Endocrine System

Question 1

Radiotracers used for thyroid

Answer 1

I 131 predominantly treatment

I 123 predominantly diagnostic

Question 2

Clinical indication for thyroid scintigraphy and percent radioactive iodine thyroid uptake

Answer 2

Functional status, detect ectopic thyroid tissue, thyroid cancer whole body scan .

Differential for thyrotoxicosis, calc I 131 dose for graves

Post thyroidectomy and pre I 131 therapy eval for disease extent
Post I 131 therapy effectiveness
Follow for recurrence

Question 3

Normal distribution of I 131 and I 123

Answer 3

Thyroid 
Nasal area
Oropharynx 
Salivary glands 
Stomach 
Intestines 

Breast and GU can be seen too

Question 4

Radiotracers for parathyroid

Answer 4

Tc 99 sestamibi

Normal parathyroid glands are not visualized

Thyroid also takes it up but washes out more rapidly than abnormal parathyroid. This is why two phase parathyroid scintigraphy is used

Question 5

Two methods to do parathyroid imaging

Answer 5

Combined thyroid and parathyroid. I 123 and Tc 99 sestamibi done and then thyroid is subtracted

Two phase parathyroid with washout of thyroid