To improve the visibility of internal body structures, Magnetic Resonance Imaging (MRI) contrast agents are administered by injection into the blood stream. Gadolinium (Gd) based MRI contrast agents are the most commonly used contrast agents for enhancement of vessels in Magnetic Resonance Angiography (MRA). However, Gd is mildly toxic in nature. Hence, a minimal injection of Gd concentration for optimal visibility of MRA images is required. In this work, the effects of Gd concentration on segmentation of cardiopulmonary vasculature in MRA images is analyzed using digital image processing techniques and a first order differential equation model. The developed mathematical model uses the Gd concentration as input variable and the pixel intensity of the acquired MRA images of cardiopulmonary vasculature as the output variable. Results demonstrate that for a reduction of Gd percentage from 100% to 60%, the accuracy in segmentation of cardiopulmonary vasculature from the MRA images was observed to be the constant. The segmentation accuracy was found to decrease for a further decrease in Gd percentage. Copyright © 2015 American Scientific Publishers.