Thyroid Imaging

Question 1

Anatomic imaging modalities

Answer 1

US, CT, MRI

Question 2

Functional imaging modality

Answer 2

radioactive iodine (I-123 or I-131; I-131 used in treatment for cancer/hyperthyroid)

Question 3

funciton of PET/CT scan

Answer 3

for staging and re-staging of differentiated thyroid cancer

Question 4

Is Xray useful for thyroid disease

Answer 4

Not for detecting thyroid lesion but you can have incidental findings that suggest thyroid lesions – mass effect or on tracheal air column

This is not specific, as other things can also cause this

Question 5

Ultrasound

Answer 5

• best modality to detect and characterize thyroid nodule (i.e. solid vs cystic) and lymph node mets in postop pt of thyroid cancer
• can also use as real-time guidance for FNA
• no radiation, -real time, doppler capability

Question 6

which US transducer would you use for thyroid imaging

Answer 6

high frequency transducer (since superficial organ)

Question 7

is higher frequency associated with more or less depth

Answer 7

less?

Question 8

use of gel

Answer 8

improves propagation of sound waves

Question 9

use of doppler on US

Answer 9

see blood flow; can compare to things like cysts

Question 10

thyroid nodule on US

Answer 10

discrete lesion within thyroid gland that is radiologically distinct from surrounding thyroid parenchyma
- to check if nodule, want to look in 2 perpendicular/orthogonal plane

Question 11

what to look at in suspected nodule

Answer 11

does it look similar/different from rest of thyroid

• size, bulges, shadowing, look with doppler to see if flow or not when dark nodule
• can have solid, cystic, mixed

Question 12

complex nodule

Answer 12

mixed features of solid/cystic

Question 13

Hashimoto’s thyroiditis on US imaging

Answer 13

undulating border, as dark as skeletal muscle, heterogeneous, also a lot of blood flow within gland with Doppler

Question 14

CT scan functionality in thyroid disease

Answer 14

• useful to define extension to lymph nodes and distant metastasis
• good anatomic evaluation of thyroid bed
• can use contrast to better ID tissue
• good for looking at LN we can’t get to on US (deep to clavicle, under mandible)

Question 15

what does nl thyroid look on CT with no contrast

Answer 15

hyperdense, hypervascular

• due to iodine content making it bright

Question 16

what does nl thyroid look like with contrast

Answer 16

even brighter, see brightness in vascular structures as well

Question 17

MRI

Answer 17

useful in identifyng infiltrative disease not so much for nodules, particularly in post-therapy neck where anatomy is distorted

• good for looking at deeper structures like lymph noes
• detection of deep nodal tissue- T2– slightly hyperintense

Question 18

Can you differentiate between solid/cystic nodule on MRI

Answer 18

no

Question 19

can you see microcancer on MRI

Answer 19

NO

Question 20

negatives of MRI

Answer 20

can’t differentiate between solid/cystic and can’t see microcancer

Question 21

PET/CT scan

Answer 21

combo of functional and anatomic images

• done with radioactive injection
• have to know half life of substance
• if you see something on PET, use CT to see exactly where…can’t really tell depth on PET

Question 22

which organs will show higher uptake of contrast in PET scan

Answer 22

brain, heart– higher metabolic so take more glucose from the contrast

Question 23

Iodine scan

Answer 23

demonstrates distribution of functioning thyrod tissue, including ectopic tissue, since thyroid only tissue that concentrates large amounts of iodine
- must discontnue iodine containing preparation/meds that could potentially affect ability of thyroid tissue to accumulate iodide (contrast, thyroid meds, amiodarone)

Question 24

what agents are used for iodine scan

Answer 24

I 123– evaluate function of thyroid gland and thyroid nodule n pt with abnormal function
- half life of I-123 = 13 hrs

I-131– diagnostic/therapeutic role; half life is 8 days. Detects local and distant thyroid cancer mets; treat of hyperthyroidism/hyperfunctioning nodule as well as for differentiated thyroid cancer

Question 25

what kind of camera used for iodine scan

Answer 25

gamma camera; can’t use CT scan

• source of radiation from scanner for CT
• source of radiation for iodine scan is from pt–ingests iodine capsule. Gamma camera detects gamma radiation emitting from pt

Question 26

how long after ingesting radioactive iodine are pts imaged

Answer 26

6 hours

Question 27

what kind of images do you get with gamma camera

Answer 27

planar, not cross-sectional, so need multiple angles/planes

- calculate uptake with thyroid probe

Question 28

what does cold nodule look like on I-123 scan

Answer 28

doesn’t take up iodine– white on black and white scan

- can be solid or cystic

Question 29

is a cold nodule solid or cystic

Answer 29

either– have to do US to tell. If solid, do biopsy

Question 30

is a cystic cold nodule benign or malignant

Answer 30

benign

Question 31

risk of cancer in solid cold nodule

Answer 31

15-25%

Question 32

Hot nodule

Answer 32

increased activity in nodule but can also have less uptake in nl gland
- malignancy unlikely in functioning nodule (

Question 33

likelihood of cancer in nonfunctioning nodules

Answer 33

5-10%

Question 34

what might also take up iodine in Iodine scan but be normal

Answer 34

normal low-level salivary gland activity

Question 35

what modality can reliably differentiate between benign and malignant thyroid disease

Answer 35

none

Question 36

next step if suspicious of a lesion

Answer 36

fine needle aspiration (FNA)

Question 37

generally speaking what size nodules should be evaluated for malignancy

Answer 37

> 1 cm

- occasionally some nodules

Question 38

imaging test of choice to evaluate thyroid lesion size, location, and simple cyst vs not simple cyst

Answer 38

ultrasound

Question 39

imaging test of choice to evaluate a pt with hyperthyroidism

Answer 39

radioactive iodine scan

Question 40

where are thyroid mets often found

Answer 40

lungs, bones