G. Trotta

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.

Evaluation of flat panel PMT for gamma ray imaging

Abstract The first position sensitive PMT, Hamamatsu R2486, developed in 1985, represented a strong technological advance for gamma-ray imaging. Hamamatsu H8500 Flat Panel PMT is the last generation position sensitive PMT: extremely compact with 2 in. active area. Its main features are: minimum peripheral dead zone (1 mm ) and height of 12 mm . It was designed to be assembled in array to cover large detection area. It can represent a technical revolution for many applications in the field of gamma-ray imaging as for example nuclear medicine. This tube is based on metal channel dynode for charge multiplication and 8×8 anodes for charge collection and position calculation. In this paper we present a preliminary evaluation of the imaging performances addressed to nuclear medicine application. To this aim we have taken into account two different electronic readouts: resistive chain with Anger Camera principle and multianode readout. Flat panel PMT was coupled to CsI(Tl) and NaI(Tl) scintillation arrays. The results were also compared with the first generation PSPMT.

Factors affecting flat panel PMT calibration for gamma ray imaging

Hamamatsu H8500 Flat Panel PMT represents the last technological advancement in gamma ray imaging. Compact size makes it attractive for medical imaging application. To study and compare image performance two Flat Panel PMTs were coupled to CsI(Tl) and NaI(Tl) scintillation arrays with 3 mm and 1.8 mm pixel size respectively and they were connected to multi-anode electronic readout (64 channel). Furthermore a pulsed blue LED coupled to an optical fiber was utilized to scan the tube with different light distribution spreading. The study took into account how PMT anode gain uniformity response, light distribution and intensity, influence spatial resolution, position linearity and image noise. Gain calibration was firstly studied because of PMT gain anode non uniformity response, which range between 27:100 and between 45:100 respectively. Furthermore each crystal pixel produces different charge distribution and this depends on the matching between anode and scintillation array lattice. The amount of anode charge can change more than a factor five for narrow light distributions. Tube gain setting results critical, in fact because of energy resolution of each anode spectra, only a factor five pulse height variation can be adequately converted by ADC. In addition there is a further gain anode variation due to PMT non uniformity response of a factor 3. This mentioned two elements, do not allow to convert all pulses in the useful pulse height ADC range. As a consequence image position distortion and background are produced. Flat Panel shows good image performance. However, because of the big anode size and PMT gain non uniformity response, the gain setting can be critical to obtain the best image performance for scintillation light distribution comparable with anode size.

Factors Affecting Hamamatsu H8500 Flat Panel PMT Calibration for Gamma Ray Imaging

The Hamamatsu H8500 Flat Panel PMT is the latest technological advancement in gamma ray imaging. Its compact size makes it attractive for medical imaging applications. To study and compare image performance a Flat Panel PMT, representing the present production, was coupled to CsI(Tl) and Nal(Tl) scintillation arrays with 3 mm and 1.8 mm pixel size respectively and connected to a multi-anode electronic readout. Furthermore, a pulsed blue LED coupled to an optical liber was utilized to scan the tube with different light distributions. This study investigated how PMT anode gain uniformity response, scintillation light distribution and intensity influence the spatial resolution, the position linearity and the image noise. Each crystal in the scintillation array produces a different charge distribution, which depends on the match between the anode size and the scintillation array lattice. The Nal(Tl) array demonstrated to fit both PMT characteristics and dynamic range of electronic read out, due to the charge distribution adequate to the anode size. For CsI(Tl) crystal, the pulse height calibration resulted more critical, due to the narrow light distribution. In conclusion, the use of Flat Panel tube with selected anode gain uniformity could represent the cheapest and easiest solution to obtain the best image quality, in particular for scintillator array with smaller pixel size.

Imaging performances of LaCl/sub 3/:Ce scintillation crystals in SPECT

Over the last three years, there is a growing interest in the development of a new class of fast scintillators like LaCl/sub 3/:Ce and LaBr/sub 3/:Ce. The new scintillation crystals for the first time, have the main characteristic in producing a light photon number higher than NaI(Tl) at a wavelength suited for the photocathode. The most important characteristic of these crystals is represented from the scintillation light to be yield proportionality as a function of incident gamma ray energy. With the aim to investigate on their potential in single photon imaging three one inch square LaCl/sub 3/:Ce continuous scintillation crystals with 3 and 6 mm thickness were specifically designed for position measurements. They have been coupled to a flat panel PMT through a 3 mm thickness glass window. In order to highlight all the characteristics of the detection system the third one, 3 mm thick, was integral assembled with a one inch PSPMT Hamamatsu R5900-C8. Free and collimated point radioactive sources were used for energy resolution measurements as well for scanning crystals to investigate spatial resolution and position response. Energy resolution values were compared with ones obtained from a sample of LaBr/sub 3/:Ce with one inch diameter and one thickness designed for spectrometric measurements. LaCl/sub 3/:Ce with 3 mm thickness shown energy resolution values worse than expected (13% at 140 KeV) due to the sub-optimal size and configuration for light collection. On the contrary LaBr/sub 3/:Ce carried out 6% relative energy resolution at 140 keV. Intrinsic spatial resolution values of 1 mm and 1.3 mm were obtained from 3 mm thickness LaCl/sub 3/:Ce crystals in the two configurations investigated.

Imaging evaluation of CsI(Tl) arrays for scintimammography

We propose the use of Hamamatsu R7600-C8 position sensitive photomultiplier tubes (PSPMTs) as a practical tool for imaging in scintimammography, through the evaluation of performance as a function of scintillation array pixellation in collimated configurations. A number of CsI(Tl) scintillating arrays with different pixel size and thickness are tested. The very high intrinsic spatial resolution of R7600 PSPMTs made it easy to implement a look up table to correct accurately the gain nonuniformity response and position distortion. Finally, an SNR analysis of a small tumor in scintimammography as a function of crystal pixellation is performed by means of a simple breast phantom.

8 inch diameter PSPMT for gamma ray imaging

This work presents preliminary measurements taken with the first prototype Hamamatsu (R6970) 8-inch Position Sensitive Photomultiplier Tube (PSPMT). These measurements are compared with similar ones obtained using a 5 inch PSPMT (Hamamatsu R3292). The new 8 inch PSPMT has 12 dynode stages, 11 with a proximity mesh structure whilst the last one is a back reflector. The entrance window is 7.5 mm thick and has an active area of 180 mm diameter. The crossed-wire anode of the 8 inch tube consists of 36/spl times/36 wires on a 4 mm pitch. These are paired together to give an 18/spl times/18 wire outputs. Both PSPMTs were coupled to a 110 mm diameter, 3 mm thick CsI(Tl) scintillating array in which each pixel has dimensions of 2/spl times/2 mm/sup 2/. Two read-out methods are compared in this paper. The first being the conventional resistive-divider technique. The second method uses a new multi-wire readout technique in which, the charge on each anode wire is individually read out and digitized. Measurements of the spatial resolution, position linearity, energy resolution and intrinsic charge distribution were carried out for both tubes using both read-out systems. Spatial resolution values of approximately 2 mm FWHM were obtained using the 8-inch PSPMT and the multiwire read-out technique. The other measured characteristics were similar to those obtained using the 5-inch PSPMT. These results obtained using the prototype 8-inch PSPMT underline the potential of this detector in the field of imaging in Nuclear Medicine.

Flat Panel PMT: advances in position sensitive photodetection

Abstract Over the last ten years there was being a strong advancement in photodetection. Different application fields are involved in their use in particular high energy physics, astrophysics and nuclear medicine. They usually work by coupling a scintillation crystal and more recent scintillation arrays with pixel size as small as 0.5 mm. PSPMT represents today the most ready technology for photodetection with large detection areas and very high spatial resolution. Flat panel PMT represents the last technological advancement. Its dimension is 50x50 mm 2 with a narrow peripheral dead zone (0.5 mm final goal). Its compactness allow to assemble different modules closely packed, achieving large detection areas with an effective active area of 97%. In this paper we analyze the imaging performances of PSPMT by coupling two scintillation arrays and by light spot scanning of photocathode to evaluate the linearity position response, spatial resolution and uniformity gain response as a function of light distribution spread and the number of photoelectrons generated on photocathode. The results point out a very narrow PMT intrinsic charge spread and low cross-talk between anodes. Energy resolution and spatial resolution show a good linearity with DRF variation. An unexpected intra-anode gain variation is carried out. In this paper we present the results obtained with this PSPMT regarding imaging performances principally addressed to nuclear medicine application.

Scintillator and photodetectors comparison for compact gamma cameras

The design of high resolution compact gamma cameras requires careful choice of scintillation crystal and photo-detector as well as their degree of pixellation. In this paper we evaluate the imaging properties of photo detectors for clinical imaging application. We compare the performances of two kinds of scintillators (CsI(Tl) and NaI(Tl)) coupled to PSPMTs of the Hamamatsu R5900 family (C8, C12, M16 and M64). To compare the imaging properties, the PSPMTs were optically coupled to CsI(Tl) and NaI (TI) scintillating arrays with pixel size of 2 /spl times/ 2 mm/sup 2/. Spatial resolution as well as energy resolution have been measured.

Gamma-ray spectroscopy with LaBr3:Ce scintillation crystal coupled to an ultra high quantum efficiency PMT

Hamamatsu has recently developed a new PMT, R7600U-200, with Ultra BiAlkali (UBA) photocathode (QE=42% @380 nm), replacing it in a BiAlkali (BA) PMT R7600U (QE=22% @380 nm). To evaluate the improvement in energy resolution, we coupled a LaBr3:Ce scintillation crystal, with size Ø12.5mm × 12.5 mm, to a UBA and to a BA R7600 PMT (22% Q.E.@ 380 nm). Moreover, the lanthanum crystal was coupled to a Hamamatsu R6231MOD, chosen as gold standard (30% Q.E.@380 nm). We utilized also a YAP and LSO scintillation crystals, in order to study the behavior of new photocathode with lower light emission than lanthanum tri-bromide The results from LaBr3:Ce crystal show an energy resolution improvement with UBA photocathode of about 20% in the energy range 32–1332 keV with respect to R7600, close to what expected from the improved quantum efficiency. This result is confirmed also with other two scintillation crystals. Unexpectedly the UBA results with Lathanum tri-bromide are in agreement with ones from R6231 PMT, thought its lower QE. This result is probably due to the different collection efficiency of first dynode stage related to different dynode structure of tubes.