Applications of Dual-Energy CT in Urologic Imaging: An Update

DECT techniques

Different techniques and hardware platforms have been explored to achieve DECT capabilities. There are mainly 3 implementations currently available from 3 different manufacturers using dual-source, fast-kV switching, and dual-layer detector techniques. Other emerging DECT techniques include using photon-counting detectors and performing 2 consecutive scans on a standard CT scanner. Each DECT technique has its advantages and disadvantages compared with other implementations.1, 2

For a dual-source

DECT images

In DECT, because the 2 data sets are acquired at different beam energies and different processing techniques can be applied, multiple-image data sets can be obtained from a single examination.

Radiation dose in DECT and dose-reduction methods

Although 2 measurements are made in DECT, the radiation dose used to acquire each measurement alone is lower and therefore the total radiation dose is not necessarily higher than single-energy CT. The mixed images are generated by blending the low-energy and high-energy images, therefore fully using all x-ray photons and radiation dose. It has been demonstrated that similar image quality and radiation dose can be obtained using a linear blending technique on a dsDECT system.²⁷

In DECT, the

Urinary stone in iodinated solution (virtual noncontrast images)

Unenhanced CT is considered the gold standard for the detection of urinary stones.46, 47 Urinary stones can be obscured by high-attenuation iodinated contrast material in the renal parenchyma or collecting systems on contrast-enhanced CT. Unenhanced CT is not routinely performed for abdominal CT; therefore, renal stones can be missed. On the other hand, unenhanced CT is routinely performed as part of CT urography, given the higher prevalence in the patient population requiring CT urography.⁸⁰

In

Urothelial tumor detection

Urothelial tumor detection is dependent on the contrast between tumor and the surrounding urine or adjacent normal urothelial wall. Urothelial tumor generally enhances moderately during the parenchymal phase of contrast enhancement, whereas surrounding normal urothelial wall shows minimal enhancement and urine does not enhance.⁸⁴ Tumors and adjacent normal urothelial wall become hypodense during the urographic phase, whereas urine becomes opacified.

In a phantom study simulating the pyelographic

Adrenal adenoma

Adrenal adenomas are characterized by a large amount of intracytoplasmic fat and typically appear hypoattenuating on standard unenhanced CT, measuring 10 HU or less at unenhanced SECT at 120 kVp, and are referred to as lipid-rich adenomas. In recent studies, DECT has been shown to be useful in characterizing adrenal masses.86, 87

In a study of adrenal nodules using unenhanced DECT at 80 kVp and 140 kVp, 13 (50%) of 26 adenomas had an attenuation decrease on the 80-kVp images relative to the 140

Summary

The recent development of DECT platforms and innovative scanning techniques has provided additional tools for the diagnosis and characterization of renal masses, urolithiasis, and disorders of the uroepithelium. Knowledge of the principal technical aspects of dual-energy scanning and the specific utility of DECT in imaging of the kidneys and urinary tract has become imperative for the radiologist in practice.