Non-invasive systems and methods for determining fractional flow reserve. At least one method of determining fractional flow reserve within a luminal organ of the present disclosure comprising the steps of positioning a monitoring device external to a luminal organ and near a stenosis, the monitoring device capable of determining at least one characteristic of the stenosis, operating the monitoring device to determine the at least one characteristic of the stenosis, and determining fractional flow reserve at or near the stenosis based upon the at least one characteristic determined by the monitoring device.
