In this study, we have developed an acoustic radiation force orthogonal excitation optical coherence elastography
(ARFOE-OCE) method for the visualization of the shear wave and the calculation of the shear modulus based on the OCT
Doppler variance method. The vibration perpendicular to the OCT detection direction is induced by the remote acoustic
radiation force (ARF) and the shear wave propagating along the OCT beam is visualized by the OCT M-scan. The
homogeneous agar phantom and two-layer agar phantom are measured using the ARFOE-OCE system. The results show
that the ARFOE-OCE system has the ability to measure the shear modulus beyond the OCT imaging depth. The OCT
Doppler variance method, instead of the OCT Doppler phase method, is used for vibration detection without the need of
high phase stability and phase wrapping correction. An M-scan instead of the B-scan for the visualization of the shear
wave also simplifies the data processing.
A novel quantitative 3D imaging system of silicon microstructures using InfraRed Transport of Intensity Equation (IRTIE) is proposed in this paper. By recording the intensity at multiple planes and using FFT or DCT based TIE solver, fast and accurate phase retrieval for both uniform and non-uniform intensity distributions is proposed. Numerical simulation and experiments confirm the accuracy and reliability of the proposed method. The application of IR-TIE for inspection of micro-patterns in visibly opaque media using 1310 nm light source is demonstrated. For comparison, micro-patterns are also inspected by the contact scanning mode Taylor Hobson system. Quantitative agreement suggests the possibility of using IR-TIE for phase imaging of silicon wafers.
Optical coherence tomography (OCT) is an emerging noninvasive imaging technique, which is based on low-coherence interferometry. OCT images suffer from speckle noise, which reduces image contrast. A shrinkage filter based on wave atoms transform is proposed for speckle reduction in OCT images. Wave atoms transform is a new multiscale geometric analysis tool that offers sparser expansion and better representation for images containing oscillatory patterns and textures than other traditional transforms, such as wavelet and curvelet transforms. Cycle spinning-based technology is introduced to avoid visual artifacts, such as Gibbs-like phenomenon, and to develop a translation invariant wave atoms denoising scheme. The speckle suppression degree in the denoised images is controlled by an adjustable parameter that determines the threshold in the wave atoms domain. The experimental results show that the proposed method can effectively remove the speckle noise and improve the OCT image quality. The signal-to-noise ratio, contrast-to-noise ratio, average equivalent number of looks, and cross-correlation (XCOR) values are obtained, and the results are also compared with the wavelet and curvelet thresholding techniques.