BACKGROUND: The lack of anatomical details in standard 131Iodine
whole body scanning (131I WBS) interferes with the proper
localization of metastatic differentiated thyroid carcinoma (DTC)
lesions. In addition, nearby or overlapping variable physiological
distribution of 131I may affect the specificity of 131I uptake,
giving indeterminate results. The aim of this study was to demonstrate
the clinical usefulness of simultaneous co-registration
of 99mTc MDP bone scanning as an anatomical landmark with
131I scanning in the evaluation of metastatic DTC.
MATERIAL AND METHODS: Twenty-five patients (16 females
and 9 males, mean age ± SD = 52 ± 13 years) with metastatic
DTC (17 papillary, 8 follicular), were included. Whole
body scanning using a 256 x 1024 matrix and an 8 cm/min
scan rate were obtained 48 hours after oral administration of
185-370 MBq 131I and 2 hours after IV administration of 185-370 MBq 99mTc MDP using a dual head gamma camera
equipped with high energy parallel hole collimators. Occasionally,
additional simultaneous co-registration of localised
detailed images was also performed using a 256 x 256 matrix size. The two planar images were fused with optional fusion
of SPECT images.
The data from standard 131I scanning and fused 131I/ 99mTc-MDP
scanning were separately assessed by two nuclear medicine
physicians. Fusion images were considered to improve image
interpretation in comparison with standard 131I scanning when
they provided better localization of lesions.
RESULTS: All lesions in the present study were validated by
radiological images and clinical follow up for at least 12 months.
Forty-eight metastatic lesions were confirmed as follows: 2 in
the skull, 10 in the neck, 20 in the thorax, 12 in the pelvic-abdominal
region and 4 in the extremities. Standard 131I WBS
showed 54 extra-thyroidal foci with 8 false positive lesions of
which 2 were located in the scalp and 6 in the pelvic-abdominal
region extra-skeleton (i.e. sensitivity 100%, specificity 86%). Out
of the 48 validated lesions, 16 were indeterminately localized:
10 in the thorax (3 mediastinal nodal lesions, 5 vertebral lesions
and 2 ribs) and 6 in the pelvic-abdominal region (2 upper sacral,
2 sacroiliac region and 2 ischial bone). Fusion images confirmed
the precise localization of the pathological uptake in the
validated 48 lesions (sensitivity 100%, specificity 100%). There
were 2 (4%) indeterminate lesions in fused planar imaging that
were clearly localized via fused SPECT images.
CONCLUSIONS: Fusion images using simultaneous co-registration
of 131I and 99mTc MDP scanning is a simple and feasible
technique that improves the anatomically limited interpretation
of scintigraphy using 131I alone in patients with metastatic differentiated
thyroid carcinoma. The diagnostic advantage of this
technique seems to be more apparent in the thoracic and pelvic-
abdominal regions in contrast to the neck and extremities
