Impact of SPECT and integrated low-dose CT after radioiodine therapy on the management of patients with thyroid carcinoma

Nucl Med Commun. 2004 Dec;25(12):1177-82. doi: 10.1097/00006231-200412000-00004.


Aim: To determine the value of single photon emission computed tomography (SPECT) with integrated low-dose computed tomography (CT) for the interpretation of inconclusive foci in planar I whole-body scans after radioiodine therapy.

Methods: Twenty-five patients with inconclusive findings in planar scanning after ablative radioiodine therapy (3.7 GBq I) due to differentiated thyroid cancer were included. SPECT/CT of the region in question was performed with the Millennium VG Hawkeye (GE Medical Systems). SPECT with and without CT fusion were evaluated by two blinded independent nuclear medicine physicians in a consensus reading (including visual plausibility control). Each focus was judged according to its topographical assignment and clinical interpretation. With regard to therapeutic relevance, this information was evaluated in a focus based and patient based analysis. All evaluations used a binary ranking system. Focus assignments were compared to clinical and imaging follow-up.

Results: Forty-one lesions were observed in 25 patients. According to follow-up, 17/41 (41%) foci were caused by thyroid residue, 13/41 (32%) were caused by metastases, and 11/41 (27%) were not malignant. Of these foci, a SPECT/CT consensus reading assigned 39 (95%) correctly, as fused images of two foci did not pass the visual plausibility control (excluding one patient due to misregistration). For the remaining 39 foci, improved anatomical assignment by SPECT/CT was seen in 17/39 (44%) cases.

Conclusions: The changed interpretation of 15/39 (38%) foci would have been relevant for therapy in the focus based analysis. In the patient based analysis the information was still therapeutically relevant in 6/24 (25%) patients. Furthermore, plausibility control is also crucial in SPECT/CT image fusion in order to rule out artifacts.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Female
  • Humans
  • Image Processing, Computer-Assisted / methods
  • Iodine Radioisotopes / therapeutic use*
  • Male
  • Middle Aged
  • Neoplasm Metastasis
  • Radiopharmaceuticals / therapeutic use*
  • Thyroid Neoplasms / diagnosis*
  • Thyroid Neoplasms / radiotherapy*
  • Tomography, Emission-Computed, Single-Photon / methods*
  • Tomography, X-Ray Computed / methods*


  • Iodine Radioisotopes
  • Radiopharmaceuticals