Read-out of LYSO : Ce Matrix Detector using Wave-Length-Shifter fibers applicable to new PET Scanner with High Spatial Resolution at Low Cost

　In building a PET scanner, crystal read-out using wave-length shifter fi bers（WLS）permits the use of many small crystals with a reduced number of photo-sensors, thus promising good spatial resolution at low cost. However, the main drawback of this method has been low efficiency of photon collection. Improvements in design of our readout system over the last several years have resulted in a factor of more than ten in the collection of photons. In the present study, a narrow gamma-ray beam is injected to a matrix detector composed of 16 × 16 LYSO : Ce crystals which are read out by using 2 × 16 Kuraray Y-11 WLS fi bers and two Hamamatsu H6568ModIII photomultipliers. A good spatial（0.34 mm RMS）and time resolution are obtained. The observed time resolution allows the use of 10 ns coincidence time window with a loss of 8.8%. A detection efficiency close to that of a single block LYSO crystal directly mounted on PM was obtained. A sketch of a full size animal PET scanner with 20 cm internal diameter is given. Building such a device by using the method developed in the present study needs only 54 photomultipliers identical to those used in this study

Depth of interaction measured with LYSO (Ce) scintillator in a new method

　The importance of the information concerning the depth of interaction (DOI) in a PET device has been stressed by many authors. In this paper, the attenuation of the emitted light in a thin LYSO (Ce) scintillator crystal has been measured for the purpose of obtaining information about DOI from the ratio of the light output measured at both ends of the crystal. A pair of photomultipliers were attached to the two ends of the crystal for this purpose. An array of wave-length shifters(WLS) attached to the crystal from a side was used in order to find the hit point of the incident gamma rays along the crystal. The attenuation constant μ determined in this measurement is μ＝0.79 ± 0.0007/cm. This value is experimentally demonstrated to be appropriate for the DOI estimation using the ratio of the amounts of light. The obtainable DOI resolution, when the crystal is read out using WLS and a new kind of position-sensitive photomultipliers in our next prototype, is estimated

Novel scheme for Lane-Bates\u27 blind deconvolution : Determinant conditions for the zeros of blurs and a simple algorithm for eliminating blurs

　The Lane-Bates method of blind deconvolution makes it possible to analytically recover the original image without prior knowledge of blurs convolved in a given image. The method utilizes the zeros of the z-transform of the given image. Its implementation, however, requires highly nontrivial analysis of the zeros. We have developed a novel scheme that considerably simplifies the analysis of the zeros. We have developed two versions of the scheme, i.e., determinant conditions (DCs) for the zeros of blurs and a search algorithm (SA) of blur images. The DCs consist of two forms, i.e., a derivative form and a multi-point form. The derivative form is given as a determinant form of conditions on derivatives of the zeros of assumed blurs that can be evaluated by using zeros of the z-transform of the given image. On the other hand, the multi-point form is given as a determinant form of conditions on the zeros of assumed blurs that are evaluated at multiple points in z space. The scheme is particularly powerful when the blurs have multiple structures as we illustrate. The SA is given as a form of simultaneous equations for blur elements of an assumed blur. The method is powerful when we try to find a single blur. This method is robust for compressed gray-scale images. These methods have been experimentally tested with model blurred images and shown to be powerful. In this report we illustrate how they are useful for the Lane-Bates blind deconvolution

Study on the light insulator between scintillator crystals

　In our current project, we undertake an R&D of a new type of PED device which can be produced with a much lower cost yet has a better spatial resolution, compared to the currently used devices. In the course of this development, we encountered a difficulty of light cross-talk between the scintillator crystals. Large amount of effort has been paid to find out the best material to be used to reduce this cross-talk without reducing the light output and the spatial resolution. The experimental result shows that a black flock paper has the most promising features

Efficient Methods of Blind Deconvolution Based on the Lane-Bates Algorithm: Comprehensive Summary

　We developed efficient methods of blind deconvolution on the basis of the Lane-Bates algorithm. The methods consist of two kinds of mathematical tools and their modified versions. We give a comprehensive summary of them in this report

Development of High-resolution Fast Gamma-ray Imager for the New-generation PET III

　The disappearance of the air layer between scintillator crystals due to their sticking seems harmful. To avoid this phenomenon, an insertion of black flock paper is tried and the effect was studied. The result seems positive. But we need to look for a better material which is light tight, thin, solid yet not sticky