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In the framework of the Clear-PEM project for the construction of a high-resolution and high-specificity scanner for breast cancer imaging, a Positron Emission Mammography tomograph has been developed and installed at the Instituto Português de Oncologia do Porto hospital. The Clear-PEM scanner is mainly composed by two planar detector heads attached to a robotic arm, trigger/data acquisition electronics system and computing servers. The detector heads hold crystal matrices built from 2 × 2 × 20 mm3 LYSO:Ce crystals readout by Hamamatsu S8550 APD arrays. The APDs are optically coupled to both ends of the 6144 crystals in order to extract the DOI information for each detected event. Each one of 12288 APD's pixels is read and controlled by Application Specific Integrated Circuits water-cooled by an external cooling unit. The Clear-PEM frontend boards innovative design results in a unprecedented integration of the crystal matrices, APDs and ASICs, making Clear-PEM the PET scanner with the highest number of APD pixels ever integrated so far. In this paper, the scanner's main technical characteristics, calibration strategies and the first spectrometric performance evaluation in a clinical environment are presented. The first commissioning results show 99.7% active channels, which, after calibration, have inter-pixel and absolute gain distributions with dispersions of, respectively, 12.2% and 15.3%, demonstrating that despite the large number of channels, the system is uniform. The mean energy resolution at 511 keV is of 15.9%, with a 8.8% dispersion, and the mean CDOI−1 is 5.9%/mm, with a 7.8% dispersion. The coincidence time resolution, at 511 keV, for a energy window between 400 and 600 keV, is 5.2 ns FWHM.

We present an overview of the Clear-PEM breast imaging scanner. Clear-PEM is a unique dual-head Positron Emission Mammography scanner using APD-based detector modules that are capable of measuring depth-of-interaction (DOl) with a resolution of2 mm in 20 mm long LYSO:Ce crystals. Such capability leads to an image spatial resolution of 1.2 mm and a high efficiency, foreseeing the detection of 3 mm breast lesions in less than 7 minutes exams. The full system comprises 192 detector modules in a total of 6144 LYSO:Ce crystals and 384 32-pixel APD arrays readout by ASICs with 192 input channels that represents an unprecedented level of integration in PET systems. Throughout the project and besides the detector module, we had developed dedicated Frontend and Data Acquisition electronics, the mechanical design and construction of the detector heads and the robotic gantry, as well as all the software that include calibration (energy, time and 001), normalization and image reconstruction algorithms. In this work we will discuss the developments and present the commissioning results of the detector before the beginning of the clinical trials program, scheduled for the end of the present year.

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