Absolute measurements of cerebral blood flow (CBF) are an important endpoint in studies of cerebral pathophysiology. Currently no accepted method exists for in vivo longitudinal monitoring of CBF with high resolution in rats and mice. Using three-dimensional Doppler Optical Coherence Tomography and cranial window preparations, we present methods and algorithms for regional CBF measurements in the rat cortex. Towards this end, we develop and validate a quantitative statistical model to describe the effect of static tissue on velocity sensitivity. This model is used to design scanning protocols and algorithms for sensitive 3D flow measurements and angiography of the cortex. We also introduce a method of absolute flow calculation that does not require explicit knowledge of vessel angles. We show that OCT estimates of absolute CBF values in rats agree with prior measures by autoradiography, suggesting that Doppler OCT can perform absolute flow measurements in animal models.

Improving our understanding of brain function requires novel tools to observe multiple physiological parameters with high resolution in vivo. We have developed a multimodal imaging system for investigating multiple facets of cerebral blood flow and metabolism in small animals. The system was custom designed and features multiple optical imaging capabilities, including 2-photon and confocal lifetime microscopy, optical coherence tomography, laser speckle imaging, and optical intrinsic signal imaging. Here, we provide details of the system's design and present in vivo observations of multiple metrics of cerebral oxygen delivery and energy metabolism, including oxygen partial pressure, microvascular blood flow, and NADH autofluorescence.

We demonstrate a high-speed and wide-tuning-range swept laser for optical coherence tomography (OCT) imaging. The repetition rate of the laser is twice the speed of the polygon filter and is achieved by using two delay fibers in a Fox-Smith cavity. The performance of the laser is the following: a scanning range of 110nm centered at 1310nm, and the output power of 10mw at a 102.2 kHz sweeping rate. © 2011 Copyright SPIE - The International Society for Optical Engineering.

In this paper, we analyzed the retinal and choroidal blood vasculature in the posterior segment of the human eye with optimized color Doppler and Doppler variance optical coherence tomography. Depth-resolved structure, color Doppler and Doppler variance images were compared. Blood vessels down to capillary level were able to be obtained with the optimized optical coherence color Doppler and Doppler variance method. For in-vivo imaging of human eyes, bulkmotion induced bulk phase must be identified and removed before using color Doppler method. It was found that the Doppler variance method is not sensitive to bulk motion and the method can be used without removing the bulk phase. A novel, simple and fast segmentation algorithm to indentify retinal pigment epithelium (RPE) was proposed and used to segment the retinal and choroidal layer. The algorithm was based on the detected OCT signal intensity difference between different layers. A spectrometer-based Fourier domain OCT system with a central wavelength of 890 nm and bandwidth of 150nm was used in this study. The 3-dimensional imaging volume contained 120 sequential two dimensional images with 2048 A-lines per image. The total imaging time was 12 seconds and the imaging area was 5x5 mm2. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Purpose

To develop geometric perfusion deficits (GPD), an optical coherence tomography angiography (OCTA) biomarker based on oxygen diffusion, and to evaluate its utility in a pilot study of healthy subjects and patients with diabetic retinopathy (DR).

Design

Retrospective cross-sectional study.

Methods

Commercial spectral-domain optical coherence tomography angiography (OCTA) instruments were used to acquire repeated 3 × 3-mm² and 6 × 6-mm² motion-corrected macular OCTA volumes. En face OCTA images corresponding to the superficial capillary plexus (SCP), deep capillary plexus (DCP), and full retinal projections were obtained using automatic segmentation. For each projection, the GPD percentage and the vessel density percentage, the control metric, were computed, and their values were compared between the normal and DR eyes. The repeated OCTA acquisitions were used to assess the test-retest repeatability of the GPD and vessel density percentages.

Results

Repeated OCTA scans of 15 normal eyes and 12 DR eyes were obtained. For all en face projections, GPD percentages were significantly higher in DR eyes than in normal eyes; vessel density percentages were significantly lower in all but 1 projection (DCP). Large GPD areas were used to identify focal perfusion deficits. Test-retest analysis showed that the GPD percentage had superior repeatability than the vessel density percentage in most cases. A strong negative correlation between the GPD percentage and the vessel density percentage was also found.

Conclusions

Geometric perfusion deficits, an OCTA biomarker based on oxygen diffusion, provides a quantitative metric of macular microvascular remodeling with a strong physiological underpinning. The GPD percentage may serve as a useful biomarker for detecting and monitoring DR.

A polarization maintaining buffered Fourier domain mode-locked (FDML) swept source at center wavelength of 1310 nm for multiplying the scanning rate of FDML swept source was demonstrated. The scanning rate of the buffered FDML swept source was doubled without sacrificing the output power of the swept source by combining two orthogonally polarized outputs with a polarization beam combiner (PBC). The stability of the swept source was improved significantly because the polarization state of the laser beam inside the cavity is maintained without any polarization controllers. With the linear polarization states of the output laser beam, the buffered FDML swept source is also ready to be used in a PSOCT system. The swept source is capable of a tuning range of more than 150 nm at a 102 kHz sweeping rate. An FDOCT system was developed with the built swept source. © 2012 SPIE.

We evaluated several, previously published, complex conjugate artifact removal methods and algorithms that have been proposed for Fourier domain optical coherence tomography (Fd-OCT). To ensure comparable conditions, only one OCT system was used, but with modified data acquisition schemes, depending on the requirements of each method/algorithm. This limited our evaluation to single spectrometer based Fd-OCT approaches. The suppression ratio of complex conjugate artifact images using a paperboard is assessed for all tested methods. Several other metrics are also used for comparison, including a list of additional hardware requirements (beyond standard Fd-OCT components) and data acquisition schemes. Finally, in vivo human finger pad and nail images are presented for comparison to the standard Fd- OCT images and full-range images. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Optical coherence tomography (OCT) is a noninvasive method for retinal imaging. In this work, we present an in vivo human retinal microvascular network measurement by an intensity-based Doppler variance (IBDV) based on sweptsource OCT. In addition, an automatic three-dimensional (3-D) segmentation method was used for segmenting intraretinal layers. The microvascular networks were divided into six layers by visualizing of each individual layer with enhanced imaging contrast. This method has potential for earlier diagnosis and precise monitoring in retinal vascular diseases.

Optical coherence tomography (OCT) is an evolving noninvasive imaging modality and has been used to image the human larynx during surgical endoscopy. The design of a long GRIN lens based probe capable of capturing images of the human larynx by use of a swept-source OCT during a typical office-based laryngoscopy examination is presented. An optical-ballast-based 4F optical relay system is proposed to realize variable working distance with a constant optical delay. In vivo OCT imaging of the human larynx is demonstrated with 40 fame/second. Office-based OCT is a promising imaging modality to study the larynx. © 2009 SPIE.