Gert Van Gompel PhD, Abstract Co-Author: Nothing to Disclose

Nico Buls DSc, PhD, Presenter: Nothing to Disclose

Koenraad Hans Nieboer MD, Abstract Co-Author: Nothing to Disclose

Inneke Willekens MD, Abstract Co-Author: Nothing to Disclose

Johan De Mey, Abstract Co-Author: Research grant, General Electric Company

In standard CT, attenuation measurements (HU-value) of objects are influenced by patient size mainly due to polychromatic x-ray beam hardening through the object. Dual Energy CT (DECT) using spectral information offers reconstruction of synthetic monochromatic images and reduces beam hardening artifacts. DECT also provides iodine images to better isolate and estimate iodine content. The purpose of this study was to determine (1) the accuracy of the iodine concentration estimation with DECT and (2) to investigate the variation in attenuation measurements compared to standard CT.

Three tubes representing iodinated blood vessels were filled with diluted (13 mg I/ml) iodine contrast (Visipaque 320, GE Healthcare) and inserted in the center of three cylindrical AAPM phantoms (CIRS, Norfolk VA.), one 23cm diameter, one 17cm and one 17cm with a Teflon ring representing bone. All phantoms were scanned at the same CTDIvol on a CT750HD scanner (GE Healthcare) with standard 120 kVp and with GSITM spectral imaging. Three measurements were made for each tube: HU-value for standard CT, HU-value for 70 keV monochromatic images and iodine concentration (mg I/ml-value) for spectral CT iodine images.

The following data (±SD) were obtained for the three respective phantoms: HU-values of 291(±9) – 318(±9) – 325(±5) for standard CT, DECT HU-values at 70 keV of 310(±6) – 314(±5) – 315(±8), and estimated iodine concentrations (mg I/ml) of 13.2(±0.3) – 13.1(±0.2) – 13.4(±0.2). The accuracy of iodine concentration by DECT was within 6% of true concentration. The variation of DECT HU-values with respect to phantom size (5 HU-values) was clearly smaller than with standard CT (34 HU-values).

The results suggest that DECT HU-values are less sensitive to variations in phantom size compared to standard CT. Future work involves extended experiments with a larger range of iodine concentrations at multiple dose levels.

DECT may have the potential to more accurately determine contrast attenuation and iodine concentration in CT angiography and CT perfusion studies.

Van Gompel, G, Buls, N, Nieboer, K, Willekens, I, De Mey, J, Influence of Phantom Size on Quantitative Iodine Measurement: Comparison of Dual-Energy CT with Standard CT.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11015429.html