Rani S. Sewatkar MBBS, Presenter: Nothing to Disclose

Kanako Kunishima Kumamaru MD, PhD, Abstract Co-Author: Nothing to Disclose

Elizabeth George MD, Abstract Co-Author: Nothing to Disclose

Shinichiro Fujimoto, Abstract Co-Author: Nothing to Disclose

Frank John Rybicki MD, PhD, Abstract Co-Author: Research Grant, Toshiba Corporation

Dimitris Mitsouras PhD, Abstract Co-Author: Nothing to Disclose

Michael Lally Steigner MD, Abstract Co-Author: Speaker, Toshiba Corporation

Amir Imanzadeh MD, Abstract Co-Author: Nothing to Disclose

Tianrun Cai MD, Abstract Co-Author: Nothing to Disclose

Marcus Yen-Ta Chen MD, Abstract Co-Author: Institutional research agreement, Toshiba Corporation

TAG is being explored to detect functionally significant CAD. However, studies to-date have used it without adjusting for the various factors that affect its value, eg, the particular coronary artery, scan kVp, or left vs right dominance. We retrospectively evaluated TAG measured from 64-slice coronary CTA for the prediction of functionally significant CAD determined by invasive FFR in a small subset of patients avoiding the various factors that can affect its value.

We included 21 consecutive patients with right-dominant coronary arteries who clinically underwent both 64-slice coronary CTA (120 kVp) and invasive FFR measurements (median time interval of the studies=27 days, IQR: 14-47, range: 4-83). Among a total of 63 major coronary arteries, FFR was measured in 18 LADs and 4 LCXs. TAG was measured in all 63 vessels and the receiver operating characteristic (ROC) area under the curve (AUC) was used to characterize the ability of TAG to predict FFR<0.8 in: a) all arteries (those with no FFR measured assumed ≥0.8), b) all arteries with FFR measured, and, c) only LADs with FFR measured.

TAG values (HU/cm) in each coronary artery independently were: -7.9±8.6 (RCA), -13.8±9.4 (LAD) and -19.3±11.9 (LCX) in vessels with no significant disease to compel FFR measurement; -15.9±10.0 (LAD) and -10.7±5.8 (LCX) in vessels with FFR≥0.8 measurements; and, -7.0±5.2 (LAD) in vessels with FFR<0.8 (Figure). As previously noted, the RCA tends to have lower TAG values than left coronaries and in this study, TAG values in RCAs were similar to those of LADs with significant stenoses. The ROC AUC to detect FFR<0.8 was 0.68 (95%CI: 0.50-0.85) when pooling all vessels; 0.81 (95%CI: 0.60-1.00) when excluding vessels with no FFR, and, 0.82 (95%CI: 0.60-1.00) in LADs with FFR measurements.

In this study of 64-slice coronary CTA, LADs with significant CAD defined by FFR<0.8 had a lower TAG magnitude than LADs with no significant disease. In right-dominant patients with normal coronary arteries the RCA is expected to have the lowest TAG magnitude and the LCX is expected to have the largest, so using a single cutoff of the TAG value regardless of vessel may diminish the ability of TAG to detect significant disease.

Caution should be exercised when interpreting TAG values for the detection of significant coronary artery disease. Specifically, different TAG cutoffs may be required for each coronary artery.

Sewatkar, R, Kumamaru, K, George, E, Fujimoto, S, Rybicki, F, Mitsouras, D, Steigner, M, Imanzadeh, A, Cai, T, Chen, M, Retrospective Evaluation of 64-Detector Row CT Angiography (CTA) Transluminal Attenuation Gradient (TAG) for the Detection of Significant Coronary Artery Disease (CAD) Determined by Fractional Flow Reserve (FFR).  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14011744.html