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Background
Dual energy CT (DECT) is a long-established concept which augments the diagnostic accuracy of conventional CT, first described in the 1970s. It has only been in regular clinical use since the early 2000s, owing to hardware and software advances enabling its clinical implementation. DECT has multiple clinical applications and has become an integral part of imaging acute and elective abdominal imaging in our institution. This educational study aims to outline the key areas, where DECT can play a role in improved diagnostic accuracy in abdominal imaging and methods to ensure that this technology is optimised for clinical use.

Educational Goals / Teaching Points
Describe and illustrate the key areas where DECT can be utilized to improve diagnostic accuracy and confidence in abdominal imaging, and discuss common imaging pitfalls and artifacts that radiologists should be aware of when interpreting abdominal DECT images.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Increased detection of hyperenhancing and hypoenhancing liver lesions. The iodine overlay and low keV images can both lead to increased conspicuity of otherwise subtle lesions. Iodine overlay improves diagnosis of bowel ischemia. The absence of mural iodine uptake effectively illustrates ischaemic/infarcted bowel loops that may be difficult to appreciate on conventional contrast-enhanced CT imaging. Differentiation of intraluminal GI tract hyperdensity on CT. The iodine overlay acts as a “radiotracer” to improve detection of extravasated intraluminal contrast. Characterization of hyperdense renal lesions and renal stone composition. DECT allows differentiation of a hyperdense hemorrhagic/proteinaceous cyst from a solid enhancing mass lesion. This obviates the need for follow-up multiphase imaging. Improved detection of isodense gallstones and CBD stones. Conventional single energy CT can fail to detect up to 57% of gallstones which are isodense to bile. Material decomposition techniques enable improved sensitivity up to 95%. Can virtual non contrast (VNC) ultimately replace true non contrast CT? VNC is an imaging technique unique to DECT whereby non-contrast images can be derived from contrast enhanced images by excluding voxels containing iodine. This allows lowering of radiation dose by elimination of true noncontrast acquisition. Optimization of window level of the iodine map is important to avoid the false impression of enhancement. A pitfall of the iodine overlay is that noisy windows can falsely create subjective enhancement. Quantification of iodine can also be performed where uncertainty exists. Pathognomonic appearance of acute/subacute hematoma on DECT. Iodine map as a “radiotracer” to detect extravasated extraluminal oral contrast. DECT acquisition can result in a number of artifacts, knowledge of which is important to prevent misinterpretation. Optimization of scan protocols can help to mitigate these artifacts.

Conclusion
DECT is a powerful tool to augment conventional abdominal CT imaging. There are many clinical applications which improve diagnostic sensitivity and confidence and can lead to reductions in radiation dose and follow-up.