ABSTRACT
Imaging had its beginning with the invention of the stationary shadow x-ray, and then evolved to simple motion tomography, thence to various forms of computed tomography (CT). X-ray imaging relies on differences in the x-ray photon absorbency of tissues, which can be very small in soft tissues such as the breast and brain. Magnetic resonance imaging (MRI) has evolved into a high-resolution imaging modality that is primarily sensitive to the water density in tissues, and which can be used to locate tumors with greater resolution than x-ray CT. The use of radioisotopes and radionuclides attached to molecules that have affinity to particular tissues has enabled positron emission tomography (PET) and single-photon emission tomography (SPECT) to locate tissues such as cancers. Infrared (IR) imaging is a completely passive means of detecting local "hot spots" which might be due to cancer growing near the skin surface, or cold spots indicative of circulatory anomalies.
