Tariq Arshad Hameed MBBS, Abstract Co-Author: Research grant, Koninklijke Philips Electronics NV

James C. Williams PhD, Abstract Co-Author: Nothing to Disclose

Jeffrey Harold Yanof PhD, Presenter: Employee, Koninklijke Philips Electronics NV

Molly Jackson, Abstract Co-Author: Nothing to Disclose

Jonas Rydberg MD, Abstract Co-Author: Institutional research collaboration, Koninklijke Philips Electronics NV

Dual-Energy CT has recently shown potential to improve the classification of renal calculi relative to conventional CT. However, a DECT acquisition irradiates each voxel twice, potentially resulting in higher radiation dose. We evaluated the effect of lowering DECT dose on the ability to classify renal calculi.

A custom CT phantom was designed with renal and water equivalent material to contain sets of renal calculi (QRM, Moehrendorf, Germany). The renal material had a 15 cm cylindrical diameter, a average CT number of ~45 HU, and bore holes (1 cm OD) for polyethylene vials; the water equivalent material was a 30x20 cm oval expansion ring (10 cm caudal-cranial length). Thirty ex vivo stones were hydrated and placed in the airtight vials. Four successively lower-dose DECT scans were performed in a single axial-mode acquisition with 128x0.624 mm collimation and 0.27 second gantry rotation time for 80 and 140 kVp. The mAs settings for (80, 140) kVp were (925, 250), (800,200), (600,150), (400,100) yielding CTDIvol values of 42.0, 34.7, 26.0, 17.4 mGy and DLP values of 336, 278, 209, and 139.2 mGy*cm. Corresponding ROIs were placed in the center region of each stone in the low and high energy CT images, and the average HU values (± standard deviation) were recorded. These coordinates were used to compute a dual-energy index (DEI) for each calculi as well as the effective atomic number, Zeff, and density, ρ, using the photoelectric-Compton basis. Paired t-tests were used to compare the average DEI, Zeff, and ρ, between CTDIvol levels.

Dual energy scatter plots (i.e., energy maps) were created for each CTDIvol level. There was not a significant difference in average DEI for the highest and lowest CTDIvol, 0.0873±0.0430 and 0.0870±0.0424 (p=0.706), respectively. The average Zeff was 10.62±1.54 and 10.61±1.51 (p=0.757) and the average ρ was 1.43±0.151 and 1.43±0.155 (p=0.908), for the highest and lowest dose.

This phantom study demonstrates that dual energy CT radiation dose can be lowered without significantly affecting quantitative dual energy indexes.

Dual energy CT allows for quantitative applications while applying radiation dose reduction and adhering to the ALARA principle.

Hameed, T, Williams, J, Yanof, J, Jackson, M, Rydberg, J, Classification of Renal Calculi with Dual-Energy CT (DECT): Evaluating the Effect of Lower CT Dose in a Phantom Study.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11015245.html