Now we shall present some examples when gamma imaging has particular impor­tance (see Table 12.5).

12.5.1 Thyroid Scintigraphy

A significant part (normally 15—25%) of iodine will be trapped in thyroid cells from the circulation, and stay there for a long time (in healthy persons it will drop to half in about four months). It will be built into tyrosine, which is converted to the thyroid hormones thyroxin (T4) and triiodo-L-thyronine (T3). Pertechnetate (obtained directly from a technetium generator) gets trapped in the thyroid the

Figure 12.8 A “cold” thyroid nodule at the upper pole of the right lobe.

Figure 12.9 A “hot” thyroid nodule in the right lobe (anterior view).

same way, but—as it cannot be built into organic molecules—it will be washed out faster. Both can be used for thyroid scintigraphy, most frequently in order to clarify the functional status of nodules that were palpated or visualized by ultrasound. While some benign and malignant tumors accumulate less radiopharmaceutical than the normal thyroid tissue (“cold” nodules; see Figure 12.8), in the so-called autonomous adenomas there will be high accumulation, escaping the regular feed­back mechanism (Figure 12.9).