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Nuclear medicine
Nuclear medicine imaging involves the administration into the patient of
radiopharmaceuticals consisting of substances with affinity for certain body
tissues labeled with radioactive tracer. The most commonly used tracers are
Technetium-99m, Iodine-123, Iodine-131 and Xenon-133. The heart, lungs, thyroid,
liver, gallbladder, and bones are commonly evaluated for particular conditions
using these techniques. While anatomical detail is limited in these studies,
nuclear medicine is useful in displaying physiological function. The excretory
function of the kidneys, iodine concentrating ability of the thyroid, blood flow
to heart muscle, etc. can be measured. The principal imaging device is the gamma
camera which detects the radiation emitted by the tracer in the body and
displays it as an image. With computer processing, the information can be
displayed as axial, coronal and sagittal images (SPECT images). In the most
modern devices Nuclear Medicine images can be fused with a CT scan taken
quasi-simultaneously so that the physiological information can be overlayed or
co-registered with the anatomical structures to improve diagnostic accuracy.
PET scanning also falls under "nuclear medicine."In PET scanning, a radioactive
biologically-active substance (most often Glucose-18) is injected into a patient
and the radiation emitted by the patient is detected to produce multi-planar
images of the body. Metabolically more active tissues, such as cancer,
concentrate the active substance more than normal tissues. PET images can be
combined with CT images to improve diagnostic accuracy.
The applications of nuclear medicine can include bone scanning which
traditionally has had a strong role in the work-up/staging of cancers.
Myocardial perfusion imaging is a sensitive and specific screening exam for
reversible myocardial ischemia, which when present requires angiographic
confirmation and potentially life-saving balloon angioplasty, stenting or
cardiac bypass grafting. Molecular Imaging is the new and exciting frontier in
this field.
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