Shadow extension for ray casting enhances volumetric visualization in real-time 4D-OCT

Progress in swept source laser technology and graphics processing unit (GPU) have led to the realization of real time four-dimensional optical coherence tomography (4D-OCT). Various rendering algorithms have been introduced for volumetric OCT leading to enhanced spatial comprehension. These algorithms still cannot provide sufficient visual realism. Shadowing is one of the advanced rendering techniques used to provide realistic spatial comprehension for objects in space. We developed and implemented a shadow extension for ray casting for real-time 4D-OCT, using both a swept source (SS)-OCT and spectral domain (SD)-OCT. Our technique builds upon previously developed ray casting techniques, adding an additional shadowing computation. The shadow extension for ray casting yields greater three-dimensionality of objects via self-shadowing, and also improves depth perception of objects. We imaged a beveled needle hovering over a flat surface and found that the positioning of a beveled needle can be accurately determined in relation to the environment. The shadowing algorithm was implemented using texture memory of the GPU, which realized video rendering rate. The complete processing pipeline requires 47 ms with a volume size of 1024 × 256 × 100, with a 100 kHz line rate SS-OCT. This new algorithm may enhance interactive surgical guidance during ophthalmic microsurgery.