliminary results using 2FDG produced by the Brookhaven National Laboratory and imaged with the PCII at the Massachusetts General Hospital. Three studies are reported showing the distribution in dog, monkey, and in brain of an essentially normal patient.