Spectral computed tomography in cancer diagnostics

Background: Spectral computed tomography (CT) systems have been in use in clinical diagnostics for nearly two decades. Despite the availability of dual-energy CT, application in general and in the field of oncology diagnostics is still limited. Dual-energy CT has not yet found its way into oncology guidelines. This review discusses the underlying CT technology with its strengths and weaknesses and then identifies potential applications of dual-energy CT in oncological diagnostics based on a selective literature review. Results: Until recently, spectral CT was synonymous with dual-energy CT (DECT). CT systems are based on different X-ray spectra reaching the detector, which can be achieved, for example, by using different tube voltages or prefilters. Photon-counting CT systems that extract spectral information directly from the energy of the incoming photons has been available for about 2 years. Theoretically, spectral CT can definitely be used to derive advantages for oncological diagnostics, be it increased sensitivity/specificity of certain examinations, therapy monitoring, prognosis estimation, or dose reduction. However, due to the variety of technical solutions and due to the many degrees of freedom in image reconstruction (e.g., monochromatic images of different keV values, virtual noncontrast [VNC] images, iodine maps), there is a lack of standardization and comparability of protocols, procedures, and reproducibility of results across different scanner types.