Optical Properties of Continuous and Pixelated Scintillation Crystals

The optical photon distribution produced inside continuous and pixelated scintillation crystals by the absorption of a γ-ray have been studied with the photon transport program DETECT 2000. With this program the charge signals recorded by a multi-wired anode system, like the Position Sensitive PhotoMultiplier Tube (PSPMT) of a γ-Camera, are simulated. Based on the analytical parametrization which is fitted to experimental data, a new position reconstruction method for PSPMTs is proposed in this work. Planar images have been reconstructed with the new method and compared to the traditional charge center of gravity technique. Data are obtained from a small field, high resolution γ-Camera system with a multi- wired crossed anode using the R2486 (HAMAMATSU) PSPMT. Systematic studies for continuous and pixelated inorganic scintillation crystals of CsI(Tl) have been performed for different phantom geometries using small capillaries of 99mTc. The developed method seems to drastically improve the resolution of the reconstructed planar information, even when homogeneous crystals are used.

The Experimental Study of Lanthanum Bromide Detector in the Gamma Ray Imaging

Cerium activated lanthanum bromide (LaBr3:Ce3+) scintillator crystal has shown very promising characteristics for high-resolution and high-sensitivity gamma ray imaging and spectrometric applications [1,2,. In this paper, we present some preliminary results of a compact gamma camera based on LaBr3:Ce3+ crystal. The detector module consists of a continuous LaBr3:Ce3+ crystal with a sensitive area of 50x50 mm2 and 5mm thickness coupling to a Hamamatsu H8500 position-sensitive photomultiplier tube (PSPMT). A compact multiplexed readout based on symmetric charge division circuit (SCD) was developed to reduce the 64 anode signal to 16 readout channels, and a resistive division network to reduce the readout channels from 16 to 4. The performance of the imaging detector module was tested using a 57Co source. The preliminary results showed that this detector module can achieve an effective field-of-view (FOV) of ~39x39 mm2 with a good intrinsic spatial resolution around 1.5mm and energy resolution of 9.2% at 122 keV.

Modernization of the small-angle neutron scattering spectrometer SANS-U by upgrade to a focusing SANS spectrometer

The small-angle neutron scattering spectrometer SANS-U at the research reactor (JRR-3) of the Japan Atomic Energy Agency, Tokai, Japan, has been successfully upgraded. This major upgrade was undertaken in order to install a high-resolution position-sensitive detector consisting of a cross-wired position-sensitive photomultiplier tube combined with a ZnS/6LiF scintillator on the SANS-U spectrometer. Without changing the total length of the spectrometer, the aim was to extend the accessible low-Qlimit (Qis the magnitude of the scattering vector) and to shorten the measurement time by employing focusing small-angle neutron scattering (FSANS). By using both spherical MgF2biconcave lenses and the new high-resolution position-sensitive detector, the accessible low-Qlimit was extended from 2.5 × 10−3to 3.8 × 10−4 Å−1. As a result, SANS-U can continuously cover a wideQrange from 3.8 × 10−4to 0.35 Å−1with a wavelength of 7 Å. FSANS can be utilized not only to improve the accessible low-Qlimit but also to increase the intensity of incident neutrons passing through the sample in the conventionalQrange from 2.5 × 10−3to 0.35 Å−1. The use of `high-intensity' FSANS also allowed a reduction of the measuring time by approximately 1/3.16 by increasing the incident neutron intensity.

Exprerimental Evaluation of a Dedicated Pinhole SPECT System for Small Animal Imaging and Scintimammography

Nuclear medicine (SPECT and PET) provides functional information, which is complementary to the structural. In cancer imaging radiopharmaceuticals allow visualization of cancer cells functionality, thus small cell population can be imaged. This allows early diagnosis, as well as fast assessment of response to therapy. Our system is a single head gamma camera based on an R3292 position sensitive photomultiplier tube (PSPMT), coupled to a 10cm in diameter CsI:Tl crystal. We have assessed two CsI:Tl crystals with pixel size of 2x2mm2 and 3x3mm2 respectively. Three collimators were tested: a) a hexagonal, 1.1mm in diameter, general purpose parallel hole collimator b) a 1mm pinhole and c) a 2mm pinhole. Systems were tested using capillary phantoms. All measurements were carried out in photon counting mode with gamma radiation produced by 99mTc. Using the 2x2mm2 crystal and the 1mm pinhole collimator - a resolution better than 1mm was achieved. This allows very detailed imaging of small animals. Using the 3x3mm2 and the 2mm pinhole collimator a resolution of 1.3mm was possible with suitable sensitivity for breast imaging. Those results indicate that this system is suitable for animal and breast studies. The next step will be clinical evaluation of the camera.