Performance characteristics of the MAMMI PEMT scanner based on NEMA NU 2–2007

The system MAMMI (acronym for MAMmography with Molecular Imaging) is a PET prototype device specifically designed for the detection of breast cancer. It is based on continuous LYSO crystals coupled to Position Sensitive Photomultiplier Tubes (PSPMTs). The scanner consists of twelve compact modules assembled on a ring configuration with an aperture of 186 mm. The scanner transaxial Field of View (FoV) is as large as 170 mm in diameter whereas the axial FoV can cover up to 170 mm recording several frames which are software overlapped. Most of the performance characteristic tests according to the National Electrical Manofacturers Association (NEMA) NU 2-2007 are specially designed to whole body PET scanners and, thus, present a dimensional limitation on a dedicated breast PET. Also, NEMA NU 4-2008 standards cannot be either conducted because are performed for small animal PETs. In this paper, we propose certain changes based on both standards, as are the dimensions of the phantoms and sources. The results showed a spatial resolution at the centre of the transaxial and axial FoVs of 1.90 1.82 and 1.63 mm in the radial, tangential and axial profiles, respectively. The system sensitivity was measured to be, on average and using different line sources and metallic sleeves, 0.77%. When using a ²²Na point source, a value of up to 1% was observed. For a specific breast phantom, the scatter fraction was determined to be 6.7% and the peak noise equivalent count rate, 25 kcps at 176 MBq/ml. Note that these measures were carried out wiyh a 50% peak energy window and and a coincidence timing window of 5 ns.