They may be effective in preventing breast cancer, but mammograms can be so uncomfortable that some women choose to skip the yearly torture and risk cancer instead. That's why a few cancer centers are testing a newer method of scanning the breast using a specially designed CT. Rather than X-raying the breast as a layer of flat tissue squeezed between two plates (as in mammography), the cone-beam CT develops a 3-D picture of the breast — the woman lies under a CT table while only her breast is exposed through a hole. The result, say doctors, is a clearer picture of the breast tissue in all dimensions, without the distorting effects of overlapping tissue in flat images taken by mammograms.