Multi-MHz retinal OCT

Abstract

Abstract:We analyze the benefits and problems of in vivo optical coherence tomography (OCT) imaging of the human retina at A-scan rates in excess of 1 MHz, using a 1050 nm Fourier-domain mode-locked (FDML) laser. Different scanning strategies enabled by MHz OCT line rates are investigated, and a simple multi-volume data processing approach is presented. In-vivo OCT of the human ocular fundus is performed at different axial scan rates of up to 6.7 MHz. High quality non-mydriatic retinal imaging over an ultra-wide field is achieved by a combination of several key improvements compared to previous setups. For the FDML laser, long coherence lengths and 72 nm wavelength tuning range are achieved using a chirped fiber Bragg grating in a laser cavity at 419.1 kHz fundamental tuning rate. Very large data sets can be acquired with sustained data transfer from the data acquisition card to host computer memory, enabling high-quality averaging of many frames and of multiple aligned data sets. Three imaging modes are investigated: Alignment and averaging of 24 data sets at 1.68 MHz axial line rate, ultra-dense transverse sampling at 3.35 MHz line rate, and dual-beam imaging with two laser spots on the retina at an effective line rate of 6.7 MHz. 58. R. Huber, D. C. Adler, V. J. Srinivasan, and J. G. Fujimoto, "Fourier domain mode locking at 1050 nm for ultrahigh-speed optical coherence tomography of the human retina at 236,000 axial scans per second," Opt. Lett. ©2013 Optical Society of America

Optical coherence tomography today: speed, contrast, and multimodality

“…Axial resolution improvement (prerequisite 1) has been the key technological milestone in the history of OCT in its first decade, [10][11][12][13][14] which has been achieved by using ultra-broadband sources. OCT imaging speed improvements (prerequisite 2) evolved in its second decade, which were accomplished by Fourier domain (FD)/spectral domain (SD) [15][16][17][18] and swept source (SS) OCT. [19][20][21][22][23] While in FD/SD OCT speed is mainly determined by the readout time of the camera in a spectrometer, the wavelength-tuning speed of swept sources is the decisive factor in SS OCT. In the past 5 to 10 years, different swept source technologies have emerged to significantly improve imaging speed in (commercial) OCT systemsespecially the ones using wavelengths >1 μm.…”

High-speed OCT light sources and systems [Invited]

“…Over the past, it has sometimes been debated if it makes any sense to achieve ever higher OCT speeds. In general, the answer is complex, depends on the particular application, and needs to take into account changing limits for maximum permissible exposure, see e.g [9]. Moreover, the availability of suitable and cost-effective hardware is certainly crucial for successful commercialization.…”

“…(B) for swept lasers with filters operating in resonance, producing a sinusoidal wavelength-over-time evolution, which yields reduced imaging range compared to a linear sweep, see Eq. (9). With buffering, only the most linear part of the sweep near the sweep center can be used, optimizing the OCT imaging range.…”

“…This may limit imaging speed for some medical and biological applications which have a limited permitted sample exposure, see e.g. the discussions in [9,119]. However, it can be shown that even for sensitive application.…”

Postprocessing algorithms to minimize fixed-pattern artifact and reduce trigger jitter in swept source optical coherence tomography

“…Swept-source OCT (SS-OCT) is able to achieve very high scan speeds and is less susceptible to interferogram fringe washout than spectral domain OCT (SD-OCT) [1,2]. Therefore, it has advantages for both structural and Doppler OCT imaging.…”