Nuclear Medicine

In radionuclide imaging (nuclear medicine, scintigraphy), a substance labeled with a radioactive isotope is injected intravenously. Depending on the specific material used, the substance will be taken up preferentially by the thyroid (technetium [Tc] 99m–labeled iodine), salivary glands (Tc 99m pertechnetate), or bone (Tc 99m methylene diphosphonate [MDP]). Gallium 67 citrate is also sometimes used to assess infections and inflammation in bone. At various times after radionuclide injection, a gamma camera is used to count the radioactivity in the various organs and tissues of the body and to display the results visually. High concentrations of the isotope show up as “hot spots” and generally indicate high metabolic activity (Figure 3-13). Nuclear-medicine scans are used to assess conditions that may be widespread, such as metastasis to bone or other tissues or such as fibrous dysplasia in an active phase. Unfortunately, areas of dental periapical and peri-
 
Nuclear Medicine

odontal inflammation also take up the tracer, presenting as hot spots in the jaws, and must be differentiated from other pathologic conditions.
A variation of bone scintigraphy that can be used to localize and quantify bone activity is single-photon emission computed tomography (SPECT). In this technique, the gamma rays given off by the Tc 99m MDP are detected by a rotating gamma camera, and the data are processed by computer to provide cross-sectional images that can later be reconstructed as images in other planes. Volumetric measurements may also be obtained to quantify the distribution of radioactivity in the tissue, allowing better assessment of tissue function.A recent study demonstrated the use of SPECT in the evaluation of osseointegration in dental implants.However, in another study, both the sensitivity and specificity of SPECT were low for the detection of painful sites in patients with idiopathic jaw pain.