We describe a compact, ultra-clean device used to deploy radioactive sources along the vertical axis of the KamLAND liquid-scintillator neutrino detector for purposes of calibration. The device ...worked by paying out and reeling in precise lengths of a hanging, small-gauge wire rope (cable); an assortment of interchangeable radioactive sources could be attached to a weight at the end of the cable. All components exposed to the radiopure liquid scintillator were made of chemically compatible UHV-cleaned materials, primarily stainless steel, in order to avoid contaminating or degrading the scintillator. To prevent radon intrusion, the apparatus was enclosed in a hermetically sealed housing inside a glove box, and both volumes were regularly flushed with purified nitrogen gas. An infrared camera attached to the side of the housing permitted real-time visual monitoring of the cable׳s motion, and the system was controlled via a graphical user interface.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We proposed and tested the a block detector for a multislice, depth-of-interaction (DOI) MR-compatible positron emission tomography (PET). The detector consists of a block detector, four optical ...fibers and photo-multiplier tubes (PMTs). The block detector is a lutetium oxyorthosilicate (LSO) DOI detector comprising eight LSOs arranged in a 2/spl times/2/spl times/2 matrix based on the concept proposed by Murayama et al. The size of a single scintillator of a prototype block detector was 2/spl times/2/spl times/2 mm. The scintillation photons are collected from the side of the scintillator block detector and are transferred to four channels of the position-sensitive PMT (PSPMT) using four optical fibers several meters long. The outputs of the PSPMT signals are calculated to determine the position of gamma interaction in the block detector. Results show that although the light loss from using the fiber was around 90%, there were sufficient transferred scintillation photons to obtain the photo-peak and to calculate the position of gamma interaction in the block detector with reasonable separation. We also modified the block detector to improve the performance of the detector. The size of a single scintillator of the modified block detector was enlarged to be 2.5 mm (transaxial) /spl times/ 3.5 mm (axial) /spl times/ 3.5 mm (depth) to improve the sensitivity. Good position responses as well as time resolution of 5.6-ns full-width at half-maximum (FWHM) were obtained for the modified block detector. With these results, we conclude that a two-rings, two-layer DOI-MR-compatible PET can be realized using the proposed block detector.
We are developing a high-performance brain PET scanner, jPET-D4, which provides 4-layer depth-of-interaction (DOI) information. The scanner is designed to achieve not only high spatial resolution but ...also high scanner sensitivity with the DOI information obtained from multi-layered thin crystals. The scanner has 5 rings of 24 detector blocks each, and each block consists of 1024 GSO crystals of 2.9 mm/spl times/2.9 mm/spl times/7.5 mm, which are arranged in 4 layers of 16/spl times/16 arrays. At this stage, a pair of detector blocks and a coincidence circuit have been assembled into an experimental prototype gantry. In this paper, as a preliminary experiment, we investigated the performance of the jPET-D4's spatial resolution using the prototype system. First, spatial resolution was measured from a filtered backprojection reconstructed image. To avoid systematic error and reduce computational cost in image reconstruction, we applied the DOI compression (DOIC) method followed by maximum likelihood expectation maximization that we had previously proposed. Trade-off characteristics between background noise and resolution were investigated because improved spatial resolution is possible only when enhanced noise is avoided. Experimental results showed that the jPET-D4 achieves better than 3 mm spatial resolution over the field-of-view.
We have proposed an ldquoOpenPETrdquo geometry, which consists of two axially separated detector rings, each of axial length W. A long and continuous field-of-view (FOV) including a 360-degree open ...gap G between two detector rings can be imaged through iterative image reconstruction. In addition to providing stress-less PET scanning and simultaneous PET/CT, the OpenPET is expected to lead to realization of in-beam PET. The OpenPET also extends the axial FOV with a limited number of detectors. However, the axial FOV is limited to 3 W because the maximum limit of G to obtain the axially continuous FOV is W. In this paper, therefore, we propose an alternative geometry to extend axial FOV even more without increasing the number of detectors. The proposed geometry consists of multiple detector rings separated by multiple gaps. By optimizing each width of the gaps based on a new concept of multiplex geometry of the OpenPET, the axial FOV can be theoretically increased to an unlimited extent without increasing the number of detectors. The multiplex OpenPET geometry was compared with the standard OpenPET and the conventional PET using numerical simulation data and experimental data. The results show that similar reconstructed images are obtained by three geometries. The proposed geometry is expected to help realize an affordable entire body PET scanner that enables whole body dynamic imaging.
A tritium radioactivity source was measured by triple-to-double coincidence ratio (TDCR) equipment of the National Metrology Institute of Japan (NMIJ), and measured data were fitted using polynomial ...approximation and the Newton–Raphson method, a technique whereby equations are solved numerically by successive approximations. The method used to obtain the activity minimizes the difference between statistically calculated data and experimental data. In the fitting, since calculated statistical efficiency and TDCR values are discrete, the calculated efficiencies are approximated by quadratic functions around experimental values and the Newton–Raphson method is used for convergence at the minimal difference between experimental data and calculated data. In this way, the activity of tritium was successfully obtained.
► The TDCR data were fitted using polynomial approximation and the Newton–Raphson method. ► Activity was then successfully obtained by this fitting. ► The fitting procedure developed in this paper enables kB to be extracted for the scintilltor being used.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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 pointlike22Na 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 pointlike22Na 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.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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