1: Cross section of human skin. Picture adapted from [1] 

Contexts in source publication

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... An example of such an indentation device can be found in [6], ( Fig. ...

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... demonstration purposes, Fig. 5.2 shows the FE simulations with the deformation at the contact point above the nodule; in the shown example, the tangential velocity decreases while the normal force ...

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... represent soft tissue with hard formations inside, the silicone phantom tissue (120 × 120 × 30 mm 3 ) with hard nodules was fabricated according to the standard approach used in this research, (Fig 6.2). Three nodules were embedded at a 5 mm depth from the surface and had diameters of 6, 8 and 10 mm respectively. Ten subjects participated in experimental studies and performed two tests on remote tele-manipulated ...

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... order to measure stiffness the device should be in direct contact with the tissue as the air from the pipette is sucked out. There should be a mechanism to measure the aspirated level of soft tissue, that is assumed to be homogeneous and then analysed to estimate Young's modulus ( Fig. 2.9). A drawback of this method is its inability to produce fast measurements over an organ areaas aspiration and release of the target area is time consuming. In addition, to create a full representation of an organ, a so- called stiffness distribution map, the positioning of the pipette should be very accurate in order to gather the information from the whole organ. The design of a pipette device is directly influencing the accuracy of the measurements. The diameter of an aspirated area and wall thicknesses of a pipette are important parameters. More information about this design can be found in ...

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... shape of an indenter should be designed in such way so as not to damage tissue dur- ing surgery. Moreover, for a complete organ representation, the measurement should be performed continuously over the surface of an organ. In addition, the indenter's shape should be similar to human fingertip, which is actively used to detect tactile in- formation during manual palpation, is similar to a sphere and provides good sliding options for interaction with viscoelastic environment. The diameter of the spherical tip of the indenter should be chosen according to the viscoelastic properties of the tissue -a very large diameter requires higher loads and more effort during measurements, while too small, a diameter will not provide the desired dynamical properties for the measurement. It has been proven that depth and stress of indentation is inversely re-lated to the diameter of the indenter, but this relationship is non-linear [52]. Hayes in 1972 [53] has derived a relationship which connects geometry of a spherical indenter, applied load and resulting indentation (Fig. 2.3). The relationship between the indentation depth ω 0 and radius of contact area is de- scribed by λ in Eq. ...

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... achieve an efficient examination RMIS tactile device that combines accuracy, minia- ture size and affordability, specially developed transducers should be developed. For instance, one can use strain gauges to measure force feedback. Such a method would allow relative flexibility in construction and therefore the possibility to design multi- dimensional sensors. An example of an indentation probe based on strain gauges can be found in [2] (Fig. 2.4), where a three-dimensional force and torque sensor was devel- oped for arthroscopic surgery: the hollow structure of the sensor in this design allows the placement of the sensor on the tip of the probe thus enabling the use of visual feed- back necessary in this type of surgery. Strain gauges are relatively cheap which allows for the disposal of the probe after use. However, because of ferromagnetic elements, such sensors cannot be used inside an MRI scanner and are sensitive to temperature changes. The same limitations apply to sensors using piezoelectric effect [56,57]. An alternative albeit expensive sensing principle is based on Fibre Bragg Grating (FBG), which gives better accuracy of estimating stiffness parameters in addition to being a miniature solution. The specific feature of FBG is variation of the refractive index, and thus of the length of the wave, on the small section of the fibre. An example of such sensor can be found in [62]: the designed sensor is 2.4 × 2.4 mm 2 in size and shows good balance between sensitivity range and linearity. In this example FBG was embedded in the flexible silicone material and was found suitable for the force measurement in ...

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... a spherical indenter of the probe is pressed down to the target tissue by air flow and a non-contact position sphere is located on the fixed distance from the opti- cal fibre. During measurements, variation in the tissue stiffness causes change in the distance between the sphere and the fibre. Thus, tissue stiffness is obtained by detect- ing indentation depth and force feedback. However, the relationship between airflow and non-linear soft tissue responses should be taken into consideration during sensor calibration. Another example of a sensor detecting two measurement variables simulta- neously can be found in [65]. A third example of a stiffness sensor ( Fig. 2.6), is based on the induction principle, where direction and amount of motion is measured along with force feedback [4]. This method is not MRI compatible and is not often used in the indentation devices, but the results show its good accuracy ...

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... indentation devices, which measure only force feedback from the target material, are suitable for static one-point measurements. Most of force feedback-based sensors measure just tissue response force while the indentation depth during measurement is assumed to be constant. This assumption leads to inaccuracy in the estimation of tissue mechanical properties. In order to estimate correct soft tissue parameters, the device should be able to measure both force feedback and indentation depth simultane- ously. Alternatively, the indentation depth can be kept constant during measurement, but this approach can be hardly implemented for real surgical applications. The work described in [3] (Fig. 2.5) is based on the optical fibre force sensing, but its construc- tion principle does not use deformable elastic material for the modulation of ...

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... from force the sensing method, the resonance-frequency based method can be used for tactile examination. However, at the moment there is no indentation device, which is capable of measuring mechanical properties of soft tissue over a continu- ous path and provide reliable results. For example, work described in [66] uses the commercial resonance sensor Venutron®, where the static measurements of soft tis- sue phantoms are performed at controlled indentation depth. The indentation devices based on the combination of mass-spring model with LVDT (linear variable differen- tial transducer) coils [5,67], sample design principle are shown in Fig. 2.7. In that case the system is measuring a shift of resonance frequency during the indentation process. The main issues in the application of such devices are problems with the mea- surement repeatability and reliability, as well as dependence on the orientation of the probe. Such issues may lead to inaccuracies during the in-vivo application of the tac- tile device. However, the significant advantage of the resonant method is its capability to measure both elastic and viscose properties of soft tissues. Figure 2.8: Schematic design and a prototype indentation de- vice to measure liver stiff- ness ...