We report on the design of a small animal PET scanner based on continuous LYSO crystals and Position Sensitive Photomultiplier Tubes (PSPMTs), together with the first results from the calibration. The scanner consists of eight compact modules forming an octagon and leaving a port of 110 mm aperture. Each module is made out of a continuous LYSO crystal and a PSPMT, and contains its associated electronics together with its power supply. For each module, five signals are read, summarizing all the information coming out from its 64 anode pads. Therefore, for the whole scanner only 40 signals are digitized. A calibration procedure has been implemented, measuring a spatial resolution of approximately 1.5 mm at the center of the Field of View and an energy resolution of 18%. The sensitivity of the system at the center of the Field of View, using only 4 modules, is observed to be of about 1%.
In this work, we present the performance characteristics of the MAMMOCARE PET prototype based on an adaptation of the NU 4-2008 NEMA standard. MAMMOCARE is a project under the European Commission's 7th Framework programme to develop a breast biopsy system guided by a dedicated breast PET (dbPET) images. The PET system is formed by two rings with twelve detector modules each. The transaxial FOV is 170 mm and the axial FOV is 94 mm. The system can separate the detectors up to 60 mm in transaxial plane to allow the biopsy needle entrance.The acquisitions are reconstructed using the LMOS algorithm with tube-of-response (TOR) backprojector, 1 iteration and 16 subsets. The voxel and pixel sizes are (1 × 1 × 1) mm 3 and (1.6 × 1.6) mm 2 respectively. The radial resolution measured is 1.62 mm in the center of the FOV and 3.45 mm at 50 mm off the center in the radial direction using the closed configuration. In the open configuration the resolution reaches 1.85 mm and 3.65 mm at center and at 50 mm offcenter. The adapted recovery coefficients (ARC) are measured for six hot rods inside a cylindrical phantom with a warm background. The ratio between hot and background regions is 10. The ARC values for the closed configuration are 0.32, 0.77 and 0.96 for the inserts with a diameter of 4.5 mm, 8.3 mm and 25 mm, respectively. These values decrease to 0.16, 0.52 and 0.77 for the open configuration. The sensitivity measured using an energy window of 250 keV-750 keV is 3.6% and 2.5% for the closed and open configurations respectively. The NEC peak is 141 kcps@68 MBq and 147 kcps@78 MBq for closed and open configurations. The performance characteristics measured with the open ring configuration decreases with respect the closed configuration, however the values remain comparable to other dbPETs.
MAMMI is a dedicated breast positron emission tomograph (PET) based on monolythic LYSO crystals, with a transaxial field of view (FOV) of 170 mm. It has been upgraded by adding a second ring of detectors that extends the axial FOV from 40 mm to 94.4 mm, in order to improve its sensitivity and reduce the acquisition time. In this work we present the performance evaluation of the dual ring MAMMI breast PET and a discussion about the contribution of the addition of a second ring of detectors, the compensation of the detector blur and the increase of the scintillator thickness.Experimental measurements suggested on NEMA NU 4-2008 and NEMA NU 2-2007 have been conveniently adapted to the dimensions of the MAMMI. The addition of the second ring of detectors leads to a rise of the sensitivity from 1.8% to 3.6%. The spatial resolution at one-fourth of the axial FOV (1.5 mm axial, 1.6 mm tangential, 1.7 mm radial) is slightly better than that measured at the axial center (1.9 mm axial, 1.8 mm tangential and radial), because of the 14 mm gap in between detection rings. The results obtained after the evaluation reflect a substantial performance improvement, specially in the absolute sensitivity, because of the changes introduced in the MAMMI PET.
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