We have successfully built and characterised a small animal PET based on 4 rotating detectors with a spatial resolution < 2 mm over its field of view and a sensitivity of 640 cps/mu Ci at the centre. The scanner is based on four matrices of 400 YAP:Ce finger crystals (2x2x30 mm(3) each) coupled to Position Sensitive PhotoMultipliers (Hamamatsu R2486-06.) We have now applied two high resolution collimators to two opposite detectors, hence realising an integrated PET-SPECT scanner for small animals. The collimators are made of lead with 20 mm long, 0.6 mm hexagonal holes with 0.15mm septa. The read-out and data acquisition system are handled by NIM-CAMAC standard electronics. The Field Of View (FOV) of the tomograph has a diameter of 4 cm and an axial length of 4 cm in both PET and SPECT configuration which is appropriate for mice and rat studies

Phantom model was performed to study the effect of breast compression on signal-to-noise ratio (SNR) for a dedicated high-resolution gamma camera (Single Photon Emission Mammography, or 'SPEM') and a conventional one as typically employed in prone scintimammography. The phantom was designed to simulate the effects of lesion size and of scatter from nearby torso activity. The phantom studies showed that lesions SNR was higher with the SPEM camera than with the conventional camera, and that SNR was always improved with compression for both cameras. Since the stage of breast cancer diagnosis affects patient prognosis, it is important to optimize breast examinations for small (i.e., T1a and T1b) lesions. For one-cm size lesions (clinical stage T1c), SNR was maximized when compression was less than 12 cm, and little additional benefit was derived from further compression. For subcentimeter (clinical stage T1b) lesions, SNR was maximized when compression was less than 6 cm. These data are consistent with a short clinical study in which detection sensitivity for small cancers was improved with the SPEM camera as compared to a conventional gamma camera. We conclude that, in order to image early breast cancers (stage T1b), it is important to apply breast compression

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