Fabrication of high quality optical coherence tomography (OCT) calibration artefacts using femtosecond inscription

Abstract

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.

Femtosecond laser inscribed advanced calibration phantom for optical coherence tomography (OCT)

“…However, those methods do not address to all the requirements to quantitatively calibrate and assess the OCT system and associated image distortion when imaging through a curved surface. Femtosecond laser direct writing technique has been used previously for the purpose of phantom inscription at Aston [5], where a non-planar multi-purpose phantom was developed [6] where the planar side could be used for a standard assessment and calibration while the curved side could be used to test the validity of the post-processing algorithm for the image distortion. However, this phantom was inscribed with grid pattern that requires a higher degree of alignment in terms of the angle of the sample to generate a useful calibration phantom for the OCT operator.…”