AN ULTRASONIC SYSTEM FOR DIAMETER PULSE TRACKING IN ARTERIES - PROBLEMS AND PITFALLS

Non-invasive ultrasonic techniques for measuring the mechanical behavi our of large arteries have a potential clinical application for physio logical studies of the circulation and early detection of degenerative arterial disorders. A newly developed system for such purposes, compr ising two double-echo trackers with zero-crossing phase-locked circuit s and interfacing a B-made real-time scanner, has been introduced for on-line recording of the diameter in a selected aortic segment. The ai m of this report is to draw attention to the limitations of the techni que in order to avoid misinterpretation of results. The various proble ms associated with the use of phase-locked echo followers for tracking sonic echoes of vessel pulse waves are summarized. The high spatial r esolution of the measuring system is essential for estimating the elas tic properties of the vessel, because the fractional changes of the di ameter waveform during a heart cycle are small compared with the swing s of intravascular pressure. Measuring errors may originate from eithe r human or technical sources. From several viewpoints correct alignmen t of the ultrasonic beam vis-a-vis the vessel segment under considerat ion is crucial for obtaining valid measures. A thorough knowledge of t he physics involved is essential for an adequate use of the instrument . With correct use, easily reproducible and reliable estimations are o btained of the mechanical properties of large vessel walls.