Optical coherence tomography (OCT) is a non-invasive three-dimensional imaging system that is capable of producing
high resolution in-vivo images. OCT is approved for use in clinical trials in Japan, USA and Europe. For OCT to be used
effectively in a clinical diagnosis, a method of standardisation is required to assess the performance across different
systems. This standardisation can be implemented using highly accurate and reproducible artefacts for calibration at
both installation and throughout the lifetime of a system. Femtosecond lasers can write highly reproducible and highly
localised micro-structured calibration artefacts within a transparent media. We report on the fabrication of high quality
OCT calibration artefacts in fused silica using a femtosecond laser. The calibration artefacts were written in fused silica
due to its high purity and ability to withstand high energy femtosecond pulses. An Amplitude Systemes s-Pulse Yb:YAG
femtosecond laser with an operating wavelength of 1026 nm was used to inscribe three dimensional patterns within the
highly optically transmissive substrate. Four unique artefacts have been designed to measure a wide variety of
parameters, including the points spread function (PSF), modulation transfer function (MTF), sensitivity, distortion and
resolution - key parameters which define the performance of the OCT. The calibration artefacts have been characterised
using an optical microscope and tested on a swept source OCT. The results demonstrate that the femtosecond laser
inscribed artefacts have the potential of quantitatively and qualitatively validating the performance of any OCT system.
The recent expansion of clinical applications for optical coherence tomography (OCT) is driving the development of
approaches for consistent image acquisition. There is a simultaneous need for time-stable, easy-to-use imaging targets
for calibration and standardization of OCT devices. We present calibration targets consisting of three-dimensional
structures etched into nanoparticle-embedded resin. Spherical iron oxide nanoparticles with a predominant particle
diameter of 400 nm were homogeneously dispersed in a two part polyurethane resin and allowed to harden overnight.
These samples were then etched using a precision micromachining femtosecond laser with a center wavelength of 1026
nm, 100kHz repetition rate and 450 fs pulse duration. A series of lines in depth were etched, varying the percentage of
inscription energy and speed of the translation stage moving the target with respect to the laser. Samples were imaged
with a dual wavelength spectral-domain OCT system (λ=800nm, ▵λ≈180nm, and λ=1325nm, ▵λ≈100nm) and point-spread function of nanoparticles within the target was measured.
As optical coherence tomography (OCT) becomes widespread, validation and characterization of
systems becomes important. Reference standards are required to qualitatively and quantitatively
measure the performance between difference systems. This would allow the performance degradation
of the system over time to be monitored. In this report, the properties of the femtosecond inscribed
structures from three different systems for making suitable OCT characterization artefacts (phantoms)
are analyzed. The parameter test samples are directly inscribed inside transparent materials. The
structures are characterized using an optical microscope and a swept-source OCT. The high
reproducibility of the inscribed structures shows high potential for producing multi-modality OCT
calibration and characterization phantoms. Such that a single artefact can be used to characterize
multiple performance parameters such the resolution, linearity, distortion, and imaging depths.
In Fourier domain optical coherence tomography (FD-OCT), a large amount of interference data needs to be resampled from the wavelength domain to the wavenumber domain prior to Fourier transformation. We present an approach to optimize this data processing, using a graphics processing unit (GPU) and parallel processing algorithms. We demonstrate an increased processing and rendering rate over that previously reported by using GPU paged memory to render data in the GPU rather than copying back to the CPU. This avoids unnecessary and slow data transfer, enabling a processing and display rate of well over 524,000 A-scan/s for a single frame. To the best of our knowledge this is the fastest processing demonstrated to date and the first time that FD-OCT processing and rendering has been demonstrated entirely on a GPU.
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