RECENT YEARS, propelled by advances in computers I and electronics, diagnostic imaging has experienced an impressive growth. The identification of tumors through the use of these techniques is expected to lead to significant improvement in the diagnosis, staging, and monitoring of cancer patients.
In the management of the cancer patient the imaging process must take into account the unique features of the tumor, including gross morphology and the natural history of the disease. As techniques have become more refined, the microextensions of a tumor and the degree of involvement of surrounding structures have assumed increasing importance in the formulation of therapeutic decisions.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) has become an accepted clinical technique, but realization of its potential is in a relative early stage. At present, clinical MRI depends upon excitation of the positively charged hydrogen nucleus. A hydrogen proton, when exposed to a strong magnetic field, behaves as a tiny bar magnet that aligns itself in the direction of the field. If an appropriate radiofrequency (RF) pulse is then applied, the protons are deflected from this alignment and spin about the axis of the magnetic field (precess) in the same way a top spins in the earth's gravitational field. When the RF pulse ceases, the protons return to their original alignment, loosing energy to the environment and emitting radiowaves that