SPECT-guided CT for evaluating foci of increased bone metabolism classified as indeterminate on SPECT in cancer patients.

UNLABELLED Hybrid cameras combining SPECT and spiral CT offer the opportunity to obtain a diagnostic-quality CT image of scintigraphically suggestive lesions that directly correlates with the SPECT image. The field of view of the CT scan can be adapted on the basis of the SPECT findings ("SPECT-guided CT"). The aim of the present study was to investigate the value of SPECT-guided CT in the assessment of foci of increased bone metabolism classified as indeterminate on SPECT. METHODS Of 272 consecutively examined patients with histologically confirmed malignancy who underwent bone scintigraphy, 112 (41%) required further workup by SPECT because a definite diagnosis could not be established using whole-body planar scintigraphy alone. In 57 of these patients, SPECT was accompanied by inline CT over the body region of interest; the remaining 55 subjects underwent only stand-alone SPECT for logistic reasons. The 57 SPECT/CT studies were retrospectively evaluated by readers who were unaware of the clinical pretest probability and the findings on the planar scans. In total, 52 lesions in 44 patients were rated as indeterminate on the SPECT images. Afterwards, the corresponding SPECT/CT images were analyzed and the findings previously rated as indeterminate were classified either as definitely benign, indeterminate, or definitely malignant. RESULTS Of the 52 indeterminate findings on SPECT, 33 (63%) could be correlated with benign findings on CT. These findings involved mostly osteochondrosis, spondylosis, and spondylarthrosis of the spine. Fifteen lesions (29%) could be correlated with osteolysis or sclerotic metastases on CT. Even after analysis of the SPECT/CT images, 4 lesions (8%) remained indeterminate. These lesions were in the ribs and the scapula. CONCLUSION SPECT-guided CT was able to clarify more than 90% of SPECT findings classified as indeterminate in an analysis that was masked as to clinical pretest probability and the planar scan findings. Further studies carefully addressing the cost efficiency of this new technology and its actual clinical value are encouraged by this observation.