Coronary artery bypass grafting (CABG) is an effective treatment of complex, multi-vessel coronary artery disease(1) .The majority of these patients receive left internal mammary artery (IMA) grafts to the left anterior descending (LAD) coronary artery and saphenous vein grafts (SVGs) or other conduits to the remaining vessels. Based on small studies of selected groups of patients, it is generally believed that SVGs have a 40% to 50% 10-year patency and that the LIMA has a 90% to 95% 10-year patency The success of coronary artery bypass grafting (CABG) is dependent on the long-term patency of the arterial and venous grafts.(2) Graft failure is a surrogate marker for future cardiac events, including repeat revascularization, myocardial infarction ,and death(3)(4). Vein graft occlusion in the perioperative period is due to thrombosis resulting from technical problems. Vein graft occlusion within the first year is attributed to intimal proliferation, although after 1 year, atherosclerosis is thought to be the dominant factor (5) . LIMA graft failure was defined as diffuse and >95% conduit narrowing ("string sign" When IMA graft failure occurs, technical error is the most common cause in the early postoperative period, while late (and rare) IMA failure include progressive fibro-intimal proliferation and atherosclerosis either in the IMA graft or in the native LAD vessel)(6) Traditionally, graft patency has been evaluated with coronary angiography (ICA) but, since the advent of multi-detector computed tomography (MDCT), the temptation to use a noninvasive and widely available technique to study coronary artery bypass graft (CABG) patients has been stronger. The introduction of scanners like 64-slice and 128-slice upwards—along with new scan protocols opens new perspectives in non-invasive assessment of graft patency.(7) The pooled sensitivity and specificity of detecting complete graft occlusions - according to( Barbero et al ,2016) ,was 99% and 99% respectively as compared to the standard of coronary angiography. (8) Computed tomographic angiography, labeled as Appropriate test for evaluation of bypass grafts and coronary anatomy (9)