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Anger cameras (SPECT etc.) presently used in nuclear medicine employ as active detector NaI crystals, obtaining intrinsic spatial resolutions ≥ 3mm. Arrays made of optically isolated single crystal elements of YAP:Ce, having sub-millimeter aperture size, read out by position sensitive photomultipliers, allow to build active detectors to employ in SPECT systems, with intrinsic spatial resolution below the millimeter, and with time resolution of the order of tens of nanoseconds. In this paper preliminary results of measurements carried on different kinds of YAP:Ce arrays are reported. The measurements have been performed aiming to optimize the geometrical and physical parameters of the crystals in order to accomplish a SPEM (Single Photon Emission Mammography) camera detector.

*INRA/CIRAD Station de Recherches Agronomiques;San Giuliano (FRA) Diffusion du document : INRA/CIRAD Station de Recherches Agronomiques;San Giuliano (FRA); National audience

En 1982, l'auteur faisait le point des principaux résultats obtenus dans les 15 essais porte-greffe "agrumes" mis en place depuis 1964. Clémentinier : les hybrides de Poncirus, citranges "Troyer" et "Carrizo" se révèlent supérieurs au bigaradier pour les rendements et la qualité des fruits. Le Poncirus dépasse les citranges pour les rendements vers la 10-12ème année mais il a un effet défavorable sur le calibre des fruits. Ce défaut est atténué avec les citranges. Parmi les différents clones de Poncirus, c'est le Pomeroy qui donne les meilleurs résultats. Citronnier et cédratiers : le Citrus volkameriana donne, pour les rendements, des résultats supérieurs à ceux du bigaradier

Rappel de la première et de la deuxième étude sur des porte-greffe des agrumes : le Poncirus trifoliata en Corse. Dans cette troisième partie, on étudie le comportement agronomique des différentes origines de Poncirus trifoliata après le greffage : reprise au greffage et à la plantation, et comportement comme porte-greffe du clémentinier. En mai 1974, mise en place d'un essai en blocs. Observation sur la vigueur, le rendement, le calibre et la qualité des fruits

In this work, we have attentively studied the performance of a new hybrid photomultiplier tube (HPMT) as detector for photons from scintillating crystals. The HPMT is equipped with a YAP window in order to improve light collection and increase measured light response from scintillating crystals. Several measurements have been performed on BGO, LSO, CsI(Tl) and NaI(Tl) planar crystals having three different surface treatments as well as on YAP : Ce and CsI(Tl) matrices. Such crystals have been coupled to two HPMTs, one equipped with a YAP window (Y-HPMT) and the other with a conventional quartz window (Q-HPMT). Measurements on crystals coupled to the Y-HPMT have shown a consistent improvement of the light response, thanks to the presence of the YAP window. Indeed, the light response measured with the Y-HPMT was on average equal to 1.5, 2.1 and 2.6 times that obtained with the Q-HPMT for planar crystals with white painted (diffusive), fine ground and polished rear surfaces, respectively. With regards to crystal matrices, we measured a light response increase of about 1.2 times.

Mesurements are described concerning the light collection efficiency of YAP:Ce and CsI(Tl) crystals pillars with thicknesses ranging between 3 and 28 mm and cross-sections of 0.6×0.6 and 1×1 mm 2 . These measurements have shown that the light collection is strongly dependent on the length of the pillar rather than on its cross-sectional area. A Monte Carlo code has been developed in order to evaluate the light collection efficiency as a function of the pillar geometry and surface treatment. Particular attention has been paid to the light transition through the crystal–photocathode window interface. The possibility to improve light detection by using a new photon detector provided with a YAP photocathode window has been verified.

Recently, particular attention has been paid to the development of small Field of View (FOV) breast imagers for Nuclear Medicine applications provided with YAP:Ce and CsI, both thallium and sodium doped, multipillar matrices. In order to improve their energy and spatial resolution performances, it is necessary to increase the light output of such scintillating matrices. We have developed a MonteCarlo code with the purpose of studying the detection efficiency as well as the light collection efficiency of crystal pillars as a function of their geometry and surfaces treatment. By analysing both the experimental and the simulations results, we have found out that the best choice for this gamma detector is represented by a CsI(Na) matrix made up of orthogonally arranged pillars whose dimensions are 2×2×3 mm 3 . For this geometry, our simulations have showed a detection efficiency of 62%, a collection efficiency of 80% and an expected light output of 68%.

Recent works show growing interest in optically isolated YAP : Ce single-crystal matrices as high spatial resolution detectors for imaging applications in Nuclear Medicine. Such matrices are manufactured by Preciosa Crytur (Czech Republic) by means of a special sticking procedure of YAP : Ce pillars about 10 mm in length and with cross section ranging between 0.6 mm × 0.6 mm and 3 mm × 3 mm. In this work, we carried out an intensive study on both the complex refractive index of YAP : Ce crystal and the reflectance, versus, the incidence angle, of the coating used as optical insulator in matrix pillar made by Preciosa Crytur.

The characteristics of segmented CsI(Tl) and YAP : Ce scintillators coupled to a position-sensitive photomultiplier tube (PSPMT Hamamatsu R2486) have been measured and compared to evaluate the potential use of such scintillators as precise X- and γ-ray imagers. For such configurations, we obtained good spatial resolution and linearity over their entire 40×40 mm2 Fields of View (FOVs). The scintillating matrices consist of orthogonal arrays of crystal pillars with 0.6×0.6 mm2 cross sections and thicknesses of 3 and 10 mm. The 3 mm thick CsI(Tl) matrix shows a light yield of 44% compared to NaI(Tl), an energy resolution of 22% FWHM at 122 keV, a single pillar spatial response of 0.5 mm FWHM, and a spatial resolution of 0.83 mm.

The YAP Camera represents refined research instrument in nuclear medicine and pharmacology because of its overall detection efficiency comparable to an Anger Camera and its submillimeter intrinsic spatial resolution. The YAP Camera consists of a YAP:Ce multicrystal matrix, whose pillars dimensions are 0.6 mm/spl times/0.6 mm/spl times/10 mm, optically coupled with a position sensitive PMT Hamamatsu R2486 and furnished with a parallel hole lead collimator 20 mm thick with holes diameter of 0.5 mm and septa of 0.15 mm. At this stage it is a miniature camera, with a field of view (FOV) of 40 mm/spl times/40 mm and a total spatial resolution of 1.0-1.2 mm, currently used for radiotracers studies on small biological specimens. A detailed analysis of the detector position linearity and energy responses are presented in this work. The intrinsic spatial resolution is studied with three different single hole collimators (1.0, 0.3, and 0.2 mm), and a theoretical equation is presented. Three different parallel hole collimators are tested to evaluate the optimal hole and septa dimensions. Finally, it is demonstrated that two correction procedures are capable of recovering the image spatial homogeneity and of removing the statistical noise. Some phantom images show the importance of the small-field YAP Camera in the radiopharmacological research.