*4.1.2 Radiopharmaceuticals*

*Medical Isotopes*

mitochondria [20], while the normal parathyroid cells do not [21]. The highest rates of uptake of 99mTc-sestamibi are seen in the solitary adenomas of the parathyroid glands [22]. Not only the amount of intracellular mitochondria is important but also the quantity of oxyphillic cells in the tumors. If the percentage of oxyphillic cells exceeded 25%, accumulation of 99mTc-sestamibi was observed in 78% of parathyroid adenomas. Also false negative results are possible if the oxyphillic cells do not content sufficient amount of mitochondria [23]. Accumulation of 99mTc-sestamibi into the cells also can be influenced by their metabolic activity, the weight and the size of the tumor. This new radionuclide rapidly replaced 201Tl chloride because it showed better quality of the images and higher sensitivity for detecting abnormal

99mTc-tetrofosmin another myocardial perfusion agent was also used for visualizing parathyroid glands in scintigraphy, but the data for its use so far are limited. 99mTc-tetrofosmin shows some similarities with 99mTc-sestamibi although the way of accumulation is different and it is retained mainly in the cytosol rather than in the mitochondria of the target cells. When used for parathyroid scintigraphy 99mTc-tetrofosmin shows slower washout from the thyroid gland, which makes it unsuitable for single-isotope dual-phase scintigraphy [25]. Nevertheless its sensitivity increases when used in combination with SPECT. Several studies [26, 27] of the diagnostic value of 99mTc-tetrofosmin scintigraphy for topic localization of the hyperfunctioning parathyroid glands in patients with PHPT, showed that this method was useful for the clinical practice and that the accumulation of 99mTc-tetrofosmin depends on

**4.1 Protocols for nuclear medicine examination of parathyroid glands**

subtraction, dual-phase single-isotope and combination of both [28].

Generally three protocols are most widely used: single-phase dual-isotope

with equal thyroid and parathyroid glands accumulation and another (123I or 99mTc-pertechnetate) with predominant uptake in the thyroid gland are applied consecutively. The obtained images are digitally subtracted and if there is a residual radionuclide accumulation on the subtracted images a hyperfunctioning parathyroid gland can be suspected [28]. Disadvantages of this method are the use of two radionuclides, the necessity of full collaboration from the patient's side to stay calm and motionless during the examination and the need of very precise positioning of the patient. In addition there is an increase possibility for the presence of artifacts

In single-phase dual-isotope modality two types of radiopharmaceuticals with different organ uptake are used. One isotope (99mTc-sestamibi or 99mTc-tetrofosmin)

The rationale of the single-isotope protocol is based upon the different washout periods of the radionuclide from the thyroid and parathyroid glands. In this method, after an injection of a single radionuclide, early (at 10–15 min) and late

There are a very few studies directly comparing the results from single-isotope dual-phase modality with single-phase dual-isotope subtractional scintigraphy and the results are inconclusive [31, 32]. So far there is no clear confirmed advantages of

No preliminary preparation of the patients before performing single isotope dual-phase scintigraphy is necessary. In subtractional modality some preliminary conditions should be followed such as: discontinuation of Levothyroxine or Iodine

parathyroid glands, with less radiation exposure [24].

the weight of the tumor and the level of PTH.

on the subtracted images [29, 30].

(at 1.5–3 h) images are obtained [28].

one type over another.

*4.1.1 Preparation of the patient*

**48**

99mTc-sestamibi and 99mTc-tetrofosmin: they are applied intravenously from 740 to 1110 MBq (20–30 mCi).

99mTc-pertechnetate has a half-life of 6 h and possesses energy of 140 keV. It is used for visualization of the thyroid gland because it accumulates in a functioning thyroid cells. Intravenously 99mTc-pertechnetate is applied form 74–350 MBq (2–10 mCi).
