Parathyroid Scintigraphy - European Association of Nuclear Medicine

cyclotron produced. Its uptake reflects amino
acid reflux into stimulated parathyroid tissue
(Otto et al. 2004; Beggs and Hain 2005). Uptake
in inflammatory conditions may pose
a problem and should be considered when
interpreting images. The typical radioactivity
dose ranges between 240 and 820 MBq, with
an average intravenous dose of 400 MBq.
18 F-FDG
18 F-FDG has a half-life of 110 min and is cyclotron
produced. 18 F-FDG allows glucose
metabolism to be assessed and evaluated
using PET. There is differential concentration
of FDG in abnormal parathyroid tissue
and this difference is used to demonstrate
the abnormal gland. FDG also accumulates
in other malignant and benign tissues, and
in inflamed or infected tissue; this potentially
limits its usefulness. The typical intravenous
dose is 400 MBq.
Radiopharmaceutical features
Multiple radiopharmaceuticals have been
described for the detection of parathyroid lesions.
Thallium, sestamibi and tetrofosmin are
the three most commonly used (Ahuja et al.
2004). All these agents were originally developed
for cardiac scanning. In the 1980s, 201 Tl
was the most commonly used agent, but it
has a longer half-life and delivers a higher radiation
dose to the patient (Kettle 2002). Consequently,
201 Tl is no longer commonly used,
and most recent literature refers to the use of
99m Tc-sestamibi. However, for the subtraction
1
method it is probable that each radiopharmaceutical
would provide the same diagnostic
information (Kettle 2002).
Subtraction agents
Thyroid-specific imaging with 123 I or 99m Tcpertechnetate
may be employed using a subtraction
method to differentiate parathyroid
from thyroid activity (Clark 2005).
The two main agents used for imaging the
thyroid are 123 I (sodium iodide) and 99m Tcpertechnetate.
There is a slight preference for
the use of 123 I, as it is organified and therefore
provides a stable image. The pertechnetate
washes out from the thyroid gland with time,
and if there is some delay in imaging there
may be a reduction in the quality of the
thyroid image (Kettle 2002). However, both
agents may be affected if the patient is taking
thyroxine or anti-thyroid medications or has
recently received iodine contrast agents.
Thyroid-specific radiopharmaceuticals may
aid delineation of the thyroid parenchyma if
required after dual-phase imaging. This may
be helpful as a second-line “visual subtraction”
procedure when no parathyroid adenoma is
visible on dual-phase parathyroid imaging
(Clark 2005).
Activities given for imaging the thyroid
and parathyroid glands are as follows: 99m Tc
pertechnetate, 80 MBq; 123 I, 40 MBq; 201 Tl,
80 MBq; 99m Tc-sestamibi, 900 MBq. If a 99m Tc-