We have introduced the Master Slave (MS) interferometry method to address the limitations due to the use of conventional FTs or its derivatives in OCT data processing. The novel MS technology replaces the FT operator with a parallel batch of correlators. An electrical signal proportional to the channeled spectrum at the interferometer output is correlated with P masks producing P signals, a signal for each point out of P in the A-scan.
In this way, it is possible to: (i) directly access the information from selected depths in the sample placed in the slave interferometer; (ii) eliminate the process of resampling, required by the FT based conventional technology, with immediate consequences in improving the decay of sensitivity with depth, achieving the expected axial resolution limit and reducing the time to display an en-face OCT image, while slightly lowering the cost of OCT assembly and (iii) tolerate the dispersion left unbalanced in the slave interferometer.
The lecture will present several developments based on the MS-OCT technology, such as: (a) an equivalent OCT/SLO (scanning laser ophthalmoscopy), where no extra optical channel for the SLO is needed; (b) coherence revival swept source OCT employing the MS tolerance to dispersion: (c) Gabor filtering, where large number of repetitions with different focus adjustments can be performed more time efficiently than when employing FT based OCT; (d) MS phase processing, which opens novel avenues in phase- and polarization-sensitive modalities; (e) achieving the theoretical axial resolution when using a ultra wide broadband source such as a supercontinuum laser; (f) down-conversion OCT that can deliver an en-face OCT image from a sample in real-time, irrespective of the tuning speed of the swept source where the mask signals are generated in real time (by a physical master interferometer) while sweeping the frequency of the swept source.
Proc. SPIE. 9697, Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XX
KEYWORDS: Digital signal processing, Diagnostics, Surgery, Optimization (mathematics), Image resolution, Optical coherence tomography, Image processing, Data processing, Real time imaging, Parallel computing, Multispectral imaging, Fourier transforms, Visualization, Curium, Signal processing
This paper presents parallel optimizations in the en-face (C-scan) optical coherence tomography (OCT) display.
Compared with the cross-sectional (B-scan) imagery, the production of en-face images is more computationally
demanding, due to the increased size of the data handled by the digital signal processing (DSP) algorithms. A
sequential implementation of the DSP leads to a limited number of real-time generated en-face images. There
are OCT applications, where simultaneous production of large number of en-face images from multiple depths
is required, such as real-time diagnostics and monitoring of surgery and ablation. In sequential computing, this
requirement leads to a significant increase of the time to process the data and to generate the images. As a result,
the processing time exceeds the acquisition time and the image generation is not in real-time. In these cases, not
producing en-face images in real-time makes the OCT system ineffective. Parallel optimization of the DSP
algorithms provides a solution to this problem. Coarse-grained central processing unit (CPU) based and fine-grained
graphics processing unit (GPU) based parallel implementations of the conventional Fourier domain
(CFD) OCT method and the Master-Slave Interferometry (MSI) OCT method are studied. In the coarse-grained
CPU implementation, each parallel thread processes the whole OCT frame and generates a single en-face image.
The corresponding fine-grained GPU implementation launches one parallel thread for every data point from the
OCT frame and thus achieves maximum parallelism. The performance and scalability of the CPU-based and
GPU-based parallel approaches are analyzed and compared. The quality and the resolution of the images
generated by the CFD method and the MSI method are also discussed and compared.