System-independent assessment of OCT axial resolution with a "bar chart" phantom

We present a optical phantom approach for the characterization of OCT axial resolution and contrast via multilayered "bar charts." We explored two methods to fabricate these phantoms: the first is based on monolayers of light-scattering microspheres with an intervening layer of transparent silicone, and the second involves alternating layers of scattering-enhanced silicone and transparent silicone. Varying the diameter of the microspheres and the thickness of the silicone layers permits different spatial frequencies to be realized in the axial dimension of the phantoms. Because the phantom's dimensions are accurately known independent of the OCT system, no information about the system's spatial calibration is required. We quantified the degree to which the bars in each phantom could be resolved with OCT, which provides insights into the axial contrast transfer function. Initial testing of these phantoms on time-resolved and Fourier-domain OCT platforms indicated that our approach can provide accurate, system-independent estimates of resolution.