# Dual-Energy CT Applications in Urological Diseases
## 4 DECT Clinical Applications
### Study of Renal Lesions  
Many incidentally discovered renal lesions are incompletely diagnosed by standard CT imaging, creating issues for radiologists and referring physicians. DECT provides an added value in characterizing renal lesions [52; 53], providing higher confidence in lesion characterization, and reducing the need for additional imaging compared to standard single-energy dual-phase computed tomography, while maintaining comparable diagnostic performance to magnetic resonance imaging [54]. \begin{table}
\begin{tabular}{p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Authors** & **Number of Patients** & **Number of Stones** & **Stone Composition** & **Gold Standard** & **Sensitivity** & **Specificity** \\ \hline [PERSON] et al. [35] & 64 & 213 & 9 patients with uric acid, 26 patients with calcium oxalate monohydrate, 4 patients with calcium oxalate dihydrate, 7 patients with calcium hydroxyapatite, 1 patient with brushite, 2 patients with mixed uric acid 14 patients with mixed 14 patients with mixed 14 patients with mixed & & & \\ [PERSON] et al. [56] & 33 & 62 & 15 uric acid, 39 calcium oxalate or phosphate, 8 cysteine & Chemical Analysis  
DECT has the potential to provide an alternative diagnostic pathway for detecting enhancing renal lesions in patients who may have difficulty adequately breath-holding or cooperating with lengthy MRI examination times, which could result in lower-quality pre-contrast and postcontrast acquisitions, and it can be also used in patients with pacemakers and other MRI contraindications [55; 56]. Even on the contrast-enhanced phase of a standard CT, renal lesions with attenuation close to water can be easily identified as simple cysts; however, a double-phased examination is needed, with one phase before and one after intravenous contrast administration, to determine whether a lesion with attenuation higher than water represents a nonenhancing hyperdense cyst or an enhancing solid renal mass [57]. To determine whether a lesion enhances or not, the measured difference in attenuation between the two phases is used: enhancement is defined as any attenuation increase of 10 HU by some radiologists, while others define true enhancement as an attenuation increase of 20 HU [57]. VNC images generated from enhanced DECT acquisition have been proven to correlate well with true unenhanced images and the attenuation measurements on the VNC are considered reasonably approximate to true unenhanced images [58]. Iodine maps can be obtained from contrast enhanced DECT acquisitions through material decomposition algorithms and allow the reliable identification of enhancing lesions [59]. Using a color-coded overlay display, an iodine map graphically depicts iodine contrast inside the interrogated voxels: as a result, nonenhancing renal cysts and enhancing solid renal tumors can be distinguished on the map reconstructed from single-phase postcontrast datasets, where nonenhancing renal cysts lack iodine content, whereas solid enhancing renal tumors uptake the iodine contrast medium [8; 9; 19]. Color-coded iodine overlay images allows an easy visual differentiation of enhancing from nonenhancing renal lesions, as enhancing masses contain color-coded pixels within them. Moreover, they can be useful for an easy visual assessment of patients with multiple renal lesions, such as polycystic kidney disease, as enhancing lesions can be easily distinguished by cysts and hemorrhagic cysts [60]. The analysis of iodine map helped the characterization of hyperdense renal masses incidentally discovered on a single-phase enhanced DECT, particularly in lesions sized \(\geq\)1.5 cm [61]. DECT enables an improved abnormalities characterization through the quantification of the iodine amount in each image pixel. An extra tool accessible with DECT datasets is represented by spectral attenuation curves [62]: when an ROI is drawn within a lesion, the lesion attenuation profile in the multi-energy scale can be assessed.