Scanless optical coherence tomography for high-speed 3d biomedical microscopy

Optical coherence tomography (OCT) is a high-resolution cross-sectional imaging modality that has found applications in a wide range of biomedical fields, such as ophthalmology diagnosis, interventional cardiology, surgical guidance, and oncology. OCT can be used to image dynamic scenes, in quantitative blood flow sensing and visualization, dynamic optical coherence elastography, and large-scale neural recording. However, the spatiotemporal resolution of OCT for dynamic imaging is limited by the approach it takes to scan the three-dimensional (3-D) space. In a typical OCT system, the incident light is focused to a point at the sample. The OCT system uses mechanical scanners (galvanometers or MEMS scanners) steer the probing beam to scan the transverse plane and acquires an A-scan at each transverse coordinate. For volumetric imaging, the OCT system scans individual voxels in a 3D Cartesian coordinate sequentially, resulting a limited imaging speed. In addition to limited spatiotemporal resolution, the use of mechanical scanners results in bulky sample arm and complex system configuration. This dissertation seeks to overcome limitations of conventional raster scanning approach for OCT data acquisition, by investigating novel methods to address OCT voxels in 3D space. Scanless OCT imaging is achieved through the use of spatial light modulator that precisely manipulates light wave to generate output with desired amplitude and phase. It is anticipated that the scanless OCT imaging technologies developed in this dissertation will introduce a significant paradigm shift in OCT scanning of 3D space and allow the observation of transient phenomena (neural activities, blood flow dynamics, etc.) with unprecedented spatiotemporal resolution. This research focuses on technology development and validation. Two approaches for scanless OCT imaging are investigated. One approach is optically computed optical coherence tomography (OC-OCT), and the other approach is Line field Fourier domain OCT (LF-FDOCT) based on spatial light modulator. OC-OCT takes a highly innovative optical computation strategy to extract signal from a specific depth directly without signal processing in a computer. The optical computation module in OC-OCT performs Fourier transform optically before data acquisition, by calculating the inner product between a Fourier basis function projected by the spatial light modulator and the Fourier domain interferometric signal. OC-OCT allows phase resolved volumetric OCT imaging without mechanical scanning, and has the capability to image an arbitrary 2D plane in a snapshot manner. LF-FDOCT illuminates the sample with a line field generated by a spatial light modulator. Interferometric signals from different transverse coordinates along the line field are dispersed by a grating and detected in parallel by the rows of a 2D camera. Cross-sectional image (Bscan) is obtained by performing Fourier transform along the rows of the camera. By scanning the line field electronically at the SLM, volumetric OCT imaging can be performed without mechanical scanning. In this dissertation, the principles of OC-OCT and LF-FDOCT technology are described. The imaging capability of OC-OCT and LF-FDOCT systems are quantitatively evaluated and demonstrated in 2D and 3D imaging experiments on a variety of samples