Thyroid: Iodine-123

Overview

The Thyroid Imaging Study with radioiodine demonstrates the distribution of functioning thyroid tissue, including ectopic tissue, since thyroid tissue is the only tissue that concentrates large amounts of iodine. The Thyroid Uptake Measurement measures the metabolic activity of the thyroid gland as reflected in its extraction of iodine from the blood.

Indications

  • Evaluation of palpable nodules.
  • Evaluation of an abnormal gland with palpation, but without definite nodules.
  • Evaluation of patients who had irradiation of the head and neck in childhood with or without palpable nodules.
  • Evaluation for ectopic thyroid tissue, e.g. struma ovarii (image over pelvis) and lingual thyroid (image upper neck and jaw).
  • Diagnosis of Graves's disease
  • Evaluation of subacute and chronic thyroidistis
  • Evaluation of patients who had radiation of the head and neck in childhood with or without palpable nodules
  • Evaluation of primary congenital hypothyroidism

Study Description

The patient is given the radiopharmaceutical (I-123) orally. Images with uptake results are taken at 6 and/or 24 hours after ingestion of the capsule(s). (Dependent on the location, time will vary of when uptakes and/or imaging will be completed. Please see specific hospital Schedule Guidebook.) During uptake measurement portion the camera/uptake probe will take counts over the patient thigh and neck for 2-3 minutes each. During the imaging portion the camera is positioned over the patients neck while they lay on the table, each image can take 5-10 minutes.

Examination Time

  • Initially, 15 minutes for radiopharmaceutical administration.
  • Imaging with uptake at 6 and/or 24 hours for 30 minutes each.
  • Uptake only at 24 hours (if applicable-only done when imaging/uptake is done at 6 hours)

Patient Preparation

  • Ensure the patient is not pregnant or breastfeeding.
  • Off anti-thyroid medications for 4-7 days
  • Off Thyroxine (T4 therapy) for 4-6 weeks
  • Off Triiodothyronine (T3 therapy) for 2 weeks
  • No contrast studies (IVP's, CT's, etc.) 4 weeks prior to exam
  • Off Amiodarone (anti-arrhythmic drug) for 3-6 months
  • Off Iodine containing multivitamin for 2 weeks
  • Off kelp and iodine solution (Lugols) for 2 weeks
  • Off Expectorants (cough/cold medicine) for 2 weeks
  • No Topical iodine (surgical skin prep) for 2 weeks
  • NPO (nothing by mouth) 6 hours before and for 1 hour after the ingestion of the radiopharmaceutical
  • Bring list of medications and a copy of thyroid lab results (if applicable)