Thyroid Imaging Flashcards
Anatomic imaging modalities
US, CT, MRI
Functional imaging modality
radioactive iodine (I-123 or I-131; I-131 used in treatment for cancer/hyperthyroid)
funciton of PET/CT scan
for staging and re-staging of differentiated thyroid cancer
Is Xray useful for thyroid disease
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
Ultrasound
- 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
which US transducer would you use for thyroid imaging
high frequency transducer (since superficial organ)
is higher frequency associated with more or less depth
less?
use of gel
improves propagation of sound waves
use of doppler on US
see blood flow; can compare to things like cysts
thyroid nodule on US
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
what to look at in suspected nodule
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
complex nodule
mixed features of solid/cystic
Hashimoto’s thyroiditis on US imaging
undulating border, as dark as skeletal muscle, heterogeneous, also a lot of blood flow within gland with Doppler
CT scan functionality in thyroid disease
- 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)
what does nl thyroid look on CT with no contrast
hyperdense, hypervascular
- due to iodine content making it bright
what does nl thyroid look like with contrast
even brighter, see brightness in vascular structures as well
MRI
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
Can you differentiate between solid/cystic nodule on MRI
no
can you see microcancer on MRI
NO
negatives of MRI
can’t differentiate between solid/cystic and can’t see microcancer
PET/CT scan
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
which organs will show higher uptake of contrast in PET scan
brain, heart– higher metabolic so take more glucose from the contrast
Iodine scan
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)
what agents are used for iodine scan
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
what kind of camera used for iodine scan
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
how long after ingesting radioactive iodine are pts imaged
6 hours
what kind of images do you get with gamma camera
planar, not cross-sectional, so need multiple angles/planes
- calculate uptake with thyroid probe
what does cold nodule look like on I-123 scan
doesn’t take up iodine– white on black and white scan
- can be solid or cystic
is a cold nodule solid or cystic
either– have to do US to tell. If solid, do biopsy
is a cystic cold nodule benign or malignant
benign
risk of cancer in solid cold nodule
15-25%
Hot nodule
increased activity in nodule but can also have less uptake in nl gland
- malignancy unlikely in functioning nodule (
likelihood of cancer in nonfunctioning nodules
5-10%
what might also take up iodine in Iodine scan but be normal
normal low-level salivary gland activity
what modality can reliably differentiate between benign and malignant thyroid disease
none
next step if suspicious of a lesion
fine needle aspiration (FNA)
generally speaking what size nodules should be evaluated for malignancy
> 1 cm
- occasionally some nodules
imaging test of choice to evaluate thyroid lesion size, location, and simple cyst vs not simple cyst
ultrasound
imaging test of choice to evaluate a pt with hyperthyroidism
radioactive iodine scan
where are thyroid mets often found
lungs, bones
