[Cancer diagnosis by medical images with reference to medical physics]

Medical imaging technology has developed dramatically during recent 15 years, triggered by X-ray computed tomography. Cancer diagnosis has been greatly influenced by newly invented devices such as XCT, ultrasound, and MRI. In this report, a brief historical review is made of medical imaging after 1973 when XCT appeared on the market. Cancer diagnosis is divided into various stages such as detection, diagnosis, staging, planning, verification, response to therapy, follow-up, relapse and restaging. The effect of each imaging modality on various stages of cancer diagnosis is explained, and future directions are suggested. Finally, the picture archiving and communication system (PACS) is illustrated in detail in relation to cancer diagnosis. PACS will not only improve the diagnostic efficacy of cancer, but also contribute to reduction in health care expenditures. Thus, it is one of the most important goals of medical physicists for medical practice in the 21st century.