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PhD Defence Niels Langhout

Optical tissue identification

Niels Langhout is a PhD student in the Nanobiophysics group. His supervisors are prof.dr. T.J.M. Ruers from the faculty of Science and Technology and prof.dr. H.J.C.M. Sterenborg from the Academic Medical Center Amsterdam.

This thesis describes the evaluation of optical tissue identification for surgical applications. Three promising techniques are examined. After exploration of near infra-red fluorescence imaging and photoacoustic imaging, the thesis will focus on diffuse reflectance spectroscopy (DRS) for surgical tissue identification.

Chapter two describes the use of an intraoperative fluorescence camera in breast cancer phantoms. The technique provides the surgeon with an image overlay of the fluorescent contrast agent in phantoms mimicking absorption and scattering properties of human breast tissue. Important benefits and drawbacks are described.

Chapter three covers the application of photoacoustic imaging in surgery. The research is focused on lymph nodes in melanoma patients. Melanin, a strong optical absorber is imaged photoacoustically. The spectral identification of both tumor and blood vessels is demonstrated in phantoms and human lymph nodes ex vivo. The photoacoustic imager used is a reflective type, with the light source incorporated in the ultrasound detector.

Diffuse reflection spectroscopy is presented as an optical technique able to identify both tumor and vital surrounding structures like blood vessels and nerves. Colorectal tumors are frequently in close relation with vital structures. In oncologic rectum surgery, bladder- and sexual dysfunctions are both feared and high in incidence. Chapter four describes the identification of colorectal tumor using DRS.

Chapter five and six describe the identification of peripheral nerves in human during surgery. Peripheral nerves are often part of the vital structures surrounding a tumor. Ideally, image guided surgery depicts both tumor and vital surrounding tissue. Chapter five describes the identification of larger nerves as proof of principle. Chapter six is committed to the detection of smaller peripheral nerves.

Optimization and validation is not necessarily executed in humans in vivo. Logistically, and patient friendly, more suited for extensive measurements are a post mortem- or animal studies. However, DRS is subject to the morphological composition and biochemical make-up of the tissue, and both will change post mortem and may differ between human and animal. Chapter seven describes the optical similarities and differences between in vivo versus post mortem and human versus swine, focused on nerve identification.

In chapter eight we explore to possibilities to incorporate the DRS technique into a clinical device. We choose a bronchoscopic tool to fully utilize the small size and flexibility of the DRS optical fibers.

This thesis concludes with a general discussion and outlook on a use of optical tissue identification.