A positron emission mammography system based on 4 mm straw detectors

Recent studies have concluded that the effectiveness of mammography is substantially degraded in patients with dense breast tissue calling for non-density responsive imaging methods. In order to bring lower cost and more effective PET technology to this area we propose an innovative design for a dedicated positron emission mammography (PEM) camera utilizing long, linear, lead- walled straw (LWS) detectors. This system can provide excellent resolution and precisely accurate depth of interaction determination. Comprehensive evaluations of two substantial sub-modules of a proposed full scale camera have been performed. Sensitivity was measured with a ²²Na line source. Spatial resolution was measured with a concentrated ⁶²Cu point source in the center field of view (CFOV). Randoms fraction (RF) was measured using a specially designed breast phantom to simulate normal breast uptake, as well as a NEMA torso phantom with a sphere insert to simulate the effects of concentrated heart uptake and uniform torso uptake (0.14 muCi/cc). The activity concentrations in heart, torso and breast were in the ratio of 9:2:1. Scatter fraction (SF) was measured using a 0.23 cc sphere filled with ⁶⁴Cu and placed inside the breast phantom with and without scattering medium. The image quality was assessed by placing two hot spheres (2.6 cc and 0.5 cc) filled with ⁶⁴Cu to simulate "lesions" in the breast phantom, and the ratios of activity concentrations in hot spheres to background were 15:1, 6:1 and 3:1. The spatial resolution was less than 3.0 mm FWHM at very high singles rate. The center field sensitivity extrapolated to the full scale camera was 0.63%. The RF was 20% and the SF was 33%. Both hot spheres in the breast phantom were well resolved in the reconstructed images. Based on these results the projected performance of the full scale device consisting of two 9 module panels promises a very effective dedicated PEM system with very advantages - cost and field of view characteristics.