Several stages are involved in the determination of a definitive diagnosis. For example, a screening mammography might reveal a suspicious lesion, which is followed with a biopsy of the lesion. Also, many people are involved in the diagnostic process and, as has been emphasized, diagnostic imaging plays a major role in that effort. In addition to radiologists, there are oncologists, surgeons, nurses, pathologists, and geneticists. The pathologists play a crucial role in performing the histologic tests on cell specimens taken from a biopsy, as does the microbiologist and geneticist, who are developing new techniques that measure gene sensitivity from DNA specimens. Three examples are described below: (1) diagnosis of metastasis of the primary melanoma lesion to the lymph nodes, (2) a biopsy of lung nodules, and (3) screening for coronary artery disease with CT.