Continuous spectral zooming for in vivo live 4D-OCT with MHz A-scan rates and long coherence

Abstract

We present continuous three-dimensional spectral zooming in live 4D-OCT using a home-built FDML based OCT system with 3.28 MHz A-scan rate. Improved coherence characteristics of the FDML laser allow for imaging ranges up to 10 cm. For the axial spectral zoom feature, we switch between high resolution and long imaging range by adjusting the sweep range of our laser. We present a new imaging setup allowing for synchronized adjustments of the imaging range and lateral field of view during live OCT imaging. For this, a novel inline recalibration algorithm was implemented that enables numerical k-linearization of the raw OCT fringes for every frame instead of every volume. This is realized by acquiring recalibration data within the dead time of the raster scan at the turning points of the fast axis scanner. We demonstrate in vivo OCT images of fingers and hands at different resolution modes and show real three-dimensional zooming during live 4D-OCT. A three-dimensional spectral zooming feature for live 4D-OCT is expected to be a useful tool for a wide range of biomedical, scientific and research applications, especially in OCT guided surgery.

Large area robotically assisted optical coherence tomography (LARA-OCT) for skin imaging with MHz-OCT surface tracking

“…Thus, it requires manual positioning of the probe above the target prior to the OCT measurement. For future applications, we will integrate spectral zooming features [9] to allow flexible depth range adjustments. This is a key factor for user-independent, safe automatic target search features to initially position the probe without the need of external ranging modalities.…”

850 nm FDML: performance and challenges

“…With an axial resolution of 6.4 m, a sweep duration of 1.202 s and the use of a balanced 700 MHz silicon photodiode, the laser roll-off should be satisfactory to acquire retinal images disregarding the deteriorating effect of ripples and the low gain to loss ratio. The laser performance might be further improved to attain 50 dB dynamic range like in [6] by reducing the PMD and increasing the gain.…”

“…Commercial FDML lasers are available at 1060 nm, 1310 nm and 1550 nm. They can be used for diverse applications such as 4D MHz-OCT [6,7], Time-Encoded Raman as a probe laser and Spectro-temporal laser imaging by diffracted excitation (SLIDE) microscopy [8,9]. In order to extend the scope of application, a shorter wavelength FDML laser is interesting since the water absorption is decreasing towards the visible spectrum and increased scattering can improve the contrast of low scattering features.…”

1190 nm Fourier domain mode locked (FDML) laser for optical coherence tomography (OCT)

“…In the past decade, we have witnessed a huge development in optical coherence tomography (OCT), especially in swept source OCT (SS-OCT) offering multi-MHz A-scan rates [1], faster than typical spectral domain OCT (SD-OCT) systems [2]. In addition to its high speed, SS-OCT improves the image ranging depth.…”