4 - Bone Metastasis: Single Photon Emission Computed Tomography/Computed Tomography

Abstract

This chapter describes the principal and clinical applications of SPECT/CT for imaging bone metastases. Computed tomography (CT) is an excellent anatomic imaging modality. The precise anatomic localization of the tracer uptake may clarify the nature of the abnormality. Careful analysis of uptake pattern and intensity and the use of single photon emission computed tomography (SPECT) are helpful for making a correct diagnosis in some cases. However, reliable differentiation between malignant and benign uptake is often difficult because of the complex anatomy of the skeletal system and lower spatial resolution of bone scintigraphy. A robust mode for inherent registration between SPECT and high-resolution CT images is achieved by image fusion using a combined SPECT/CT system. Combined SPECT/CT systems make use of a full diagnostic CT scanner in combination with a dual-headed gamma camera. These combined scanners are suitable for assessing the bone lesions in cancer patients. Correlation of SPECT and CT or magnetic resonance imaging (MRI) is necessary for determining the specific region and anatomical change of such indeterminate lesions. A combined SPECT/CT system provides rigorous registration of functional and anatomical information, and increased diagnostic confidence in differentiating between malignant and benign bone lesions in cancer patients. Fused images facilitate the differentiation of benign from metastatic foci that are difficult to differentiate on scintigraphic and CT images viewed side by side. The information gained by SPECT and CT image fusion can be greater than the sum of their individual contributions. Regarding benign lesions, fused images are especially useful for differentiating osteoarthritis.