Optical coherence tomography (OCT) is one of useful diagnostic devices for retinal diseases. Recently, optical coherence tomography based angiography (OCTA) extends the OCT applications from structural images to functional images by enabling blood vessel networks mapping. As the use of OCT and OCTA increases in ophthalmology, it is necessary to develop retinal phantoms for performance evaluation of clinical OCT devices for retinal imaging.
In this study, we have developed a retinal layer-mimicking phantom including microfluidic channels to assess OCT and OCTA image quality and to evaluate software accuracy. The phantom is constructed of thin scattering films based on polydimethylsiloxane (PDMS) and titanium dioxide (TiO2) powder. We adjusted TiO2 particle concentration in PDMS for matching intensity of retinal OCT images. Particles were well dispersed throughout PDMS using a probe tip sonicator. Mixed PDMSs were carried out spin coating on a glass slide to make thin films. Before spin coating, silane was applied to the glass substrate to provide a hydrophobic coating for easily removing of cured PDMS. After spinning, thin filmed PDMSs were cured. Microfluidic channels were also made with PDMSs mixed with TiO2 powder, and were designed with sizes of 50 um, 100 um, and 200 um. thin films of cured PDMS were stacked on microfluidic channels. We used diluted dye liquids containing microbeads to occur optically scattered liquid flow like blood vessel. Dye liquids containing microbeads were flowed into an inlet port of the channel through a syringe pump
Finally, we successfully obtained cross-sectional volumetric OCT and OCTA images of completed retinal phantom using lab-made OCT system and clinical OCT system.
We present a method for an intraoperative microscope-mounted Fourier-domain optical coherence tomography (FD-OCT) system to maintain high image contrast while dynamic adjusting focal planes. Because two imaging system with different imaging depth are integrated into one system, active control of OCT imaging conditions is indispensible for functioning high quality imaging modality. For the purpose of active adjustment of the focal plane, an electrically focus tunable lens (FTL) was used in the sample arm of the OCT system. Because the OCT image contrast at a depth is given by roll-off characteristics of the FD-OCT that is a function of difference in OPL between the sample and reference arm, we should compensate the difference in the OPL to enhance image contrast. We proposed the use of a piezoelectric actuator (PZT) attached to a reflection optic to actively control the OPL in the reference arm. With active controlling the FTL and PZT simultaneously, we can optimize and keep the OCT image contrast while maintaining image depth positions. From a surface position in the OCT image, the focal length variations with the FTL are calculated and the focal length of the FTL is tuned to match on the sample surface. Contrast optimization with the PZT is performed with compensating the optical path length difference from the additional focal length of the FTL. We integrated the OCT to a conventional surgical microscope and demonstrate feasible observation of OCT image with high contrast at constant imaging depth under the change of focal plane of the microscope.
Microparticles including biological cells were trapped and manipulated using a continuous wave tweezer and a femtosecond laser tweezer. The difference of the optical trapping force between CW and femtosecond optical tweezers increased as the particle size decreased, possibly due to the self-focusing effect of the ultrashort pulses. Also, the white damage spots were generated near the focus during femtosecond optical trapping of biological cells even with extremely low average power. The instantaneous optical damage threshold was measured as a function of the trap depth as well. These results may help to optimize the optical trapping of biological cells using femtosecond lasers.
Using an acousto-optic beam deflector and a line scan camera, we constructed a non-mechanical, slit-scanning confocal microscope. It generates two-dimensional 512x512 images with speed of 60 frames/sec, which can be easily expanded, to 100 frames/sec. The measured axial and lateral resolutions of the system are 3.3 mm and <1 mm, respectively, with a 50X objective. This simple design can produce frames rates faster than other commercial products with comparable resolution, which may be useful for analysis of rapid interactions in various biological applications.
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