Utility of Dual-Energy Computed Tomography in Clinical Conundra

Abstract

Advancing medical technology revolutionizes our ability to diagnose various disease processes. Conventional Single-Energy Computed Tomography (SECT) has multiple inherent limitations for providing definite diagnoses in certain clinical contexts. Dual-Energy Computed Tomography (DECT) has been in use since 2006 and has constantly evolved providing various applications to assist radiologists in reaching certain diagnoses SECT is rather unable to identify. DECT may also complement the role of SECT by supporting radiologists to confidently make diagnoses in certain clinically challenging scenarios. In this review article, we briefly describe the principles of X-ray attenuation. We detail principles for DECT and describe multiple systems associated with this technology. We describe various DECT techniques and algorithms including virtual monoenergetic imaging (VMI), virtual non-contrast (VNC) imaging, Iodine quantification techniques including Iodine overlay map (IOM), and two- and three-material decomposition algorithms that can be utilized to demonstrate a multitude of pathologies. Lastly, we provide our readers commentary on examples pertaining to the practical implementation of DECT's diverse techniques in the Gastrointestinal, Genitourinary, Biliary, Musculoskeletal, and Neuroradiology systems.

Keywords: dual energy CT application; dual energy CT system; dual energy scanned projection radiography; gastrointestinal; genitourinary; musculoskeletal; neuroradiology.

Figure 1

From left to right—Contrast enhanced conventional 120 kVp and iodine overlay map (IOM) coronal images of the abdomen. Closed-loop small bowel obstruction secondary to a right inguinal hernia (*). The small bowel loop demonstrates no mural enhancement; more conspicuous on the IOM (*) which is highly suggestive of an incarcerated hernia.

Figure 2

From left to right—Conventional CT KUB and DECT renal stone analysis axial images of the abdomen. The right midpole calculus (*) is identified on the color-coded stone analysis DECT application as a uric acid calculus (*) which can be treated medically with urine alkalinization.

Figure 3

From left to right—Contrast-enhanced (portal venous) and Iodine overlay map (IOM) axial images of the abdomen. Right exophytic hyperattenuating lesion (*) is further characterized as lacking internal enhancement on the IOM (*) image and is therefore likely to represent a benign hyperdense cyst rather than an enhancing lesion.

Figure 4

From left to right—Conventional mixed 120 kVp equivalent, 40 keV virtual monoenergetic and gallstone analysis application axial images through the abdomen. Gallstones are not visible on the conventional image as they isoattenuate to the surrounding bile. However, they are visible on the DECT images and appear hypodense (filling defect) on the virtual monoenergetic image (*) and hyperdense (*) on the gallstone analysis application.

Figure 5

From left to right—Conventional mixed 120 kVp equivalent and bone marrow edema (BME) overlay sagittal images of the lumbar spine. Subtle L3 superior endplate compression fracture is difficult to detect on the conventional images(*). BME is, however, confidently demonstrated on the overlay map (orange arrow).

Figure 6

From left to right—Conventional mixed 120 kVp equivalent and 3D bone marrow edema overlay coronal images of the right knee. Subtle intercondylar tibial fracture extending into the tibial condyle (*) is confidently diagnosed when appreciating the associated BME on the overlay image (orange arrow).

Figure 7

DECT gout application readily identifies the color-coded monosodium urate (MSU) crystals (green color) and assesses disease burden.

Figure 8

From left to right—Unenhanced conventional 120 kVp equivalent, iodine overlay map (IOM) and virtual non-contrast (VNC) axial images of the brain post Endovascular thrombectomy (EVT). Hyperdensity within the left basal ganglia on the conventional image (*) could be caused by contrast staining (CS) or hemorrhagic transformation (HT). The hyperdensity persists on the IOM (*) but is not detectable on the VNC image; confirming this to be secondary to CS and not HT.