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Hasegawa T.,Kitasato University | Oda K.,Positron | Sato Y.,Japan National Institute of Advanced Industrial Science and Technology | Ito H.,Kanagawa Industrial Technology Center | And 5 more authors.
Medical Physics | Year: 2012

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 22Na 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 22Na 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. © 2012 American Association of Physicists in Medicine. Source


Hasegawa T.,Kitasato University | Oda K.,Tokyo Metropolitan University | Wada Y.,RIKEN | Sato Y.,Japan National Institute of Advanced Industrial Science and Technology | And 6 more authors.
IEEE Nuclear Science Symposium Conference Record | Year: 2012

We have been developing reliable and convenient calibration methods based on the use of point-like radioactive sources. In the present study, we used a newly developed traceable point-like Ge 68/Ga 68 radioactive source for determining calibration factors of a PET scanner. The point-like Ge 68/Ga 68 radioactive source consists of a spherical aluminum absorber with an outer diameter of 8 mm and a small radioactive bead in it. The physical characteristics of the source were evaluated with a Monte Carlo simulation code based on Geant4. The source radioactivity was calibrated at an accredited calibration facility. The point-like source was placed in the field-of-view of a clinical PET scanner, SET-2400W (Shimadzu Co.). The calibration factors determined with the point-like source were consistent with those determined by a conventional standard calibration method within a reasonable uncertainty. In conclusion, the proposed method with newly developed traceable point-like sources is useful for calibrating PET scanners. © 2011 IEEE. Source


Hasegawa T.,Kitasato University | Oda K.,Positron | Wada Y.,RIKEN | Sasaki T.,Iwate Medical University | And 10 more authors.
Annals of Nuclear Medicine | Year: 2013

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 22Na sources, special care should be taken to avoid the effects of 1.275-MeV γ rays accompanying β + decays. The purpose of this study is to validate this new calibration scheme with traceable point-like 22Na sources on various types of PET scanners. Method: Traceable point-like 22Na 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 22Na point-like sources was successfully validated for six types of commercial PET scanners. © 2013 The Japanese Society of Nuclear Medicine. Source


Hasegawa T.,Kitasato University | Oda K.,Tokyo Metropolitan University | Wada Y.,RIKEN | Sato Y.,Cancer Institute Hospital | And 11 more authors.
IEEE Nuclear Science Symposium Conference Record | Year: 2012

Purpose: We have been developing a practical and reliable calibration scheme based on the use of traceable point-like sources. In using 22Na sources, special care should be taken to avoid the effects of 1.275-MeV γ rays accompanying β+ decays. The purpose of this study is to validate this calibration method with traceable point-like 22Na sources on various types of PET scanners. Method: The traceable point-like 22Na sources with a spherical absorber design used in this study were of the same type as those used in a previous study. The tested PET scanners included one clinical whole-body PET scanner, four types of clinical PET/CT scanners from different manufacturers, and one small-animal PET scanner. The ROI (region of interest) diameter dependence of ROI values were 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 calibration factors determined using the point-like source were consistent with those by the standard cross-calibration method within ±4%, which was comparable to the uncertainty of the standard cross-calibration method. Conclusion: The novel calibration scheme based on the use of traceable 22Na point-like sources was validated for six types of commercial PET scanners. © 2012 IEEE. Source

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