Principles and Applications of Dual-Layer Spectral CT in Gastrointestinal Imaging

Abstract

The advance in technology allows for the development of different CT scanners in the field of dual-energy computed tomography (DECT). In particular, a recently developed detector-based technology can collect data from different energy levels, thanks to its layers. The use of this system is suited for material decomposition with perfect spatial and temporal registration. Thanks to post-processing techniques, these scanners can generate conventional, material decomposition (including virtual non-contrast (VNC), iodine maps, Z-effective imaging, and uric acid pair images) and virtual monoenergetic images (VMIs). In recent years, different studies have been published regarding the use of DECT in clinical practice. On these bases, considering that different papers have been published using the DECT technology, a review regarding its clinical application can be useful. We focused on the usefulness of DECT technology in gastrointestinal imaging, where DECT plays an important role.

Keywords: X-ray-computed; computer-assisted; diagnostic techniques; digestive system; image interpretation; tomography.

Figure 1

Schematic representation of DECT. It is based on a single energetic radiation tube associated with a detector panel constituted of two layers (sandwich detector) that simultaneously detect two energy levels. Different post-processing techniques are available due to spectral properties, such as material composition images (virtual non-contrast (VNC)), iodine maps, Z-effective imaging, and virtual monoenergetic images (VMIs).

Figure 2

A 42 y-o patient with right upper pain underwent abdominal CT with a final diagnosis of cholecystitis. (A) Conventional CT image acquired after intravenous contrast media injection shows diffuse thickening of the gallbladder wall, without evidence of any calcific stone; (B) low mono-energetic map shows a hypoattenuating round stone, due to cholesteric composition; (C) opposite that, the high mono-energetic map demonstrates the hyperattenuating mass consistent with the cholesteric gallstone; (D) the Z-effective map allows us to better define the different structures of the images via the different atomic values of the gallbladder: blue (contrast agent), red (lipid content), and green (fluid).

Figure 3

A 49 y-o male with known Crohn’s disease, diffuse abdominal pain, and suspected relapse of disease underwent abdominal CT. (A) Conventional CT images on the coronal plane acquired after intravenous contrast media injection show a poor layered enhancement appearance of the distal ileum; (B) iodine map enhances iodine’s uptake by the mucosa layer, and the hypoattenuating appearance of the submucosa one, consistent with edema; (C) the Z-effective map allows us to define the pattern of enhancement due to the atomic number of iodine.

Figure 4

A 66 y-o male with diffuse abdominal pain underwent abdominal CT with a final diagnosis of distal ileum bowel ischemia. (A,C) Axial and coronal conventional CT images acquired after intravenous contrast media injection show a slight difference in attenuation value (HU) of the small bowel walls, with reduced enhancement in the distal ileum and regular enhancement in jejunum and proximal ileum; (B,D) iodine maps clearly show the difference in iodine uptake between the normal walls of the jejunum and proximal ileum and the poor iodine uptake of the distal tract of the ileum; (E) the Z-effective map allows us to better and more simply define the different enhancement in terms of colors between healthy and ischemic bowels due to the atomic number of iodine.