The properties of multi-spectral fluorescence imaging using deep-UV-illumination have recently been explored using a fiber-coupled thermal source at 280 nm. The resulting images show a remarkable level of contrast thought to result from the signal being overwhelmingly generated in the uppermost few cell layers of tissue, making this approach valuable for the study of diseases that originate in the endothelial tissues of the body. With a view to extending the technique with new wavelengths, and improving beam quality for efficient small core fiber coupling we have developed a mobile self-contained tunable solid-state laser source of deep UV light. An alexandrite laser, lasing at around 750 nm is frequency doubled to produce 375 nm and then tripled to produce 250 nm light. An optical deck added to the system allows other laser sources to be incorporated into the UV beam-line and a lens system has been designed to couple these sources into a single delivery fiber with core diameters down to 50 microns. Our system incorporates five wavelengths [250 nm, 375 nm, 442 nm (HeCd), 543 nm (HeNe) and 638 nm (diode laser)] as the illumination source for a small diameter falloposcope designed for the study of the distal Fallopian tube origins of high grade serous ovarian cancer. The tunability of alexandrite offers the potential to generate other wavelengths in the 720–800, 360–400 and 240–265 nm ranges, plus other non-linear optical conversion techniques taking advantage of the high peak powers of the laser.
Stray light in an endoscope largely contributes to whether a signal can be detected or not. This FRED analysis
used a novel endoscope designed for the fallopian tubes to show how common endoscope elements cause stray light
contamination, and to offer suggestions on how to mitigate it. Standard and advanced optical raytracing was performed.
Raytrace reports determined which ray paths caused the highest power and irradiance distributions after reflecting one or
more times from an element in the system. The analysis revealed that the cover plate introduced significantly more stray
light into the system than other endoscope components. The imaging lenses and variable stop reflectivity had a
negligible impact on the signal. To obtain acceptable signal-to- noise ratio, the source numerical aperture (NA) was
lowered to 0.35 and 0.25 to keep the stray light within the same order of magnitude and an order of magnitude lower,
respectively than the desired signal. There was a single specular reflection off of the cover plate distal surface. This
illumination reflected back into the imaging fiber without first scattering off the tissue, which resulted in high stray
power at the back of the imaging lenses. The specular light appeared brighter at higher source NAs and saturated the
desired signal at the edge of the imaging fiber. An NA between 0.25 and 0.35 provides maximum illumination to image
the tissue, with minimal stray light degrading the desired signal.
The five year survival rate for ovarian cancer is over 90% if early detection occurs, yet no effective early screening method exists. We have designed and are constructing a dual modality Optical Coherence Tomography (OCT) and Multispectral Fluorescence Imaging (MFI) endoscope to optically screen the Fallopian tube and ovary for early stage cancer. The endoscope reaches the ovary via the natural pathway of the vagina, cervix, uterus and Fallopian tube. In order to navigate the Fallopian tube the endoscope must have an outer diameter of 600 μm, be highly flexible, steerable, tracking and nonperforating. The imaging systems consists of six optical subsystems, two from OCT and four from MFI. The optical subsystems have independent and interrelated design criteria. The endoscope will be tested on realistic tissue models and ex vivo tissue to prove feasibility of future human trials. Ultimately the project aims to provide women the first effective ovarian cancer screening technique.