Juan Carlos Ramirez Giraldo PhD, Presenter: Employee, Siemens AG

Marilyn J. Siegel MD, Abstract Co-Author: Research Consultant, Siemens AG Speakers Bureau, Siemens AG

Bernhard Schmidt PhD, Abstract Co-Author: Employee, Siemens AG

To evaluate the effect of spectra separation in the image quality of monoenergetic images estimated from dual-energy CT data acquired in pediatric-sized phantoms

Three phantoms representing small (12 x 8 cm), medium (16 x 12 cm), and large (27 x 18 cm) pediatric sizes were scanned using second generation dual-source CT (Somatom Flash) with a thoracic DECT protocol at 100/140 kVp (default) and 80/140kVp; and with a third generation dual-source CT (Somatom Force) with DECT protocol using 70/150 kVp. All scans used additional tin filtration in the high energy tube to increase spectra separation. Automatic exposure control was used for all scans and volume CT dose index (CTDIvol) was recorded. Monoenergetic images were calculated between 40 and 85 keV, in 5 keV steps, using commercially available software (Syngo DE Monoenergetic). To assess the impact of the spectra separation in image quality, the image noise, contrast, contrast-to-noise ratio (CNR), and dose-weighted CNR [CNRD = CNR/sqrt(CTDIvol)] were calculated. Parameters were compared with paired t-test.

For the 70/150, 80/140, and 100/140 kVp protocols, the radiation output values were 0.40, 0.52, 0.49 mGy (small phantom); 1.33, 1.42, 1.50 (medium phantom); and 1.96, 2.32, 2.24 mGy (large phantom); respectively. Image noise in monoenergetic images decreased significantly in the 70/150 kVp protocol, relative to both the 80/140 and 100/140 kVp protocols (P < .05); and also decreased significantly when comparing the 80/140 kVp relative to the 100/140 kVp (P < .05). Image contrast values measured in monoenergetic images were comparable for all kVp protocols and independent of phantom size, with contrast differences which were consistently less than 17.6% (range 0.3 to 17.6%). CNR and CNRD significantly increased with use of the 70/150 kVp protocol relative to the 80/140 and 100/140 kVp protocols (P < .05), and also increased with use of 80/140 kVp relative to 100/140 kVp protocol (P < .05).

In pediatric sizes, kilovoltage pairs for dual-energy CT leading to larger x-ray spectra separation result in a significant decrease of image noise in synthetized monoenergetic images, with a corresponding improvement in CNR and dose tradeoff.

For contrast-enhanced DECT imaging in pediatric patients this study favors the use 70/150 kVp (with tin) for third generation DSCT, and of 80/140 kVp (with tin) for the second generation.

Ramirez Giraldo, J, Siegel, M, Schmidt, B, Impact of Spectra Separation for Monoenergetic Extrapolation Using Dual-energy Dual-source CT in Pediatric-sized Phantoms.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14045709.html