The impact of dual energy CT on pseudo enhancement of kidney lesions

Renal lesion detection and characterization using Computed Tomography is an important application in genitourinary radiology. Although in general the detection of renal lesions has been shown to be exceedingly accurate, the detection of benign renal cysts is still problematic. Under certain circumstances, the attenuation values inside a cyst increase incorrectly with an increase in the iodine concentration in the surrounding soft tissue. This so called pseudoenhancement complicates the classification of cysts and creates severe difficulties to distinguish a benign nonenhancing lesion from an enhancing mass. In the present study, the standard procedure based on a single energy 120 kV mode is compared to three dual energy modes available on the Siemens Somatom Definition Flash scanner. In order to simulate the kidney and the lesions, several plastic rods were placed inside a small container filled with different iodine concentrations. This phantom is then positioned inside water tanks of different sizes. The rods simulating the lesions are made out of a special plastic with constant HU value throughout the relevant X-ray energy range. During the project, three important aspects have been discovered: 1) for normal situations, a 100/140 Sn kV mode on the Siemens Flash scanner is similar to the traditional single energy 120 kV mode. 2) For small patient sizes, all dual energy modes show a reduction of pseudoenhancement. 3) For larger patients, only the 100/140 Sn kV mode results in a reduction of pseudoenhancement. Both the 80/140 kV and the 80/140 Sn kV mode show a worse performance than the 120 kV single energy mode in a very large phantom size.