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The correct quantification of the dose released in charged particle therapy treatments requires the knowledge of the double differential fragmentation cross section of particles composing both the beam and the target. The FragmentatiOn Of Target (FOOT) experiment aims at measuring these cross sections for ions of interest for charged particle therapy applications. This article describes the performance of the time-of-flight (TOF)-wall detector of the experiment. The detector is composed of two layers of 44 cm $\times 2$ cm $\times 3$ mm plastic scintillator bars (20 for each layer), arranged orthogonally and read-out by silicon photomultipliers. The detector is designed to identify the charge of fragments ranging from protons to oxygen ions, with a maximum energy of 700 MeV/u, by measuring the energy released in the scintillators and the TOF with respect to a start counter. In this study, the detector was scanned with carbon ions of energy between 115 and 400 MeV/u and with a 60-MeV proton beam. The measurements show an energy resolution ( $\sigma _{E}/\mu _{E}$ ) between 6% and 4% and a contribution of the detector to the TOF system time resolution between 25 and 20 ps (standard deviation) for carbon ions and between 100 and 80 ps for protons.

Spectroscopy-based photon-counting detector systems, Medipix, have many applications in medicine. Medipix detectors benefit from providing energy information as well as high spatial resolution. In this article, a review of Medipix detector technology applied to medicine and imaging techniques are presented. The technology has been used to develop quality assurance (QA) measurement devices in radiation-based treatments. A gamma camera system for radiotherapy has been developed to measure dose delivered to prostate treatments in real-time. The advantage of a high-resolution detector has been utilized in proton and heavy ion therapy for dose QA, measuring the charge particle spectra, and beam geometry for mini-beams. Applications in medical imaging using helium ion beams have been investigated to replace CT for ion beam radiotherapy. This technique provides many advantages over conventional CT such as high-resolution imaging and spectroscopy-based information for planning in helium ion treatments. The Medipix technology has shown it can be broadly applied in radiation and particle therapy applications for accurate QA as well as proving high-resolution imaging in medicine.

This paper describes the development and characterization of a Δ E-TOF detector composed of a plastic scintillator bar coupled at both ends to silicon photomultipliers. This detector is a prototype of a larger version which will be used in the FOOT (FragmentatiOn Of Target) experiment to identify the fragments produced by ion beams accelerated onto a hydrogen-enriched target. The final Δ E-TOF detector will be composed of two layers of plastic scintillator bars with orthogonal orientation and will measure, for each crossing fragment, the energy deposited in the plastic scintillator ( Δ E), the time of flight (TOF), and the coordinates of the interaction position in the scintillator. To meet the FOOT experimental requirements, the detector should have energy resolution of a few percents and time resolution of 70 ps, and it should allow to discriminate multiple fragments belonging to the same event. To evaluate the achievable performances, the detector prototype was irradiated with protons of kinetic energy in the 70–230 MeV range and interacting at several positions along the bar. The measured energy resolution σ Δ E ∕ Δ E was 6–14%, after subtracting the fluctuations of the deposited energy. A time resolution σ between 120 and 180 ps was obtained with respect to a trigger detector. A spatial resolution σ of 1.9 cm was obtained for protons interacting at the center of the bar.

FOOT (FragmentatiOn On Target) is an applied nuclear physics experiment aimed at measuring the production cross sections of fragments for energies, beams and targets relevant in particle therapy and radioprotection in space. The Δ E-TOF detector will measure the energy deposited by the fragments in a wall of plastic scintillators and the time of flight with respect to a start detector. These two quantities allow to determine the charge Z of the fragment. In this work, we summarize the charge identification procedure of a detector prototype with two scintillator modules.

Nuclear physics processes are an important source of uncertainty in dose calculations in particle therapy and radioprotection in space. Accurate cross section measurements are a crucial ingredient in improving the understanding of these processes. The FOOT (FragmentatiOn Of Target) experiment aims at measuring the production cross sections of fragments for energies, beams and targets that are relevant in particle therapy and radioprotection in space. An experimental apparatus composed of several sub-detectors will provide the mass, charge, velocity and energy of fragments produced in nuclear interactions in a thin target. A crucial component of the FOOT apparatus will be the Δ E-TOF detector, designed to identify the charge of the fragments using plastic scintillators to measure the energy deposited and the time of flight with respect to a start counter. In this work, we present a charge reconstruction procedure of produced fragments at particle therapy energies. We validate it by measuring the charges of various fragments at an angle of 3.2°and 8.3°with respect the beam-axis, using a small-scale detector and clinical beams of carbon ions at the CNAO oncology center. Experimental results agree well with FLUKA Monte Carlo simulations.

The FOOT experiment aims at identifying the fragments produced in the human body during hadrontherapy and at measuring their cross sections. The apparatus is composed of several detectors which allow a complete reconstruction of the tracks of the fragments. In particular, the Δ E-TOF detector measures the energy released in a thin plastic scintillator and the time of flight of the fragments. In this work, we report the energy and time resolution of a Δ E-TOF detector prototype with proton and carbon irradiations, and we compare the results with a Monte Carlo simulation of the optical transport in the detector. With carbon ions, we measured time resolutions of ∼ 50 ps and energy resolutions of ∼ 6%. The Monte Carlo simulation was able to model the dependence of the number of detected photons on the proton interaction position.

Hadrontherapy permits treating cancer with very conformable dose distributions and increased radiobiological effects. Monitoring systems to verify particle range while treating are needed to fully exploit these advantages. The INSIDE project aims at building a bimodal system to acquire photons, coming from positron annihilations, and prompt charge particles related to the beam position inside patients [1] . In January 2016, the in-beam PET detector was installed at the Italian Center of Oncological Hadrontherapy (CNAO) and characterized with phantoms [2] , [3] . In December 2016, the INSIDE in-beam PET monitored two consecutive treatment sessions with protons on its first patient. In-beam PET images must be compared with an expected prior image, therefore a FLUKA-based [4] , [5] simulation tool has been developed. The framework includes the simulations of the patient/phantom, the detector, the beam line and temporal structure. The beam delivery follows either the treatment plan or the measurements from the Dose Delivery System and the detector geometry and resolution are taken into account. During the characterization phase, a good agreement between measurements and simulations was found [2] , [3] . Preliminary results on the first patient treatments indicate that after about two minutes of a four-minutes long irradiation the PET image has significant statistics to be compared with the prior image. During the 2017, the INSIDE in-beam PET system and simulation tool will be further tested in-vivo and optimized for clinical routine.

We have developed a flexible, cost-efficient PET architecture adaptPositron Emission Tomographyable to different applications and system geometries, such as positron emission mammography (PEM) and in-beam PET for dose delivery monitoring (ibPET). The acquisition system has been used to implement modularized dual planar detectors with very low front-end dead time, as required in PEM or in ibPET. The flexibility is obtained thanks to the FPGA-based, reprogrammable, TDC-less coincidence processor. The final goal is to propose an effective acquisition methodology and the construction of a compact, low-cost instrument able to provide early diagnosis and to improve the effectiveness of follow-up studies for smaller tumours with respect to those studied with present clinical equipment (e.g., whole-body PET, SPECT, or scintigraphy).

We present some results obtained with silicon and gallium arsenide pixel detectors to be applied in the field of digital mammography. Even though GaAs is suitable for medical imaging applications thanks to its atomic number, which allows a very good detection efficiency, it often contains an high concentrations of traps which decrease the charge collection efficiency (CCE). So we have analysed both electrical and spectroscopic performance of different SI GaAs diodes as a function of concentrations of dopants in the substrate, in order to find a material by which we can obtain a CCE allowing the detection of all the photons that interact in the detector. Nevertheless to be able to detect low contrast details, efficiency and CCE are not the only parameters to be optimized; also the stability of the detection system is fundamental. In the past we have worked with Si pixel detectors; even if its atomic number does not allow a good detection efficiency at standard thickness, it has a very high stability. So keeping in mind the need to increase the Silicon detection efficiency we performed simulations to study the behaviour of the electrical potential in order to find a geometry to avoid the risk of electrical breakdown.

The use of thermoluminescent dosimeters (TLDs) in heavy charged particles’ dosimetry is limited by their non-linear dose response curve and by their response dependence on the radiation quality. Thus, in order to use TLDs with particle beams, a model that can reproduce the behavior of these detectors under different conditions is needed. Here a new, simple and completely analytical algorithm for the calculation of the relative TL-efficiency depending on the ion charge Z and energy E is presented. The detector response is evaluated starting from the single ion case, where the computed effectiveness values have been compared with experimental data as well as with predictions from a different method. The main advantage of this approach is that, being fully analytical, it is computationally fast and can be efficiently integrated into treatment planning verification tools. The calculated efficiency values have been then implemented in the treatment planning code TRiP98 and dose calculations on a macroscopic target irradiated with an extended carbon ion field have been performed and verified against experimental data.

A digital mammography system based on a GaAs pixel detector has been developed by the INFN (Istituto Nazionale di Fisica Nucleare) collaboration MED46. The high atomic number makes the GaAs a very efficient material for low energy X-ray detection (10-30 keV is the typical energy range used in mammography). Low contrast details can be detected with a significant dose reduction to the patient. The system presented in this paper consists of a 4096 pixel matrix built on a 200 /spl mu/m thick semi-insulating GaAs substrate. The pixel size is 170/spl times/170 /spl mu/m/sup 2/ for a total active area of 1.18 cm/sup 2/. The detector is bump-bonded to a VLSI front-end chip which implements a single-photon counting architecture. This feature allows to enhance the radiographic contrast detection with respect to charge integrating devices. The system has been tested by using a standard mammographic tube. Images of mammographic phantoms will be presented and compared with radiographs obtained with traditional film/screen systems. Monte Carlo simulations have been also performed to evaluate the imaging capability of the system. Comparison with simulations and experimental results will be shown.

We have investigated the detection performance of GaAs detectors made with different thickness and contact geometries. A comparison is made between these detection capabilities and the imaging requirements for the following medical applications: digital mammography, digital chest radiography and nuclear medicine. Experimental results and preliminary images are presented and discussed.

We present an autoradiography tool to be used mainly for genetic studies. It performs a quantitative analysis of radioactivity and can follow a dynamic process. We designed several applications, in particular one aimed at detecting hybridization of radio-labeled DNA fragments with known DNA-probes deposited on a micro-array. The technique is based on GaAs pixel array detector and low threshold, large dynamic range and good sensitivity integrated electronics developed for medical applications, suitable to detect markers (gamma or beta) such as 14C, 35S, 33P, 32P, 125I, even at very low activities. A Monte Carlo simulation of β− detection in GaAs is presented here in order to study the spatial resolution characteristics of such a system. For several biological applications, the electronics is required to perform at high temperatures (from 37° to 68°): we present here studies of noise and minimum threshold as a function of the temperature.

A GaAs pixel detector designed for digital mammography, equipped with a 36-channel single photon counting discrete read-out electronics, was tested using a test object developed for quality control purposes in mammography. Each pixel was 200×200 μm2 large, and 200 μm deep. The choice of GaAs with respect to silicon (largely used in other applications and with a more established technique) has been made because of the much better detection efficiency at mammographic energies, combined with a very good charge collection efficiency achieved thanks to new ohmic contacts. This GaAs detector is able to perform a measurement of low-contrast details, with minimum contrast lower (nearly a factor two) than that typically achievable with standard mammographic film+screen systems in the same conditions of clinical routine. This should allow for an earlier diagnosis of breast tumour masses. Due to these encouraging results, the next step in the evolution of our imaging system based on GaAs detectors has been the development of a VLSI front-end prototype chip (MEDIPIX ) in order to cover a much larger diagnostic area. The chip reads 64×64 channels in single photon counting mode, each one 170 μm wide. Each channel contains also a test input where a signal can be simulated, injecting a known charge through a 16 f F capacitor. Fake signals have been injected via the test input measuring and equalizing minimum thresholds for all the channels. On an average, in most of the performing chips available up to now, we have found that it is possible to set a threshold as low as 1800 electrons with an RMS of 150 electrons (10 standard deviations lower than the 20 keV photon signal roughly equivalent to 4500 electrons). The detector, bump-bonded to the chip, will be tested and a ladder of detectors will be prepared to be able to scan large surface objects.

During particle therapy irradiation, positron emitters with half-lives ranging from 2 to 20 min are generated from nuclear processes. The half-lives are such that it is possible either to detect the positron signal in the treatment room using an in-beam positron emission tomography (PET) system, right after the irradiation, or to quickly transfer the patient to a close PET/CT scanner. Since the activity distribution is spatially correlated with the dose, it is possible to use PET imaging as an indirect method to assure the quality of the dose delivery. In this work, we present a new dedicated PET system able to operate in-beam. The PET apparatus consists in two 10 cm × 10 cm detector heads. Each detector is composed of four scintillating matrices of 23 × 23 LYSO crystals. The crystal size is 1.9 mm × 1.9 mm × 16 mm. Each scintillation matrix is read out independently with a modularized acquisition system. The distance between the two opposing detector heads was set to 20 cm. The system has very low dead time per detector area and a 3 ns coincidence window, which is capable to sustain high single count rates and to keep the random counts relatively low. This allows a new full-beam monitoring modality that includes data acquisition also while the beam is on. The PET system was tested during the irradiation at the CATANA (INFN, Catania, Italy) cyclotron-based proton therapy facility. Four acquisitions with different doses and dose rates were analysed. In all cases the random to total coincidences ratio was equal or less than 25%. For each measurement we estimated the accuracy and precision of the activity range on a set of voxel lines within an irradiated PMMA phantom. Results show that the inclusion of data acquired during the irradiation, referred to as beam-on data, improves both the precision and accuracy of the range measurement with respect to data acquired only after irradiation. Beam-on data alone are enough to give precisions better than 1 mm when at least 5 Gy are delivered.

A digital autoradiography system based on double sided silicon strip detectors (1.6 × 1.6 mm2 active surface with 100 μm pitch) has been developed and successfully tested with beta-emitting tracers. It is shown here that the system is able to perform imaging of organic material with specific sensitivity as small as 0.002 nCi/mm2, and to record activity measurements with good linearity in the range 0.002–20 nCi/mm2. Autoradiographic images of clusters of mammary cells marked with ortho-(32P)phosphate, obtained with an exposure time of about 10 min are presented.

In the past few years we have developed a technological process allowing for the fabrication of radiation detectors with integrated electronics on high-resistivity silicon substrates. We report on some recent results relevant to the process optimisation and to device/circuit characterization.

Ion beam therapy is a valuable method for the treatment of deep-seated and radio-resistant tumors thanks to the favorable depth-dose distribution characterized by the Bragg peak. Hadrontherapy facilities take advantage of the specific ion range, resulting in a highly conformal dose in the target volume, while the dose in critical organs is reduced as compared to photon therapy. The necessity to monitor the delivery precision, i.e. the ion range, is unquestionable, thus different approaches have been investigated, such as the detection of prompt photons or annihilation photons of positron emitter nuclei created during the therapeutic treatment. Based on the measurement of the induced β+ activity, our group has developed various in-beam PET prototypes: the one under test is composed by two planar detector heads, each one consisting of four modules with a total active area of 10 × 10 cm2. A single detector module is made of a LYSO crystal matrix coupled to a position sensitive photomultiplier and is read-out by dedicated frontend electronics. A preliminary data taking was performed at the Italian National Centre for Oncological Hadron Therapy (CNAO, Pavia), using proton beams in the energy range of 93–112 MeV impinging on a plastic phantom. The measured activity profiles are presented and compared with the simulated ones based on the Monte Carlo FLUKA package.

The pixel identification capability is a common problem of detector systems consisting of scintillating matrices coupled to photodetectors. In positron emission tomography (PET) systems, a better pixel identification leads directly to an improvement of the spatial resolution of the system. To gain pixel identification efficiency especially at the peripheral active area, ultra-transmitting (UT) glasses can be inserted between the crystal and PMT array in order to promote light spread and avoid overlap of responses due to the enhanced light spread. Measurements with three different UT glass thicknesses ( d = 0.7 , 1.0 and 1.35 mm) have been performed in order to study their impact on pixel identification properties compared to direct coupling.

Proton beam radiotherapy is highly effective in treating cancer thanks to its conformal dose deposition. This superior capability in dose deposition has led to a massive growth of the treated patients around the world, raising the need of treatment monitoring systems. An in-treatment PET system, DoPET, was constructed and tested at CATANA beam-line, LNS-INFN in Catania, where 62 MeV protons are used to treat ocular melanoma. The PET technique profits from the beta+ emitters generated by the proton beam in the irradiated body, mainly 15-O and 11-C. The current DoPET prototype consists of two planar 15 cm × 15 cm LYSO-based detector heads. With respect to the previous versions, the system was enlarged and the DAQ up-graded during the years so now also anthropomorphic phantoms, can be fitted within the field of view of the system. To demonstrate the capability of DoPET to detect changes in the delivered treatment plan with respect to the planned one, various treatment plans were used delivering a standard 15 Gy fraction to an anthropomorphic phantom. Data were acquired during and after the treatment delivery up to 10 minutes. When the in-treatment phase was long enough (more than 1 minute), the corresponding activated volume was visible just after the treatment delivery, even if in presence of a noisy background. The after-treatment data, acquired for about 9 minutes, were segmented finding that few minutes are enough to be able to detect changes. These experiments will be presented together with the studies performed with PMMA phantoms where the DoPET response was characterized in terms of different dose rates and in presence of range shifters: the system response is linear up to 16.9 Gy/min and has the ability to see a 1 millimeter range shifter.

Range verification with in-beam PET techniques is a powerful tool for monitoring the correctness of dose delivery in particle therapy. Among the major limitations of in-beam PET systems are the limited detectors size due to the constrained space in which they can be placed to allow the irradiation, and the necessity of a high read-out modularization, due to high activity rates during the irradiation. In this work we present the data acquired at the CNAO (Centro Nazionale di Adroterapia Oncologica) treatment center in Pavia, Italy, with the new DoPET system, specifically designed to operate in in-beam conditions. The new prototype consists of two planar 15cm × 15cm LYSO-based detectors, read out by 9 PMT detector modules each. In particular, we test the capability of our system to determine particle range in various irradiation conditions. Several plastic phantoms were irradiated at the CNAO treatment centre with protons and carbon ions of various energies. The used dose in treatment plans is 2 Gy and the monitoring feedback is produced in a few minutes after the end of the treatment.

International audience; Nuclear fragmentation processes are relevant in different fields of basic research and applied physics and are of particular interest for tumor therapy and for space radiation protection applications. The FIRST (Fragmentation of Ions Relevant for Space and Therapy) experiment at SIS accelerator of GSI laboratory in Darmstadt, has been designed for the measurement of different ions fragmentation cross sections at different energies between 100 and 1000 MeV/nucleon. The experiment is performed by an international collaboration made of institutions from Germany, France, Italy and Spain. The experimental apparatus is partly based on an already existing setup made of the ALADIN magnet, the MUSIC IV TPC, the LAND2 neutron detector and the TOFWALL scintillator TOF system, integrated with newly designed detectors in the interaction Region (IR) around the carbon removable target: a scintillator Start Counter, a Beam Monitor drift chamber, a silicon Vertex Detector and a Proton Tagger for detection of light fragments emitted at large angles (KENTROS). The scientific program of the FIRST experiment started on summer 2011 with the study of the 400 MeV/nucleon 12C beam fragmentation on thin (8mm) carbon target.

KENTROS (Kinetic ENergy and Time Resolution Optimized on Scintillator) is a relatively compact detector that has been projected and constructed in the framework of the INFN FRAG and TPS experiments. KENTROS has been designed for energy deposition and time of flight measurements of charged particles. The detector ensures an angular coverage from about 5 degrees up to about 90 degrees polar angle in the laboratory frame. Recently KENTROS has been used as part of the FIRST experiment, devoted to measure double differential fragmentation cross sections, with the aim to detect light fragments produced in the nuclear fragmentation process.

The electrical characteristics of a LPE n-type GaAs crystal have been fully measured. The experimental results were used to build a model, including the parametrization of the electric field inside the crystal, and to study the features of such material as a detector in view of a possible application for digital radiography. The predictions of a Monte Carlo based on this model are in very good agreement with the measured performances of this crystal when used as a detector for X-rays in the diagnostic energy range.

The use of a double sided mu -strip silicon crystal for X-ray detection is being investigated. The detector is 300 mu m thick and the read-out pitch is 100 mu m for both sides. It operates in capacitance charge division mode by means of floating strips between read-out strips. The detector has been irradiated by /sup 241/Am and /sup 109/Cd sources. Different zones within the 100- mu m read-out pitch have been individually exposed. The following characteristics have been studied as a function of the impact point of the photon: (a) the charge collection mechanism; (b) the relative detection efficiency; (c) the energy resolution; and (d) the spatial resolution. The absolute efficiency of the detector has been measured at three energy values. >

A time efficient optical model is proposed for GATE simulation of a LYSO scintillation matrix coupled to a photomultiplier. The purpose is to avoid the excessively long computation time when activating the optical processes in GATE. The usefulness of the model is demonstrated by comparing the simulated and experimental energy spectra obtained with the dual planar head equipment for dosimetry with a positron emission tomograph (DoPET). The procedure to apply the model is divided in two steps. Firstly, a simplified simulation of a single crystal element of DoPET is used to fit an analytic function that models the optical attenuation inside the crystal. In a second step, the model is employed to calculate the influence of this attenuation in the energy registered by the tomograph. The use of the proposed optical model is around three orders of magnitude faster than a GATE simulation with optical processes enabled. A good agreement was found between the experimental and simulated data using the optical model. The results indicate that optical interactions inside the crystal elements play an important role on the energy resolution and induce a considerable degradation of the spectra information acquired by DoPET. Finally, the same approach employed by the proposed optical model could be useful to simulate a scintillation matrix coupled to a photomultiplier using single or dual readout scheme.

The selective energy deposition of hadrontherapy has led to a growing interest in quality assurance techniques such as 'in-beam' PET. Due to the current lack of commercial solutions, dedicated detectors need to be developed. In this paper, we compare the performances of two different 'in-beam' PET systems which were simultaneously operated during and after low energy carbon ion irradiation of PMMA phantoms at GSI Darmstadt. The results highlight advantages and drawbacks of a novel in-beam PET prototype against a long-term clinically operated tomograph for ion therapy monitoring.

We have developed a novel logic scheme for the estimation of the random count distribution based on a dual symmetrical delayed window technique. The solution has been applied to a dual head PET case. We have also implemented a new method for noise variance reduction in the random count distribution.

High energy protons represent a very promising alternative in the tumor irradiation, as respect the photon and electron beams. In Italy, the first and at present the only proton-therapy facility, CATANA (Centro di AdroTerapia e Applicazioni Nucleari Avanzate), was built in Catania, at the Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali del Sud (INFN-LNS). Here a 62 MeV proton beam, produced by a Superconducting Cyclotron (SC), is used for the treatment of shallow tumors like those of the ocular region. A beam monitoring system, based on ion chambers for dose monitoring and on silicon diodes scanning the beam cross section for the beam quality control. Moreover, gaf-chromic films are used to measure the geometric features of the beams. Even though these systems are stable and reliable, nevertheless they are time consuming and, in the gas-chromic film case, they require an off-line analysis. In this paper we present a feasibility study for using a silicon pixel detector as device for proton beams imaging and characterization. We present the performance of such a device exposed to the CATANA proton beam in terms of dose, dose rate and exposure time response.

Recent advances in semiconductor pixel detectors and read-out electronics allowed to build the first prototypes of single photon-counting imaging systems that represent the last frontier of digital radiography. Among the advantages with respect to commercially available digital imaging systems, there are direct conversion of photon energy into electrical charge and the effective rejection of electronic noise by means of a thresholding process. These features allow the photon-counting systems to achieve high imaging performances in terms of spatial and contrast resolution. Moreover, the now available deep integration techniques allow the reduction of the pixel size and the improvement of the functionality of the single cell and the read-out speed so as to cope with the high fluxes found in diagnostic radiology. In particular, the single photon-counting system presented in this paper is based on a 300-microm thick silicon pixel detector bump-bonded to the Medipix2 read-out chip to form an assembly of 256 x 256 square pixels at a pitch of 55 microm. Each cell comprises a low-noise preamplifier, two pulse height discriminators and a 14-bit counter. The maximum counting rate per pixel is 1 MHz. The chip can operate in two modalities: it records the events with energy above a threshold (single mode) or between two energy thresholds (window mode). Exploiting this latter feature, a possible application of such a system as a fast spectrometer is presented to study the energy spectrum of diagnostic beams produced by X-ray tubes.

We are implementing an X-ray breast Computed Tomography (CT) system on the gantry of a dedicated single photon emission tomography system for breast Tc-99 imaging. For the breast CT system we investigated the relevance of the beam hardening artifact. We studied the use of a single photon counting silicon pixel detector (0.3 mm thick, 256 � 256 pixel, 55mm pitch, bump-bonded to the Medipix2 photon counting readout chip) as detector unit in our X-ray CT system. We evaluated the beam hardening ‘‘cupping’’ artifact using homogeneous PMMA slabs and phantoms up to 14 cm in diameter, used as uncompressed breast tissue phantoms, imaged with a tungsten anode tube at 80 kVp with 4.2 mm Al filtration. For beam hardening evaluation we used a bimodal energy model. The CT data show a ‘‘cupping’’ artifact going from 4% (4-cm thick material) to 18% (14-cm thick material). This huge artifacts is influenced by the low detection efficiency and the charge sharing effect of the silicon pixel detector. r 2007 Published by Elsevier B.V. PACS: 85.57.cp; 87.57.Q

In digital imaging the ability to detect low contrast details is an aim that must be pursued. In order to achieve this result we have developed an acquisition system based on silicon pixel detector. The detector is a matrix of 256×256 square pixels of 55 μm size. It is bump-bonded to a readout chip developed by the Medipix2 Collaboration [X. Llopart, et al., IEEE Trans. Nucl. Sci, NS-49 (5) (2002) 2279]. To see the low contrast details with this system, it is necessary to reduce inside the image the fluctuations of pixel-to-pixel counts, [1] down to statistical fluctuations. This has been achieved equalizing the phantom image with a high statistics flat field acquired in the same irradiation condition. We have studied the dependence of the image uniformity for different flat field and we have investigated the dependence of the image quality on the thickness of the phantom and on the energy window selected inside the incident spectrum.

The Integrated Mammographic Imaging (IMI) project aims to realize innovative instrumentations for morphological and functional mammography, in particular, one of the research topics is the design and development of a prototype of a mammographic head. Innovative industrial processes for the production of GaAs pixel detectors and for their bump-bonding to the read-out VLSI electronics have been developed by AMS. The data acquisition and processing have been developed by LABEN; the power supply and distribution system has been realized by CAEN; while the integration of the head in a standard mammograph has been carried on by the Laboratori di Ricerca Gilardoni.

As the use of digital radiographic equipment in the morphological imaging field is becoming largely diffuse, the research of new and more performing devices from public institutions and industrial companies is in constant progress. Many of these devices are based on solid-state detectors as X-ray sensors. Semiconductor pixel detectors, originally developed in the high energy physics environment, have been then proposed as digital detector for medical imaging applications. In this paper a digital single photon counting device, based on silicon and GaAs pixel detectors, is presented. The detector is a thin slab of semiconductor crystal equipped with an array of 64 by 64 square contacts, 170-μm side. The data read-out is performed by a VLSI integrated circuit named Photon Counting Chip (PCC), developed within the MEDIPIX collaboration. Each chip cell geometrically matches the sensor pixel. It contains a charge preamplifier, a threshold comparator and a 15 bits pseudo-random counter and it is coupled to the detector by means of bump-bonding. Most important advantages of such a system, with respect to a traditional X-rays film/screen device, are the wider linear dynamic range (3x10 4 ) and the higher performance in terms of MTF and DQE. Electronics read-out performance as well as imaging capabilities of the digital device will be presented. Images of mammographic phantoms acquired with a standard mammographic tube will be compared with radiographs obtained with traditional film/screen systems.

We describe a VLSI-based data acquisition to perform X-Y coincidences with a two side microstrip digital detector, optimized for applications in digital mammography. A two components chip set is described in detail: a low noise Front-End analog amplifier and an 80 MHz synchronous digital encoder. These two components can be used to solve the problems arising with the use of a large number of channels and low signal amplitude as in our application.

An analog CMOS integrated circuit (IC) for low-noise, precise timing (peak detector double discriminator) has been developed. The IC processes signals detected by a double sided microstrip detector used in the 9-18 keV energy range. The timing information is provided by a novel architecture based on a double discriminator. The leading edge of the output pulse is determined by a fixed threshold discriminator while timing information is provided by a zero crossing discriminator able to detect the maximum of the shaped signal that corresponds to the trailing edge. The PD/sup 3/ is a 64 channel front-end IC designed to be part of the MEDIM experiment, whose aim is to build a system suitable for digital mammography based on a silicon microstrip detector. Low-noise was achieved by using HP 1.2 /spl mu/m technology and optimizing the cascaded integrator with the 3.4 pF detector capacitance. In this paper we will describe the overall topology of the PD/sup 3/ and analyze the main goals of the IC which are low-noise and good timing information. In the third section circuit performance is presented, including noise and time walk measurements. The last section will present some concluding remarks on timings achievable with low-noise front-end circuits.

The double coincidence probability is a well known limitation to the rate capability of a 2-D detector with independent X- and Y-readout. The authors have implemented a parametric Monte Carlo simulation which could help in optimizing the double coincidence recovery. They have applied the parametric simulation to a specific 2-D solid state detector, they are developing for application in digital mammography.

In mammography, the first cause of image contrast reduction arises from the photons scattered inside the examined organ. The amount of Compton scattering strongly depends on the irradiation area and on the distance between the organ and the X-ray detector. We have experimentally evaluated how these geometrical conditions affect the scattering fraction. Our experimental setup includes a single photon counting device based on a silicon pixel detector as X-ray sensor; a lucite cylinder to simulate the breast tissue, and a lead collimator to define the irradiation area. We have evaluated the contrast and the signal-to-noise ratio for images acquired in different conditions.

We are studying the performance of various thickness GaAs pixel detectors bump-bonded to a dedicated photon counting chip (PCC) for medical imaging applications in different energy ranges. In this work we present the experimental results obtained with a 600 μm thick pixel matrix (64×64 square pixels, 170 μm side) in the 60–140 keV energy range to evaluate the possible use of such a system in the nuclear medicine field. In particular, we have measured the spectroscopic properties of the detector (charge collection efficiency, energy resolution and detection efficiency) and evaluated the discrimination capability of the electronics. Then we have measured the imaging properties of the whole system in terms of Point Spread Function and using a home made thyroid phantom. We present also a comparison with a traditional gamma camera and an evaluation, made by both experimental measurements and software simulations, of the imaging characteristics related to the use of a collimation system.

We report the status of the art of a prototype based on a GaAs pixel detector bump-bonded to a dedicated VLSI chip to be possibly used for imaging in the nuclear medicine field. This device, with a 200 μm thick pixel matrix (64×64 square pixels, 170 μm side), has already been tested with very good results for digital mammography applications (mean energy 20 keV). For more energetic photons, as in nuclear medicine, a 600 μm thick detector has been chosen. Using radioactive sources ( 241 Am, 60 keV and 99 m Tc, 140 keV photons) we have measured the performance of our prototype in terms of charge collection and detection efficiency of the detector, discrimination capability of the electronics and imaging properties of the whole system. In particular, we have evaluated the spatial resolution properties measuring the Point Spread Function and the imaging capabilities using a home made thyroid phantom. We present also the comparison between these results and those obtained with a traditional gamma camera and the evaluation, made by both experimental measurements and software simulations, of the geometry related to the use of a collimator.

We are characterising a prototype GaAs pixel detector able to perform digital mammography which contains two features which give enhanced performance compared with standard mammographic systems: it can detect low contrast test objects, inaccessible for traditional systems and, using its higher intrinsic detection efficiency, can reduce the radiation dose to the patient. The prototype is a hybrid assembly of a GaAs detector divided into 64×64 pixels, each of which measures 170 μm on the side, which is bump-bonded to a photon counting chip, PCC, developed by the Medipix collaboration. The cells of the readout chip are identical in size to the detector pixels and work in single photon counting mode. We have studied the detection efficiency of some assemblies for different bias voltages, reaching in some cases the detector breakdown point. To test the assembly in the same clinical conditions used in a standard mammographic system we have tested the prototype with radiation produced by a standard mammographic X-ray tube operating at 28 kVp. In particular, working not too far from the detector breakdown point, we are checking its imaging capabilities using a mammographic test phantom with known composition of the materials and therefore known contrast.

We have tested the imaging properties of a system based on a GaAs matrix that performs the direct detection of photons in the range of radiographic interest. The detector is bump-bonded to a VLSI single photon counting electronics. The imaging properties of the system have been evaluated in terms of the presampling MTF and the DQE(ν), that allow an absolute characterization of imaging properties of digital systems. We have tested other radiographic imaging systems in standard clinical conditions, using the same functions and we have compared them with the GaAs matrix system.

We present a proposal for a PET detector with a specific design oriented to its application to in-beam treatment monitoring in hadron therapy. The design is focused to the reduction of the uncertainty on the depth of the interaction of the gamma rays in the scintillator to improve the final spatial resolution of the reconstructed images. A small detector prototype, based on two staggered scintillator matrices, was assembled and irradiated with a β + emitting radioactive source. The obtained results are presented.

Aim of this paper is to give a general idea of the characteristic of a system for medical digital imaging based on a GaAs pixel detector bump-bonded to a VLSI electronic chip. After a discussion on the characteristics of the GaAs detector, and its detection and charge collection efficiency properties, it follows a description of the high-density channel VLSI chip named Photon Counting Chip (PCC). Then, a description of the apparatus used to characterize the detector and to perform electrical measurements is made. Finally are discussed irradiation tests and the laboratory setup used at the laboratory course of the ICFA 99 school.

An analog CMOS-Integrated Circuit has been developed as Front-End for a double-sided microstrip silicon detector. The IC processes and discriminates signals in the 5–30 keV energy range. Main features are low noise and precise timing information. Low noise is achieved by optimizing the cascoded integrator with the 8 pF detector capacitance and by using an inherently low noise 1.2 μ m CMOS technology. Timing information is provided by a double discriminator architecture. The output of the circuit is a digital pulse. The leading edge is determined by a fixed threshold discriminator, while the trailing edge is provided by a zero crossing discriminator. In this paper we first describe the architecture of the Front-End chip. We then present the performance of the chip prototype in terms of noise, minimum discrimination threshold and time resolution.

A 4096 pixel Photon Counting Chip (PCC) has been developed and tested. It is aimed primarily at medical imaging although it can be used for other applications involving particle counting. The readout chip consists of a matrix of 64 by 64 identical square pixels, whose side measures 170 micrometers and is bump-bonded to a similar matrix of GaAs or Si pixel diodes covering a sensitive area of 1.18 cm2. The electronics in each cell comprises a preamplifier, a discriminator with variable threshold and a 3-bit threshold tune as well as a 15-bit counter. Each pixel can be individually addressed for electrical test or masked during acquisition. A shutter allows for switching between the counting and readout modes and the use of static logic in the counter enables long data taking periods. Electrical test of the chip have shown a maximum counting and readout modes and the use of static logic in the counter enables long data taking periods. Electrical test of the chip have shown a maximum counting rate of up to 2 MHz in each pixel. The minimum reachable threshold is 1400 e with a variation of 350 e rms that can be reduced to 80 e rms after tuning with the 3-bit adjustment. Electrical noise at the input is 170 e rms. Several read-out chips have been bump bonded to 200 micrometers thick GaAs pixel detectors. Test with (gamma) -ray and (beta) sources have been carried out. A number of objects have been imaged and a 260 micrometers thick aluminum foil which represents a contrast to the surrounding air of only 1.9 percent has been correctly imaged.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present the first results obtained using a digital imaging system, operating at room temperature, developed for medical applications working with a standard mammogrphic beam.

Solid state detectors made of Si (4.8/spl times/8 mm/sup 2/) and GaAs (6.4/spl times/8 mm/sup 2/) pixel matrices bump-bonded to the Omega2 and Omega3 electronic read-out systems, developed at CERN for H.E.P. experiments, have been used to obtain autoradiographic images of clusters of human epithelial cells and DNA fragments separated via electrophoresis, both labeled with /sup 32/P. The system has shown a good minimum detectable activity per unit area of 2.10/sup -4/ cps mm/sup -2/, and has proved linear for a count rate in the range 0.2-20 cpa, typical of autoradiography. The pixel dimensions are 75/spl times/500 /spl mu/m/sup 2/ (Si-Omega2) and 50/spl times/500 /spl mu/m/sup 2/ (GaAs-Omega3), respectively. We are able to clearly localize clusters of cells which have incorporated the radioactive tracer and DNA fragments on an electrophoretic gel on paper (blots).

We describe a VLSI-based processing system performing X - Y coincidence at a very high rate in the synchronous mode. The processor has been designed for applications in digital mammography with two-sided μ-strip silicon detectors but can be used to provide the computational section of any imaging system that needs fast coincidence. The VLSI chip has been successfully tested on a 32 + 32 channels DAQ chain.