[en] We have developed a mini gamma camera based on the new 'flat-panel'-type multianode PSPMT (H8500) from Hamamatsu Photonics. The gamma camera is intended for intra-surgical use. The dimensions of the camera are 14 cmx7 cmx7 cm, with a useful field of view of 44 mm, and a weight of 1.2 kg. Its intrinsic resolution is better than 1.5 mm and its energy resolution is about 13%, when using a CsI(Na) scintillating crystal. We present here the most important performance features of the camera and the image reconstruction process followed. Several clinical tests, on breast cancer and melanoma patients, were performed and compared with conventional cameras, to check the quality of the camera. For an administered dose of 3 mCi of ^99mTc around the tumour, 1 h before the lymphscintigraphy, we take high-quality images of the nodes in about 30 s using a pinhole collimator

[en] A small, portable and low-cost gamma camera for medical applications has been developed and clinically tested. This camera, based on a scintillator crystal and a Position Sensitive Photo-Multiplier Tube, has a useful field of view of 4.6 cm diameter and provides 2.2 mm of intrinsic spatial resolution. Its mobility and light weight allow to reach the patient from any desired direction. This camera images small organs with high efficiency and so addresses the demand for devices of specific clinical applications. In this paper, we present the camera and briefly describe the procedures that have led us to choose its configuration and the image reconstruction method. The clinical tests and diagnostic capability are also presented and discussed

[en] We describe the construction of the electronics for a set of scintillating fiber detectors for the detection of elastically scattered particles at the CERN pp Collider for the UA4-2 experiment. Main requirements are large band-width, small cross-talk and reliability. A total of 400 channels have been built and implemented in 25 NIM modules. Results with real data are shown. (Author) 8 refs

[en] A portable gamma camera based on the multianode technology has been built and tested. The camera consists in optically coupling four 'Flat Panel' H8500 PSPMTs to a 100x100x4 mm³ CsI(Na) continuous scintillation crystal. The dimensions of the camera are 17x12x12 cm³ including the pinhole collimator and it weighs a total of 2 kg. Its average spatial resolution is 2 mm, its energy resolution is about 15%, and it shows a field of view of 95 mm. Because of its portability, its FOV and its cost, it is a convenient choice for osteological, renal, mammary, and endocrine (thyroid, parathyroid and suprarenal) scintigraphies, as well as other important applications such as intraoperatory detection of lymph nodes and surgical oncology. We describe the simulations performed which explain the crystal choice, the mechanical design of the camera and the method of calibration and algorithms used for position, energy and uniformity correction. We present images taken from phantoms. We plan to increase the camera sensitivity by using a four-holes collimator in combination with the MLEM algorithm, in order to decrease the exploration time and to reduce the dose given to the patient

[en] The final configuration of our small gamma-camera for medical applications is presented. Emphasis has been put on low cost and portability. The camera, based on a scintillator crystal and a position-sensitive photomultiplier tube, has a useful field of view of 4.6 cm diameter and provides around 2 mm of intrinsic spatial resolution. In its final configuration, the camera weights less than 2 kg and the collimator is of the pinhole type. The camera is only connected through a single USB cable to a portable PC. It images small organs with high efficiency as proven with patients at the hospital

[en] Design optimization, manufacturing, and tests, both laboratory and clinical, of a portable gamma camera for medical applications are presented. This camera, based on a continuous scintillation crystal and a position-sensitive photomultiplier tube, has an intrinsic spatial resolution of ≅2 mm, an energy resolution of 13% at 140 keV, and linearities of 0.28 mm (absolute) and 0.15 mm (differential), with a useful field of view of 4.6 cm diameter. Our camera can image small organs with high efficiency and so it can address the demand for devices of specific clinical applications like thyroid and sentinel node scintigraphy as well as scintimammography and radio-guided surgery. The main advantages of the gamma camera with respect to those previously reported in the literature are high portability, low cost, and weight (2 kg), with no significant loss of sensitivity and spatial resolution. All the electronic components are packed inside the minigamma camera, and no external electronic devices are required. The camera is only connected through the universal serial bus port to a portable personal computer (PC), where a specific software allows to control both the camera parameters and the measuring process, by displaying on the PC the acquired image on 'real time'. In this article, we present the camera and describe the procedures that have led us to choose its configuration. Laboratory and clinical tests are presented together with diagnostic capabilities of the gamma camera

[en] PESIC is an integrated front-end for multianode photomultiplier based nuclear imaging devices. Its architecture has been designed to improve position sensitive detectors behavior by equalizing its response over its whole area. Its preamplying stage introduces two main benefits: digitally programmable gain adjustment for every photomultiplier output, and isolation from other front-end electronics by means of current buffers. This last feature allows to use different types of photomultipliers and optimizes front-end deadtime, reducing impact position dependent output delay. PESIC also includes an indirect measurement of the depth of interaction of the gamma ray inside the scintillator crystal, based on the width of its light distribution. Test measurements have been carried out in an experimental dual detector PET setup in order to quantify improvements obtained from integrated front-end calibration capabilities.

[en] A method to improve light collection efficiency of γ-ray imaging detectors by using retroreflector arrays has been tested, simulations of the behaviour of the scintillation light illuminating the retroreflector surface have been made. Measurements including retroreflector arrays in the setup have also been taken. For the measurements, positron emission tomography (PET) detectors with continuous scintillation crystals have been used. Each detector module consists of a continuous LSO-scintillator of dimensions 49x49x10 mm³ and a H8500 position-sensitive photo-multiplier (PSPMT) from Hamamatsu. By using a continuous scintillation crystal, the scintillation light distribution has not been destroyed and the energy, the centroids along the x- and y-direction and the depth of interaction (DOI) can be estimated. Simulations have also been run taking into account the use of continuous scintillation crystals. Due to the geometry of the continuous scintillation crystals in comparison with pixelated crystals, a good light collection efficiency is necessary to correctly reconstruct the impact point of the γ-ray. The aim of this study is to investigate whether micro-machine retro-reflectors improve light yield without misestimation of the impact point. The results shows an improvement on the energy and centroid resolutions without worsening the depth of interaction resolution. Therefore it can be concluded that using retroreflector arrays at the entrance side of the scintillation crystal improves light collection efficiency without worsening the impact point estimation

[en] Traditionally, the most popular technique to predict the impact position of gamma photons on a PET detector has been Anger's logic. However, it introduces nonlinearities that compress the light distribution, reducing the useful field of view and the spatial resolution, especially at the edges of the scintillator crystal. In this work, we make use of neural networks to address a bias-corrected position estimation from real stimulus obtained from a 2D PET system setup. The preprocessing and data acquisition were performed by separate custom boards, especially designed for this application. The results show that neural networks yield a more uniform field of view while improving the systematic error and the spatial resolution. Therefore, they stand as a better performing and readily available alternative to classic positioning methods.

[en] The center of gravity algorithm leads to strong artifacts for gamma-ray imaging detectors that are based on monolithic scintillation crystals and position sensitive photo-detectors. This is a consequence of using the centroids as position estimates. The fact that charge division circuits can also be used to compute the standard deviation of the scintillation light distribution opens a way out of this drawback. We studied the feasibility of maximum likelihood estimation for computing the true gamma-ray photo-conversion position from the centroids and the standard deviation of the light distribution. The method was evaluated on a test detector that consists of the position sensitive photomultiplier tube H8500 and a monolithic LSO crystal (42mmx42mmx10mm). Spatial resolution was measured for the centroids and the maximum likelihood estimates. The results suggest that the maximum likelihood positioning is feasible and partially removes the strong artifacts of the center of gravity algorithm.