[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: The work presented here was developed in the framework of the SENTINEL Project and is devoted to the analysis of dental radiology dosimetric data. The procedure of data processing allows the analysis of some important aspects related to the protection of the patient and the staff because of the position of the operators near the patient and their exposure to the radiation scattered by the patient. Dental radiology data was collected in an Italian hospital. Following the Italian quality assurance (QA) protocols and suggestions by the leaders of the SENTINEL Project, X-ray equipment performances have been analysed in terms of: kVp accuracy, exposure time accuracy and precision, tube output, dose reproducibility and linearity, beam collimation, artefacts and light tightness. Referring to these parameters the physical quality index (QI) was analysed. In a single numerical value between 0 and 1, QI summarises the results of quality tests for radiological devices. The actual impact of such a figure (as suggested by international QA protocols or as adopted by local QA routine) on the policy of machine maintenance and replacement is discussed.
[Show abstract][Hide abstract] ABSTRACT: The beam and detector, used for the NA48 experiment, devoted to the measurement of Re(ε′/ε), and for the NA48/1 experiment on rare KS and neutral hyperon decays, are described.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 05/2007; 574(3-574):433-471. DOI:10.1016/j.nima.2007.01.178 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 06/2001; DOI:10.1016/S0168-9002(01)00827-0 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Digital radiography is a field of great interest; a wide range of different imaging systems is now becoming available and it is very important to have powerful instruments to characterize and compare their imaging properties. We have evaluated imaging properties for several digital radiographic systems in terms of resolution and noise properties. For the resolution properties, we have used the Modulation Transfer Function (MTF) and the presampling MTF, for undersampled systems. We have characterized noise properties by Detective Quantum Efficiency, that is an absolute parameter that allows comparison between different systems.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 06/2001; 466(1). DOI:10.1016/S0168-9002(01)00830-0 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 04/2001; 461(1). DOI:10.1016/S0168-9002(00)01257-2 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The CALMA (Computer_Assisted Library for MAmmography) project was born as a collaboration between radiologists and physicists. Its goal is to collect a set of digital mammographic images and to work out a suitable Computed Assisted Diagnosis tool to be used in screening mammography. The project is an Italian collaboration among the Istituto Nazionale di Fisica Nucleare sections of Bologna, Pisa, Torino, Udine and Trento and the Hospitals of Bari, Bologna, Livorno, Udine and Trento. Some preliminary results obtained in the classification of breast disease are described here.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 04/2001; DOI:10.1016/S0168-9002(00)01266-3 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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 200μm thick pixel matrix (64×64 square pixels, 170μm side), has already been tested with very good results for digital mammography applications (mean energy 20keV). For more energetic photons, as in nuclear medicine, a 600μm thick detector has been chosen. Using radioactive sources (241Am, 60keV and 99mTc, 140keV 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.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 04/2001; 461(1):422-424. DOI:10.1016/S0168-9002(00)01264-X · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper we present the Computer-Aided Library for MAmmography (CALMA Project), i.e. an automated search for the mammograms’ texture, the massive lesions and microcalcifications clusters. CALMA's main purpose is to collect a database of mammographic images, developing CAD tools to be used as a second radiologist in the classification of breast cancer diseases. In this moment, 2200 images are already in our database, which is, to our knowledge, the largest in Europe. One-third of our digitized images are pathological, and they are fully characterized by a consistent description and diagnosis. We try to perform automatically the classification of mammographic images on the bases of tissues’ textures. Such a classification should be done in an unbiased way with respect to radiologists and should support their interpretation of the mammographic image. Results obtained with non supervised neural networks are shown, as well as results coming from a mixed approach (features extraction combined with FF-ANN). Massive lesions are rather large objects to be detected, but they show up with a faint contrast slowly increasing with time. The need for tools able to recognize such a lesion at an early stage is therefore apparent. Our tools are based on a ROI hunter procedure for spiculated lesions showing a number of false positives of the order of 1.4 per image and keeping a 85% sensitivity on our sample. A microcalcication is a rather small (0.1–1.0 mm in diameter) but very brilliant. Some of them, either grouped in cluster or isolated may indicate the presence of a tumor. Up to now only 40 images with microcalcications from our database have been analyzed, and a CAD tool has been designed to detect clusters, reaching a correct classification of 90%.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 03/2001; DOI:10.1016/S0168-9002(00)01103-7 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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 170μm 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 28kVp. 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.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 03/2001; 460(1):50-54. DOI:10.1016/S0168-9002(00)01095-0 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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 μm thick semi-insulating GaAs substrate. The pixel size is 170×170 μm<sup>2</sup> for a total active area of 1.18 cm<sup>2</sup> . 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.
[Show abstract][Hide abstract] ABSTRACT: 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. .
[Show abstract][Hide abstract] ABSTRACT: . A new precision measurement of the # 0 mass has been performed at the NA48 experiment at the CERN SPS. The value obtained is [1314.820.06 (stat.) 0.2 (syst.)] MeV/c 2 . The branching ratios of # 0 radiative decays have been measured as: Br(# 0 # ##)=[1.90 0.34(stat.) 0.19(syst.)] 10 -3 and Br(# 0 # # 0 #)=[3.14 0.76(stat.) 0.32(syst.)] 10 -3 . The NA48 Collaboration: Precision measurement of the # 0 mass 1 Introduction A precise measurement of hyperon masses permits the checking of the mass splitting related to radiative corrections. The mass of the # 0 hyperon is known with less pre- a Present address: Dipartimento di Fisica dell'Universitae Sezione dell'INFN di Perugia, 06100 Perugia, Italy. b Present address: Physics-Astronomy Building, Michigan State University, East Lansing, MI 48824 USA. c Present address: NIKHEF, PO Box 41882,1009 DB Amsterdam, The Netherlands. d Funded by the UK Particle Physics and Astronomy Research Council....
[Show abstract][Hide abstract] ABSTRACT: We present the imaging and spectroscopic capabilities of a system
based on a single photon counting chip (PCC) bump-bonded on a Si pixel
detector. The system measures the energy spectrum and the flux, produced
by a standard mammographic tube. We have also made some images of low
contrast details, achieving good results
[Show abstract][Hide abstract] ABSTRACT: A new precision measurement of the Ξ0 mass has been performed at the NA48 experiment at the CERN SPS. The value obtained is [1314.82±0.06 (stat.) ±0.2 (syst.)] MeV/c2. The branching ratios of Xi;0 radiative decays have been measured as: Br(Ξ0 → Λγ) = [1.90 ± 0.34(stat.) ± 0.19(syst.)] · 10-3 and Br(Ξ0 → ∑0γ) = [3.14 ± 0.76(stat.) ± 0.32(syst.)] · 10-3.
[Show abstract][Hide abstract] ABSTRACT: The NA48 experiment at CERN has performed a new measurement of direct CP violation, based on data taken in 1997 by simultaneously collecting KL and KS decays into π0π0 and π+π−. The result for the CP violating parameter is (18.5±4.5(stat)±5.8(syst))×10−4.
Physics Letters B 11/1999; 465(1-4-465):335-348. DOI:10.1016/S0370-2693(99)01030-8 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 09/1999; 434(1-434):14-17. DOI:10.1016/S0168-9002(99)00422-2 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/1999; 422(1-3-422):201-205. DOI:10.1016/S0168-9002(98)01094-8 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/1999; 422(422):242-246. DOI:10.1016/S0168-9002(98)01102-4 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present the results for a direct search for light gluinos through the appearance of η→3π0 with high transverse momentum in the vacuum tank of the NA48 experiment at CERN. We find one event within a lifetime range of 10−9–10−3 s and another one between 10−10–10−9 s. Both events are consistent with the expected background from neutrons in the beam, produced by 450 GeV protons impinging on the Be targets, which interact with the residual air in the tank. From these data we give limits on the production of the hypothetical bound state, the R0 hadron, and its decay in the R0 mass range between 1 and 5 GeV.
Physics Letters B 01/1999; 446(2-446):117-124. DOI:10.1016/S0370-2693(98)01459-2 · 6.13 Impact Factor