<p>We present a technique to reduce speckle in visible-light optical coherence tomography (vis-OCT) that preserves fine structural details and is robust against sample motion. Specifically, we locally modulate B-scans orthogonally to their axis of acquisition. Such modulation enables acquisition of uncorrelated speckle patterns from similar anatomical locations, which can be averaged to reduce speckle. To verify the effectiveness of speckle reduction, we performed <italic>in-vivo</italic> retinal imaging using modulated raster and circular scans in both mice and humans. We compared speckle-reduced vis-OCT images with the images acquired with unmodulated B-scans from the same anatomical locations. We compared contrast-to-noise ratio (CNR) and equivalent number of looks (ENL) to quantify the image quality enhancement. Speckle-reduced images showed up to a 2.35-dB improvement in CNR and up to a 3.1-fold improvement in ENL with more discernable anatomical features using eight modulated A-line averages at a 25-kHz A-line rate.</p>
There is strong evidence that the morphological parameters of multicellular tumor spheroids (MCTS), particularly size, sphericity, and growth pattern, play a role in their cytochemical responses. Because tumor spheroids accurately represent the three-dimensional (3D) structure of in vivo tumors, they may also mimic in vivo cytochemical responses, thus lending them relevance to cancer research. Knowledge of MCTS attributes, including oxygen and nutrient gradients, hypoxia resistance, and drug response, assist specialists seeking the most efficient ways to treat cancer. Structural information on tumor spheroids can provide insight into these attributes, and become a valuable asset for treatment in vivo. Currently, high-resolution bioimaging modalities, most notably bright field imaging, phase contrast imaging, fluorescent microscopy, and confocal imaging, are being employed for this purpose. However, these modalities lack sufficient penetration depth to resolve the entire geometry of large spheroids (>200um). In response to this deficiency, we propose a potential high-throughput imaging platform using optical coherence tomography (OCT) to quantify MCTS morphology. OCT’s high resolution and depth penetration allow us to obtain complete, high-detailed, 3D tumor reconstructions with accurate diameter measurements. Furthermore, a computer-based voxel counting method is used to quantify tumor volume, which is significantly more accurate than the estimations required by 2D-projection modalities. Thus, this imaging platform provides one of the most complete and robust evaluations of tumor spheroid morphology, and shows great potential for contribution to the study of cancer treatment and drug discovery.