APPLICATION OF VIBRO-ACOUSTOGRAPHY IN DETECTION OF SINGLE LEG SEPARATION (SLS) IN THE BJORK-SHILEY CONVEXO-CONCAVE (BSCC) HEART VALVES

Abstract

Background: Occurrence of SLS in the BSCC mechanical heart valves may cause the fracture of outlet strut and total valvular failure. If SLS is detected, it is possible to prophylactically replace the valve. This study has aimed at differentiating the acoustic characteristics of BSCC valves with SLS from those of intact valves. An innovative method of Vibro-Acoustic Spectrography (VAS) has been utilized in this study. Methods: VAS utilizes the radiation force of ultrasound to actively vibrate the object at a range of kHz frequencies, and records the resulting vibrations with a sensitive detector. The recorded data are then used to determine the mechanical frequency response of the object by the Fourier transform. The stress field produced by this technique is highly localized, allowing one to target only the strut and thus avoid interference from vibrations of other structures. Twenty-four BSCC valves were selected: 12 intact valves (25, 27, 29 mm) and 12 explanted valves with SLS (27, 29, 31, 33 mm). The center frequency of the VAS system was 3.0 MHz with the radiation force frequency of 1–15 kHz. Results: It has been demonstrated that the two ends of the fractured leg created three basic configurations: completely separated, partially separated, and completely attached. Also, explanted BSCC valves with SLS consistently exhibited different resonance frequencies than those of the intact valves. Intact valves outlet struts showed resonance frequencies of 6.8–10.8 kHz (size dependent). The corresponding frequencies for the SLS valves ranged from 2.1 kHz to 4.8 kHz, depending on the fracture types. This study has shown that threshold frequency values of 4.8–6.8 kHz can be effectively used to differentiate SLS from intact valves. Conclusions: VAS can be effectively used as an active probing method for remote detection of SLS in the BSCC heart valves.