Experimental Evaluation of a SiPM-Based Scintillation Detector for MR-Compatible SPECT Systems

Abstract

In the present work we briefly describe the architecture of a photo-detection module, designed in the framework of the INSERT (INtegrated SPECT/MRI for Enhanced Stratification in Radio-chemoTherapy) project, supported by the European Community. We focus on two main elements of the module: the SiPM photo-detector unit and the multi-channel ASIC. These two components have been investigated with dedicated and independent setups to assess preliminary performance of INSERT architecture. In details, we designed a 25.30 mm x 25.85 mm tile, comprising 9 pixels, each one with an 8 mm x 8mm active area. We developed an Anger camera to characterize the tile coupled to a CsI:Tl scintillator (6 mm thick). We measured an average spatial resolution (FWHM) of 2 mm in the central region of the Field of View and a 15.3% energy resolution using a Co-57 source (122 keV), when the tile is cooled down to 0 degrees C to reduce the impact of the dark count rate. Furthermore, we developed ANGUS, a 36-channels 0.35 mu m CMOS technology ASIC designed to cope with input capacitance up to 5 nF, typical of large area SiPM pixels. The spectroscopic capability of single readout channels were evaluated by coupling an 8 mm x 8 mm pixel with a cylindrical CsI:Tl scintillator (8 mm diameter, 10 mm thickness). Energy resolution at room temperature provided values between 13% and 13.5% (FWHM) at the 122 keV line for the nine pixels

Development of a Practical Calibration Procedure for a Clinical SPECT/MRI System Using a Single INSERT Prototype Detector and Multimini Slit-Slat Collimator

“…crystals and silicon photomultiplier (SiPM) readout with a size of 10×5 cm 2 [6], [7]. The good intrinsic resolution of 1 mm [8] supports minification, which is obtained by using a collimator-detector distance smaller than the collimator-patient distance. This enables the design of a compact and highsensitivity collimator based on slit-slat collimation, the multimini slit-slat (MSS) collimator [9], [10], [11], [12].…”

Effects of the collimator magnification factor in the geometrical calibration of SPECT systems

“…Projection data were acquired for 30 angles covering 360 o with an INSERT prototype detector [7] of size 5×5 cm, a Mini-Slit-Slat (MSS) collimator [8] and four 99m Tc line sources placed on a rotating stage at different radial locations within the FoV: 69.00, 51.75, 34.50 and 17.25 mm from the centre of rotation (CoR) at 90 o intervals. The procedure was repeated for three distances from the collimator to the CoR: 165.00 mm, 106.78 mm, and 48.57 mm (Figure 2), adjusting the radial positions accordingly, in order to get different magnification factors.…”

“…the INSERT SPECT/MRI system [7], [8], small cameras can be used to image large FoVs, trading off minification with high intrinsic resolution to achieve a system resolution similar to that of a standard SPECT system. However, with minification, precise measurement in the projection space, required for calibration purposes, may be compromised.…”

A novel approach to image reconstruction and calibration for a multi-slit-slat SPECT system

“…T B. Rebinning Sinograms were generated, using the following formulae: (2) where and are the sinogram coordinates for a line-ofresponse (LOR) defined by the camera angle and the detector angle , and is the detector radius, the focal length and the lateral slit-position (Fig. 3).…”

“…The fundamental unit of the INSERT system is a compact gamma camera with high intrinsic resolution [2], allowing for the use of diverging collimators with minification. One drawback of this system is the limited angular sampling, as no rotation is used for practical reasons.…”