Optical coherence tomography (OCT) apparatus and OCT method for axial tracking and flattening

An optical coherence tomography (OCT) apparatus, comprising:

• an optical imaging source launching a beam of light into a two arm imaging interferometer, and wherein due to interference of light returning from the two arms, an optical spectrum at an output of the two arm imaging interferometer is modulated to produce an optical channeled spectrum,
• wherein the optical imaging source is a swept source, an arm of the two arm imaging interferometer comprises a lateral scanner and an object to be imaged, and the lateral scanner scans the beam of light from the source towards the object in two lateral directions over r=1, 2 . . . R lateral pixels, where R is an integer,
• where the OCT apparatus further comprises:
• an imaging detector,
• a corrector,
• a sensor,
• an imaging Master Slave (MS) processor comprising a mask selector and a dynamic MS comparator with at least two inputs and,
• where the mask selector delivers at least one mask signal at its output, to the dynamic MS comparator,
• wherein for each lateral pixel, r, addressed by the lateral scanner, the OCT apparatus performs a spectral scan, comprising scanning the optical channeled spectrum at the two arm imaging interferometer output and where due to the spectral scan, the imaging detector delivers an electrical signal due to the optical channeled spectrum at the output of the two arm imaging interferometer,
• wherein the dynamic MS comparator comprises at least one MS-calculator, the at least one MS-calculator comprising two inputs, wherein one of the two inputs is for receiving the at least one mask signal delivered by the mask selector and the other input is for receiving the signal delivered by the imaging detector,
• wherein the mask selector comprises a store for two system functions g and h, the function g incorporating a chirp of the optical channeled spectrum due to nonlinear sweeping of the swept source and the function h incorporating the chirp of the optical channeled spectrum due to dispersion in the interferometer, and a mask-calculator, and where the mask selector is under a control input,
• where the mask signal represents an electrical replica of the optical channeled spectrum at the imaging interferometer output for a specific depth in the object z=mδ where δ is an axial resolution interval of the OCT and m is a mask index,
• where the mask-calculator in the mask selector operates a Master Slave algorithm that, based on the functions g and h, calculates any mask signal for any specific mask index determining any specific depth in the object, where a choice of mask indices of the mask signals to be calculated is controlled by signal received from the control input,
• where the sensor further comprises a sensor storage of mask indices,
• where the sensor measures an axial distance up to a part of the object, where that part coincides with the part being imaged by an optical beam from the imaging interferometer or is different than the part being imaged by the optical beam from the imaging interferometer, and where the axial distance measured is converted into the mask index, that is deposited in the sensor storage of mask indices,
• wherein mask indices for each r are converted by the corrector into a difference of mask indices in respect to a reference mask index that the corrector sends to the control input of the mask selector,
• wherein, based upon the difference of mask indices received at its control input, the mask selector calculates the at least one mask signal, and
• where the MS-calculator operates based on a Master Slave algorithm to deliver a reflectivity value from a depth z inside the object, that is the specific depth of the mask signal delivered by the mask selector to the dynamic MS comparator.