R. Pani

Scintillation properties of YAP:Ce

Abstract Yttrium aluminium perovskite activated by cerium (formula YAlO 3 :Ce, abbreviated YAP:Ce) is systematically investigated in view of its use as efficient scintillator for various applications. The basic physical and chemical properties of YAP:Ce monocrystals are summarized in this paper. The luminescence, scintillation and absorption characteristics, the γ-ray detection capability, energy resolution in the range of 30–600 keV, light yield and radiation hardness are presented and compared with existing literature.

High-resolution scintimammography improves the accuracy of technetium-99m methoxyisobutylisonitrile scintimammography: use of a new dedicated gamma camera

Abstract. The main disadvantage of technetium-99m methoxyisobutylisonitrile (MIBI) prone scintimammography is its limited sensitivity for T1a and T1b cancers with a size of less than 1 cm. We have developed a high-resolution scintimammographic technique using a gamma camera based on a new concept, namely a position-sensitive photo-multiplier tube. The field of view of this camera, previously known as the SPEM (single photon emission mammography) camera, was 10 cm diameter. Scintimammographic images were acquired in the axial view; each breast was compressed to a thickness of 3–6 cm, modal class 4 cm. When the compressed breast was larger than the field of view, more than one study was performed in order to image the entire gland. Fifty-three patients were studied with high-resolution-scintimammography (HRSM) and Anger camera prone scintimammography (ACPSM). HRSM was performed 70 min after i.v. administration of 740 Mbq of 99mTc-MIBI; ACPSM images were acquired 10 and 60 min following the injection. Early 10-min ACPSM images were only evaluated for routine diagnostic purposes, while comparison was carried out between the 60-min ACPSM and 70-min HRSM images. At fine-needle aspiration (FNA) and/or open biopsy, 31 patients showed cancer: 15 T1c, 11 T1b and 5 T1a. In T1a-T1b cancers, the sensitivity of scintimammography was 50% with ACPSM and 81.2% with HRSM (P<0.01). Specificity was 86% with both techniques. HRSM is a promising new technique that improves the sensitivity of 99mTc-MIBI scintimammography in tumours sized less than 1 cm without apparently reducing its specificity. We are now working on a larger field-of-view camera.

Multi-PSPMT scintillating camera

Gamma ray imaging is usually accomplished by the use of a relatively large scintillating crystal coupled to either a number of photomultipliers (PMTs) (Anger Camera) or to a single large Position Sensitive PMT (PSPMT). Recently the development of new diagnostic techniques, such as scintimammography and radio-guided surgery, have highlighted a number of significant limitations of the Anger camera in such imaging procedures. In this paper a dedicated gamma camera is proposed for clinical applications with the aim of improving image quality by utilizing detectors with an appropriate size and shape for the part of the body under examination. This novel scintillation camera is based upon an array of PSPMTs (Hamamatsu R5900-C8). The basic concept of this camera is identical to the Anger Camera with the exception of the substitution of PSPMTs for the PMTs. In this configuration it is possible to use the high resolution of the PSPMTs and still correctly position events lying between PSPMTs. In this work the test configuration is a 2 by 2 array of PSPMTs. Some advantages of this camera are: spatial resolution less than 2 mm FWHM, good linearity, thickness less than 3 cm, light weight, lower cost than equivalent area PSPMT, large detection area when coupled to scintillating arrays, small dead boundary zone (<3 mm) and flexibility in the shape of the camera.

SCINTILLATING ARRAY GAMMA CAMERA FOR CLINICAL USE

Abstract Dedicated gamma cameras for specific clinical application are representing a new trend in Nuclear Medicine. They are based on Position Sensitive Photo Multiplier Tubes (PSPMT). The main intrinsic limitation of large area PSPMT (5″ diameter) is the photocathode glass window. Coupling to a planar scintillation crystal strongly affects the useful active area and the intrinsic spatial resolution. To overcome this limitation at University of Rome “La Sapienza” was developed the first 5″ diameter gamma camera consisting of a Hamamatsu R3292 PSPMT coupled to 50 × 50 YAP: Ce scintillating array. The array pixel size is 2 × 2 mm2 and the overall dimension of multi-crystal is 10 × 10 × 1 cm3. Resistive chains were used to calculate the centroid. The scintillating array produces a focused light spot minimising the spread introduced by PSPMT glass window. The intrinsic spatial resolution varied between 2 and 2.7 mm. The position linearity and useful active area resulted in good agreement with intrinsic one obtained by light spot irradiation. The real limitation was the poor energy resolution of an individual crystal (40%) and the poor uniformity response of PSPMT (within ±15%). A correction matrix was then carried out by which a 57% of total energy resolution was obtained for the whole matrix. The camera is currently operating as Single Photon Emission Mammography (SPEM) and it is producing breast functional images for malignant tumour detection using the same geometry as standard X-ray mammography.

A 3D high-resolution gamma camera for radiopharmaceutical studies with small animals

The results of studies conducted with a small field of view tomographic gamma camera based on a Position Sensitive Photomultiplier Tube are reported. The system has been used for the evaluation of radiopharmaceuticals in small animals. Phantom studies have shown a spatial resolution of 2mm in planar and 2-3mm in tomographic imaging. Imaging studies in mice have been carried out both in 2D and 3D. Conventional radiopharmaceuticals have been used and the results have been compared with images from a clinically used system.

Use of a YAP:Ce matrix coupled to a position-sensitive photomultiplier for high resolution positron emission tomography

A new scintillation detector system has been designed for application in high resolution Positron Emission Tomography (PET). The detector is a bundle of small YAlO/sub 3/:Ce (YAP) crystals closely packed (0.2/spl times/0.2/spl times/3.0 cm/sup 3/), coupled to a position sensitive photomultiplier tube (PSPMT). The preliminary results obtained for spatial resolution, time resolution, energy resolution and efficiency of two such detectors working in coincidence are presented. These are 1.2 mm for the FWHM spatial resolution, 2.0 ns for the FWHM time resolution and 20% for the FWHM energy resolution at 511 keV. The measured efficiency is (44/spl plusmn/3)% with a 150 keV threshold and (20/spl plusmn/2)% with a 300 keV threshold.

Multi-crystal YAP: Ce detector system for position sensitive measurements

Abstract Yttrium aluminum perovskite (YAP:Ce) scintillation crystal has a light efficiency of about 40% relative to NaI. Because of the yttrium atomic number ( Z = 39) and the relatively high density (5.37 g/cm 3 ) it has a good gamma-ray absorption. Furthermore it is not hygroscopic and is inert. Its peculiarity consists of material processing that provides us with crystal pillars down to 0.3 × 0.3 mm 2 aperture size and up to some centimeters in length. An array consisting of 11 × 22 YAP:Ce elements was made where each crystal has an aperture of 0.6 × 0.6 mm 2 and a length of 7 mm. Each scintillation crystal is optically separated by a reflective material resulting in a separation layer between elements of about 5 μm. The multicrystal detector was optically coupled to a Hamamatsu Position Sensitive Photomultiplier Tube (R2486). The intrinsic spatial resolution of the PSPMT is better than 0.3 mm but it is strongly dependent on the Point Spread Function (PSF) generated on the photocathode. The multicrystal detector very well matched the PSPMT characteristics resulting in a spatial resolution of about 0.7 mm at 140 keV ( 99m Tc) gamma irradiation.

First Results from a YAP:Ce Gamma Camera for Small Animal Studies

The YAP (yttrium aluminum perovskite) camera is a novel gamma camera with intrinsic submillimeter spatial resolution and detection efficiency comparable to a standard Anger camera. At the first stage, it is a miniature gamma camera with a field of view of 4/spl times/4 cm/sup 2/ and is currently utilized for radio tracer studies on small animals. The YAP camera consists of a multicrystal array coupled to a position sensitive photomultiplier tube (Hamamatsu R2486) with a parallel hole collimator. The preliminary results are presented and discussed, in particular the intrinsic characteristics of the scintillating array, which are measured, as well as the position linearity and the spatial resolution, with a parallel collimator. Images were obtained from /sup 99m/Tc line source and nude Balb C mice, which have been injected with /sup 99m/Tc MDP, a bone-seeking agent. The observed images show the importance of the small-field YAP camera in radiopharmaceutical research.

The use of cadmium telluride detectors for the qualitative analysis of diagnostic x-ray spectra.

A method is introduced for the evaluation of x-ray spectra from x-ray machines operating in the range 50-100 kVp using a cadmium telluride (CdTe) detector with low detection efficiency. The pulse height distribution obtained with this kind of detector does not represent the true photon spectra owing to the presence of K-escape, Compton scattering, etc.; these effects were evaluated using a Monte Carlo method. A stripping procedure is described for implementation on a Univac 1100/82 computer. The validity of our method was finally tested by comparison with experimental results obtained with a Ge detector and with data from the literature; the results are in good agreement with published data.

Imaging performance comparison between a LaBr3: Ce scintillator based and a CdTe semiconductor based photon counting compact gamma camera.

The authors report on the performance of two small field of view, compact gamma cameras working in single photon counting in planar imaging tests at 122 and 140 keV. The first camera is based on a LaBr3: Ce scintillator continuous crystal (49 x 49 x 5 mm3) assembled with a flat panel multianode photomultiplier tube with parallel readout. The second one belongs to the class of semiconductor hybrid pixel detectors, specifically, a CdTe pixel detector (14 x 14 x 1 mm3) with 256 x 256 square pixels and a pitch of 55 microm, read out by a CMOS single photon counting integrated circuit of the Medipix2 series. The scintillation camera was operated with selectable energy window while the CdTe camera was operated with a single low-energy detection threshold of about 20 keV, i.e., without energy discrimination. The detectors were coupled to pinhole or parallel-hole high-resolution collimators. The evaluation of their overall performance in basic imaging tasks is presented through measurements of their detection efficiency, intrinsic spatial resolution, noise, image SNR, and contrast recovery. The scintillation and CdTe cameras showed, respectively, detection efficiencies at 122 keV of 83% and 45%, intrinsic spatial resolutions of 0.9 mm and 75 microm, and total background noises of 40.5 and 1.6 cps. Imaging tests with high-resolution parallel-hole and pinhole collimators are also reported.