Radionuclide thyroid imaging nuclear med

Radionuckide

1. Radionuclide Thyroid Imaging

2. Indications: Assessment of the gland size and shape. Assessment of the gland function (hyper- or hypo- thyroidism ). Post-operative (e.g. post- thyroiectomy ) assessment. Detection of thyroid nodules and differentiate between cold and hot ones. Detection of ectopic thyroid tissue . CONTRAINDICATIONS: Radioisotope is secreted in breastmilk. Women who are breastfeeding need to make special preparations after the test to stop breastfeeding for 24 hours. Expressing breastmilk before the scan is an alternative option. This study may not be suitable for pregnant women. The benefit versus risk should be discussed with the nuclear medicine specialist.

3. Radiopharmaceuticals: 99m Tc Pertechnetate  (mostly commonly used): Mode of action: Pertechnetate ions are trapped in the thyroid tissue by an active transport mechanism, but are not organified . It carries the properties of  99m Tc: Gamma-emitter = 140 Kev Physical half life = 6 hrs. Dose: 3-5 mCi . Route: IV. Advantages: cheap and available.

4. 123  I-sodium iodide: Mode of action: Iodide ions are trapped by the thyroid in the active transport, and organified , allowing overall assessment of thyroid function. Gamma-emitter = 159 Kev Half life: 13 hours. Dose: 100 mCi Route: orally. Advantage: it is the agent of choice, not emit B particles Disadvantage: expensive with limited availability (as it is a cyclotron product).

5. 131 I-sodium iodide: Mode of action: as Gamma-emitter = 364 Kev Half life: 8 days. Dose: 100 mCi (5 mCi orally in case of whole body scan) Route: Orally. Disadvantage: expensive with limited availability (as it is a cyclotron product) and emits B particles (not pure gamma-rays).

6. Equipment: Large field gamma camera with  pinhole  collimator (in cases of I-labeled pharmaceuticals) with 20% window at 140 kev of  99m Tc and 159 kev for  123 I, 20% window at  364 kev of  131 I Patient preparation: Stoppage of anti-thyroid drugs e.g. Carbimazole for 2 days before scanning. Stoppage of thyroid hormones e.g. thyroxin 4 weeks prior to examination. Stop food containing iodine as cabbage, turnip nd sea food The patient should avoid IV contrast media e.g. for IVP for 4 weeks before examination. Glass of water before imaging to clear esophageal activity

7. Patient position: The patient lies supine, with extended neck and the camera anterior to the neck. Technique: Static scan Imaging starts 15 - 20 min after IV  99m Tc injection and 4 hours after IV  131 I. The patient is asked not to move and not to swallow or talk during imaging Views : Anterior view andr ight and left anterior oblique 45 0  views. Anterior view with markers to the thyroid cartilage and the suprasternal notch.

8. Dynamic scan Imaging starts immediately after IV   99M Tc injection and images taken every 15 sec. for 30 min. It is useful in assessment of perfusion and blood supply of the gland and lesions detected. Whole-body scan (using  131 I): Used for locating sites of metastasis

9. Interpretation: (normal thyroid scan) The normal gland exhibits homogenous distribution of the tracer. Its configuration has the appearance of a butterfly or wide “V”. Each lobe has a height about 5 cm  (with the right being 0.5 cm larger than the left in ¾ of patients)  and   width of about 2 cm. The size of the isthmus varies from thin and barely visible, to wide producing an intense image. The pyramidal lobe can be found in a small proportion of normal scans. No retro-sternal extension.

10. Thyroid Whole body scan a whole body scan ( wbs ) is a scan performed in a nuclear medicine. This scan is done to check for the return of spread of thyroid cancer cells. Patients must be off thyroid medications 3-4 weeks. For thyrotoxic patients neomercazole etc. must be cease.

11. Contraindication Pregnant patients must not be treated with iodine 131. Breastfeeding patients should not breastfeed following a treatment. Patients preparation Discontinue thyroid medications ( eg. Levothyroxine sodium Synthroid, levoxyl , and levothroid . Npo for 4 hours before study. Dosage 2 mci of iodine 131 5 mci if there is operation or undergone rai therapy (radio active iodine therapy).

12. Procedure: Check the request for a whole body scan form the patient . Check how many mci is requested by the doctor (see the refered request). Perform the procedure, let the patient drink the iodine 131 using a straw and don’t let spit. Tell the patient to go back after 2 days (48 hrs.) Position hyperextended neck/semi Collimator used: High energy

13. Radiopharmaceutical used: Iodine- 131 Testing time: Allow 2-3 hours in the nuclear medicine department. Post therapy: The purpose of this is to determine if there is still iodine left in the thyroid of the patient. The activity of iodine should be low when you scan during post-therapy.