MEMO: dataset and methods for robust multimodal retinal image registration with large or small vessel density differences.

The measurement of retinal blood flow (RBF) in capillaries can provide a powerful biomarker for the early diagnosis and treatment of ocular diseases. However, no single modality can determine capillary flowrates with high precision. Combining erythrocyte-mediated angiography (EMA) with optical coherence tomography angiography (OCTA) has the potential to achieve this goal, as EMA can measure the absolute RBF of retinal microvasculature and OCTA can provide the structural images of capillaries. However, multimodal retinal image registration between these two modalities remains largely unexplored. To fill this gap, we establish MEMO, the first public multimodal EMA and OCTA retinal image dataset. A unique challenge in multimodal retinal image registration between these modalities is the relatively large difference in vessel density (VD). To address this challenge, we propose a segmentation-based deep-learning framework (VDD-Reg), which provides robust results despite differences in vessel density. VDD-Reg consists of a vessel segmentation module and a registration module. To train the vessel segmentation module, we further designed a two-stage semi-supervised learning framework (LVD-Seg) combining supervised and unsupervised losses. We demonstrate that VDD-Reg outperforms existing methods quantitatively and qualitatively for cases of both small VD differences (using the CF-FA dataset) and large VD differences (using our MEMO dataset). Moreover, VDD-Reg requires as few as three annotated vessel segmentation masks to maintain its accuracy, demonstrating its feasibility.

Plexus-Specific Retinal Capillary Blood Flow Analysis Using Erythrocyte Mediated Angiography and Optical Coherence Tomography Angiography.

Purpose: The purpose of this study was to identify and measure plexus-specific absolute retinal capillary blood flow velocity and acceleration in vivo in both nonhuman primates (NHPs) and humans using erythrocyte mediated angiography (EMA) and optical coherence tomography angiography (OCTA). Methods: EMA and OCTA scans centered on the fovea were obtained in 2 NHPs and 11 human subjects. Scans were also obtained in NHP eyes while IOP was experimentally elevated. Erythrocyte velocity and acceleration in retinal arteries, capillaries, and veins were measured and capillaries were categorized based on location within the superficial vascular (SVP), intermediate capillary (ICP), or deep capillary plexus (DCP). Generalized linear mixed models were used to estimate the effects of intraocular pressure (IOP) on capillary blood flow. Results: Capillary erythrocyte velocity at baseline IOP was 0.64 ± 0.29 mm/s in NHPs (range of 0.14 to 1.85 mm/s) and 1.55 ± 0.65 mm/s in humans (range of 0.46 to 4.50 mm/s). Mean erythrocyte velocity in the SVP, ICP, and DCP in NHPs was 0.69 ± 0.29 mm/s, 0.53 ± 0.22 mm/s, and 0.63 ± 0.27 mm/s, respectively (P = 0.14 for NHP-1 and P = 0.28 for NHP-2). Mean erythrocyte velocity in the human subjects did not differ significantly among SVP, ICP, and DCP (1.46 ± 0.59 mm/s, 1.58 ± 0.55 mm/s, and 1.59 ± 0.79 mm/s, P = 0.36). In NHPs, every 1 mm Hg increase in IOP was associated with a 0.13 mm/s reduction in arterial velocity, 0.10 mm/s reduction in venous velocity, and 0.01 mm/s reduction in capillary velocity (P < 0.001) when accounting for differences in mean arterial pressure (MAP). Conclusions: Blood flow by direct visualization of individual erythrocytes can be quantified within capillary plexuses. Capillary velocity decreased with experimental IOP elevation.

Precise frequency measurements of iodine hyperfine transitions at 671 nm.

We report absolute frequency measurements on the a(1), a(10), and a(15) hyperfine components of the R(78) 4-6 line of (127)I(2). An external-cavity diode laser system at 671 nm is frequency-stabilized to the saturated absorption center obtained by modulation transfer spectroscopy in an iodine vapor cell. Its absolute frequency is measured by an optical frequency comb. The effect of pressure shift is investigated to obtain the absolute transition frequency at zero pressure. Our determination of the line centers reaches a precision of better than 40 kHz and will provide useful input for theoretical calculations. This frequency-stabilized laser can be used as a reference laser for the spectroscopy of lithium D lines.

ZnO thin film with nanorod arrays applied to fluid sensor.

A ZnO guiding layer with nanorod arrays grown on a 90°-rotated ST-cut (42°45) quartz substrate was used to fabricate a Love wave fluid sensor. ZnO nanorod arrays synthesized on the guiding layer enhance the sensitivity of the flow rate. ZnO thin films were deposited by radio frequency magnetron sputtering and ZnO nanorod arrays were then synthesized on the thin films via the hydrothermal method. The crystalline structure and surface morphology of ZnO thin films and nanorod arrays were examined by X-ray diffraction and scanning electron microscopy. The effects of the thickness of ZnO thin film and the surface morphology of ZnO nanorod arrays on the sensitivity of flow rate were investigated. A linear response between flow rate and the return loss of the sensor with one-port resonator type can be obtained by adjusting the thickness of ZnO thin film and the length of nanorod arrays.