Separation of haemodynamic flow waves measured by MR into forward and backward propagating components

Physiological information on the action of the heart and on the reflection sites in the arterial system can be derived respectively from the forward a nd the backward propagating pressure or Row wave components. Earlier work o n the separation of these components was exclusively based on invasive meas urements of pressure or Bow In this study magnetic resonance (MR), which is a non-invasive imaging technique, was used to measure the blood Bow wavefo rm simultaneously at multiple positions along a vessel. Linear one-dimensio nal transmission-line theory was used to separate the flow waves into forwa rd and backward propagating components. First results, obtained from the th oracic aorta of five healthy male volunteers, consistently showed a negativ e reflection with a delay of about 100 ms between the foot of the forward a nd the foot of the backward propagating Row wave. Our model, consisting of a single vessel segment with constant diameter and wall properties, was val idated by the excellent agreement between the vessel area as calculated fro m the Row data using the law of mass conservation and as directly measured with a different independent MR technique.