Pixelated scintilator

Keywords— Inter-crystal scattering. Penetration, GATE, Small Animal imaging, Pixelated Scintilator. 

This opens perspectives for obtaining phase contrast information in a microfocus tomographic system Recently we have developed a desktop X-ray microtomographic system [4] with a spot size of 8 micrometer (70 KeV) and equipped with a (1024) pixel CCD, lens coupled to a scintillator. The system is now commercially available [5], The setup is sketched in Figure 1 In this work we used the system to demonstrate the feasibility for phase contrast microtomography. 

For this test, the target was scanned by the read-out beam in 256 x 256 steps. The full width of the point-spread function (PSF) is 3 pixels, corresponding to 43 TV-line pairs . At FWHM, the width is 1.5 pixels, or 85 TV-line pairs . Thus the 256 pixels in both directions are not at all independent. This result clearly shows the degradation of the imaging performances of a Vidicon system by the scintillation screen. 

Quantitate the radioactivity, as a measure of RT activity in 1 pL of the culture supernatant, either by liquid scintillation counting (cut out the spots and place them directly into scintillation fluid), by phosphorimage analysis and quantitation of relative pixel units, or by autoradiography and laser densitometry. 

Another case which is of increasing importance is where the detector is divided into a large number of well defined pixels of finite size e.g. CCD pixels, discrete scintillator elements, or Germanium detectors). If we assume that all relative positions of the boundaries of the detector pixels and the mask element shadows are equally likely to occur, then a typical value for the sensitivity can be found by considering the coding power of the mask convolved with the detector pixel shape e,g, a square or circular patch). 

The detector geometry used is a 3 layer design, with a semiconductor array top layer, and two lower layers which are scintillator/photodiode arrays. The semiconductor layer is made of CdTe 2mm thick and the scintillator arrays are 3cm of CsI(Tl). All the pixels are hexagonal with an across flats dimension of 11mm and a centre to centre spacing of 11.75mm. The detector is surrounded on all sides, and on the bottom by a 2cm thick BGO veto crystal. 

The Imager consists of three layers, where the bottom two layers each consist of 2880 thallium doped caesium iodide (CsI(Tl)) scintillation crystals. Each of these 3 cm deep crystals is viewed by a photodiode. The CsI(Tl) crystals are hexagonal in cross section and have a cross sectional area of Icm, forming a pixelated array of independent detectors. 

The light from the scintillation is sampled by the PMT array, which determines both the x and y coordinates of the event and its energy. If the energy signal falls within the window of the pulse height analyzer, the x and y coordinates are used to increment the appropriate pixel. This process is... 

Figure 3 shows the percentage of detected mispositioned events in different scintillator with different size, when the photons irradiated perpendicular to central pixel of detector array. Percentage of detected photons in one of the adjacent pixel in crystal array is illustrated In Figure 4. As it can be seen, quantitative variations of detected photons are negligible for 0 to 10 degree.

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