Development of an opposed-type high-resolution PET (PEM) dedicated to mammary gland checkup and its performance

In breast cancer screening, palpation and X-ray mammography are recommended. Although positron emission tomography (PET) has high detectability against advanced cancer, it has difficulty in finding breast cancer of 1 cm or smaller. This paper described the features of mammary gland purpose high-resolution flat-plate opposed-type PET device for breast cancer diagnosis (position emission mammography [PEM]) developed jointly by Tohoku University and a private company. By developing and mounting a Pr: LuAG detector with high resolution lutetium doped with praseodymium, detector spacing became variable and photographing time could be shortened. Although the opposed flat-plate type PEM has the problem of anisotropy of resolving power, there is an advantage that a wider field of view can be obtained with fewer electronic circuits compared with a ring-type PEM. Because the detector spacing is variable, it is possible to even photography close up shots or thick subjects. Even in mammogram imaging, this device can cope with various chest wall shapes, breast forms, breast cancer occurrence positions in the breast, and is suitable for Asians. Judging from diagnosis cases, PEM has 2.1 mm of resolving power, better than 7.1 mm of PET. There are cases, where PET and PEM cannot perform the aim by itself. However, in the cancer cases of 1 cm or smaller, the detection sensitivity of PEM is 57.9%, which is better than 36.8% of PET, and it increases to 68% with the combined use. Further improvement of resolution is a future task. (A.O.)