• Dual-Energy CT in Patients Suspected of Having Renal Masses: Can Virtual Nonenhanced Images Replace True Nonenhanced Images?

    Anno Graser, MD Thorsten R.C. Johnson, MD Elizabeth M. Hecht, MD Christoph R. Becker, MD Christianne Leidecker, PhD Michael Staehler, MD Christian G. Stief, MD, PhD Henriette Hildebrandt, RT Myrna C.B. Godoy, MD Myra E. Finn, MD Flora Stepansky, MD Maximilian F. Reiser, MD Michael Macari, MD

    Purpose: To qualitatively and quantitatively compare virtual nonen­hanced (VNE) data sets derived from dual-energy (DE) computed tomography (CT) with true nonenhanced (TNE) data sets in the same patients and to calculate potential radiation dose reductions for a dual-phase renal multide­tector CT compared with a standard triple-phase protocol. This prospective study was approved by the institutional review board; all patients provided written informed con­sent.

    Materials and Methods: Seventy one men (age range, 30-88 years) and 39 women (age range, 22-87 years) underwent preoperative DE CT that included unenhanced, DE nephrographic, and delayed phases. DE CT parameters were 80 and 140 kV, 9(5 mAs (effective). Collimation was 14 X 1.2 mm. CT numbers were measured in renal parenchyma and tumor, liver, aorta, and psoas muscle. Image noise was measured on TNE and VNE images. Exclusion of relevant: anatomy with the 26-cm field of view detector was quantified with a five-point scale (0 = none, 4 = >75%). Image quality and noise (1 = none, 5 = severe) and acceptability for VNE and TNE images were rated. Effective radiation doses for DE CT and TNE images were calculated. Differences were tested with a Student t test for paired samples.

    Results:Mean CT numbers (± standard deviation) on TNE and VNE images, respectively, for renal parenchyma were 30.8 HU ± 4.0 and 31.6 HU ± 7.1, P = .29; liver, 55.8 HU ± 8.6 and 57.8 HU ± 10.1, P= .11; aorta, 42.1 III) ± 4.1 and 43.0 HU ± 8.8, P = .16; psoas, 47.3 HU ± 5.6 and 48.1 HU ± 9.3 HU, P = .38. No exclusion of the contralat­eral kidney was seen in 50 patients, less than 25% was seen in 43, 25%-50% was seen in 13, and 50%-75% was seen in four. Mean image noise was 1.71 ± 0.71 for VNE and 1.22 ± 0.45 for TNE (P < .001); image quality was 1.70 HU ± 0.72 for VNE and 1.15 HU ± 0.36 for TNE (P < .0001). In all but three patients radiologists accepted VNE images as replacement for TNE images. Mean effective dose for DE CT scans of the abdomen was 5.21 mSv ± 1.86 and that for nonenhanced scans was 4.97 mSv ± 1.43. Mean dose reduction by omitting the TNE scan was 35.05%.

    Conclusion:In patients with renal masses, DE CT can provide high quality VNE data sets, which are a reasonable approxima­tion of TNE data sets. Integration of DE scanning into a renal mass protocol will lower radiation exposure by 35%.