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K J Kearfott

Publications and source records attributed to K J Kearfott.

17 recordsLinked to original sources
PubMed1992

Radiation protection design for a clinical positron emission tomography imaging suite.

Radiation exposures due to patient sources, a pneumatic transport system, and gas lines in a positron emission tomography imaging facility are estimated for heavy clinical work loads. For simple source approximations and estimated study activities and times, exposure rates are computed that are larger than those anticipated in traditional nuclear medical imaging facilities. Measurements of exposure rates indicate that such an approach will result in conservative estimates of exposure by a factor of 1.2-6.3. Exposure rates due to gas lines may be kept at reasonable levels by careful planning of the routing of the line and by using high flow rates and small bore tubing. If reasonable care is taken to maintain the system so that only a limited number of failures occur, the doses due to pneumatic transport system operation are also small. The nonextremity doses to personnel and other individuals not involved in radiotracer preparation are estimated to be highest due to exposure to the patient sources. Shielding for 511 keV photons may help to minimize exposure. Several practical suggestions are given for further reducing exposure to personnel.

Equipment Design↗
PubMed1992

Underground air returns as active transportation pathways for radon gas entry into homes.

Levels of elevated 222Rn in homes can fail to correlate with measured radium concentrations in soils and surrounding rocks for reasons which can include water sources, building materials, and unusual variations in climate or building construction. Several homes were identified in the Phoenix, AZ metropolitan area with soil radium concentrations of < 0.074 Bq g-1 (2.0 pCi g-1) which had elevated radon concentrations unexplained by geological sources alone. Continuous monitoring of eight houses under different conditions of cooling system usage revealed a definite role of the underground air returns as active transport pathways contributing to the enhancement of the indoor concentration of 222Rn in six of the houses. The ratio of indoor 222Rn concentrations on days when the cooling system was operated continuously compared to days the system was off ranged from essentially one up to a factor exceeding 10.

Air Conditioning↗
PubMed1992

Mitigation of elevated indoor radon gas resulting from underground air return usage.

Underground air returns have been found to be active transportation pathways for radon gas entry into homes. Several homes for which underground air returns were contributing to elevated indoor 222Rn concentrations were evaluated for possible mitigation. Two houses with such problems were successfully mitigated by inserting flexible ducts into the returns. In one of these houses, the initial mitigation attempt resulted in an exacerbation of the problem due to leakage of the ducting. This was solved by re-sleeving the returns using a stronger material. Mitigation of elevated indoor radon gas caused by use of underground air returns by inserting flexible ducts is not possible for all situations, especially those for which the returns are small, filled with debris, misaligned, or inaccessible.

Air Conditioning↗
PubMed1991

Dual-lumen catheters: quality control tests for radiopacity.

A protocol utilizing a single-point densitometer was developed for the quality control (Q.C.) of the radiopacity of dual-lumen radiographic catheters where x-rays generated at 80 kVp are typically used. Catheter contrast, defined as the difference between catheter radiopacity and background optical density (O.D.) when an aluminum plate is imaged, forms the basic Q.C. parameter. When a given catheter is repeatedly measured, catheter contrast varies with a standard deviation of 0.013 O.D. units. The effects of minor background O.D. variations on contrast are significant, but empirically correctable. A variation in measured contrast of approx. 0.01 O.D. units is observed per 10 kVp energy variation. Aluminum plate thickness has a significant effect on the results; however, other details of the protocol geometry are less important. Variations due to catheter orientation were examined and imaging of packaged catheters was demonstrated.

Catheterization↗
PubMed1991

Apparent dose equivalents resulting from severe heating of film dosimeters.

Unusual reported dose equivalents due to high-energy photons for two individuals prompted the investigation of the effects of severe heating conditions expected in closed vehicles during southwestern summer months on commercial film dosimeters. A historical review of dosimetry records revealed several additional reported high-energy photon exposures for individuals using only beta-emitting radioisotopes during hot summer months. Between 20-100% of experimentally heated badges had apparent dose equivalents exceeding the minimal detectable dose equivalent that were not flagged as being heat damaged or having unusual exposure patterns by the dosimetry companies. Reported dose equivalents for these badges were as high as 2.1 mSv.

Climate↗
PubMed1990

Design of a positionally sensitive laser-heated thermoluminescent detector system.

The design and performance of a positionally sensitive system for the laser read-out of dosimetric information contained in LiF chips and a specially designed composite detector having a thin LiF layer is reported. A 2 cm X 3 cm X 0.254 mm LiF layer was successfully manufactured with a glass backing; however, this was subject to thermal cracking at high temperatures encountered with laser heating. Multiple spot heating of this plate resulted in dosimetric images having a spatial resolution of approximately 2.5 mm, limited primarily by the laser beam radius, a homogeneity of better than 10%, a reproducibility of less than 7%, and a minimum detectable dose of approximately 3.12 X 10(-4) C kg-1 (1.21 R). Observed glow curves were consistent with those predicted theoretically using a first-order kinetic model and assuming rapid heating conditions. Several images of positional radiation dose produced using an x-ray machine are presented.

Equipment Design↗
PubMed1990

Evaluation of two thermoluminescent detection systems for medical imaging environments.

Thermoluminescent detectors (TLDs) can provide accurate and precise measurements for both patient and personnel dosimetry in the medical imaging environment. They have the advantages of tissue equivalency, an excellent dynamic range, and dose rate independence. In the work reported here, experiments with planar x-ray, fluoroscopy, and a 57Co source were conducted to test the repeatability and energy dependence of an LiF TL ribbon/automatic reader system and a four-element CaSO2 and Li2B4O7 badge/automatic reader system for diagnostic radiology and nuclear medicine dosimetry. The results indicate the usefulness and appropriateness of the TLD systems tested for both personnel and patient dosimetry in the medical diagnostic environment.

Evaluation Studies as Topic↗
PubMed1990

A high spatial resolution computerized electro-optic radiation detector array.

A novel computerized electro-optic detector was designed, constructed, and characterized. The results of the experiments performed were as follows: (1) To obtain a maximum SNR when operating at any radiation intensity, the designed detector must be operated at the lowest temperature-- -5 degrees C in this configuration. This temperature permits a maximum integration time of 9.7 s without signal distortion. (2) The detector was found to be linear in the range of operation studied, 2.8 X 10(-3) to 2.0 X 10(-2) C kg-1 h-1 (11-78 R h-1), with a sensitivity of 4.2 X 10(4) mV per C kg-1 h-1 (10.8 mV per R h-1). (3) A simulated stepped phantom was imaged, illustrating the possibility of positional measurements. (4) Very little blooming was noticed.

Cadmium↗
PubMed1989

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.

Air Pollutants, Radioactive↗
PubMed1989

Performance of a well counter and a dose calibrator for quantitative positron emission tomography.

Quantitative nuclear medicine techniques such as positron emission tomography (PET) require precise and accurate knowledge of both the amount of radioactivity administered to a patient and the radioactivity concentration in blood as a function of time. In addition, the uncertainties in such measurements must be known so that the accuracy and precision of quantitative in vivo metabolic measurements may be estimated. In order to characterize and minimize the measurement errors for PET, well counter and dose calibrator performances were studied over long and short time periods using positron-emitting isotopes. To ensure accurate quantitation with well counters, the use of correction factors for sample volume and high count rate effects is essential. Only small drifts in well counter sensitivity were observed during a 24-h period, but longer-term drifts and poor performance emphasized the need for continuing quality control procedures. Similar behavior was observed for dose calibrators. Dose calibrator, rather than well counter, data should be used for PET imaging instrument calibration. The methods presented have direct application to any quantitative nuclear medicine program.

Radiation Dosage↗
PubMed1989

Long-term performance of a multiplanar positron emission tomograph.

A protocol for the daily quality assurance (QA) of a multiplanar positron emission tomographic (PET) system was developed. This was implemented on a daily basis for the PC 4600 Neuro-PET, a multiplanar PET system designed for quantitative brain imaging. Sensitivity data collected as part of the protocol are presented for a 22-mo time period. These data show the need to periodically monitor instrument performance if meaningful quantitation is to be achieved. The methods presented have direct application to any quantitative multiplanar emission tomographic imaging program.

Brain↗
PubMed1985

In vivo measurement of brain tumor pH using [11C]DMO and positron emission tomography.

In vivo measurements of regional brain tissue/tumor pH (rpH) have been accomplished in 9 patients with primary or metastatic brain tumors using [11C]dimethyloxazolidinedione [( 11C]DMO) and positron emission tomography. Tumor rpH values ranged from 6.88 to 7.26, whereas gray matter and white matter rpH values ranged from 6.74 to 7.09 and from 6.77 to 7.03, respectively. Our results, which are consistent with reported [14C]DMO autoradiographic measurements of brain and tumor pH, suggest that the pH microenvironment of brain tumors is not more "acidic" than that of normal gray or white matter.

Adult↗
PubMedDate not supplied

Median polish for quality assurance of a PET scanner.

Sensitivity data for the PC 4600, a multiplanar positron emission tomograph system, were obtained over a period of several months during installation and routine clinical operation. These data were analyzed using the exploratory data analysis techniques of median polish (MP), box and whisker plots, and coded residuals. These techniques proved to be useful in spotting trends and identifying problems. Median polish had advantages over traditional percent difference techniques under some conditions because it allows separate study of more than one effect and is particularly resistant to the influence of outliers. The other exploratory data analysis techniques used are of value in interpreting the results of the MP procedure. The methods presented have direct application to any quantitative multiplanar emission tomographic imaging quality assurance program.

Humans↗
PubMedDate not supplied

Effects of axial spatial resolution and sampling on object detectability and contrast for multiplanar position emission tomography.

A multiplanar positron emission tomography (PET) system is simulated using Gaussian curves to model the axial point spread functions (PSFs) of the planes to study the effects of resolution and sampling. Poor spatial resolution or insufficient sampling may cause deleterious data losses or artifacts in the reconstructed image. For a multiplanar PET system with an axial full width at half-maximum (FWHM) of 6 mm and a 12 to 13 mm ring separation, a ripple in sensitivity of 9% is observed. A 1 mm object placed at the central direct plane results in detection of 59% of the signal in that plane. The theoretical observed contrast of a 3 mm object positioned at the center plane is 25% of the true contrast and decreases to 24% when the object is positioned between the central direct and cross planes. A PET system with an axial FWHM of 12 mm and a ring separation of 5-6 mm has a uniform sensitivity. A 1 mm object placed at the central direct plane detects 14% of the object signal in that plane. The theoretical observed contrast for a 3 mm object is 13% of true contrast when the object is positioned between the central direct and cross planes. It should be noted that all dimensions refer to the z direction through the center of the gantry in the simulated multiplanar system. The uniform sensitivity due to wider axial FWHMs decreases the amount of data loss for inter-ring gaps; however, the blurring associated with wider FWHMs decreases observed contrast.(ABSTRACT TRUNCATED AT 250 WORDS)

Health Physics↗
PubMedDate not supplied

Positional radiotherapy beam dosimetry using a laser heated thermoluminescent plate.

A 4-W, laser-based system for the positional readout of thermoluminescent (TL) plates was utilized to obtain dose profiles for a 60Co radiotherapy beam. Experimentally obtained glow curves for LiF resulting from the rapid heating rates characteristic of laser heating agreed well with results predicted using a first-order kinetic model. Excellent system linearity was obtained for sensitivity to 60Co. The useful dynamic range for this tissue-equivalent system could extend over 8 orders of magnitude. A minimum detectable signal of 1.2 R was estimated for the presently configured system, whose spatial resolution is limited by the laser beam diameter, 1.7 mm. Depth dose profiles for the radiotherapy beam obtained using the prototype laser TL system with a specially designed composite 2.2 cm x 3.3 cm x 0.254 mm LiF plate agreed to within 14% of ionization chamber measured doses.

Cobalt Radioisotopes↗