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Dual-Energy Computed Tomography Angiography of the Lower Extremity Runoff: Impact of Noise-Optimized Virtual Monochromatic Imaging on Image Quality and Diagnostic Accuracy

Wichmann, Julian L. MD*†; Gillott, Matthew R. MD*; De Cecco, Carlo N. MD, PhD*; Mangold, Stefanie MD*‡; Varga-Szemes, Akos MD, PhD*; Yamada, Ricardo MD*; Otani, Katharina PhD§; Canstein, Christian MSc; Fuller, Stephen R. BS*; Vogl, Thomas J. MD; Todoran, Thomas M. MD; Schoepf, U. Joseph MD

doi: 10.1097/RLI.0000000000000216
Original Articles
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Objective The aim of this study was to evaluate the impact of a noise-optimized virtual monochromatic imaging algorithm (VMI+) on image quality and diagnostic accuracy at dual-energy computed tomography angiography (CTA) of the lower extremity runoff.

Materials and Methods This retrospective Health Insurance Portability and Accountability Act–compliant study was approved by the local institutional review board. We evaluated dual-energy CTA studies of the lower extremity runoff in 48 patients (16 women; mean age, 63.3 ± 13.8 years) performed on a third-generation dual-source CT system. Images were reconstructed with standard linear blending (F_0.5), VMI+, and traditional monochromatic (VMI) algorithms at 40 to 120 keV in 10-keV intervals. Vascular attenuation and image noise in 18 artery segments were measured; signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Five-point scales were used to subjectively evaluate vascular attenuation and image noise. In a subgroup of 21 patients who underwent additional invasive catheter angiography, diagnostic accuracy for the detection of significant stenosis (≥50% lumen restriction) of F_0.5, 50-keV VMI+, and 60-keV VMI data sets were assessed.

Results Objective image quality metrics were highest in the 40- and 50-keV VMI+ series (SNR: 20.2 ± 10.7 and 19.0 ± 9.5, respectively; CNR: 18.5 ± 10.3 and 16.8 ± 9.1, respectively) and were significantly (all P < 0.001) higher than in the corresponding VMI data sets (SNR: 8.7 ± 4.1 and 10.8 ± 5.0; CNR: 8.0 ± 4.0 and 9.6 ± 4.9) and F_0.5 series (SNR: 10.7 ± 4.4; CNR: 8.3 ± 4.1). Subjective assessment of attenuation was highest in the 40- and 50-keV VMI and VMI+ image series (range, 4.84–4.91), superior to F_0.5 (4.07; P < 0.001). Corresponding subjective noise assessment was superior for 50-keV VMI+ (4.71; all P < 0.001) compared with VMI (2.60) and F_0.5 (4.11). Sensitivity and specificity for detection of 50% or greater stenoses were highest in VMI+ reconstructions (92% and 95%, respectively), significantly higher compared with standard F_0.5 (87% and 90%; both P ≤ 0.02).

Conclusions Image reconstruction using low-kiloelectron volt VMI+ improves image quality and diagnostic accuracy compared with traditional VMI technique and standard linear blending for evaluation of the lower extremity runoff using dual-energy CTA.

From the *Division of Cardiovascular Imaging, Department of Radiology and Radiological Science, Medical University of South Carolina, Charleston, SC; †Department of Diagnostic and Interventional Radiology, University Hospital Frankfurt, Frankfurt, Germany; ‡Department of Diagnostic and Interventional Radiology, University Hospital of Tübingen, Tübingen, Germany; §Imaging and Therapy Systems Division, Healthcare Sector, Siemens Japan K.K., Tokyo, Japan; ∥Siemens Medical Solutions, CT Division, Malvern, PA; and ¶Division of Cardiology, Department of Medicine, Medical University of South Carolina, Charleston, SC.

Received for publication July 28, 2015; and accepted for publication, after revision, August 13, 2015.

Conflicts of interest and sources of funding: none declared: No support was received for this project. No funding was received. U.J.S. is a consultant for and/or receives research support from Astellas, Bayer, Bracco, GE, Medrad, and Siemens. K.O. and C.C. are employees of Siemens. The other authors have no conflicts of interest to disclose.

Correspondence to: U. Joseph Schoepf, MD, Department of Radiology and Radiological Science, Medical University of South Carolina, Ashley River Tower, MSC 226, 25 Courtenay Dr, Charleston, SC 29425. E-mail: schoepf@musc.edu.

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