Evaluation of fusion imaging of 99mTc- MDP SPECT and low-dose CT in assessing suspected spinal bone metastasis

Abstract

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Objectives: To evaluate retrospectively the diagnostic value of single photon emission computed tomographic (SPECT) imaging, low doge computed tomographic (CT) imaging and fusion imaging of SPECT and low-dose CT in assessing suspected spinal bone metastases for those cancer patients with abnormal uptakes on 99mTc- MDP planar whole body scan.

Methods: SPECT and low dose CT were performed with a combined SPECT/low-doge CT system in 49 cancer patients with abnormal uptake only in spine (lesion number less than 3) on 99mTc- MDP whole body scan. Image diagnostic criteria were as following: On 99mTc- MDP SPECT, lesions involved the pedicle of vertebral arch were defined as metastasis, and lesions located in the small vertebral articulation or protruded to the vertebra as benign. On low-dose CT, osteolytic lesions in the vertebra were regarded as metastasis, and lesions located in the small vertebral articulation or lip-like hyperplasia/osteophyte formed in the surround of the vertebra, as benign. On fusion imaging, lesions involved the pedicle of vertebral arch on SPECT and/or osteolytic changes on CT were regarded as metastasis, and lesions located in the small vertebral articulation on SPECT and/or hyperosteogeny existed on CT, as degeneration. All patients were diagnosed by the follow-up MRI or high-resolution CT. In addition, of the 49 patients, image diagnosis with low-dose CT was compared with that high resolution CT in 155 vertebras in 21 patients.

Results: Of the 49 patients, total of 94 uptake foci were found on whole body scan. Final clinical diagnosis for the lesions was metastasis 51 and benign 43. For assesing spinal bone metastasis, the diagnostic sensitivity, specificity and accuracy was 81.4%, 72.5% and 76.6%, respectively, by using 99mTc- MDP SPECT. And was 83.7%, 87.7% and 92.7%, respectively, by using low-dose CT. When fusion imaging was used, the diagnostic sensitivity, specificity and accuracy improved into 100%, 96.1%, and 97.9%, respectively. Through vertebra by vertebra comparison, Imaging diagnostic interpretations of low-dose CT were concordance with that of high resolution CT in 94.2% of the 155 vertebras.

Conclusions: Fusion imaging of SPECT and the low-dose CT provided an increased diagnostic value compared with separate sets of SPECT and low-dose CT images for assesing spinal bone metastasis in cancer patients, and should be used as a supplementary examination to the 99mTc- MDP whole body scintigraphy for the patients with undetermined abnormal uptakes in spinal.