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<div class="block title"><h1>IV. An example of the development of a multi-channel acquisition device</h1></div> | <div class="block title"><h1>IV. An example of the development of a multi-channel acquisition device</h1></div> | ||
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− | <p></p> | + | <p>Olivier Rossel, in his thesis, chose to work on improving the selectivity of the cuff electrodes. He chose this type of electrode because they respect the integrity of the nerve and its fascicles membranes and that they make it possible to limit both the number of implants and the complexity surgical gesture. The electrode need reject the EMG signals and to measure local ENGs at multiple sites around the nerve.</p> |
+ | <p>In this part, all the results use the electrical models of the nerve developed in the previous part.</p> | ||
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− | <div class="block title"><h3 style="text-align: left;"></h3></div> | + | <div class="block title"><h3 style="text-align: left;">1. Tripolar electrode</h3></div> |
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− | <p></p> | + | <p>As we saw previously, it is possible to reject the EMG signal by using a tripolar cuff electrode (Cf. Figure 6). A tripolar cuff and the adapted electrical treatment is used.</p> |
+ | <img src=""> | ||
+ | <div class="legend"><b>Figure : 6</b>Schematic of a tripolar cuff electrode.</div> | ||
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− | <div class="block title"><h3 style="text-align: left;"></h3></div> | + | <div class="block title"><h3 style="text-align: left;">2. Tripolar treatment analysis</h3></div> |
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− | <p></p> | + | <p>The tripolar cuff electrode is considered as a spatial filter with a 1/h periodic frequency response, where h is the distance between the poles. For the spatial frequencies inferior at 1/h, the filter is a bandpass filter with a gain of 2 and a bandwidth of -6 dB between 1/4h and 3/4h.</p> |
+ | <p>If we consider the larger “d” of the electrode poles (Cf. Figure 6), the impulse response associated with each of the poles of the electrode is then a gate function of width d and amplitude 1/d.</p> | ||
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− | <div class="block title"><h3 style="text-align: left;"></h3></div> | + | <div class="block title"><h3 style="text-align: left;">3. Electrode sizing</h3></div> |
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− | <p></p> | + | <p>n order to increase neural information relative to the noise, it is vital to optimize the cuff dimensions. The literature suggests that the best compromise between cuff length and available place is a cuff length close to the wavelength of the transmembrane action potential. This one is approximately linear with fiber diameter.</p> |
+ | <p>According to Struijk, the action potential propagation velocity can be approximated as 55.800 nodes/s and the duration, of the transmembrane action potential is approximately 0,4 ms.</p> | ||
+ | <p>Thus, to have an optimal measurement, the cuff electrode must cover 22 nodes of Ranvier. The inter-pole distance must therefore be adjusted to h = 11 lmy (lmy is the length of myelin separating two nodes of Ranvier). So, for a typical fiber, the inter-electrode distance h should be about 1 cm, which is used in most ENG measuring electrodes.</p> | ||
+ | <img src=""> | ||
+ | <div class="legend"><b>Figure 7: </b>Extra-neural potential of monopolar action according to the position of the measuring point. The diagram at the top left shows the simulated situation. At the top right, the simulation corresponding to this configuration is represented: calculation of twice five monopolar potentials, for a typical axon (diameter of 8.7 μm, and lmy= 1 mm). The distances from this axon to the measurement points are ρ1=100 μm for site A and ρ2=500 μm for site B. Below, the monopolar signals at points “a” to “e” are shown for each of the measurement sites.</div> | ||
+ | <p>Knowing the characteristics of the electrode we want, it is possible to evaluate the distance h between the poles. This distance is of the order of a hundred micrometers which is much lower than that of a classical tripole which is of the order of a centimeter. This is why we will call, in the rest of this work, the tripole proposed a "small tripole".</p> | ||
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− | <div class="block title"><h3 style="text-align: left;"></h3></div> | + | <div class="block title"><h3 style="text-align: left;">4. Local variations of the potential</h3></div> |
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− | <p></p> | + | <p>The spatial low frequencies of the electric field generated by an active axon, has almost the same amplitude at each point of the nerve surface, regardless of the location of the axon inside the nerve. Conversely, the amplitudes of the high-frequency components of this electric field depend on the distance between the axon and the point of observation.</p> |
+ | <p>It was possible for several poles placed online, to determine the depth of the axon. Indeed, for axons close to the surface of the nerve, there is a difference in amplitude (as a function of the relative position of each pole relative to that of Ranvier's nodes), while for those who are far from the surface the measured amplitude is the same for each of the poles (Cf. Figure 7). Thus, it is necessary to suppress the common mode and amplify only the difference of the signals collected on several poles.</p> | ||
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− | <div class="block title"><h3 style="text-align: left;"></h3></div> | + | <div class="block title"><h3 style="text-align: left;">5. Sensibility of a small:</h3></div> |
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− | <p></p> | + | <p>For the small tripole, we have a fast attenuation depending on the distance compared to big tripole (Cf. Figure 8). As figure 8 confirms it, the small tripole is much more selective than the big tripole. Moreover, figure 9 shows that despite the low power level of the targeted signals and the spatial filtering performed, the peak-to-peak amplitude of the output signals of the tripole can reach 6 μV for a single active fiber. Considering the superposition of signals - the simultaneous activity of several fibers - we can hope to reach larger amplitude. Even if it is the case, the output signals of a small tripole remain of very low amplitude and it will thus be necessary to be very attentive to the sources of noise to maintain an acceptable signal-to-noise ratio.</p> |
+ | <img src=""> | ||
+ | <div class="legend"><b>Figure 8: </b>Peak-to-peak amplitudes of the output action potential of a small tripole and of a big one</div> | ||
+ | <img src=""> | ||
+ | <div class="legend"><b>Figure 9: </b> Peak-to-peak amplitudes measure at the output of a big tripole (left) or a small tripole (right) in function of the position of the active axon (diameter 8, 7 µm, and lmy=1 mm) in a cylindrical nerve of 300 µm in diameter.</div> | ||
+ | </div> | ||
+ | <div class="block title"><h3 style="text-align: left;">6. Selectivity study:</h3></div> | ||
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+ | <p>Olivier ROSSEL developed a new electrode architecture he compared to the FINE electrode. The FINE electrode used is the one developed by Paul YOO and Dominique DURAND (Cf. Figure 7).</p> | ||
+ | <img src=""> | ||
+ | <div class="legend"><b>Figure 10: </b>FINE electrode, h = 0,5 mm.</div> | ||
+ | <p>Olivier ROSSEL tried to improve this electrode replacing each measure point by a small tripole and by deleting two external ring. He called this electrode the FORTE electrode for “FINE with Original Recording Tripolar Electrode” (Cf. Figure 11). The main difference between these two electrodes is the inter-poles distance in the longitudinal way.</p> | ||
+ | <img src=""> | ||
+ | <div class="legend"><b>Figure 11: </b>FORTE electrode, h = 375 μm.</div> | ||
+ | <img src=""> | ||
+ | <div class="legend"><b>Figure 12: </b>Two fascicles represented in the electrode. These disposition of the fascicles is the one used for the simulations made to obtain figure 13 and figure 14</div> | ||
+ | <p>The activity of two fascicles is simulated (Cf. Figure 12) and the peak-to-peak amplitudes of the output signals are compared (Cf. Figure 13). The first difference we see is the signal from the FORTE electrode is attenuated 20 dB compared to the FINE electrode. In figure 13, we see that when only one fascicle is active, the FORTE electrode makes it possible to locate the active fascicle much more easily than the FINE electrode.</p> | ||
+ | <img src=""> | ||
+ | <div class="legend"><b>Figure 13: </b>Peak-to-peak tension received by the tripole n (from tripole 1 to tripole 13) for the red and black fascicles.</div> | ||
+ | <p>Moreover, in the general case of a simultaneous activity of different fascicles, the signals from the different active fascicles are summed at the level of each tripoles (Cf. Figure 14). We can see that for the FINE electrode the amplitude measured makes it impossible to differentiate the active fascicles. However, for the FORTE electrode, since the small tripole is locally sensitive, we can’t see the difference between the figure 13 and the figure 14. It is easy to differentiate the active fascicles.</p> | ||
+ | <img src=""> | ||
+ | <div class="legend"><b>Figure 14: </b>Simulated ENG for FINE electrode (A) and for the FORTE electrode (B) for the two fascicles in the case of a simultaneous activity. The contribution of each fascicles is designed by the color avec the fascicles in the figure 13. Each fascicle contains around two hundred active axons.</div> | ||
+ | <p>Finally, we see the FORTE electrode can surpass in selectivity the FINE electrode. The FORTE electrode is a great example of an electrode we could use for our device.</p> | ||
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+ | <div class="block separator-mark"></div> | ||
+ | <div class="block full"><p><b>Thus, thanks this example, we understand it is possible to develop our own type of electrode. We gathered a lot of different information. First, having a good electrical model of the nerve is crucial to understand what are the parameters we need to take into account to develop our electrode. Moreover, it is primordial in order to be able to simulate the performance of an electrode. We now know that different algorithms that improve the output signal of an electrode already exist. We would like to test and use such algorithms for our device. Finally, thanks to the example of the FORTE electrode, we have already thought about how it will be possible to incorporate such an electrode in our device.</b></p></div> | ||
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+ | <li style="list-style-type: decimal;">MicroProbes for Life Sciences, « Nerve Cuff Electrodes ». Retrieved Oct. 14th, 2018 from https://microprobes.com/products/peripheral-electrodes/nerve-cuff</li> | ||
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+ | <li style="list-style-type: decimal;">Yoo, P. B., & Durand, D. M. (2005). Selective Recording of the Canine Hypoglossal Nerve Using a Multicontact Flat Interface Nerve Electrode. IEEE Transactions on Biomedical Engineering, 52(8), 1461–1469. doi:10.1109/tbme.2005.851482</li> | ||
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+ | <li style="list-style-type: decimal;">Foldes EL, Ackermann DM, Bhadra N, Kilgore KL, Bhadra N. Design, fabrication and evaluation of a conforming circumpolar peripheral nerve cuff electrode for acute experimental use. Journal of neuroscience methods. 2011;196(1):31-37. doi:10.1016/j.jneumeth.2010.12.020.</li> | ||
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+ | <li style="list-style-type: decimal;">Olivier Rossel. Dispositifs de mesure et d’interprétation de l’activité d’un nerf. Electronique. Université Montpellier II - Sciences et Techniques du Languedoc, 2012. Français.</li> | ||
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+ | <li style="list-style-type: decimal;">Leventhal, D. K., & Durand, D. M. (2003). Subfascicle Stimulation Selectivity with the Flat Interface Nerve Electrode. Annals of Biomedical Engineering, 31(6), 643–652. doi:10.1114/1.1569266</li> | ||
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+ | <li style="list-style-type: decimal;">Harb, A., & Sawan, M. (2005). Fully integrated rectification and bin-integration analog circuit for biomedical signal processing. 2005 12th IEEE International Conference on Electronics, Circuits and Systems. doi:10.1109/icecs.2005.4633430</li> | ||
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+ | <li style="list-style-type: decimal;">Pachnis, I., Demosthenous, A., & Donaldson, N. (2007). Passive Neutralization of Myoelectric Interference From Neural Recording Tripoles. IEEE Transactions on Biomedical Engineering, 54(6), 1067–1074. doi:10.1109/tbme.2007.891170</li> | ||
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+ | <li style="list-style-type: decimal;">Taylor, J., Donaldson, N., & Winter, J. (2004). Multiple-electrode nerve cuffs for low-velocity and velocity-selective neural recording. Medical & Biological Engineering & Computing, 42(5), 634–643. doi:10.1007/bf02347545</li> | ||
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+ | <li style="list-style-type: decimal;">Wodlinger, B., & Durand, D. M. (2009). Localization and Recovery of Peripheral Neural Sources With Beamforming Algorithms. IEEE Transactions on Neural Systems and Rehabilitation Engineering, 17(5), 461–468. doi:10.1109/tnsre.2009.2034072</li> | ||
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+ | <li style="list-style-type: decimal;">Wodlinger, B., & Durand, D. M. (2011). Selective recovery of fascicular activity in peripheral nerves. Journal of Neural Engineering, 8(5), 056005. doi:10.1088/1741-2560/8/5/056005</li> | ||
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+ | <li style="list-style-type: decimal;">L. N. S. ANDREASEN et J. J. STRUIJK. “Signal Strength Versus Cuff Length in Nerve Cuff Electrode Recordings”. IEEE Transactions on Biomedical Engineering 49.9 (2002), p. 1045–1050</li> | ||
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+ | <li style="list-style-type: decimal;">J. Struijk, “The extracellular potential of a myelinated nerve fiber in an unbounded medium and in nerve cuff models,” Biophys. J., vol. 72, pp. 2457–2469, 1997.</li> | ||
</ul> | </ul> | ||
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Revision as of 12:30, 15 October 2018
MEMBRANE
When manipulating genetically engineered organisms, it is crucial to guarantee the confinement of these organisms. In our case, we want the genetically modified bacteria to stay at the interface between the prosthesis and the external organic medium. At the same time, one of the main issues our project wants to tackle is the conduction of the neuron influx to the prosthesis. The answer to these questions came as a double solution: confinement of the bacteria by conductive nanoporous membranes. The membrane’s nanoporosity allows substances produced by our modified biofilm to pass through the membrane, but the bacteria remain confined. We tested the conductivity and biocompatibility of two types of membranes.
Membrane
Nerve modelisation
As seen in the other parts of this wiki, we chose to use an nanoporous membrane in our device. The first goal of the membrane was to confine our biofilm, so it does not escape the prosthesis. Moreover, we also used our membrane as a conductive electrode. This solution was interesting since we didn’t have enough time to develop an entire electrical device which collect and treat the signal of the nerves. However, we know we still need to improve our interface if we want the patient to fully control his prosthesis. That is why we decided to look at what is already made in this field. So, first, we detailed how it is possible to model the electrical characteristics of a nerve. Then, we searched information on electrodes and signal treatment.