Ultrasound Induced Improvement In OCT Resolution

Abstract

Optical coherence tomography (OCT) is a rapidly emerging technology for high-resolution biomedical imaging. With commercially available diode sources, axial resolutions for OCT are generally in the range of 10-20 pm. Investigators have used solid state lasers to increase the resolution to less than 10 pm, such as the Kerr lens, mode locked, chromium Forsterite laser. However, these lasers require considerable expertise to use and generally costs are over $100,000. Since increasing resolution results in improved imaging, which is particularly important in areas such as early cancer detection where the analysis of nuclei would be useful, other methods for improving resolution should be pursued. In this study, OCT will be combined with ultrasound in an attempt to increase resolution. The theory is that, by using an ultrasound beam in parallel with the OCT beam, multiple scattering will be reduced because the light is Doppler shifted outside the bandpass filter of the OCT system. A 7.5 Hz ultrasound transducer was used approximately 10 degrees off axis of the OCT system. A reflecting metal plate was placed with fresh fish and the point spread function (PSF) was assessed off the reflector. The PSF was determined in the presence of no ultrasound, pulsed ultrasound, and CW ultrasound. CW ultrasound resulted in a 13% improvement (p<0.001) in resolution while the effect of pulsed ultrasound was 9% (p <0.01). Combining OCT with a parallel ultrasound beam results in an improvement in resolution. The proposed mechanism is a reduction in multiple scattering. Future studies will examine different the effect of different ultrasound parameters and bandpass filters in an attempt to increase these effects.