SPECT-CT: applications in musculoskeletal radiology

This article reviews the technique, basic science principles and applications of integrated single photon emission CT (SPECT)-CT in musculoskeletal radiology. A review of the current evidence on the topic was undertaken, and selected clinical cases from the authors'' institution have been used for illustration. SPECT-CT is a technology with emerging applications that offers technical advantages to image fusion of separately acquired SPECT and CT studies. The prevailing evidence indicates that there may be benefit in adding SPECT-CT to conventional imaging algorithms during the evaluation of some malignant and benign musculoskeletal conditions. SPECT-CT can improve both sensitivity and specificity by reducing equivocal interpretation in comparison to planar scintigraphy or SPECT alone. The evidence base for SPECT-CT in musculoskeletal radiology is still evolving. There is a lack of evidence comparing SPECT-CT with MRI in many key indications, and further research is required in these areas.A wide range of pathological conditions may affect the musculoskeletal system, including infection, trauma and malignant disease. Advances in MRI, multidetector CT (MDCT) and high-frequency ultrasound have provided considerable improvements in imaging musculoskeletal disease over the past decade. There are, however, limitations associated with each of these techniques. MRI image acquisition remains relatively time consuming and, particularly in musculoskeletal radiology, image quality can be degraded significantly by metal artefact from internal fixation and prostheses. MDCT offers exquisite characterisation of bone and can rapidly generate high-quality three-dimensional reconstructions; however, the contrast resolution for soft tissues is limited and the modality can also suffer metal-related artefact, although like MRI, imaging parameters can be adjusted to reduce this artefact. High-frequency ultrasound, although operator dependent, provides excellent spatial and contrast resolution for superficial structures but is suboptimal for deeper structures and is unable to penetrate cortical bone.Bone scintigraphy remains an important and highly sensitive tool to the musculoskeletal radiologist but this is frequently criticized for its lack of specificity. Radionuclide imaging, however, may be the only modality to demonstrate pathology before it becomes evident on anatomical imaging. Developments in gamma camera technology now allow high-resolution imaging with shortened scan times, and single photon emission CT (SPECT) imaging has become commonplace in the UK. SPECT is able to increase sensitivity further and improves lesion localisation, but the paucity of anatomical markers on radionuclide imaging remains a constant challenge. Thus, the importance of correlating anatomical and functional imaging has become increasingly recognised [1].Use of a combined SPECT/CT system allows for sequential acquisition of both anatomical and functional information with a high degree of image fusion accuracy.In this article, we briefly review the technique, basic science principles and technical challenges of SPECT-CT, and discuss the applications of this hybrid modality in musculoskeletal radiology.