Dual-energy CT iodine overlay technique for characterization of renal masses as cyst or solid: a phantom feasibility study

The aim of this study was to assess the ability of dual-energy computed tomography (DECT) to classify phantom renal lesions as cysts or enhancing masses. Six cylinders ranging in diameter from 0.5 to 3.0 cm were filled with distilled water or titrated iodinated contrast solutions with CT attenuation values at 120 kVp of 0 Hounsfield units (HU) for a cyst proxy or 10, 20, or 40 HU to represent enhancing masses. These were placed in a 12-cm-diameter renal phantom containing puréed beef mixed with iodinated contrast medium to simulate enhancing renal parenchyma of 100 and 250 HU and submerged within a 28-cm water bath. These combinations produced 48 individual phantom renal lesions of differing sizes, internal and parenchymal enhancement (12 cysts and 36 enhancing masses). DECT using 80 and 140 kVp was performed on a dual-source CT scanner. Commercial software created a color-encoded overlay indicating the location of iodine within the phantom. The lesions were individually graded as a cyst or enhancing mass by blinded, consensus interpretation of two genitourinary radiologists. Thirty-five of 36 enhancing masses and 10/12 cysts were correctly identified, equating to a sensitivity and specificity of 97% (95% CI 84–100%) and 83% (95% CI 51–97%), respectively. All lesions of 20- and 40-HU enhancement and 92% of 10-HU lesions were identified correctly. In a phantom model, the DECT iodine overlay technique is highly sensitive in detecting enhancing renal masses. Refinement of the technique remains necessary to improve specificity. If validated in patients, this may obviate the need for unenhanced acquisitions for renal mass characterization.