Improving the Transverse Resolution of Optical Coherence Tomography with a Finite Impulse Response Filter and a Series of Numerically Refocused Images

Abstract

Among the numerous methods for improving the informative value of the optical coherence tomography (OCT), a special place is taken by the methods for increasing the spatial resolution of the resulting images. Increasing the resolution allows one to identify more clinically significant structures in OCT images and thus improve the diagnostic value of OCT. Since the transverse resolution of OCT images is determined by the physical principles different from those for the longitudinal resolution, the ways of their improvement are also different. The aim of the study is to develop a method for increasing the transverse resolution of OCT by using a finite impulse response (FIR) filter for numerical refocusing and by combining the numerically refocused images. Results. We have developed a FIR filter able to transfer the focal plane of an OCT image using the data from 17 consecutive measurements of the field scattered by the object. In addition, we propose an original method for automatic synthesis of the final OCT image with an improved transverse resolution over the entire object depth from a series of images having different focal plane positions. This will enable the OCT instrument to produce a sharply focused beam for the scanning and thus obtain images with an improved transverse resolution in the focal plane, restore the required resolution in the out-of-focus areas using numerical transfer of the focal plane, and also synthesize the final OCT image with an improved transverse resolution. The method has been tested with model objects using an OCT device operating at a central wavelength of 1 μm with the 60 nm range and a beam focused onto a spot with a diameter of 5 μm. Conclusion. The proposed method of numerically increasing the transverse resolution of OCT images allows one to obtain images with an improved transverse resolution using only a small number of OCT measurements; in the future, it will allow for creating an OCT device that produces high-resolution images in real time.