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Abstract
Tissue optical and mechanical properties are correlated to tissue pathologic changes. This manuscript describes a dual-mode ultrasound modulated optical imaging system capable of sensing local optical and mechanical properties in reflection geometry. The optical characterisation was achieved by the acoustic radiation force assisted ultrasound modulated optical tomography (ARF-UOT) with laser speckle contrast detection. Shear waves generated by the ARF were also tracked optically by the same system and the shear wave speed was used for the elasticity measurement. Tissue mimicking phantoms with multiple inclusions buried at 11 mm depth were experimentally scanned with the dual-mode system. The inclusions, with higher optical absorption and/or higher stiffness than background, were identified based on the dual results and their stiffnesses were quantified. The system characterises both optical and mechanical properties of the inclusions compared with the ARF-UOT or the elasticity measurement alone. Moreover, by detecting the backward scattered light in reflection detection geometry, the system is more suitable for clinical applications compared with transmission geometry.
Highlights
Measuring optical and mechanical properties of biological tissue provides complementary information for clinical diagnosis
The optical characterisation was achieved by the acoustic radiation force assisted ultrasound modulated optical tomography (ARF-UOT) with laser speckle contrast detection
Shear waves generated by the ARF were tracked optically by the same system and the shear wave speed was used for the elasticity measurement
Summary
Measuring optical and mechanical properties of biological tissue provides complementary information for clinical diagnosis. To improve the image resolution at depth, several methods have been developed including ultrasound modulated optical tomography (UOT) [1], time-reversed ultrasonically encoded light focusing [2] and photo-acoustic tomography [3]. In addition to the ultrasound modulation, several studies have shown that the acoustic radiation force (ARF) - resulting from the momentum transfer from propagating ultrasound waves to the tissue - can increase the modulation by elevating the displacement of optical scatterers (in the order of μm) [10]. Using the laser speckle contrast detection method with properly adjusted exposure times of a charge-coupled device (CCD) camera, the ARF-assisted UOT is shown to increase the signal strength by 100% [11]. ARF-assisted UOT can have broadened lateral resolution if the optical measurement takes long and the measurement starts to contain shear wave effects
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