High resolution imaged laser speckle strain gauge for vascular applications

Area of Science:

• Biomedical Engineering
• Optical Measurement Techniques
• Vascular Mechanics

Background:

• Current speckle interferometry methods for strain measurement often rely on cross-correlations.
• These methods can be complex and may have limitations in accurately capturing dynamic strain rates in soft tissues.

Purpose of the Study:

• To describe a new imaged laser speckle strain gauge designed for direct measurement of strain rates in vascular applications.
• To present a novel method that bypasses the need for cross-correlations between reference and strain-modulated images.

Main Methods:

• The technique utilizes a two-dimensional frequency transform of "stacked speckle histories."
• Speckle histories are time series of 1D views of speckle patterns, arranged in a spatio-temporal array.
• The tilt of these histories directly relates to the time rate of speckle pattern shift, indicating strain rate.

Main Results:

• The strain gauge is sensitive to in-plane strains.
• In vitro evaluations on a human tibial artery and rat inferior vena cava yielded strain rates of 30.1 ± 3.2 and 24.83 ± 2.1 µε/s, respectively.
• Measured total strains were 21.6 and 19.86 µε, demonstrating high sensitivity.

Conclusions:

• The described laser speckle strain gauge provides direct measurement of strain rates.
• This method is significantly more sensitive (at least one order of magnitude) than existing soft-tissue strain measurement techniques.
• The technique shows promise for advanced vascular applications requiring precise strain rate analysis.