The purpose of this study is to design and develop a high-resolution handheld gamma camera for thyroid and sentinel lymph nodes imaging. The detector of the camera is based on a continuous NaI(Tl) crystal directly coupled to a Position Sensitive Photo Multiplier Tube (PSPMT) with a highly integrated readout circuit to achieve an intrinsic spatial resolution, Ri, at ~1 mm at a much lower cost than a pixelated CZT detector based camera with similar Ri. A novel readout electronic system based on the scintillation light distribution function and least square estimation (LSE) positioning algorithm implemented on a previously developed FPGA board to provide the high Ri, throughout the entire detector area. Two prototype parallel-hole collimators were designed and fabricated for general purpose and high sensitivity thyroid and sentinel imaging. Preliminary test results show that the Ri of our detector meet the designed target, which has exceeded that of most commercially available handheld gamma cameras. The other imaging characteristics are compatible to the designed parameters. In conclusion, the new handheld gamma camera has the potential for small organ imaging with higher performance characteristics at a lower cost than those that are currently available.

Recently, dual-modality systems have been developed, aimed to correlate anatomical and functional information, improving disease localization and helping oncological or surgical treatments.Moreover, due to the growing interest in handheld detectors for preclinical trials or small animal imaging, in this work a new dual modality integrated device, based on a Ultrasounds probe and a small Field of View Single Photon Emission gamma camera, is proposed.

In this work, we developed a model that is able to predict in a few seconds the response of a gamma camera based on continuous scintillator in terms of linearity and spatial resolution in the whole field of view (FoV). This model will be useful during the design phase of a SPECT or PET detector in order to predict and optimize gamma camera performance by varying the parameter values of its components (scintillator, light guides, and photodetector). Starting from a model of the scintillation light distribution on the photodetector sensitive surface, a theoretical analysis based on the estimation theory is carried out in order to find the analytical expressions of bias and FWHM related to four interaction position estimation methods: the classical Center of Gravity method (Anger Logic), an enhanced Center of Gravity method, a Mean Square Error fitting method, and the Maximum Likelihood Estimation method. Afterwards, spatial resolution as well as depth of interaction (DOI) distribution effects are evaluated by processing biases and FWHMs at different DOIs. The comparison between the model and GEANT4 Monte Carlo simulations of four different detection systems has been carried out. Our model prediction errors of spatial resolution, in terms of percentage RMSDs with respect to the simulated spatial resolution, are lower than 13.2% in the whole FoV for three estimation methods. The computational time to calculate spatial resolutions with the model in the whole FoV is five order of magnitudes faster than an equivalent standard Monte Carlo simulation.

46 Objectives To develop a new approach for modeling and compensating for the spatially variant point response function (PRF) for small animal pinhole SPECT Methods We pre-calculate and store the system matrix (SM) generated at a subvoxel density (dense SM, dSM) at one projection view; the SM at all projection views can be obtained from a recombination of the dSM entries. The dSM generation only needs knowing the intrinsic parameters of the pinhole collimator. Imaging configurations with the same intrinsic but different extrinsic parameters can reuse the same dSM. Unlike the rotation-based projector, the dSM approach replaces the image rotation step by a SM rotation at the subvoxel density. The higher the subsample factor, the higher the PRF calculation accuracy and the longer the run-time computation. We evaluate the PRF accuracy of using different subsample factors and their effects on the reconstructed images. The proposed method was applied to an in-house SA SPECT system with 10 cm2 NaI continuous crystal with 4 Hamamatsu H8500 photomultipliers and custom-built data acquisition electronics. Results The nominal data acquisition parameters are shown in Table 1. Denoting by dn, where n is the subsample factor in the linear dimension, we observed that (1) the relative PRF error between d2(3) and d4 were much smaller than that between d1 and d4; (2) there was little difference between d2-d4 and d3-d4. The reconstructed images at d1-d4 agreed with the PRF prediction. Reconstructed images from a multi-head, multi-pinhole experiment further validated the dSM approach. Conclusions The dSM approach for pinhole SA SPECT image reconstruction can be applied to multi-pinhole and multi-head SPECT acquisitions with imperfect circular or helical geometries. The extrinsic parameters can be incorporated to select the dSM entries at runtime. The dSM approach eliminates the image rotation step that is prone to cause extraneous blurring effects.

In this work, we report on the development of a mathematical model for the propagation of scintillation photons from a given point of a continuous scintillating crystal to a detection surface, through an interposed light guide. The model was used to calculate the radial distribution of the scintillation photons, in order to speed up the design of the optical system. The proposed method allows to generate a random distribution of coordinates of the scintillation photons similar to that obtained with a Monte Carlo simulation but the procedure is considerably faster. The radial light distribution of the proposed model is in good agreement with the GEANT4 Monte Carlo simulation. The computational time of the photon coordinate generation for our method is four order of magnitude smaller with respect to the GEANT4 Monte Carlo simulation.

Preliminary study of metabolic radiotherapy with Re via small animal imaging A. Antoccia, G. Baldazzi, M. Bello , D. Bernardini P. Boccaccio , D. Bollini, F. de Notaristefani, F. Garibaldi G. Hull, U. Mazzi, G. Moschini , A. Muciaccio, F.-L. Navarria, V. Orsolini Cencelli, G. Pancaldi, R. Pani A. Perrotta, M. Riondato, A. Rosato, A. Sgura, C. Tanzarella, N. Uzunov o and M. Zuffa Dept. of Biology, Univ. Roma3, V.le G. Marconi, I-00146 Roma INFN, Sezione Roma3, Via della Vasca Navale 84, I-00146 Roma Dept. of Physics, Univ. Bologna, V.le C. Berti-Pichat 6/2, I-40127 Bologna INFN, Sezione Bologna, V.le C. Berti-Pichat 6/2, I-40127 Bologna Dept. of Physics, Univ. Padova, Via F. Marzolo 8, I-35131 Padova INFN LNL, V.le dell’Università 2, I-35020 Legnaro Dip. Scienze Cliniche Veterinarie, Univ. Padova, c/o Agripolis, V.le dell’Università 16, I-35020 Legnaro Dept. of Physics, Univ. Roma3, Via della Vasca Navale 84, I-00146 Roma Ist. Superiore di Sanità, V.le Regina Elena 299, I-00161 Roma Dept. of Pharm. Sc., Univ. Padova, Via F. Marzolo 5, I-35131 Padova Faculty of Pharmacy, Univ. Bologna, Via S. Donato 19/2, I-40126 Bologna Dip. Medicina Sperimentale e Patologia, Univ. Roma1, V.le Regina Elena 324, I-00161 Roma INFN, Sezione Roma1, P.le Aldo Moro 2, I-00185 Roma Dept. of Oncological and Surgical Sc., Univ. of Padova, Via Gattamelata 64, I-35128 Padova Dept. of Natural Sciences, “K. Preslavsky” Univ. of Shumen, Bulgaria

In this work we report on a compact electronic readout system for position-sensitive photomultipliers (PSPMT) that are characterized by a large number of channels in a very small space, typically 64 over a 2" × 2" area. The proposed system allows the reading of all individual channel from a PSPMT, that is useful to fully exploit the information that can be acquired by this kind of system. The readout is controlled by an FPGA that collects the digitalized data from all the channels and send to a remote computer the events that are inside a configurable energy range. An electronic characterization of the readout is proposed, showing very low noise level and very good efficiency up to 20 thousand events per second. The proposed readout can be used for nuclear imaging application like SPECT and PET to improve spatial and energy resolution.

The introduction of Lanthanum Bromide crystal, characterized by a fast and high light emission, offers the possibility to improve both imaging spatial resolution and energy resolution in SPECT in the 80–300 kev energy range, without compromising detection efficiency. The expected performances may be limited if the crystal is used with a multi-anode PMT with Position Sensitive response due to the wide differences in the segmented anode pad gains, ranging from 2:1 to 10:1, . These characteristics may strongly deteriorate the overall energy resolution and, consequently, impair the detector imaging capability. For this reason, a 256 independent channel electronic read out was developed, based on an FPGA control, to individually read the charge on each anode. The electronics features a very low electronic noise ( < 1%) and a wide dynamic range. The readout electronics was used to build a gamma camera based on a single 100 mm × 100 mm continuous LaBr3:Ce crystal coupled to a 2 × 2 array SBA photocatode (38{%} QE) Hamamatsu H8500. An offline calibration procedure is also shown in order to compensate the anode gain variation and to exploit the LaBr3:Ce capabilities, obtaining on the whole detection area an 8.0–8.5{%} energy resolution at 140 kev. The high energy resolution performances of this gamma camera permitted to discriminate emissions from two different isotope ( Tc99m and Co57) with very close photon energy (140 and 122 kev respectively). This capability can be used to provide the gamma image with references coming from Co57 point sources (marker) fixed at known positions. These results confirm the LaBr3:Ce crystals as one of the most interesting for all single photon emission applications.

This paper reports on the tests of a low-noise, multi-channel readout integrated circuit used as a readout electronic front-end for a diamond multi-pixel dosimeter. The system is developed for dose distribution measurement in radiotherapy applications. The first 10-channel prototype chip was designed and fabricated in a 0.18 um CMOS process. Every channel includes a charge integrator with a 10 pF capacitor and a double slope A/D converter. The diamond multi-pixel detector, based on CVD synthetic single crystal diamond Schottky diodes, is made by a 3 × 3 sensor matrix. The overall device has been tested under irradiation with 6 MeV radio therapeutic photon beams at the Policlinico ``Tor Vergata'' (PTV) hospital. Measurements show a 20 fA RMS leakage current from the front-end input stage and a negligible dark current from the diamond detector, a stable temporal response and a good linear behaviour as a function of both dose and dose rate. These characteristics were common to each tested channel.

The bimodal diagnostic systems like ultrasound/scintigraphic ones have the benefit of providing both morphological and physiological information. In the case in which it intends to develop a compact bimodal probe it is important that, as the readout electronics are doubled, the acquisition system is the most compact possible. In this paper we present the characterization and preliminary measurements on a multi-channel readout ASIC for PSPMTs.The chip is equipped with 32 readout channels, as different works show that single channel readout allows to exploit the performances of a gamma detector, especially for linearity. Each single channel readout is composed by a variable capacitor CSA, a sample&hold and a variable gain amplifier (VGA). The possibility to change the gain of the amplifier allows to compensate for the differences in gain of the anodes of the PSPMT, while the possibility of changing the integrator capacitor allows to adapt the input dynamic of the chip depending on the PMT used (BA or SBA photocatode) and on the scintillation crystal coupled to the PMT itself.The preliminary measurements show that a 200 kHz maximum sampling rate is achievable, with 1 V input dynamic and an overall linearity of the whole channel with respect to the input charge impulse of than 2%.To validate the performances of the ASIC different operative measurement was made in two configurations: with a single chip and two R11265-M16 PMTs, and, parallelizing two chips with a single PMT H8500. The tubes were coupled with scintillation crystals with different response speeds, from CsI to LaBr3.

Many modern molecular imaging techniques, based on radiopharmaceuticals, can take advantage of sophisticated devices but are still based on the scintillation detector mechanism proposed by Anger. These devices can perform with millimeter spatial resolution and high detection efficiency, but the final performance is strongly affected by the algorithm used for the scintillation position detection. In this work, a detailed comparison of the effect on the imaging performances of three new position detection algorithms, in terms of spatial resolution, detection linearity and useful Field of View is performed on a prototype gamma detector. The detector, built by the authors, is based on a continuous LaBr3:Ce scintillation crystal coupled to an Hamamatsu MA-PMT H8500 and a single anode readout electronics. The experimental data are obtained scanning the detector surface with a Tc99m collimated source (0.4 mm ϕ) at 1.5 mm step. The overall imaging performances of the device are also tested by mean of a bar phantom. We conclude that the Anger-like algorithms give a 50% uFoV with a 1.30 mm ±0.05 mm spatial resolution while the proposed algorithms give a 80% uFoV and 1.10 mm ±0.06 mm spatial resolution.

A Monte Carlo simulation of a 50 mm x 50 mm x 4 mm continuous crystal has been developed to investigate the correlation between the scintillation light width (sigma) and the Depth of Interaction (DoI) within the crystal. Our studies are based on a LaBr(3)(Ce) crystal, in order to take advantage of its high light yield to reduce the statistic uncertainties on the estimators of the sigma. The first one, the standard deviation of the light distribution, has demonstrated a poor, though linear, correlation to DoI, that is not experimentally detectable. Otherwise, the second estimator, N/I, is the ratio of the total number of photoelectrons to the maximum number of photoelectrons collected from a single anode, in a scintillation event. N/I has been found to have the best correlation to DoI, that provides 2 mm resolution.

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 LaBr3(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.

1 INFN, Roma1, Roma, Italy. 2 Molecular Medicine Dept “Sapienza” University, Roma, Italy. 3 Dept of Radiology “Sapienza” University, Roma, Italy. 4 INFN, Laboratori Nazionali di Legnaro, Legnaro (Padova), Italy. 5 Physics Dept, University of Padova, Padova, Italy. 6 INFN, Sez. di Bologna, Bologna, Italy. 7 Physics Dept, University of Bologna, Bologna, Italy. 8 INFN, Roma3, Roma, Italy. 9 INAIL Roma, Italy. 10 EDEMOM PhD school of Electronics, “Roma Tre” University, Roma, Italy. 11 Physics Dept, “Roma Tre” University, Roma, Italy.

In the last few years, integrated dual-imaging systems have emerged as a new modality for cancer staging with the aim to offer both functional and anatomic information. At moment the prevalent dual modality devices are based on Computer Tomography and Positron Emission Tomography. In this sense, the scientific community is debating about the high effective dose to the patient, representing an indicator of the stochastic risk, especially from Computer Tomography examination. So, a new dual modality imager, based on a Ultrasound probe and a Single Photon Emission Tomography was made in order to combine functional information, from gamma camera with structural one, obtained from the Ultrasound equipment. The Ultrasound probe is the most diffuse anatomical examination device at zero-dose, using a cost-effective and reliable method with few restriction in use. The proposed Single Photon Emission Tomography detector is a compact gamma camera (10×10 cm2 active area), based on LaBr3:Ce scintillation crystal coupled to 4×4 array of Hamamatsu H8500C-MOD8 Multi Anode Photomultiplier, with high spatial and energy resolution performances, equipped with rotating slant-hole collimator. A calibration phantom, made of a Co57 point source inside a water filled box, was utilized to acquire 3D dual modality images. The detector has shown good performances in terms of spatial resolution and localization along z-axis of object of interest. This project was developed by several Italian Universities under an INFN collaboration.

The aim of this work is to present a 64-independent channels, low noise and wide dynamic range readout system for multi-anodes photo-multiplier tubes (MA-PMTs). The results consist of some imaging tests obtained with a Hamamatsu H8500 MA-PMT coupled to different scintillation crystals, like a LaBr(3)(Ce) continuous crystal and NaI(Tl), CsI(Tl) and YAP pixilated scintillation arrays. Moreover, the Hamamatsu H8500C-Mod8 new series equipped with a super bialkali (SBA) photocatode was also studied. Energy and spatial resolutions showed an improvement with respect to the previous generation of multi-channel read-out electronics and we also reported some very interesting results with LaBr(3)(Ce) crystal coupled to the new Hamamatsu H8500-Mod8 with high quantum efficiency. That demonstrated the excellent response characteristics and versatility of our proposed electronic system and its potential use with all gamma-ray detectors.

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.

In this paper the response in term of pulse height linearity of two Hamamatsu photomultipliers is investigated, when coupled to a LaBr3: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 LaBr3: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.