Scintigraphy is a nuclear medicine procedure that produces a two-dimensional visual display of specific tissues (mostly hyperfunctional thyroid tissues and bone tumors) based on the selective uptake of various radiopharmaceuticals by these tissues. In nuclear medicine, a radioisotope is administered to the patient via an intravenous or subcutaneous injection. The isotope is then taken up in different amounts by different organs. The radioisotope is a low energy gamma emitter that is detected by a camera that converts the gamma energy to light, thus producing an image. A diagnosis is made by imaging the distribution of the radioactive element within the tissue. The procedure is quick and painless. Because the radiation doses are low, your pet will not feel any untoward effects from their nuclear medicine procedure and will only have to stay overnight for a diagnostic procedure
 At NCVS we use a wide-field gamma camera that allows us to scan a large field of view. That means that a large anatomic volume of tissue can be visualized during a study.
The radiation emitted from the radioisotope (which is concentrated in a specific organ) is detected by the gamma camera and a digital image of the radioactivity is produced and printed on film. The resulting image may look like a gray- scale (radiograph-like) or a color coded image (see below).
Thyroid scintigraphy: The Thyroid scan
Thyroid scintigraphy is one of the more common applications of nuclear medicine in veterinary medicine. Because of the number of older cats suspected to have hyperthyroidism, the use of scintigraphy has become the gold standard for evaluating this common feline disorder. Thyroid imaging is most commonly used in veterinary medicine for evaluating cats with known or suspected hyperthyroidism. The most common use of thyroid scintigraphy in dogs is for assessing the functional behavior of thyroid conditions. Thyroid disease in cats is almost always benign (not cancer).
A small amount (tracer dose) of radioactive sodium pertechnetate is administered subcutaneously. Twenty minutes later the patients are gently laid on their belly (ventral view) or on the side (lateral view) on the gamma camera to acquire an image . The scanning process takes about 30 seconds.
Normal Feline Thyroid Scan Study
In normal cats, the thyroid gland appears on scintigrams as two well-defined focal (ovoid) areas of radionuclide accumulation in the cranial to middle cervical region viewed as slightly brighter areas on the gray-scale image. The two thyroid lobes are symmetrical and located side by side. Activity in the normal thyroid closely approximates activity in the salivary glands with an expected visual ratio of 1:1.
Thyroid Scan in Feline Hyperthyroidism
The standard scintigraphic appearance of thyroid hyperfunctional tissue is a gray-scale image (i.e. image formed of shades of gray) where bright spots (area of high radionuclide uptake) identify lesions (a). Digital images maybe processed into color-coded images (b) using a range of color where the lesions are identified with a specific color (ie, red). Although more attractive, color-coded images do not provide as much information as gray-scale images.
 Planar thyroid scintigraphy of a hyperthyroid cat with bilateral thyroid adenomas as (a) gray-scale image and (b) color-code image. Notice the increased uptake of the radionuclide in the thyroid tissue bilaterally
Feline hyperfunctional thyroid tissue can include unilateral or bilateral enlargement of the thyroid gland and occasionally ectopic thyroid tissue (abnormal thyroid tissue located outside the normal anatomic position).
The procedure provides valuable information regarding both thyroid anatomy and physiology and can play an integral role in the diagnosis and management of cats with hyperthyroidism. Thyroid scintigraphy allows the direct visualization of the hyperfunctional thyroid tissue responsible for the development of hyperthyroidism. For this reason, thyroid scintigraphy will allow the diagnosis of hyperthyroidism before laboratory tests are consistently abnormal. Thyroid scintigraphy can also exclude a diagnosis of hyperthyroidism in cats with thyroid hormone elevations of nonthyroidal origin. Thyroid scintigraphy provides an additional method for determining the relative severity of thyroid disease that is less affected by the presence of concurrent nonthyroidal illness than laboratory evaluations.
Thyroid Scan in Canine Thyroid Cancer
Thyroid scans in dogs are useful to determine whether a cervical mass arises from the thyroid or from other tissues, when the histological diagnosis is equivocal. It is also very useful to ascertain whether the thyroid mass is operable (a) or inoperable (b):
Bone scintigraphy: The Bone scan
A bone scan is a valuable tool in the examination of the skeletal system. It is useful for evaluation of primary and metastatic cancer affecting bones. Although survey radiographs are the standard imaging modality for the evaluation of primary bone tumors in dogs and cats, a bone scan is superior for identifying the presence of metastatic lesions in bone and soft tissues prior to amputation or limb-sparing techniques.
Bone scans are also indicated for evaluation of infectious arthritis or osteomyelitis, difficult to diagnose lamnesses and stress fractures.
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