In the laboratory of Biomedical Physics, a system was built for Virtual, Fluorescence Optical-Sectioning Tomography (VFOST) or High Resolution Orthogonal Plane Fluorescence Optical Sectioning microscopy (HROPFOS). In this relatively new technique, a plane of laser light is directed through a decalcified, transparent and fluorescent biomedical specimen, and a camera observes the fluorescence image of this virtual section in orthogonal direction. By moving the specimen with a stepper motor and each time registering the virtual section, we can create 3D-reconstructions. In the first phase of the current project, the HROPFOS technique will be further developed, to obtain nearly real-time virtual optical sections in a specimen with high resolution (1 micrometer). This way, the technique will become a valuable addition to confocal microscopy of decalcified biomedical objects and fills a gap between MRI- and CT-tomography, as it images bone and soft tissue simultaneously.
Another topic will be the investigation of 3D-vascularisation in the middle ear by use of corrosion-cast techniques in combination with HROPFOS. In our research, HROPFOS will be applied on middle ear ossicles and vascularisation.
During the previous activities, a broad knowledge of electro-optics, segmentation and 3D-modelling is obtained, which will be used to create a new method to measure small deformations of small objects, based on endoscopic moiré-interferometry. The big challenge to measure deformation from moiré topograms, is to compensate for the distortion introduced by endoscopy.
A specific application of this technique will be to diagnose tympanic membrane disorders, which for the moment can only be done qualitatively by doctors. By measuring deformation of the tympanic membrane caused by small pressure variations, this technique will possibly be able to detect retraction pockets and cholesteatoma in a very early stage. The technique will also be used for fundamental research of the tympanic membrane.
After the measuring technique and the image processing are accomplished, the method will be first tested on in-vitro specimen, later on in in-vivo ears of laboratory animals. The method is completely non-invasive. When measuring in-vivo, compensation of movement artifacts will then be necessary.
Because moiré is a geometric technique, sub-wavelength stability is not necessary, which is a major advantage over f.i. laser-interferometry.
In a next stage, we will increase the resolution by implementing phase-shifting, which is accomplished by moving the projection grating in its own plane. We will try to use an LCD as a moiré grid, which is a new approach. This way, miniaturization will be possible.
The technique will be able to measure all kinds of small deformations, but a first application will be to measure the deformation of human tympanic membranes, in cooperation with ENT surgeons, who will establish the diagnostic value of the apparatus. Of course, tests will first be performed on laboratory animals before being applied on humans, although the method is harmless en non-invasive.
A last extension of this project can be the combination of laser-vibrometry and endoscopic moiré interferometry. This way, deformation and vibration can be measured at the same time on the same object.
In general, this project will produce several new measuring techniques, applicable in different fields of biomedical research, especially for diagnostic purposes and fundamental research of hearing.