S. Marcatili

Characterization of a PET detector head based on continuous LYSO crystals and monolithic, 64-pixel silicon photomultiplier matrices

The characterization of a PET detector head based on continuous LYSO crystals and silicon photomultiplier (SiPM) arrays as photodetectors has been carried out for its use in the development of a small animal PET prototype. The detector heads are composed of a continuous crystal and a SiPM matrix with 64 pixels in a common substrate, fabricated specifically for this project. Three crystals of 12 mm × 12 mm × 5 mm size with different types of painting have been tested: white, black and black on the sides but white on the back of the crystal. The best energy resolution, obtained with the white crystal, is 16% FWHM. The detector response is linear up to 1275 keV. Tests with different position determination algorithms have been carried out with the three crystals. The spatial resolution obtained with the center of gravity algorithm is around 0.9 mm FWHM for the three crystals. As expected, the use of this algorithm results in the displacement of the reconstructed position toward the center of the crystal, more pronounced in the case of the white crystal. A maximum likelihood algorithm has been tested that can reconstruct correctly the interaction position of the photons also in the case of the white crystal.

Electrical Characterization of Silicon Photo-Multiplier Detectors for Optimal Front-End Design

Silicon Photo-Multiplier (SiPM) detectors represent an attractive solution for the detection of low energy photons in several fields of both high energy physics and medical imaging. We present here an accurate electrical model for this kind of detectors, which can be conveniently used to perform reliable simulations at circuit level. A suitable extraction procedure for the parameters involved in the model is also described, based on both static and dynamic measurements. The proposed model allows to reproduce accurately the waveform of the signal generated by the SiPM when coupled to the front-end electronics, as shown by excellent fittings obtained between simulations and measurements taken on real devices. This is particularly useful in order to choose the most suitable front-end architecture for SiPM detectors, since the performance of the whole detection system, especially in terms of dynamic range and timing resolution, can be correctly predicted as a function of the detector parameters and of the main characteristics of the coupled electronics.

Energy, Timing and Position Resolution Studies With 16-Pixel Silicon Photomultiplier Matrices for Small Animal PET

A high resolution small animal PET scanner that employs Silicon Photomultiplier (SiPM) matrices as photodetectors is under development at the University of Pisa and INFN Pisa. The first SiPM matrices fabricated by the Center for Scientific and Technological Research, FBK-irst (Trento, Italy), are being evaluated for this purpose. The devices are composed of 16 (4 times4) pixel elements of 1 mmtimes1 mm in a common substrate. The first tests have been carried out employing the ASIC MAROC2 for the readout. Energy and timing resolution, and position determination tests have been performed coupling both pixellated and continuous LYSO scintillator crystals to the matrix, and the results have been compared with the ones obtained for single SiPMs. The first tests on position determination with continuous crystals and SiPM matrices have been performed. An intrinsic spatial resolution of 0.61 mm FWHM has been obtained.

Novel Silicon Photomultipliers for PET Applications

Silicon photomultipliers (SiPMs) with quantum efficiency maximized for a wavelength between 420 and 470 nm have been developed at ITC-irst Trento (Italy), and are being tested for their application in the construction of a ultra high resolution small animal PET tomograph. The devices have an area of 1 mm times 1 mm and 625 microcells. The breakdown voltage is around 30 V, and the gain of the order of 106. The intrinsic timing resolution is 70 ps rms at the single photoelectron level. The first tests as readout for scintillators show an energy resolution of 21% FWHM with Na-22 employing LSO crystals. The first matrices of SiPMs have been produced and are being tested.

Energy and Timing Resolution Studies With Silicon Photomultipliers (SiPMs) and 4-Pixel SiPM Matrices for PET

A high performance detector head with matrices of silicon photomultipliers (SiPMs) as photodetectors is under development at the University of Pisa and INFN Pisa. The silicon photomultipliers fabricated at FBK-irst (Trento, Italy) are being evaluated for this purpose. Single SiPM detectors of 1 mm x 1 mm size and the first SiPM test matrices composed of four (2 x 2) pixel elements in a common substrate have been tested with LYSO crystals. The energy and timing resolution of single SiPMs have been evaluated, obtaining an energy resolution of 20% FWHM at 511 keV, and a coincidence timing resolution of 1.4 ns FWHM. In addition, the first tests performed with the SiPM matrices prove the feasibility of such devices.

Silicon photomultipliers and SiPM matrices as photodetectors in nuclear medicine

A high performance detector head with matrices of silicon photomultipliers (SiPMs) is under development at the University of Pisa. The detector head will be employed in the construction of a high spatial resolution, MR compatible small animal PET scanner. Silicon photomultipliers from FBK- irst (Trento, Italy) are being evaluated for this purpose. SiPM elements of 1 mm x 1 mm size and SiPM matrices composed of four (2 x 2) pixel elements have been tested. An intrinsic timing resolution of 60 ps sigma has been measured. The results with LSO crystals show an energy resolution of 20% FWHM at 511 keV, and a coincidence timing resolution of 600 ps rms. New devices with improved characteristics and active area, as well as SiPM matrices with 16 (4 x 4) SiPM elements have been produced, and will be evaluated.

Preliminary results from a current mode CMOS front-end circuit for silicon photomultiplier detectors

We propose a CMOS front-end circuit suitable for Silicon Photomultiplier detectors (SiPM) based on a current buffer, as input stage, which features small input impedance and large bandwidth, thanks to the application of current feedback techniques. The current mode approach enhances the dynamic range of the front-end and does not suffer from possible voltage limitations due to deep-submicron CMOS implementation. We report the first measurement results obtained by coupling the circuit prototype to a SiPM detector excited by a blue LED light source. The measurements confirm the effectiveness of the proposed front-end approach and demonstrate its capability of managing large current signals with good linearity.

New results on the characterization of ITC-irst Silicon Photomultipliers

In this paper we report briefly on the development of Silicon Photomultipliers at ITC-irst. First, details on the technology and geometry are given. Then, experimental data are shown including static IV characterization, signal characterization, noise properties and photodetection efficiency.

Monolithic 64-channel SiPM matrices for small animal PET

The University of Pisa and INFN Pisa are developing a small animal PET prototype scanner employing continuous LYSO crystals and the silicon photomultiplier (SiPM) matrices fabricated at FBK-irst. The SiPM matrices have 64 SiPM pixel elements in a common substrate. The SiPM elements are 1.4 mm × 1.5 mm size, in a 1.5 mm × 1.5 mm pitch. The test of the first detector heads is taking place in collaboration with IFIC, Valencia. The detectors consist of a LYSO crystal of 12 mm × 12 mm coupled to a SiPM matrix. Characterization and position determination tests have been carried out. The energy resolution obtained is 14.5% FWHM at 511 keV. The spatial resolution with center-of-gravity algorithms is 0.9 mm FWHM. A Maximum likelihood method is also being tested. This method allows to separate points at 1 mm distance, and to reconstruct correctly the interaction position also at the edges of the detector.

Evaluation of the first Silicon Photomultiplier matrices for a small animal PET scanner

A high resolution small animal PET scanner that employs Silicon Photomultiplier (SiPM) matrices as photodetectors is under development at the University of Pisa. The first SiPM matrices fabricated by the Center for Scientific and Technological Research, FBK-irst, Trento, Italy, are being evaluated for this purpose. The devices are composed of 16 (4×4) pixel elements of 1 mm × 1 mm in a common substrate. The first tests have been carried out employing the ASIC MAROC2 for the readout. Energy and timing resolution, and position determination tests have been carried out coupling both pixellated and continuous LYSO scintillator crystals to the matrix, and the results have been compared with the ones obtained for single SiPMs.