lecture 3 Flashcards
purpose of thyroid scans
- correlate physical findings with functional imaging
- in conjunction or separate from uptakes
Thyroid scan indications
- differential diagnosis of thyrotoxicosis
- gland and nodule assessment
- therapy doose determination
- ectopic tissue
- assess treatment effectiveness
- wb thyroid cancer
Radiopharmaceuticals used
- 99mTcO4- (IV)
- 131I NaI (Oral) *
- 123I NaI (Oral)
- 201 Tl (IV)
- 99mTc MIBI (IV)
- 18F-FDG (IV)
- 123I/131I MIBG (IV)
- 111In-Octreotide (IV)
TcO4 procedure and prep
- 111-185 MBq
- scan at 20 min
- 4 hr fast
- discontinue meds
- requires iodine for accurate uptake
- biodistribution
131-INaCl procedure and prep
- 3.7-15 MBq
- scan @ 2-6 hrs
- 4 hr fast
- discontinue meds
- pinhole
- uptake and scan with one radiopharmaceutical
- bidistribution
positioning
- supine
- chin up
- neck extended
pinhole aperture
- 3-6 mm
- small, increases resolution, decreases sensitivity
- spatial resolution: 5mm vs. 1 cm
- parrallex effect
Views in the scan
- standard distance
- standard views: ant, 45 lao, 45 rao
- extra views: 10 cm anterior, marker
- 100-250 kcounts per view
Describe a normal thyroid scan
*Homogenous uptake
* Normal variations:
* Pyramidal lobe
* Left < Right
* Lateral portions of lobe warmer
* Isthmus decreased
* Oblique defect in contralateral lobe
* Due to cartilage
* Esophageal activity
abnormal thyroid scan
*Non (poor) visualization
*Nodules (hot or cold)
*Non-homogenous uptake
*Shape
causes of non or poor visualization
*Iodine pool increased
*Foods that free thiocyanates
* (Iodine competition)
*ATD’s
* PTU
* Methimazole
*Thyroiditis
*1, 2, 3-degree hypothyroidism
*Ectopic thyroid
incidence of nodules
- more common in women
- increase risk with age
cold, hot, warm, indeterminate nodules
- 85-95% are cold
- Cold - increased risk malignancy
solitary vs multiple
- Singular - increased risk malignancy
- Cold solitary
- Malignant 10-20%
- Adenoma
- Cyst/hyperplasia
- Fibrosis
discordant nodules
◦ 99mTc hot, 123I cold
◦ Trapping, but no organification
◦ Rapid turn over or wash out
◦ Concern for malignancy
younger, male, recent nodue
increased risk of malignancy
query malignany
- FNA
- Ultrasound
graves disease
*Autoimmune
*Middle-aged females
*Diffusely enlarged, firm, non-tender gland
* Occasionally gland not enlarged
*Elevated uptake
*Diffuse homogenous scan
*Treatment
* ATD
* 131I
* Surgery
hashimotos
- Autoimmune: lupus, RA
- Organification defect
- Elevated thyroid antibodies
- 131I uptake depends on stage
- Scan variable
- Typically, diffusely enlarged
- Pyramidal lobe often visualized
Reidels struma
- Unknown etiology
- Rare; very hard gland
- Cold scan
Acute thyroiditis
-bacterial infection
-pain, fever, chills; hot, tender, enlarged gland
-uptake varies depending on stage
-scan appears as cold region
Viral acute thyroiditis
• Suppression in recovery phase
• Inhomogenous, regional or focal hypofunction
Subacute thyroiditis common causes
•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
Subacute thyroiditis
•Typically, tender gland
•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 in weeks/months
•TSH & RAIU normal
