How do nuclear medicine scans work?

1 Answer
Sep 8, 2014

The most common types of nuclear medicine scans are PET and SPECT.

PET (Positron Emission Tomography)

Isotopes like C-11, N-13, O-15, or F-18 are positron emitters. Substances containing these isotopes collect in disease sites in the body.

A positron from the isotope collides with an electron in the tissue and produces two X-rays at 180° from each other.

The patient is placed on a flat table that moves in increments through a "doughnut" shaped housing.

The X-rays hit multiple rings of crystals that emit photons of light. A computer uses the coincident signals to generate a thin slice image (tomo + graphy = "slice" + "writing").

The table is then moved, and the process is repeated many times. A computer combines the series of images into a single image with "hot spots" where the isotope has collected.

The above image shows a patient with bone marrow leukemia before and after treatment.

SPECT (Single-Photon Emission Computed Tomography)

SPECT is similar to PET. It uses isotopes (Tc-99, I-123, Xe-133) that have longer decay times and emit single instead of double gamma rays.

SPECT uses a gamma detector that rotates around the body. The images have less sensitivity and are less detailed, but the technique is also less expensive than PET.