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

Mark Olszewski PhD, Abstract Co-Author: Employee, Koninklijke Philips Electronics NV

Ethan Joseph Halpern MD, Abstract Co-Author: Support, Lantheus Medical Imaging, Inc Equipment support, Toshiba Corporation

Characterization of coronary plaque composition can pose challenges in single energy CT related to overlapping HU distributions and partial volume averaging (PVA). The purpose of this phantom study was to evaluate dual energy MDCT and post-processing methods for characterizing regions of varying lipid composition.

Dual-energy CT at 80 and 140 kVp was performed in a prototype rotate-rotate un-gated axial scanning mode with 400 and 100 mAs respectively each resulting in an CTDIvol of 11 mGy. The Philips 256 CT scanner was used with parameter settings: field-of-view=25 cm and collimation=32x0.625. The vascular phantom contained five lipid samples in 7 mm inner diameter tubes filled with iodinated contrast diluted to have an intensity of about 300 HU. Three lipid slabs with varying adipose:glandular compositions of 100:0, 50:50, 0:50 percent (A16 Mammography, CIRS, Norfolk, VA) were machined to 4.0 mm diameter cylinders and placed within the tubes. Samples of olive oil and beef fat were also included as references.  For each sample, corresponding and homogeneous-appearing dual-energy regions-of-interest (ROIs) were placed in tubular cross-sections. Dual-energy ROI voxels were mapped to a dual-energy scatter plot (80 vs 140 kVp), and compact lipid clusters were identified. Cluster centers [CT80,CT140] were computed using a trimmed mean to minimize volume averaging, and the differences CT80 - CT140 were recorded.      

Increasing lipid content of samples within the vascular phantom showed a decrease in the CT number at the 80 kVp setting, and the average difference in CT attenuation numbers increased with increasing lipid content [CT80,CT140,CT80-CT140](% adipose:% glandular): [-109.7,-66,-43.7] (100:0), [-29.2, 3.1, -32.3] (50:50), [47.9,73.9,-26.0] (0:100), [-180.0, 118.1,-61.9] (olive oil), [-151,-121,-29.9] (beef fat). Lipid content was correlated in the dual energy plot with a linear regression slope of 1.10 (correlation coeficient = 0.99).

Our phantom study demonstrates energy-dependent changes in lipid x-ray attenuation with dual energy CT could have a potential role in the characterization of lipids such as those in atherosclerotic plaque and further studies are warranted.

Improved characterization of coronary plaque may improve the prognostic power of coronary CT angiography.

Yanof, J, Olszewski, M, Halpern, E, In Vitro Characterization of Lipids with Dual Energy MDCT.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8002847.html