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We present an innovative compact dual-modality detector, which integrates an ultrasound probe with a scintigrafic γ -camera for molecular imaging in medicine, in order to get both morphological and functional information in a single three-dimensional image. The scintigraphic detector consists of a 2 × 2 array of a multi-anode PMT Hamamatsu H8500-Mod8 and a 4.0 mm thick continuous LaBr 3 (Ce) crystal equipped with four segment slant-hole collimators for single photon imaging (SPET). The collimator permits to recover the depth of a lesion by rotating around its vertical axis (z) without the need of rotating the camera around the investigated object. This detector can take advantage from being positioned close to the object and overcome the intrinsic limitations in spatial resolution arising from the geometry of SPET/CT gantry. The aim of this work is to describe preliminary phantom analysis and to provide a 3D US/SPET image.

The development of the molecular imaging technique based on radiopharmaceuticals is requiring sophisticated devices with sub-millimeter spatial resolution and high detection efficiency. Recently, in the field of scintillation gamma camera, it has been demonstrated that continuous crystals may improve spatial resolution with respect to the use of scintillation arrays. In this work we propose a new algorithm that improves spatial resolution. It calculates the position from a single scintillation event by squaring the charge collected on a multi-anodes photomultiplier tube (MA-PMT). It is able to remove the position linearity distortion due to the light reflections and the truncations at the crystal edge. We present measurements from a compact gamma camera based on a 51 mm × 51 mm × 4.0 mm LaBr3:Ce continuous scintillation crystal, coupled to a MA-PMT Hamamatsu H8500. The results show a strong improvement in spatial resolution and confirm the high potential in using of LaBr continuous crystal for molecular imaging applications. © 2009 Elsevier B.V. All rights reserved.

The performance of the new prototype of high quantum efficiency PMT (43% at 380 nm), Hamamatsu R7600U-200, was studied coupled to a LaBr 3 :Ce crystal with the size of ∅12.5 mm×12.5 mm. The energy resolution results were compared with ones from two PMTs, Hamamatsu R7600U and R6231MOD, with 22% and 30% quantum efficiency (QE), respectively. Moreover, the photodetectors were equipped with tapered and un-tapered voltage dividers to study the non-linearity effects on pulse height distribution, due to very high peak currents induced in the PMT by the fast and intense light pulse of LaBr 3 :Ce. The results show an energy resolution improvement with UBA PMT of about 20%, in the energy range of 80–662 keV, with respect to the BA one.

In this paper the response in term of pulse height linearity of two Hamamatsu photomultipliers is investigated, when coupled to a LaBr 3 :Ce scintillation crystal. The two photodetectors have high quantum efficiency and in particular 30% for R6231-01 and 42% for R7600-200 tube. The substantial difference is in the dynode structure, linear focused and metal channel for R6231 and R7600 respectively. In this work in order to verify the non-linearity effects on the pulse height distribution, due principally to the high and fast light production of LaBr 3 :Ce scintillator, we propose a ‘peak by peak’ procedure to calibrate the pulse height distribution. Utilizing a specific fragmentation of the calibration curve in subsets, the calculated energy values are very similar for both PMTs. This result confirmed the potentiality of the procedure to highlight the non-linearity effects on pulse height distribution.

In this work we propose an analysis of a novel Low Energy (LE) parallel hole collimator for high resolution SPET applications. The tested prototype, realized jointly with Nuclear Fields, is a lead parallel hole collimator with 1.0 mm hexagonal hole, 18 mm length, 0.2 mm septa and 10x10 cm2 of useful detection area. It was planned to match the high spatial resolution performances of a compact gamma camera based on LaBr3(Ce) continuous scintillation crystal. The imaging performance of this prototype is compared with a tungsten pinhole collimator (1.0 mm diameter) and with a couple of 1.5 mm parallel hole collimators, 22 mm and 40 mm length with 0.2 mm septa respectively. All the collimators were individually coupled to a scintillation gamma camera based on LaBr3(Ce) continuous crystal and multi anode PMT Hamamatsu H8500. The high intrinsic spatial resolution of the crystal enhances the response of collimators at short source-to-collimator distance –SCD overcoming problems in alignment with the collimator pattern. Spatial resolution and sensitivity were evaluated by scanning the detector field of view at different SCD using a Co57 point source. The parallel hole prototype showed SR better than pinhole with 28 mm FoV. In term of sensitivity, it showed values greater than pinhole one at FoV larger than 2.4 cm. In comparison with LEHR parallel hole collimators, the prototype carried out better SR values at SCD lower than 20 mm with two times more sensitivity. Moreover, the overall SR improved of 20% with respect to the LEGP one at all SCD, with only 35% loss of sensitivity. The collimator prototype seemed complementary with the use of pinhole one and in addition when coupled to the compact LaBr3(Ce) gamma camera can allow a very attractive trade-off between spatial resolution, sensitivity and detection area for radionuclide molecular imaging applications.