**5.1. Patient preparation, instrumentation and image acquisition**

and development, result in growth retardation, brain damage due to craniosynostosis and

Although the manifestations are mostly similar to adults, the initial clinical presentation may be different in the pediatric age and even the symptoms may vary within this age group according to (prepubertal or pubertal population). A highlight of certain symptoms as an example of such atypical presentation and that are subject to confusion are mood changes and emotional lability, fatigue, sleep disturbance and increased appetite (prepubertal children more commonly present with poor weight gain and frequent bowel movements), attentiondeficit hyperactivity disorder, poor school performance, irritability, fatigue, palpitations, heat

Definitive diagnosis can be more challenging in pregnancy. A diffuse goiter, ophthalmopathy, hyperthyroid symptoms prior to pregnancy and serum thyroid hormone receptor antibody (TRAb) positivity favor the diagnosis of *Graves' disease*. Transient gestational thyrotoxicosis is more common in women with morning sickness, especially those with the most severe form,

The normal thyroid gland and anatomic variants can be visualized by numerous imaging modalities including scintigraphy, ultrasound and computed tomography. Although magnetic resonance imaging (MRI) is capable of providing excellent anatomic detail of the thyroid gland using proton density imaging, it is not usually used in routine clinical practice [7].

Thyroid ultrasonography utilizes reflected sound waves that allow to identify and evaluate gland size, location, the presence of nodules and to differentiate between cystic and solid lesions [7]. There are certain echographic characteristics such as echogenic behavior of the thyroid nodule (as purely cystic or hyperechoic nodules), good demarcation and external vascularization suggesting signs of benign course (e.g., a thyroid adenoma). On the contrary, solid hypoechogenic nodules, irregular borders, internal vascularization, presence of microcalcifications or

Ultrasound is, therefore, an image modality from which morphological information of the thyroid gland is obtained. On the other hand, thyroid scintigraphy is a functional imaging test that visualizes the distribution of active thyroid tissue and is used as a complementary test for

*American Thyroid Association (ATA)* and other guidelines have published their recommendations suggesting that thyroid scintigraphy is useful in the assessment of diffuse goiter *(Graves' disease)*, the simple thyroid nodule and multinodular goiter, acute or chronic local inflammation (thyroiditis), suspected ectopic thyroid (such as lingual thyroid), the study of cervical embryonic development anomalies of thyroid origin (thyroglossal cysts) to evaluate the extent of retroesternal goiter and patients undergoing treatment with radioactive iodine, which is important to know about the anatomical distribution, active thyroid tissue informa-

**4. Diagnostic methods in the evaluation of hyperthyroidism**

recent increase in size on follow-up are associated with malignancy [10].

tion and select the appropriate therapeutic dose/activity of 131-Iodine [6].

cognitive impairment [8].

34 Thyroid Disorders

intolerance, fine tremor and a goiter [2].

hyperemesis gravidarum [9].

definite diagnosis [6, 10].

Usually no prior patient preparation is needed for thyroid scintigraphy [6]. It is not necessary to carry out any special diet or suspend the usual medication. In case the patient is taking thyroid hormone replacement therapy (levothyroxine), it is necessary to stop taking such medication at least 30 days before the imaging study.

That medication can be restarted as usual once the image is acquired. If the patient is taking an iodine supplement or has recently had an intravenous iodine test (such as a CT scan with intravenous contrast), the study should be delayed 4–6 weeks later [6].

On the other hand, women who are pregnant or breastfeeding should inform the nuclear medicine physician before any testing of the service. Although the exposure to the radiation involved is very low with 99mTc-pertechnetate, the benefit/risk of the test must be compared, using the lowest possible dose to obtain an adequate image (optimization criterion) [6].

Breastfeeding will be suspended for 24 h after performing the thyroid scan and the importance of drinking plenty of water for an early elimination of the radiotracer will be reported, which will reduce the exposure time of the embryo/fetus to radiation.

About radiation protection measures, it is recommended not to be in contact with pregnant women or young children for 24 h after the scintigraphy. If this condition cannot be met, a distance of at least 1 m from the patient should be maintained.

Regarding scintigraphic technique, the images begin 20 min after the intravenous injection of 5 mCi (185 MBq) of 99mTc-pertechnetate [12]. In pediatric population, these fixed doses are not used (5–10 mCi [185–370 MBq]); the dose administered to make the image is adjusted to the weight of the patient.

The acquisition is done with gamma cameras, which are composed of collimators of scintillation crystals and photomultipliers, which allow the image obtained to be the projection of the radiotracer distribution. In our department, we use a pinhole collimator with a 3.5 mm opening, as well as an energy setting of 140 keV photopeak for 99mTc. Images are obtained on a 128 x 128 matrix with a zoom 5 and at 100,000 counts in the anterior and 30° anterior oblique views (right and left anterior oblique) with the collimator placed as close as possible to the patient's extended neck [5, 12]. The duration of the image is usually about 5 min.

In cases where we want to visualize more specifically the thyroid gland and adjacent structures (as in the case of intrathoracic goiters), we can perform the SPECT/CT hybrid technique *(Tomography by Emission of a Single Photon)*. Several rotating gantry are incorporated to the gamma cameras and they rotate around a central axis of the patient, what allows a rotation arc of 180° to 360°. Finally three-dimensional images are obtained, unlike the two-dimensional planar images of the scintigraphy.

## **5.2. Evaluation of thyrotoxicosis associated with thyroid hyperfunction (clinical examples)**

The biodistribution of 99mTc-O4 in the body is taken up by the thyroid, but this is also taken up by other structures such as salivary glands. Its secretion by saliva, sweat or urine may give false positive image [10].

**Figure 1.** It is noted a diffuse enlargement of thyroid with a homogeneous distribution of the radiotracer and markedly increased uptake of both thyroid lobes, suggestive of hyperfunction. *Courtesy of H.R.U. Málaga, Spain. Nuclear Medicine Department.*

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**Figure 2.** Thyroid scintigraphy shows an uptake-tracer nodule at the base of the right thyroid lobe and another nonfunctioning nodule at the base of the left thyroid lobe. *Courtesy of H.R.U. Málaga, Spain. Nuclear Medicine Department.*

Therefore, in a normal thyroid scintigraphy, the gland is symmetrical and the lateral borders of lobes are straight to convex. Tracer is normally seen in salivary glands and in capillary network of the neck tissue also, called as 'blood pool' (i.e., seen as a light background along the neck contour) [6].

In the case of diffuse goiter due to *Graves' disease*, thyroid scintigraphy shows a diffuse enlargement of thyroid with a homogeneous distribution of the radiotracer and markedly increased uptake of both thyroid glands suggestive of hyperfunction [8]. Activity throughout the gland is increased relative to the background due to both increased stimulation and function of the gland (**Figure 1**). Such stimulation at times results in visualization of the pyramidal lobe (a remnant of the thyroglossal duct). Owing to its relatively small size, the pyramidal lobe is normally not seen unless the gland is overly stimulated [12].

The toxic multinodular goiter is shown as an enlarged thyroid with a heterogeneous distribution of the radiotracer. Non-functioning and uptake-tracer thyroid nodules are both present, whose activity is above normal (hyperfunction) (**Figure 2**).

With respect to the pretoxic nodular goiter, the thyroid gland usually presents a hyperfunctioning nodulation in one of its thyroid lobes, while the rest of the thyroid parenchyma presents a slight decrease in the uptake of the radiotracer, which suggests the existence of braking phenomena (**Figure 3**).

Nuclear Medicine in the Assessment of Thyrotoxicosis Associated with Increased Thyroid… http://dx.doi.org/10.5772/intechopen.77161 37

Regarding scintigraphic technique, the images begin 20 min after the intravenous injection of 5 mCi (185 MBq) of 99mTc-pertechnetate [12]. In pediatric population, these fixed doses are not used (5–10 mCi [185–370 MBq]); the dose administered to make the image is adjusted to the

The acquisition is done with gamma cameras, which are composed of collimators of scintillation crystals and photomultipliers, which allow the image obtained to be the projection of the radiotracer distribution. In our department, we use a pinhole collimator with a 3.5 mm opening, as well as an energy setting of 140 keV photopeak for 99mTc. Images are obtained on a 128 x 128 matrix with a zoom 5 and at 100,000 counts in the anterior and 30° anterior oblique views (right and left anterior oblique) with the collimator placed as close as possible to the

In cases where we want to visualize more specifically the thyroid gland and adjacent structures (as in the case of intrathoracic goiters), we can perform the SPECT/CT hybrid technique *(Tomography by Emission of a Single Photon)*. Several rotating gantry are incorporated to the gamma cameras and they rotate around a central axis of the patient, what allows a rotation arc of 180° to 360°. Finally three-dimensional images are obtained, unlike the two-dimensional

The biodistribution of 99mTc-O4 in the body is taken up by the thyroid, but this is also taken up by other structures such as salivary glands. Its secretion by saliva, sweat or urine may give

Therefore, in a normal thyroid scintigraphy, the gland is symmetrical and the lateral borders of lobes are straight to convex. Tracer is normally seen in salivary glands and in capillary network of the neck tissue also, called as 'blood pool' (i.e., seen as a light background along

In the case of diffuse goiter due to *Graves' disease*, thyroid scintigraphy shows a diffuse enlargement of thyroid with a homogeneous distribution of the radiotracer and markedly increased uptake of both thyroid glands suggestive of hyperfunction [8]. Activity throughout the gland is increased relative to the background due to both increased stimulation and function of the gland (**Figure 1**). Such stimulation at times results in visualization of the pyramidal lobe (a remnant of the thyroglossal duct). Owing to its relatively small size, the pyramidal lobe is

The toxic multinodular goiter is shown as an enlarged thyroid with a heterogeneous distribution of the radiotracer. Non-functioning and uptake-tracer thyroid nodules are both present,

With respect to the pretoxic nodular goiter, the thyroid gland usually presents a hyperfunctioning nodulation in one of its thyroid lobes, while the rest of the thyroid parenchyma presents a slight decrease in the uptake of the radiotracer, which suggests the existence of braking

normally not seen unless the gland is overly stimulated [12].

whose activity is above normal (hyperfunction) (**Figure 2**).

patient's extended neck [5, 12]. The duration of the image is usually about 5 min.

**5.2. Evaluation of thyrotoxicosis associated with thyroid hyperfunction (clinical** 

weight of the patient.

36 Thyroid Disorders

planar images of the scintigraphy.

false positive image [10].

the neck contour) [6].

phenomena (**Figure 3**).

**examples)**

**Figure 1.** It is noted a diffuse enlargement of thyroid with a homogeneous distribution of the radiotracer and markedly increased uptake of both thyroid lobes, suggestive of hyperfunction. *Courtesy of H.R.U. Málaga, Spain. Nuclear Medicine Department.*

**Figure 2.** Thyroid scintigraphy shows an uptake-tracer nodule at the base of the right thyroid lobe and another nonfunctioning nodule at the base of the left thyroid lobe. *Courtesy of H.R.U. Málaga, Spain. Nuclear Medicine Department.*

As for the toxic adenoma, the thyroid gland appears enlarged at the expense of a thyroid lobe, which is occupied by a hyperfunctioning nodulation. The contralateral thyroid shows a notable decrease in uptake, due to more advanced braking phenomena than in the previous

Nuclear Medicine in the Assessment of Thyrotoxicosis Associated with Increased Thyroid…

http://dx.doi.org/10.5772/intechopen.77161

39

The most common reason for hyperthyroidism is *Graves' disease*. Toxic nodular goiter is a clinical situation that includes toxic multinodular goiter and toxic adenoma and is the second

Current therapeutic options for these pathologies include antithyroid drugs (ATD), radioactive iodine and thyroidectomy. The choice of treatment depends on the type of pathology (*Graves' disease*, toxic multinodular goiter, pretoxic or toxic adenoma), physiological characteristics of the patient (age, pregnancy, breastfeeding), co-morbidities (advanced age, heart failure, large compressive intrathoracic goiters, thyroid ophthalmopathy), as well as refracto-

Antithyroid drugs (ATD) therapy is usually recommended as the initial treatment for hyperthyroidism (especially in *Graves' disease*), achieving normalization of thyroid function in

There are several antithyroid drugs, the most used in our environment are methimazole and propylthiouracil. For several reasons, propylthiouracil is preferred during pregnancy. Avoidance of the use of propylthiouracil (PTU) was recently recommended in childhood because of the high risk of PTU-induced hepatitis. Because methimazole (active metabolite of carbimazole) has a longer half-life and is effective as a single daily dose, it is particularly helpful in younger children. Daily loading doses of 10–30 mg of methimazole or 100–300 mg

The medication is prescribed for 12–18 months normally, with the aim of achieving remission of the disease. However, the frequency of recurrences (more frequently in young males) and severe side effects like cytopenias, vasculitis, liver failure or agranulocytosis (higher in pedi-

Radioiodine therapy and surgery are usually the second-line treatments in *Graves' disease*. It does not happen in the case of toxic nodular goiter (toxic multinodular goiter and toxic adenoma), where definite and effective treatment can be achieved only with radioiodine or surgery [13]. So, both are considered as the first line of treatment for these pathologies and not

The use of 131-Iodine in the treatment of hyperthyroidism is increasing, as it is easy to administer, relatively inexpensive, safe and highly effective with a cure rate approaching 100% after

**6. Treatment in hyperthyroidism: different therapeutic options.** 

**Radioiodine (131I) administration protocol in our center**

case (**Figure 4**).

4–6 weeks [8].

most common reason of hyperthyroidism [13].

riness to the treatment administered [8, 14].

the second line as in *Graves' disease* [17].

one or more activity [18].

**6.1. Different therapeutic options in hyperthyroidism**

of propylthiouracil are appropriate for most patients [15, 16].

atric patients than adults) are a main limitation of ATD treatment [8, 14, 16].

**Figure 3.** Hyperfunctioning nodulation is seen at the base of the right thyroid lobe. *Courtesy of H.R.U. Málaga, Spain. Nuclear Medicine Department.*

**Figure 4.** We can see the existence of a large hyperfunctioning nodulation that occupies the left thyroid lobe. *Courtesy of H.R.U. Málaga., Spain. Nuclear Medicine Department.*

As for the toxic adenoma, the thyroid gland appears enlarged at the expense of a thyroid lobe, which is occupied by a hyperfunctioning nodulation. The contralateral thyroid shows a notable decrease in uptake, due to more advanced braking phenomena than in the previous case (**Figure 4**).

The most common reason for hyperthyroidism is *Graves' disease*. Toxic nodular goiter is a clinical situation that includes toxic multinodular goiter and toxic adenoma and is the second most common reason of hyperthyroidism [13].
