Optimal spectral reshaping for resolution improvement in optical coherence tomography

Department of Biomedical Engineering, Northwestern University, Evanston, Illinois, United States
Optics Express (Impact Factor: 3.49). 07/2006; 14(13):5909-15. DOI: 10.1364/OE.14.005909
Source: PubMed


We analyze the resolution limit that can be achieved by means of spectral reshaping in optical coherence tomography images and demonstrate that the resolution can be improved by means of modelessly reshaping the source spectrum in postprocessing. We show that the optimal spectrum has a priory surprising "crater- like" shape, providing 0.74 micron axial resolution in free-space. This represents similar to 50% improvement compared to resolution using the original spectrum of a white light lamp. (c) 2006 Optical Society of America.

Download full-text


Available from: Vadim Backman
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We review laser applications for primarily in vivo ocular imaging techniques, describing their constraints based on biological tissue properties, safety, and the performance of the imaging system. We discuss the need for cost effective sources with practical wavelength tuning capabilities for spectral studies. Techniques to probe the pathological changes of layers beneath the highly scattering retina and diagnose the onset of various eye diseases are described. The recent development of several optical coherence tomography based systems for functional ocular imaging is reviewed, as well as linear and nonlinear ocular imaging techniques performed with ultrafast lasers, emphasizing recent source developments and methods to enhance imaging contrast.
    Preview · Article · Oct 2008 · Laser & Photonics Review
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A novel technique for axial resolution improvement of Optical Coherence Tomography (OCT) systems is proposed. The technique is based on step-frequency encoding, using frequency shifting, of the OCT signal. A resolution improvement by a factor of approximately 7 is achieved without the need for a broader bandwidth light source. This method exploits a combination of two basic principles: the appearance of beating, when adding two signals of slightly different carrier frequencies, and the resolution improvement by deconvolution of the interferogram with an encoded autocorrelation function. In time domain OCT, step-frequency encoding can be implemented by performing two scans, with different carrier frequencies, and subsequently adding them to create the encoded signal. When the frequency steps are properly selected, deconvolution of the resulting interferogram, using appropriate kernels, results in a narrower resolution width.
    Full-text · Article · May 2010 · Optics Express
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate ultrahigh speed swept source retinal OCT imaging using a Fourier domain mode locked (FDML) laser. The laser uses a combination of a semiconductor optical amplifier and an ytterbium doped fiber amplifier to provide more than 50 mW output power. The 1050 nm FDML laser uses standard telecom fiber for the km long delay line instead of two orders of magnitude more expensive real single mode fiber. We investigate the influence of this "oligo-mode" fiber on the FDML laser performance. Two design configurations with 684,400 and 1,368,700 axial scans per second are investigated, 25x and 50x faster than current commercial instruments and more than 4x faster than previous single spot ophthalmic results. These high speeds enable the acquisition of densely sampled ultrawide-field data sets of the retina within a few seconds. Ultrawide-field data consisting of 1900 x 1900 A-scans with ~70° angle of view are acquired within only 3 and 6 seconds using the different setups. Such OCT data sets, more than double as large as previously reported, are collapsed to a 4 megapixel high definition fundus image. We achieve good penetration into the choroid by hardware spectral shaping of the laser output. The axial resolution in tissue is 12 µm (684 kHz) and 19 µm (1.37 MHz). A series of new data processing and imaging extraction protocols, enabled by the ultrawide-field isotropic data sets, are presented. Dense isotropic sampling enables both, cross-sectional images along arbitrary coordinates and depth-resolved en-face fundus images. Additionally, we investigate how isotropic averaging compares to the averaging of cross-sections along the slow axis.
    Full-text · Article · Feb 2011 · Optics Express
Show more