Optical coherence tomography (OCT) is an optical imaging method based on low-coherence interferometry that is capable of high-resolution cross-sectional imaging of internal microstructure by measuring light backscattered from the sample. OCT has the capacity to perform non-contact in vivo imaging and has been applied in medical and scientific fields such as ophthalmology, dermatology, developmental biology, and cardiology. Extensions of OCT such as Doppler OCT and polarization-sensitive OCT (PS-OCT) provide additional information about biological tissues. However, the heavy computational load required to process the acquired data stream creates a limit in realization of real-time OCT. Performing multi-functional OCT imaging demands additional processing for reconstruction of functional images, further increasing the total processing time. Graphics processing unit (GPU) processing has been implemented into MRI, CT and ultrasound as well as intensity-only OCT systems to accelerate image processing using its inherent parallel computation architecture. In this thesis, the development and applications of a GPU accelerated real-time 4D multi-functional SD-OCT system was presented.
Chapter 1 describes the construction and characterization of a multi-functional SD-OCT system at 1300nm. The axial resolution, lateral resolution, imaging depth, signal sensitivity drop-off, spectrometer efficiency, phase noise, system noise, polarization noise, computation of phase retardation, optic axis and diattenuation were characterized. Multiple samples were imaged to demonstrate each imaging facet (intensity, polarization and flow) of the system.
In Chapter 2, GPU was included into the imaging system. CUDA C++ was implemented into the real-time data acquisition and processing program to realize real-time data processing and display. The hybrid GPU-CPU program can process all intensity, polarization and flow images 100 times faster than a comparable previous CPU program. The efficient line processing rate realized was 379kHz for all three image types simultaneously, and represents a computational speed 8 times faster than camera line acquisition rate.
In Chapter 3, volume ray casting using GPU was incorporated into the real-time data acquisition and processing program for real-time volume rendering of all intensity, polarization and flow volume images. Arterial pulsation flow was identified and differentiated from venal flow in flow volume images when imaging mouse femoral artery and vein in vivo. The real-time volume images allowed visualization of burn progression in a volume as well as identification of burn injury boundaries in chicken muscle tissue.
The application of PS-OCT for the study of peripheral nerve degeneration and regeneration post crush injury is described in Chapter 4. Results from a preliminary non-longitudinal study showed that axonal birefringence decreased post crush injury and then increased with nerve repair. A longitudinal study was initiated in order to reduce the variation caused by different animals. The facilitated visualization of the real-time 3D volume rendering program was used to rapidly identify the micro-suture markers used to demarcate the wound area in order to minimize operational time while ensuring the imaging region was consistent over repeated imaging sessions.
In Chapter 5, PS-OCT was applied on a study of human skin photo aging as a factor of age, gender. Thirty-seven volunteers were recruited in accordance with an approved protocol for skin imaging on sun exposed area (face) and sun protected area (inner upper arm). The results showed a significantly lower birefringence value in the older age group (>=55 years old) than that of younger age group (18-35 years old). There was no significant difference found between young male and young female as well as old male and old female groups.