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.
Highlights
Optical Coherence Tomography (OCT) is an optical interferometric imaging technique analogous to ultrasound and has its main applications in tissue structure imaging [1]
The introduction of Fourier-Domain OCT (FD-OCT) technology has played an important role in the increasing popularity of OCT due to its improved detection sensitivity and acquisition speed compared to Time-Domain OCT technology [2,3,4]
The FD-OCT form uses spectral detection to measure interference fringes as a function of wavenumber, which can be realized by two different hardware implementations
Summary
Optical Coherence Tomography (OCT) is an optical interferometric imaging technique analogous to ultrasound and has its main applications in tissue structure imaging [1]. In OFDI the mechanical wavelength tuning creates small variations in wavelength sweeps, trigger timing and sampling which adversely affects the reproducibility of interference fringes This gives potential difficulties with phase-resolved detection and fixed-pattern noise removal, OFDI has an advantage over SD-OCT since it is less sensitive to fringe washout [9,10] and has a lower signal decay with depth [8]. An alternative solution was found in the correction of the measured phase during post-processing [22,23,24,31] These methods were focused on the imaging of (blood) flow only and are either not suitable or never shown for the purpose of fixed-pattern noise removal. Received 5 Jul 2011; revised 10 Sep 2011; accepted 17 Sep 2011; published 5 Oct 2011 24 October 2011 / Vol 19, No 22 / OPTICS EXPRESS 20889
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