Clinical usefulness of fusion of 131I SPECT and CT images in patients with differentiated thyroid carcinoma.

Precise localization of the foci of (131)I uptake for management of patients with differentiated thyroid carcinoma can be difficult because of a lack of anatomic landmarks. The objective of the present study was to demonstrate the clinical usefulness of (131)I SPECT/CT fusion images in patients with differentiated thyroid carcinoma. METHODS: CT and SPECT were performed 7 d after administration of a therapeutic dose of (131)I to 17 patients with differentiated thyroid carcinoma. External markers were placed at 3 locations on the skin of the patient to adjust the sections of CT and SPECT in the same geometric plane. Fusion images were constructed by combining the digital CT and SPECT images on a computer workstation. The data from both planar and SPECT (131)I images and CT images were first separately assessed by 2 nuclear medicine physicians. (131)I SPECT/CT fusion images were then interpreted. Fusion images were considered to improve image interpretation in comparison with CT and scintigraphy separately when they provided better localization of sites of increased radiopharmaceutical uptake. RESULTS: Both CT and (131)I SPECT showed the pathologic sites in 5 of 17 patients (29%). Fusion images were considered to be of benefit in 15 of 17 patients (88%). In 4 patients, CT showed normal-sized lymph nodes, whereas (131)I SPECT showed abnormal findings. In 3 patients with bone metastasis, fusion images confirmed the precision of the localization of abnormal (131)I uptake. Five bone metastases and 1 muscle metastasis were occult and were not seen on the CT images. Finally, (131)I scintigraphy findings were abnormal for 2 patients for whom the CT findings were initially considered normal. Fusion images confirmed the precision of the localization of physiologic (131)I uptake. CONCLUSION: For registration of anatomic and functional images in fusion imaging, the method using external markers was simple and practical. (131)I SPECT/CT fusion images using this technique may improve anatomically limited interpretation of (131)I scintigraphy alone in patients with differentiated thyroid carcinoma.