Lecture 2 Flashcards
1
Q
Purpose of thyroid uptakes
A
functional assessment of the thyroid gland
2
Q
Indications for iodine uptake
A
- Differential diagnosis of thyrotoxicosis
- used to calculate dose required for therapy
- done with whole body scan for thyroid cancer
- Estimate residual function post- surgery
- Assess effectiveness of 131-I therapy
3
Q
131-Sodium Iodine decay
A
- T1/2 8 days
- Beta decay of 606 keV
- gamma photon of 364 keV
4
Q
131-sodium iodine Biodistribution
A
- thyroid- critical
- salivary glands
- stomach
- mammary glands
- choroid plexus
5
Q
Dose given for 131-sodium iodine
A
0.185-0.370 MBq
6
Q
123-Sodium iodine decay
A
- T1/2 13.2 hours
- electron capture
- gamma photons of 159 keV
7
Q
123-sodium iodine biodistribution
A
- thyroid- critical
- salivary glands
- stomach
- mammary glands
- choroid plexus
8
Q
dose of 123-I
A
1.85-3.7 MBq
9
Q
Explain the Iodine uptake procedure
A
- ingest radioactive tracer
- 90% is absorbed by small intestine within an hour
- trapped, organified, incorperated into hormones
- assess funcitonal status of gland
- determine % uptake of administered dose at 4-6 hours and at 24 hours
- patient % compared to normal rangre
10
Q
Standards
A
-new probes vs old probes may need decay correction
11
Q
Backgrounds
A
- room background
- thigh (patient background)
- malfunctions
- setting errors
- contamination
- alters background measurement
12
Q
Uptake probe positioning
A
- placed 25-30 cm from the anterior neck
- directly aligned with the thyroid gland, ensures accuracy
13
Q
Normal values
A
- 6hrs: 6-18%
- 24hrs: 15-35%
- abnormal values are attributed to hyperthyroidism and hypothyroidism
14
Q
Explain TcO4 uptake procedure
A
- T1/2 is 6hrs
- gamma 140 keV photons
- suited for gamma cameras
- uptake done on the camera
- does not measure organification
15
Q
Explain the TcO4 uptake procedure
A
- syringe counted under thhe camera
- patient injected
- residual in syringe counted, dose recorded
- patient is imaged
- ROIs generated and % uptake is calculated
16
Q
Pros of the TcO4 uptake procedure
A
- results in 30 min
- decreased exposure
17
Q
cons of the TcO4 uptake procedure
A
- decreased accuracy
- only measures trapping
- normal range not well-defined
18
Q
Decreased uptake in non-pathological cases
A
- thyroid hormones
- excess iodine
- contrast media
- non-iodine containing drugs
- prior radiation to the thyroid
19
Q
Increased uptke in non-pathological cases
A
- iodine deficinecy
- estrogens like birthcontrol and pregnancy
- rebound after therapy withdrawal
- lithium
20
Q
Thyroxin
A
- decrease use for 4-6 weeks
- causes decreased RAIU
- T4
- eltroxin
- l-thyroxin
- synthroid
21
Q
Triiodothyronine
A
- discontinue for 2 weeks
- causes decreased RAIU
- T3
- cytomel
- liothyronine
22
Q
causes for excess iodine
A
- iodine solution like ssk or lugols in the past 2-4 weeks
- mineral supplements in the past 2-4 weeks
- vitamins 2-4 weeks
- antitussives 2-4 weeks
- antihistimines 2-4 weeks
- iodinated skin ointments 2-4 weeks
- amioderone in the past 2 weeks
- iodinated drugs in the past few weeks or months
- nitrates
- foods high in iodine
- CHF
- renal failure
23
Q
decreased uptake due to prior radiation and contrast media
A
- no IV contrast the past 1-2 months
- no oral contrast the past 4 weeks
- no fat soluble media for months to years
- prior radiaiton to the neck affects iodine
24
Q
non-iodine containing drugs which decrease RAIU
A
*ACTH
*Adrenal steroids
*Perchlorate
*Penicillin
*Anti-thyroid drugs
* Propylthiouracil (PTU): 2-8 days
* Methimazole (Tapazole): 5-7 days
*Bromides
25
what is thyrotoxicosis
A condition caused by excess thyroid hormones (T3 & T4) in the bloodstream, leading to an overactive metabolism
26
which pathologies are associated with thyrotoxicosis
*Grave’s 70%
*Thyroiditis 20%
*Toxic multinodular goitre 5%
*Toxic thyroid adenoma 5%
*Others 1%
27
what is grave's disease
*Autoimmune
*Autonomously functioning thyroid gland
* Immunoglobulins bind to follicular cells
* Stimulates production of thyroid hormone
*Middle-aged females most common
* Diffusely enlarged, firm, non-tender gland
*Uptake results
* 50-60%
28
what is multinodular toxic goiter
*aka Plummer’s Disease
*Elderly patients
*Symptoms
* Tachyarrhythmia, weight loss, depression, anxiety, insomnia
*Uptake results
* High normal or moderately elevated
* Suppresses extranodular non-autonomous tissue
* Long term: necrotic
29
what is a single autonomous nodule
*5% of patients with solitary nodules
*> 2.5 cm creates thyrotoxicosis
*Elderly or iodine-deficient regions most common
*Iodine therapy or surgery option
*Uptake results
* Normal
* Suppresses rest of gland
30
what is chronic thyroiditis
*Hashimoto’s
*Autoimmune
* Elevated thyroid antibodies
*Middle-aged females
*Diffusely enlarged gland, non-tender, firm
* Cells inefficient at organification, enlarge to compensate
*Uptake results
* 50-70% (3-5% present at this stage)
* Decreased over time
31
What is subacute thyroiditis
*Typically, tender gland
*Most common causes:
* Respiratory infection
* Granulomatous thyroiditis
* Silent thyroiditis
* Elderly
* Not tender
* No infection, ? viral
* Postpartum thyroiditis
* Weeks to months post-delivery
32
what is subacute thyroiditis at the hormonal level
*Hormone released as result of inflammation
*Increased thyroid hormone levels, decreased TSH
*Inflammation resolves, thyroid hormones depleted
*Decreased hormone levels, increased TSH
*Uptake results
* Depend on stage, damage, thyroid response
*Hypothyroidism resolves weeks-months
*TSH & RAIU normal
33
thyrotoxicosis factitia
Hyperthyroidism due to intake of excessive thyroid
hormone
34
Struma ovarii thyrotoxicosis
* Benign ovarian tumour
* May release thyroid hormone, inducing thyrotoxicosis
35
Patient preparation for uptake
*Off any interfering medications
*Fast x4 hours
*Thyroid indices for correlation
*Ensure not pregnant
* Fetal thyroid development: 10-12 weeks
* Hypothyrodism or Cretinism
*Breastfeeding
* 131I
* 123I
* TcO4-
