Is Coronary Stent Assessment Improved with Spectral Analysis of Dual Energy CT? 1 Ethan J. Halpern, MD, David J. Halpern, Jeffrey H. Yanof, PhD, Sigal Amin-Spector, PhD, David Fischman, MD, Galit Aviram, MD, Jacob Sosna, MD Rationale and Objectives. The aims of this study were to distinguish stents from iodinated contrast on the basis of spectral characteristics on dual-energy computed tomographic (DECT) imaging and to determine whether DECT imaging might provide a more accurate measurement of true stent lumen. Materials and Methods. Three stainless steel stents and one cobalt chromium stent were scanned using a multidetector, single- source DECT scanner. Stents 2.5, 3.5, and 4.0 mm in diameter were filled with iodinated contrast, submerged in water, and scanned. Spectral analysis was performed to assess the separation of stents from iodinated contrast. Two independent reviewers measured stent lumen diameter and strut thickness on low-energy (L 0 ), high-energy (L 1 ), and combined-energy (L c ) images. Dual-energy full-width half-maximum edge detection analysis was used to provide an independent assessment of stent luminal diameter and strut thickness. Results. Two-dimensional graphical plots of computed tomographic attenuation for the L 0 and L 1 images did not demonstrate a sharp separation between the absorption characteristics of stents and iodinated contrast material. Stent lumens were underes- timated by approximately 50% on L c images. Observer measurements on L 1 images demonstrated a 24% decrease in strut thickness and a 25% increase in stent luminal diameter compared to L 0 images (P < .0001). Full-width half-maximum mea- surements did not demonstrate significant changes in stent luminal diameters or strut thicknesses between L 0 and L 1 images. Conclusions. Spectral analysis did not clearly distinguish stents from iodinated contrast with the DECT system used in this study. The larger stent lumens visualized by the high-energy components of the x-ray spectrum were not related to improved computed tomographic delineation of stent thickness. Key Words. Coronary artery, coronary stent, CT angiography, dual energy CT, spectral classification. ª AUR, 2009 Computed tomographic (CT) evaluation of coronary stent restenosis is limited by blooming artifacts from high x-ray–attenuating materials, such as metal struts and mural calcium. Artifacts from high-density stent material lead to the overestimation of stent strut thickness and the underestima- tion of stent luminal diameter (1). In vitro evaluation on a four-slice scanner revealed that luminal narrowing of a stainless steel stent may be as great as 62% to 94.3% (2). The newer 64–detector row CT scanners provide near iso- tropic pixels with improved spatial resolution that can reduce blooming artifacts and minimize the importance of stent orientation compared to earlier 16-detector scanners (3,4). Nonetheless, imaging of coronary stents on computed to- mography (CT) remains a technically challenging task. Conventional CT scanners display an image on the basis of differences in the x-ray attenuation of different tissues. Dual-energy CT (DECT) imaging improves the differentia- tion of tissues on the basis of CT data obtained from syn- chronous CT acquisitions at two different energies (5). On the basis of the preferential absorption of photons by different materials, high-density structures such as calcium and iodine Acad Radiol 2009; 16:1241–1250 1 From the Department of Radiology (E.J.H., D.J.H.) and the Division of Cardiology, Department of Internal Medicine (D.F.), Thomas Jefferson University, 132 S 10th Street, Philadelphia, PA 19107-5244; Philips Medical Systems, Cleveland, OH (J.H.Y., S.A.-S.); the Department of Radiology, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel (G.A.); and the Department of Radiology, Hadassah Hebrew University Hospital, Jerusalem, Israel (J.S.). Received March 24, 2009; accepted April 21, 2009. Address correspondence to: E.J.H. e-mail: ethan.halpern@jefferson.edu ª AUR, 2009 doi:10.1016/j.acra.2009.04.011 1241