Type A aortic dissection is a highly morbid condition, where the patient's effective circulating blood volume (ECBV) is one of many predictors of outcomes. The authors propose a new parameter titled “effective circulating volume fraction" that serves to be a more precise measurement of ECBV. This was achieved by measuring the cross-sectional areas of the true lumens and the aorta at each level of computed tomography angiography, multiplying by the slice thickness, and then summing the results to calculate the overall volumes of the true lumens and the aorta, respectively.