ABSTRACT
Spectral photon counting CT (SPCCT) is a new imaging modality that has rapidly emerged in recent years and is now being investigated for its feasibility in clinical use. SPCCT imaging has inherent advantages over traditional computed tomography (CT) such as higher spatial resolution, reduced noise level, and reduced patient radiation exposure due to lower dosage levels per scan and the elimination of pre-contrast agent injection scans. It can also differentiate between multiple materials and quantify their concentrations simultaneously (sometimes termed K-edge imaging), providing vital diagnostic information to radiologists that cannot be conveyed with conventional CT scanners.
Recent studies with human patients have demonstrated the advantages of SPCCT imaging over conventional CT imaging as well as the outlook of its clinical use in near future. Currently, more than half of all CT imaging is contrast-enhanced, and so the same is expected for SPCCT imaging. However, the K-edge energy of iodinated contrast agents, the only clinically approved CT blood pool agents, is too low to take advantage of K-edge imaging. Therefore, experimental contrast agents made of heavy metal elements whose K-edge energies are closer to the mean photon energy X-ray spectra (e.g., gadolinium, ytterbium, tantalum, gold, bismuth) have been formulated for preliminary investigation.
In this book chapter, the principles of CT, dual energy CT, and SPCCT have been briefly introduced, along with the necessary considerations of potential elements for SPCCT-specific contrast agent development. In addition, we have summarized several candidate elements' previous uses in biomedical applications, particularly for X-ray imaging, and their development into nanoparticle-based contrast agents. For each of these candidate elements, studies that have investigated their efficacy in SPCCT imaging have been highlighted.
