ABSTRACT
OBJECTIVE: To improve the reliability and convenience of the calibration procedure of positron emission tomography (PET) scanners, we have been developing a novel calibration path based on traceable point-like sources. When using (22)Na sources, special care should be taken to avoid the effects of 1.275-MeV γ rays accompanying ß (+) decays. The purpose of this study is to validate this new calibration scheme with traceable point-like (22)Na sources on various types of PET scanners. METHOD: Traceable point-like (22)Na sources with a spherical absorber design that assures uniform angular distribution of the emitted annihilation photons were used. The tested PET scanners included a clinical whole-body PET scanner, four types of clinical PET/CT scanners from different manufacturers, and a small-animal PET scanner. The region of interest (ROI) diameter dependence of ROI values was represented with a fitting function, which was assumed to consist of a recovery part due to spatial resolution and a quadratic background part originating from the scattered γ rays. RESULTS: The observed ROI radius dependence was well represented with the assumed fitting function (R (2) > 0.994). The calibration factors determined using the point-like sources were consistent with those by the standard cross-calibration method within an uncertainty of ±4 %, which was reasonable considering the uncertainty in the standard cross-calibration method. CONCLUSION: This novel calibration scheme based on the use of traceable (22)Na point-like sources was successfully validated for six types of commercial PET scanners.
Subject(s)
Algorithms , Positron-Emission Tomography/instrumentation , Positron-Emission Tomography/standards , Sodium Radioisotopes/analysis , Sodium Radioisotopes/standards , Calibration , Equipment Design , Equipment Failure Analysis , Japan , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
PURPOSE: The purpose of this study is to propose a microfocus x-ray imaging technique for observing the internal structure of small radioactive sources and evaluating geometrical errors quantitatively, and to apply this technique to traceable pointlike (22)Na sources, which were designed for positron emission tomography calibration, for the purpose of quality control of the pointlike sources. METHODS: A microfocus x-ray imaging system with a focus size of 0.001 mm was used to obtain projection x-ray images and x-ray CT images of five pointlike source samples, which were manufactured during 2009-2012. The obtained projection and tomographic images were used to observe the internal structure and evaluate geometrical errors quantitatively. Monte Carlo simulation was used to evaluate the effect of possible geometrical errors on the intensity and uniformity of 0.511 MeV annihilation photon pairs emitted from the sources. RESULTS: Geometrical errors were evaluated with sufficient precision using projection x-ray images. CT images were used for observing the internal structure intuitively. As a result, four of the five examined samples were within the tolerance to maintain the total uncertainty below ±0.5%, given the source radioactivity; however, one sample was found to be defective. CONCLUSIONS: This quality control procedure is crucial and offers an important basis for using the pointlike (22)Na source as a basic calibration tool. The microfocus x-ray imaging approach is a promising technique for visual and quantitative evaluation of the internal geometry of small radioactive sources.
Subject(s)
Phantoms, Imaging/standards , Radiography/instrumentation , Radiography/standards , Sodium Radioisotopes/analysis , Sodium Radioisotopes/standards , Equipment Design , Equipment Failure Analysis , Japan , Radiopharmaceuticals/analysis , Radiopharmaceuticals/standards , Reference Values , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
In order to calibrate PET devices by a sealed point source, we contrived an absolute activity measurement method for the sealed point source using scintillation detector arrays. This new method was verified by EGS5 Monte Carlo simulation.
Subject(s)
Scintillation Counting/methods , Sodium Radioisotopes/standards , Monte Carlo Method , Positron-Emission Tomography/standards , Reference StandardsABSTRACT
Samples of 24Na, 42K, 76As and 198Au were produced by irradiation in the National Institute of Standards and Technology (NIST) reactor, and examined for impurities before and after measurement. Half-life measurements were carried out in the NIST 4pigamma pressurized ionization chamber. The results are compared to presently accepted values and previous NIST measurements.
