Endoscope Design for Volume Holographic Imaging

Abstract

Early stage detection of cancerous tissue is critical to increasing the 5-year survival rate for patients. The development of devices capable of accessing and visualizing these tissue sites plays an important role in this process. Many cancer types have existing screening methods however many have proven ineffective in large clinical trials. Since early stages of cancer development often has subtle changes from normal tissue, traditional non-invasive imaging techniques such as ultrasound or magnetic resonance imaging are not able to detect them. The following work evaluates the feasibility of miniaturization of Volume Holographic Imaging (VHI) systems into laparoscopic endoscopes for tissue and cancer screening. The work is divided into two main sections discussing the design and evaluation of each imaging system. The first system is a Reflectance VHI Endoscope designed for simultaneous imaging of two imaging depths within a tissue sample. The system is evaluated for resolution and contrast through imaging of resolution bar targets and soft tissue samples. The second system is a Wavelength Coded VHI Endoscope which combines the Reflectance VHI Endoscope imaging properties with axial chromatic dispersion effects of Gradient Index (GRIN) optics to improve the volume holographic element performance and reduce excess background light. Both Reflectance and Wavelength Coded VHI systems utilize a sub-4 mm diameter rigid relay probe which has been approved for in-vivo applications. The sub-4.4 µm/lp resolution produced by both VHI Endoscope systems and tissue depth separations of 50 µm and 100 µm for the Reflectance and Wavelength Coded designs, respectively, make VHI systems a candidate for clinical evaluation of early stage cancer development.