(124)I positron emission tomography versus (131)I planar imaging in the identification of residual thyroid tissue and/or metastasis in patients who have well-differentiated thyroid cancer

Thyroid. 2010 Aug;20(8):879-83. doi: 10.1089/thy.2009.0430.


Background and objective: (124)I emits a positron and can be imaged with a positron emission tomography (PET) scanner. The objective of this study was to compare the ability of diagnostic (124)I PET images versus (131)I planar whole-body imaging in detecting residual thyroid tissue and/or metastatic well-differentiated thyroid cancer (WDTC).

Methods: Patients were recruited prospectively for this study who (i) had WDTC, (ii) were suspected of having metastatic WDTC, and (iii) were referred for (131)I whole-body dosimetry. The prescribed activity was 1-2 mCi (37-74 MBq) and 1.7 mCi (62.9 MBq) for (131)I and (124)I, respectively. For each image, one blinded reader (D.V.N.) categorized every focus of (131)I and (124)I radioiodine uptake as 1 = definite physiological uptake/artifact, 2 = most likely physiological uptake/artifact, 3 = indeterminate, 4 = residual thyroid tissue/metastases in the neck/bed, 5 = most likely metastases, or 6 = definite metastases. Foci categorized as 4, 5, or 6 were considered positive. When available, foci categorized as 4, 5, or 6 were correlated with other diagnostic studies.

Results: Of the 25 patients, 8 patients (32%) had more positive foci on (124)I images than on (131)I, of which 3 patients to date have had metastases confirmed in one or more of the additional positive (124)I foci. (124)I demonstrated the same number of foci as on (131)I in 16 patients (14 with no positive foci, and 2 with two positive and five positive foci each). One patient had one additional positive focus on (131)I not seen on (124)I, which has not yet been confirmed as a metastasis. A total of 97 positive foci were identified on either (124)I or (131)I. (124)I identified 49 positive foci not seen with (131)I, and (131)I identified one positive focus not seen with (124)I.

Conclusion: Relative to (131)I planar whole-body imaging, (124)I PET identified as many as 50% more foci of radioiodine uptake suggestive of additional residual thyroid tissue and/or metastases in as many as 32% more patients who had WDTC.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Diagnostic Imaging / methods*
  • Female
  • Humans
  • Iodine Radioisotopes / chemistry*
  • Male
  • Middle Aged
  • Neoplasm Metastasis
  • Positron-Emission Tomography / methods*
  • Thyroid Gland / diagnostic imaging*
  • Thyroid Neoplasms / diagnosis*
  • Thyroid Neoplasms / diagnostic imaging*
  • Whole Body Imaging / methods


  • Iodine Radioisotopes