Iodinated contrast delivery is a key component of coronary CT angiography. However, the purpose of contrast delivery has been limited to morphology alone. Specifically, iodine opacification of the coronary lumen has been used to separate it from the coronary artery wall and lesions within the coronary arteries. Because contrast is delivered to the coronary arteries according to the coronary blood flow, there is flow information encoded within the contrast opacification which, depending on CT hardware and acquisition protocol, can be recognized in coronary CT angiography. In addition, metrics related to flow have been identified and studied. They include coronary contrast opacification differences and contrast opacification gradients.