**2. Iodine and the thyroid gland**

Iodine is an element with a high atomic number 53, it is purple in colour and it is represented by the symbol I, and the iodine is an essential component of the hormones

Physiologic and False Positive Pathologic Uptakes on Radioiodine Whole Body Scan 3

salts (sodium iodide or potassium iodide), inorganic diatomic iodine or organic monoatomic iodine. (Ahad and Ganie 2010) Iodide, represented by I <sup>−</sup> , is the ion of iodine and it combines with another element or elements to form a compound. Although the iodine content of iodised salt may vary from country to country, common table salt has a small

Fig. 2. Cellular mechanism for iodine uptake in thyroid follicular cells. This commences with the uptake of iodide from the capillary into the follicular cell of the thyroid gland. This process occurs against chemical and electrical gradients via the sodium iodide symporter (NIS) located in the basal membrane of the follicular cell. Increased intracellular sodium is pumped out by the action of Na+/K+ ATPase. The iodide within the follicular cell moves towards the apical membrane to enter into the follicular lumen and then it is oxidized to iodine by peroxidase. Organification of the iodine follows the oxidation by iodination of the tyrosine residues present within the thyroglobulin (TG) molecule, and the iodine stays in the follicle before it is released into the circulation as thyroid hormones. Thyroid stimulating hormone (TSH) activates the follicular cell via TSH receptor (TSH-R) and increases the

expression of the NIS and the TG.

portion of sodium iodide to prevent iodine deficiency.(Hall 2011)

Fig. 1. Simplified diagram of the metabolic circuit of iodine. Iodine (I) ingested orally is absorbed from the small bowel into the circulating iodine pool. About one fifth of the iodine in the pool is removed by the thyroid gland and surplus iodine is rapidly excreted by the kidney and bowel. In the thyroid gland, iodine is used to produce thyroid hormones (Hr), which act in peripheral tissues. Iodine released from thyroid hormones re-enter into the circulating iodine pool.

produced by the thyroid gland. The thyroid hormones are essential for the health and wellbeing for mammals. Iodine comprises about 60% of the weights of thyroid hormones. The body of an adult contains 15~20mg of iodine, of which 70~80% is in the thyroid gland.(Ahad and Ganie 2010) To produce a normal quantity of thyroid hormone, about 50 mg of ingested iodine in the form of iodides are required each year. Oceans are the world's main repositories of iodine and very little iodine is found in the soil.(Ahad and Ganie 2010) The major dietary sources of iodine are bread and milk in the US and Europe, but the main source is seaweed in some Asian countries.(Zimmermann and Crill; Ahad and Ganie 2010; Hall 2011) Iodine is found in various forms in nature such as inorganic sodium or potassium

Fig. 1. Simplified diagram of the metabolic circuit of iodine. Iodine (I) ingested orally is absorbed from the small bowel into the circulating iodine pool. About one fifth of the iodine in the pool is removed by the thyroid gland and surplus iodine is rapidly excreted by the kidney and bowel. In the thyroid gland, iodine is used to produce thyroid hormones (Hr), which act in peripheral tissues. Iodine released from thyroid hormones re-enter into the

produced by the thyroid gland. The thyroid hormones are essential for the health and wellbeing for mammals. Iodine comprises about 60% of the weights of thyroid hormones. The body of an adult contains 15~20mg of iodine, of which 70~80% is in the thyroid gland.(Ahad and Ganie 2010) To produce a normal quantity of thyroid hormone, about 50 mg of ingested iodine in the form of iodides are required each year. Oceans are the world's main repositories of iodine and very little iodine is found in the soil.(Ahad and Ganie 2010) The major dietary sources of iodine are bread and milk in the US and Europe, but the main source is seaweed in some Asian countries.(Zimmermann and Crill; Ahad and Ganie 2010; Hall 2011) Iodine is found in various forms in nature such as inorganic sodium or potassium

circulating iodine pool.

salts (sodium iodide or potassium iodide), inorganic diatomic iodine or organic monoatomic iodine. (Ahad and Ganie 2010) Iodide, represented by I <sup>−</sup> , is the ion of iodine and it combines with another element or elements to form a compound. Although the iodine content of iodised salt may vary from country to country, common table salt has a small portion of sodium iodide to prevent iodine deficiency.(Hall 2011)

Fig. 2. Cellular mechanism for iodine uptake in thyroid follicular cells. This commences with the uptake of iodide from the capillary into the follicular cell of the thyroid gland. This process occurs against chemical and electrical gradients via the sodium iodide symporter (NIS) located in the basal membrane of the follicular cell. Increased intracellular sodium is pumped out by the action of Na+/K+ ATPase. The iodide within the follicular cell moves towards the apical membrane to enter into the follicular lumen and then it is oxidized to iodine by peroxidase. Organification of the iodine follows the oxidation by iodination of the tyrosine residues present within the thyroglobulin (TG) molecule, and the iodine stays in the follicle before it is released into the circulation as thyroid hormones. Thyroid stimulating hormone (TSH) activates the follicular cell via TSH receptor (TSH-R) and increases the expression of the NIS and the TG.

Physiologic and False Positive Pathologic Uptakes on Radioiodine Whole Body Scan 5

table 2. Imaging should be delayed for a long enough period to eliminate the effects of these interfering factors. The goal of a low iodine diet and the drug withdrawal is to make a 24-hour

Allowed Not-allowed

Meats Fresh unsalted Canned and processed

Table 1. Food guide for a low iodine diet. Some items on the allowed list may not be low in iodine in some forms or merchandise brands. The labels must be checked to be sure that the items meet the requirements of the low-iodine diet. (Amin, Junco et al.; Nostrand, Bloom et

I-131 is produced in a nuclear reactor by neutron bombardment of natural tellurium (Te-127) and decays by beta emission with a half-life of 8.02 days to xenon-133 (Xe-133) and it emits gamma emission as well. It most often (89% of the time) expends its 971 keV of decay energy

Egg Whites of eggs Egg yolks

breads, cereal and crackers without salt unsalted pasta, rice, rice cakes, and

Coffee or tea without milk or cream Fruit juice without red dye#3

Fruit smoothies made without dairy or

Cola, diet cola, lemonade

Beer, wine and spirits

Sea salt

Rhubarb

Fish Shellfishs Seaweeds Seaweed tableets Agar-agar

Milk Cheese Yogurt Butter Ice cream

Whole eggs

with salt

dairy

red dye#3

Fruit or juice with red dye # 3

Chocholate (has milk content)

Breads, cereals or crackers made

Milk, cream or drinks made with

Fruit juice and soft drinks with

Salted pasta, rice or popcorn

Canned or preserved

Salts Non -iodized salt Iodized salt

urine iodine output of about 50 ug.(Silberstein, Alavi et al. 2006).

Fruits and

Seafood and sea products None

Dairy

Paultries and

Grain products

drinks

al. 2004)

**3.2.1 I-131** 

**3.2 Types of radioiodine** 

products None

vegetables Fresh fruits and juices

popcorn

soy products
