An evaluation of usefulness of CT/SPECT imaging of I-131 in the post thyroidectomy patients with thyroid carcinoma

Objectives CT/SPECT system has been reported to be useful for evaluation of abnormal uptake on a radioionuclide imaging, because the system provides more anatomic information than planar imaging. Therefore, the system may have a superior ability to distinguish abnormal uptake from physiological uptake. We hypothesized that CT/SPECT imaging of radioiodine-131 (I-131) might be able to reduce false-positive and false-negative interpretations, in particular, the system might be useful to evaluate an uptake in the neck and mediastinum to differentiate abnormal uptake in metastatic tumors from physiological uptake of the esophagus. The purpose of this study was to evaluate the usefulness of CT/SPECT imaging of I-131 in the patients with thyroid carcinoma, who received I-131 therapy.

Methods Thirty-eight patients after the total thyroidectomy for differentiated thyroid carcinoma were studied. Four days after the administration of I-131 (5.55GBq), planar and CT/SPECT imaging acquisition were performed in the neck and mediastinum. First, two radiologists interpreted the planar imaging only, and after that, they performed interpretation based on planar imaging and CT/SPECT imaging. Chi square test was performed to estimate whether there was a significant difference or not in these interpretations.

Results The sensitivity improved from 83.3% to 100% and the specificity also improved 50.0% to 100%, by addition of CT/SPECT. A statistically significant difference was detected by Chi square test (p < 0.005) in the mesiastinum, although, no significant difference was detected in the neck(p = 0.464).

Conclusions CT/SPECT imaging improved the sensitivity and specificity. This result showed that CT/SPECT must reduce the false-positive and false-negative interpretations. CT/SPECT may be useful for evaluation of uptake in the neck and mediastinum