A Study of the Application of MWPC-Based Positron Cameras for Breast Imaging

The quad-HIDAC positron camera, designed for laboratory animal imaging, has been evaluated as a potential positron emission mammography system. With a detection efficiency for 511 keV photons of ~1.6% for a centrally placed line source and an intrinsic spatial resolution of 1.25 mm FWHM the camera has many of the attributes needed for PEM. Small spherical ´lesions´ with volumes between 0.04ml and 0.46ml were imaged in a small ´breast´ phantom filled with ⁶⁸Ga. Results were compared to those obtained from a similar study carried out previously with the VUBPET system which had an average spatial resolution of ~3.5 mm. The data show that the HIDAC system was able to detect the smallest (4 mm diameter, 0.04 ml) lesion at a tumour to background (T/B) ratio of 5:1. The VUBPET system could just detect the 6 mm diameter lesion at a T/B ratio of 8:1. We conclude that for mammography an MWPC-based detector with high resolution would be fine and could be achieved by reducing the frame thicknesses of the MWPC on the side closest to the chest wall.