A method for three-dimensional (3D) image calibration for a spectral domain optical coherence tomography (OCT) system, the OCT system including a scanning arrangement configured to laterally scan a sample light beam across a surface of a sample, an optical detection system configured to detect light reflected back from the sample to obtain an optical image of the sample, and a reference light beam, the OCT system being configured to generate axially resolved optical information from the sample as the sample light beam is scanned laterally across the sample using optical path length differences (OPLD) between the reference light beam and the sample light beam, the method comprising:
- providing a first calibration sample comprising a first substrate having laterally arranged structural elements providing optical contrast, the structural elements having at least one of known dimensions or known position values on the substrate;
- scanning, using a first set of scanner parameters for the scanning arrangement, the sample light beam laterally across a first two-dimensional scan area of the calibration sample so as to acquire a first image representation of the structural elements of the calibration sample by the optical detection system;
- identifying first structural features in the first image representation pertaining to the structural elements of the calibration sample;
- adjusting the first set of scanner parameters based on identified first structural features in the first image representation to obtain a desired field of view (FoV), thereby obtaining a second set of scanner parameters;
- scanning, using the second set of scanner parameters, the sample light beam laterally across a second two-dimensional scan area pertaining to the desired field of view (FoV), so as to acquire a second image representation of the structural elements of the calibration sample by the optical detection system;
- identifying second structural features in the second image representation of the structural elements of the calibration sample;
- correlating the at least one of the known dimensions or the known position values on the substrate for the structural elements corresponding to the identified second structural features in the second image representation with corresponding scanner parameter values from the second set of scanner parameters;
- obtaining a mathematical relationship between the at least one of the known dimensions or the known position values and the corresponding scanner parameter values to calculate a lateral scanning distortion across the desired field of view (FoV);
- correcting the lateral scanning distortion by adjusting the scanner parameters of the second set of scanner parameters using the mathematical relationship so as to obtain a calibrated set of scanner parameters for obtaining calibrated lateral images with the OCT system;
- providing a second calibration sample comprising a second substrate having a curved structural element thereon;
- scanning, using the calibrated set of scanner parameters, the sample light beam laterally across a fourth two-dimensional scan area pertaining to the desired field of view (FoV) so as to acquire a fourth image representation of the curved structural element of the second calibration sample by the optical detection system;
- identifying a curved structural feature pertaining to the curved structural element of the calibration sample in the fourth image representation;
- determining axial position values along an axial direction for the curved structural feature across the desired field of view (FoV);
- obtaining a mathematical relationship for the determined axial position values for the curved structural feature;
- and
- applying a flattening transformation on the mathematical relationship for the determined axial position values to obtain a constant axial position value along the curved structural feature so as to obtain an image representation comprising an iso-surface for the curved structural feature.