Parathyroid

Question 1

RP

Dose

Answer 1

Tc99m Pertechnetate: 5-23 mCi
Tl201 thallium chloride - 2-3 mCi
Tc99m Sestamibi - 20-25 mCi
I123 sodium iodide - 200-400 μCi

Question 2

Indications

Answer 2

Detect and localize parathyroid adenoma
Localize recurrent hyperparathyroidism
Detect and localize primary and secondary parathyroid cancer

Question 3

Contraindications

Answer 3

Patient on calcium medications
Patient on thyroid meds – must DC for 5 days
Recent contrast study – 7-10 days

Question 4

Patient Prep

Answer 4

None

Question 5

Positioning

Answer 5

Supine, pillow under shoulders, head back, neck extended

Question 6

Target Organ
Critical Organ
Method of Localization
Route or Excretion

Answer 6

Target Organ – Parathyroid gland, thyroid gland, parathyroid adenoma
Critical Organ – GI tract, salivary glands, heart
Method of Localization
TcO4 – Active Transport
Tl201 – K+ pathway with Na+/K+ pump
Tc99m MIBI – Passive transport
I123 – Organified and trapped by thyroid
Route of Excretion – Urinary

Question 7

Procedure - MIBI only

Answer 7

Inject RP and wait 15-20 min and image
ANT neck w/ 1.5 zoom, ANT neck w/ 2.0 zoom, LAO neck w/ 2.0 zoom, RAO neck w/ 2.0 zoom
2-3 hours post injection - Repeal immediate images
Sestamibi is taken up by both thyroid and parathyroid, MIBI in the thyroid and parathyroid washes out and concentration in the parathyroid adenoma remains
SPECT possible at 2+ hours

Question 8

Procedure - Tl201/ Tc99

Answer 8

Inject Tl201 and wait 5 min to image Tl201 uptake
ANT neck w/ 1.5 zoom, ANT neck w/ 2.0 zoom, LAO neck w/ 2.0 zoom, RAO neck w/ 2.0 zoom
Inject TcO4- and wait 20 minutes to image again
Subtract dual isotope from single isotope
Tl201 is taken up by both, TcO4- is taken up by thyroid only
Subtract TcO4- in thyroid only from Tl201 in thyroid and parathyroid. Result in abnormal parathyroid tissue remaining

Question 9

Procedure - MIBI/ I123

Answer 9

Give patient 1123 capsule and wait 4 hrs to image
Inject Tc99m MIBI and wait 30 minutes and image again
Subtract dual isotope from single isotope
Tc99m MIBI taken up by both, I123 taken up by thyroid only
Subtract I123 from Tc99m MIBI. Only abnormal parathyroid tissue remaining.

Question 10

Computer Set Up

Answer 10

LEAP
Statics: 128x128x8 or 64x64x16
1 million counts or 5-15 minutes
SPECT - Elliptical 360°, 64 stops, 20-30 sec/stop, 128x128

Question 11

Normal

Answer 11

Normal PTH – 160-350 ng/L

Symmetric, homogenous uptake

Question 12

Abnormal

Answer 12

Increased areas of uptake in and around thyroid