Phase-stabilized optical frequency domain imaging at 1-µm for the measurement of blood flow in the human choroid

Abstract

In optical frequency domain imaging (OFDI) the measurement of interference fringes is not exactly reproducible due to small instabilities in the swept-source laser, the interferometer and the data-acquisition hardware. The resulting variation in wavenumber sampling makes phase-resolved detection and the removal of fixed-pattern noise challenging in OFDI. In this paper this problem is solved by a new post-processing method in which interference fringes are resampled to the exact same wavenumber space using a simultaneously recorded calibration signal. This method is implemented in a high-speed (100 kHz) high-resolution (6.5 µm) OFDI system at 1-µm and is used for the removal of fixed-pattern noise artifacts and for phase-resolved blood flow measurements in the human choroid. The system performed close to the shot-noise limit (<1dB) with a sensitivity of 99.1 dB for a 1.7 mW sample arm power. Suppression of fixed-pattern noise artifacts is shown up to 39.0 dB which effectively removes all artifacts from the OFDI-images. The clinical potential of the system is shown by the detection of choroidal blood flow in a healthy volunteer and the detection of tissue reperfusion in a patient after a retinal pigment epithelium and choroid transplantation.

Computational optical coherence tomography [Invited]

“…Using this reference object, the phase of each A-line can be aligned in post-processing to restore phase stability. To account for unstable triggering of a swept-source sweep, a fiber Bragg grating can be used to generate a wavelength-dependent trigger to synchronize each A-line [142], while instabilities within the wavelength sweep can be calibrated out using a reference interferometer [143].…”

“…Jitter of high-speed scanning mirrors used in point-scanning systems can be a source of instability [140], and the rotational scanning mechanisms in catheter-based OCT imaging are typically very unstable [141]. The imprecise triggering of swept-source lasers can also lead to phase instability within and between scan lines [142,143].…”

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

“…However, to the best of our knowledge, removal of the residual fixed-pattern noise with these methods has not been demonstrated. Braaf et al demonstrated an effective method to eliminate the residual fixed-pattern noise and improve the phase stability by resampling the wavenumber using a simultaneously recorded calibration signal from an interferometer [8]. Although effective, this method requires another reference calibration signal as well as another digitizer channel.…”

Focus-extension by depth-encoded synthetic aperture in Optical Coherence Tomography

“…It has become an essential tool for clinical diagnosis and disease monitoring in ophthalmology and it shows great potential in other clinical areas such as dermatology, cardiology and gastroenterology [2][3][4][5][6][7]. The axial resolution of OCT imaging at moderate numerical aperture is determined primarily by the light source as illustrated by the equation:   …”