Laser speckle imaging of atherosclerotic plaques through optical fiber bundles

Abstract

Laser speckle imaging (LSI), a new technique that measures an index of plaque viscoelasticity, has been investigated recently to characterize atherosclerotic plaques. These prior studies demonstrated the diagnostic potential of LSI for detecting high-risk plaques and were conducted ex vivo. To conduct intracoronary LSI in vivo, the laser speckle pattern must be transmitted from the coronary wall to the image detector in the presence of cardiac motion. Small-diameter, flexible optical fiber bundles, similar to those used in coronary angioscopy, may be incorporated into an intravascular catheter for this purpose. A key challenge is that laser speckle is influenced by inter-fiber leakage of light, which may be exacerbated during bundle motion. In this study, we tested the capability of optical fiber bundles to transmit laser speckle patterns obtained from atherosclerotic plaques and evaluated the influence of motion on the diagnostic accuracy of fiber bundle-based LSI. Time-varying heliumneon laser speckle images of aortic plaques were obtained while cyclically moving the flexible length of the bundle to mimic coronary motion. Our results show that leached fiber bundles may reliably transmit laser speckle images in the presence of cardiac motion, providing a viable option to conduct intracoronary LSI.

Correction of optical absorption and scattering variations in laser speckle rheology measurements

“…Utilizing the intensity of only one coherent area, necessitates temporal averaging of several g 2 (t) curves and acquisition times of several minutes to hours. The high speed CMOS camera, used for multi-speckle acquisition here, improves the statistical accuracy of the measured g 2 (t) and eliminates the need for longtime acquisition [6][7][8][9][10][11][12].…”

“…The customary tool for measuring the viscoelastic properties is a mechanical rheometer, which evaluates the ratio of an applied oscillatory stress to the consequential strain in the specimen, over a limited oscillation frequency range to calculate the frequency-dependent viscoelastic modulus, G*(ω). The capability of LSR for measuring this quantity in a non-destructive/non-contact manner from the speckle fluctuations is appealing, particularly in applications where mechanical manipulation may alter the sample properties and in cases where only small sample volumes are available for measurement [1][2][3][4][5][6][7][8][9][10][11]. In LSR, a small volume of the sample is illuminated by a mono-chromatic laser source and a high-speed CMOS camera is used to capture the temporal fluctuations of back-scattered speckle patterns, induced by Brownian displacements of scattering particles [1,[6][7][8][9][10][11][12][13].…”

“…The capability of LSR for measuring this quantity in a non-destructive/non-contact manner from the speckle fluctuations is appealing, particularly in applications where mechanical manipulation may alter the sample properties and in cases where only small sample volumes are available for measurement [1][2][3][4][5][6][7][8][9][10][11]. In LSR, a small volume of the sample is illuminated by a mono-chromatic laser source and a high-speed CMOS camera is used to capture the temporal fluctuations of back-scattered speckle patterns, induced by Brownian displacements of scattering particles [1,[6][7][8][9][10][11][12][13]. Cross correlation analysis of time-varying speckle image series yields the speckle intensity temporal autocorrelation curve, g 2 (t), from which the mean square displacement (MSD) of scattering particles, <Δr 2 (t)>, is retrieved [1,10,11,[14][15][16][17][18].…”

“…Laser Speckle Rheology (LSR), an optical approach for the non-contact evaluation of the viscoelastic properties of the materials, has a number of industrial, chemical and biomedical applications related to material sciences, polymer engineering, food sciences, and clinical diagnosis [1][2][3][4][5][6][7][8][9][10][11]. The customary tool for measuring the viscoelastic properties is a mechanical rheometer, which evaluates the ratio of an applied oscillatory stress to the consequential strain in the specimen, over a limited oscillation frequency range to calculate the frequency-dependent viscoelastic modulus, G*(ω).…”

Assessing blood coagulation status with laser speckle rheology

“…In this study, we have investigated and validated a new optical approach, Laser Speckle Rheology (LSR) [13][14][15][16][17][18][19], for assessing the viscoelastic properties of blood during coagulation, therefore opening the opportunity to assess the patient's coagulation state rapidly using just a few drops of whole blood.…”