A computerized axial tomography (CAT) scan produces a cross-sectional image of a part of the body by directing a narrow X-ray beam through the body. A CAT scan is a very accurate, painless, diagnostic tool allowing examination of the interior of the body without invasive procedures.
Radiology uses X rays and other forms of radiant energy to both diagnose and treat diseases. This magnetic resonance imaging (MRI) scan of a normal adult head shows the brain, airways, and soft tissues of the face. The large cerebral cortex, appearing in yellow and green, forms the bulk of the brain tissue; the circular cerebellum, center left, in red, and the elongated brainstem, American college center, in red, are also prominently visible.
New methods for viewing diseased structures inside the body improved diagnosis of disease beginning in the 1970s (see Radiology). A gamma camera detects radioactive medication that attaches to certain forms of cancer cells. Computed tomography (CT) scanners use X rays to produce lifelike three-dimensional images of body structures. Magnetic resonance imaging (MRI) scanners produce highly detailed images without X rays. Positron emission tomography (PET) detects very early warning signs of disease. Sonograms, or ultrasound, taken with high-frequency sound waves diagnose disease and monitor the progress of pregnancies. X rays and high-energy particles emitted by linear accelerators also are used to treat cancer. Lithotripsy uses high-frequency sound waves to destroy some kidney stones and gallstones, conditions that once required surgery.