Ultrasonic measurement of prosthetic heart valve action

An in-vitro study has been made of the echo patterns obtained during ultrasonic Time-Motion (T-M) scanning of commonly used prosthetic heart valves. Studies have been undertaken of Starr-Edwards, Beal, and Bjork-Shilley valves. From the recorded traces information has been obtained regarding the orientations of the ultrasound beam to the central axes of the valves for which accurate measurements can be made. The orientations have been determined for which the opening and closing times of the valves can be measured to within 20 ms. Characteristics of the T-M traces have been noted which allow the angle between the direction of an ultrasound beam and a central valve axis to be reduced to less than 20°. This makes the error due to angular misalignment of the beam less than — 6% when the range of movement of a ball, disc, or flap is being measured. Finally a number of artefacts are considered which can arise when prosthetic valves are examined with ultrasound.