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Optical system design of a laser-based stethoscope
Sileshi, Girum A. (2012)

Optical system design of a laser-based stethoscope


Issue Date

Thesis or Dissertation

In this paper, we demonstrate the development of a new type of stethoscope using laser technology to visualize the heart beat signal. This heartbeat detection technique could overcome the limitation of the acoustic stethoscope brought by the poor ability of human ears to hear low frequency heart sounds. This is important, as valuable information from sub-audio sounds is present at frequencies below the human hearing range. Moreover, the diagnosis accuracy of the acoustic stethoscope is also very sensitive to noise from the immediate environment. In this laser-based stethoscope, the heartbeat signal is correlated to the optical spot of a laser beam reflected from a thin mirror attached to the patient’s chest skin. The motion of the mirror with the chest skin is generated by heartbeat and breathing. A linear optical sensor is applied to detect and record the motion of the optical spot, from which the heart sound signal in time-domain is extracted. The heart sound signal is subsequently transformed to frequency domain through digital signal processing. Both time domain and frequency-domain signals are analyzed in order to classify different types of heart murmurs. A digital filter is designed to remove other activities associated with the movement of chest skin, such as respiration. We developed the prototype of the system and tested the prototype on a dummy human body with various heartbeat patterns and breathing. We compared the laser generated results with the concurrent testing results from phonocardiography. Results reveal that the laser based heart sound detection approach has the advantage over the phonocardiography for low frequency sounds (≤ 50Hz) while the phonocardiography is more sensitive to higher frequency sounds ≥ 200Hz).

University of Minnesota M.S. thesis. June 2012. Major: Clinical Research. Advisor: Professor Jing Bai. 1 computer file (PDF); ix, 59 pages.

Suggested Citation
Sileshi, Girum A.. (2012). Optical system design of a laser-based stethoscope. Retrieved from the University of Minnesota Digital Conservancy,

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