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Tissue aspiration experimentThe device consists of a tube with an opening at the end, the so called “aspiration hole” (typically 10 mm diameter). The experiment is performed by pushing gently the tube on the tissue, and then creating a (time variable) vacuum inside the tube so that the tissue is sucked in through the aspiration hole. The experimental set-up has been designed originally by Vuskovic and Kauer [V. Vuskovic, Diss. ETHZ Nr. 14222; M. Kauer, Diss. ETHZ Nr. 14233] for in-vivo applications addressing issues associated with: safety, sterilization, space limitation and a short interruption of the actual surgical procedure. A detailed description of this system can be found in [2t].
The pressure sensor provides the feedback signal for the control system consisting of a pump, an air reservoir and two valves. Control algorithms allow achieving the predefined pressure history, thus ensuring the repeatability of the experimental protocol. An optic fiber connected to a source of light illuminates the surface of the tissue. A digital video camera captures images of the side view of the deformed tissue. The images are processed off-line in order to extract the profiles of the deformed tissue. For an isotropic and homogeneous tissue a complete description of the kinematics of the deformation can be obtained by these side-view profiles. The time histories of measured pressure and deformation profiles are used to determine the constitutive model (inverse problem), thereby considering the influence of (time variable) contact force and tissue in-homogeneity, [10p, 17p, 5s, 3s].
The above descriptions and the sketch correspond to the “standard” version of our device, used for example for in vivo measurements on human liver during abdominal surgery ([15p], [13p], [2t]). Dedicated and optimized devices have been developed based on the same operation principle for other medical applications, such as for the measurements on the human cervix during pregnancy ([19p], [11p], [9p], [8p]), or for prolaps diagnosis. The latest development is represented a new device which can be applied on internal organs during laparoscopic interventions, [4s].
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