Mechanical aspects of fiber optics
iMIT focuses on developing instruments for minimally invasive care equipped with fiber optic technology. There are many types of fiber optic measurements that are being used in vivo, such as scattering or fluorescence spectroscopy. Until now, research generally focused on the interaction between light and tissue and the photonic components required to generate and detect the light, e.g. for oncologic applications. The mechanical effects of the fiber optics on measured tissue properties, such as resulting from mechanical pressure while touching tissue or from deforming while steering, are generally ignored, while this may have an tremendous influence on clinical outcome. Tissue properties (e.g. perfusion) may change when pushing with the fiber against tissue. The current project addresses these issues and aims to exploit the novel opportunities for measuring additional features of the tissue presented by the interaction between pressure and optical properties.
In the project we will increase the clinical performance of current fiber optic instrumentation by: i) applying multi-core optical fibers to prevent reduction of the numerical aperture (NA) due to the necessary bending of the instrument; ii) developing a sensor to detect the quality of the contact between fiber and tissue; iii) developing an approach to assure there is a predetermined constant pressure of the fiber on the surface of the tissue, necessary for reproducible measurements. In addition we will enable measurement of a novel selection of tissue parameters (for example the tissue deformability, the local blood pressure and the oxygen consumption) by development of a device that periodically scans the pressure of the fiber optic probe on the tissue in a controlled manner.
WP1.1.1: Development of fiber optic pressure controllers and scanner (TUD)
We will develop an instrument consisting of a needle tip with an optical fiber interferometric technique to monitor needle advancement through different types of tissue. When the needle encounters the interface between two layers a fiber-top indenter inside the needle is protruded and used to accurately measure the stiffness of the tissue that is about to be perforated. The fiber-top indenter consists of a micromachined cantilever, fabricated on top of an optical fiber. Upon contact with the tissue, the cantilever bends, depending on the stiffness of the tissue. By coupling light from the opposite end of the fiber, the cantilever position is assessed. Measurements of cantilever bending and needle motion will be combined to accurately assess tissue stiffness.
Deliverable: A fiber-top indenter allowing local tissue stiffness measurements at the tip of the needle, allowing analysis of the mechanical properties of the tissue layers in front of the needle.
WP1.1.2: Evaluate mechanical effects on fiber optic measurements (ErasmusMC)
PhD1 will first develop a fiber optic catheter with a hydrostatic pressure sensor based on a flow of saline through the catheter. This device will be used by PhD2 for tissue experiments. After that PhD1 will focus on the development of MEMS based pressure actuators. These constant force complaint micro mechanism (CF-CMM) will ensure that the fiber is kept in contact with the tissue and that interaction force between the fiber optics and tissue will remain in the operation range.