Endocrine Flashcards
Rationale for parathyroid imaging
Hyperparathyroidism, localization of parathyroid adenomas
Parathyroid contraindications
Pregnant, breast feeding, recent nuc med study, inability to stay still
Parathyroid pt prep
No special prep, just focused Hx and labs
Serum calcium and PTH levels measured 1 month prior
Parathyroid RP and doses
99mTc Sestamibi 20-30mCi
99mTc sodium pertechnetate 2-10mCi
I123 Sodium iodide 200-600 uCi oral
Parathyroid RP injection to imaging time
10 mins with Sestamibi
30 mins with pertechnetate
4 hours with I123
Parathyroid collimator
LEHR and pinhole
3 ways parathyroid imaging protocols
Dual phase Sestamibi
Dual isotope with tech and Sestamibi
Dual isotope with i123 and sestamibi
Parathyroid dual phase protocol
-Inject Sestamibi
-Take ANT images 10-30 mins after inj
-Wait 1.5-2.5 hours and take delay ANT images
-take spect or pinhole images in ANT and ANT OBL
Parathyroid dual isotope tech/Sestamibi protocol
-Inject either one first but wait 10 mins with Sestamibi and 30 mins with tech
-obtain images of head and neck after appropriate wait times
*can immediately inject next RP after images are taken of first RP
Parathyroid dual isotope i123/sestamibi
*administer i123 FIRST and wait 4 hours
-take ANT images
-inject sestamibi and wait 10 mins
-take ANT images
Parathyroid subtraction technique
For tech/sestamibi: subtract the tech images from the sestamibi images
For i123/sestamibi: subtract the i123 images from the sestamibi images
What reconstruction method is recommended for spect parathyroid
Iterative reconstruction
How is iodine/iodide localized
Accumulated in thyroid follicular cells by an active transport mechanism (trapping) and then oxidized and bound to tyrosyl residues on thyroglobulin (organification)
Indications of thyroid imaging
-Differentiation of hyperthyroidism (graves vs toxic nodular goiter)
-Detection and evaluation of hyperthyroidism and hypothyroidism
-localization of ectopic thyroid tissue
-exaltation of neck mass
-differentiation of thyroiditis
Indications of thyroid uptake
-determination of i131 therapy dose
-differentiation of subacute or painless thyroiditis and factitious hyperthyroidism from graves
-confirmation of hyperthyroidism due to Graves’ disease
Contraindications to thyroid uptake and imaging
Pregnant, breast feeding, recent nuc med study
Pt not properly prepped
Pt prep for thyroid uptake and imaging
AVOID:
-thyroid hormones and antithyroid drugs
-iodine containing medications
-food rich in iodine
-large meals for 2 hours prior and 2 hours post administration
How long to D/C contraindicated meds for thyroid uptake and imaging
-Antithyroid drugs withheld 2-4 days
-T4 therapy withheld 4-6 weeks
-T3 therapy withheld 2 weeks
-iodinated contrast within 3 weeks
-Amiodarone d/c for 6 months
-Betadine within 2-4 weeks
Thyroid uptake and imaging RPs
I123 sodium iodide 100-300 uCi
99mTc pertechnetate 2-10 mCi
I131 sodium iodide 0.004 - 0.01 mCi
Collimator for thyroid imaging
Pinhole
Thyroid administration to uptake time
Tech: immediately
I123: 2-6 and 18-24 hrs
I131: 2-6 and 18-24 hrs
Thyroid administration to imaging time
Tech: 15-30 minutes
I123: 3-4 hours
I131: not recommended for imaging, uptake only
Which RP is not recommended for thyroid imaging, uptake only
I131
Thyroid imaging views
ANT
LAO, RAO
ANT with marker
Where to put radioactive markers for thyroid imaging
Sternal notch and thyroid cartilage
On nodules
Where/how to use uptake probe
25-30 cm and take counts for 1 min
Neck
Thigh
Phantom
Room background
Collimator for WB thyroid imaging
LEAP
Percent Radioiodine uptake (RAIU) formula
Neck counts - thigh counts
______________________________
Phantom counts - background counts
I131 is no longer useful for:
Imaging the thyroid gland, as a diagnostic tracer
I131 is useful for
WB imaging after a thyroidectomy,
therapy for hyperthyroidism, thyroid remnant ablation, and thyroid cancer
I131 T1/2 and energy
T1/2: 8.01 days
363 keV
I131 emission
Beta and gamma
I131 produced by
Fission/nuclear reactor
I123 decays by
Electron capture
I123 T1/2 and energy
T1/2: 13 hr
159 keV
I123 uses
Thyroid imaging + uptake
Calculating an uptake only, pretreatment diagnostic mets survey for thyroid cancer
Normal values for 4 hr uptake
6-18%
Normal values for 24 hr uptake
10-35%
In parathyroid study, tech and i123 go where? Ate sestamibi and thallium go where? And which is subtracted from which?
- Tech and i123 go to thyroid
- Mibi and thallium go to thyroid and abnormal parathyroid (but wash out of thyroid
- Subtract 1-2
