Isaac Leichter PhD, Presenter: Nothing to Disclose

Tzvi Lipschuetz, Abstract Co-Author: Nothing to Disclose

Zimam Romman, Abstract Co-Author: Employee, Koninklijke Philips Electronics NV

Michal Haviva Gabbai MD, Abstract Co-Author: Nothing to Disclose

Jacob Sosna MD, Abstract Co-Author: Consultant, ActiViews Ltd Research Grant, Koninklijke Philips Electronics NV

Simultaneous dual-energy CT (DECT) data can be used to generate virtual mono-energy images at varying keV levels. These images include in-plane and object-size beam-hardening corrections. We aimed to evaluate the stability of iodine density measurements in virtual mono-energy images, using a phantom of two sizes.

A customized water-equivalent anthropomorphic CT phantom (QRM, Moehrendorf, Germany) was scanned with and without a 2.5 cm extension ring to enable measurements at 2 phantom sizes (20x30 cm and 25x35 cm). The phantom included 8 tubes of 11.1 mm diameter, 2 tubes of 7.9 mm diameter, and 2 tubes of 6.4 mm diameter, all filled with 7 mg/ml iodine solution. The tubes were arranged 3–11 cm from the phantom center (Fig. 1). Conventional and 65 keV mono-energy images for both phantom sizes were obtained at 120 kVp and 500 mAs using a novel Spectral Detector CT (SDCT) prototype (Philips Healthcare, Cleveland, OH, USA). Variation between HU values of the iodine tubes was analyzed (paired T-test) for tube location, tube diameter, image type, and phantom size.

Mono-energy image HU values for the iodine tubes were independent of tube location, tube diameter, or phantom size. There was no significant difference (p=0.39) in the standard deviation (SD) of HU values at different tube locations in the small-size phantom (SD=0.76%) vs. the large-size phantom (SD=0.88%). Variation of the HU values between tubes with different diameters was even smaller, 0.46% in the small-size and 0.64% and large-size phantom. Compared to mono-energy images, in the conventional images the variation of HU values at different tube locations was significantly higher (p<0.04) for both small-size (SD=2.62%) and large-size (SD=4.39%) phantoms. The variation between tubes of different diameters was also somewhat larger in conventional images for both phantom sizes (3.10% and 3.89%, respectively).

The quality of virtual mono-energy images at 65 keV was superior to that of conventional images, with no beam-hardening effect. Mono-energy images demonstrated stable iodine density measurements, independent of phantom size, tube location, and tube diameter.

Stable density measurements of contrast material, independent of patient size and ROI location, are important for integration of Spectral Detector CT into clinical practice.

Leichter, I, Lipschuetz, T, Romman, Z, Gabbai, M, Sosna, J, Stability of Iodine Density Measurements with Spectral Detector CT in an Anthropomorphic Phantom of Varying Size: Comparison of Conventional and Virtual Mono-energy Images.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13021714.html