Dual-Energy CT in Patients Suspected of Having Renal Masses: Can Virtual Nonenhanced Images Replace True Nonenhanced Images?
Abstract
Our results show that in addition to contrast-enhanced imaging, dual-energy multidetector CT can provide virtually unenhanced data sets,that are a reasonable approximation of true unenhanced multidetector CT data sets at a dose less than that required for two acquisitions performed separately.
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.
Materials and Methods
This prospective study was approved by the institutional review board; all patients provided written informed consent. 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, 96 mAs (effective). Collimation was 14 × 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 HU ± 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%.
© RSNA, 2009
References
- 1 . Multiphasic helical CT of the kidney: increased conspicuity for detection and characterization of small (< 3-cm) renal masses. Radiology 1997; 202: 211– 217.
- 2 . Multiphasic renal CT: comparison of renal mass enhancement during the corticomedullary and nephrographic phases. Radiology 1996; 200: 753– 758.
- 3 . How I do it: evaluating renal masses. Radiology 2005; 236: 441– 450.
- 4 . Material separation with dual-layer CT.
Proceedings of IEEE Nuclear Science Symposium 2005; Conference record M03[367]. [El Conquistador] San Juan, Puerto Rico: Institute of Electrical and Electronic Engineers 2005; 1876– 1878. - 5 . Dual energy CT of peripheral arterial disease with single-source 64-slice MDCT.
Presented at the Ninth Annual International Symposium on MDCT ,San Francisco Calif ,June 12–15, 2007 . - 6 . First performance evaluation of a dual-source CT (DSCT) system. Eur Radiol 2006; 16: 256– 268.
- 7 . Quantitative bone mineral analysis using dual energy computed tomography. Invest Radiol 1977; 12: 545– 551.
- 8 . Noninvasive quantitation of liver iron in dogs with hemochromatosis using dual-energy CT scanning. Invest Radiol 1982; 17: 375– 380.
- 9 . Quantification of calcium in solitary pulmonary nodules using single- and dual-energy CT. Radiology 1982; 145: 493– 496.
- 10 . Tissue signatures with dual-energy computed tomography. Radiology 1979; 131: 521– 523.
- 11 . Material differentiation by dual energy CT: initial experience. Eur Radiol 2007; 17: 1510– 1517.
- 12 . Technical principles of dual source CT. Eur J Radiol 2008; 68: 362– 368.
- 13 . Dual energy CT: preliminary observations and potential clinical applications in the abdomen. Eur Radiol 2009; 19: 13– 23.
- 14 . Abdominal aorta: evaluation with dual-source dual-energy multidetector CT after endovascular repair of aneurysms—initial observations. Radiology 2008; 249: 692– 700.
- 15 . Dose reduction and image quality in MDCT colonography using tube current modulation. AJR Am J Roentgenol 2006; 187: 695– 701.
- 16 . European guidelines for multislice computed tomography. Brussels, Belgium: European Commission, 2004.
Article History
Received March 31, 2008; revision requested May 28; revision received January 12, 2009; accepted February 18; final version accepted February 25.Published in print: Aug 2009
