Three things every radiologist should know about dual-energy CT

Excerpt

Images used for daily diagnosis with DECT tend to be either blended (dual source and detector-based DECT) or simulated monoenergetic (rapid kV-switching DECT), and these both are optimized to appear similar to 120 kVp images obtained with standard polychromatic beam CT. Lower keV simulated monoenergetic images with energies approaching the k edge of iodine capitalize on higher inherent image contrast when intravenous iodinated contrast is utilized, providing benefits similar to scanning with standard polychromatic beam CT at 80 kVp. Besides simulated monoenergetic images which can be viewed through a range of energies from 40 through 200 keV, material density images can be created, and each vendor achieves this through different mechanisms. The most common material density images utilized in clinical practice are Iodine images. These in particular have been shown to aid detection of various soft tissue tumors in the abdomen, particularly pancreas and liver. Other types of material specific or enhanced images help identify pathologic conditions in the abdomen and pelvis (some examples are renal stone composition or identification of tiny serosal peritoneal implants adjacent to positive oral contrast-containing bowel loops), and in other body regions can be used to identify image signatures of marrow edema in patients with trauma or uric acid-containing deposits in patients with gout. The non-invasive quantification of materials in tissues is one promise of DECT techniques. Quantification of iodine for detection of renal neoplasms is robust, and is achieved in the absence of HU-based enhancement that for years has required pre- and post-scan techniques. This quantification can even allow differentiation of papillary RCCs from complex cysts on a post contrast only scan, as Zarzour et al report in Quantitative iodine content threshold for discrimination of renal cell carcinomas using rapid kV-switching dual energy CT. Quantification of iodine on material density images or iodine maps successively through therapy in patients with various forms of cancer may be utilized for novel response assessment, an active area of DECT research. …