Modelling noxious laser stimulation for both Neodymium: Yttrium-Aluminium-Perovskite and Carbon Dioxide lasers: Experimental validation
Translated title
Modelleing af smerful stimulation for både Neodymium: Yttrium-Aluminium-Perovskite og Carbon Dioxide lasers: Eksperimentel validering
Author
Tahhan, Alan
Term
4. term
Publication year
2017
Submitted on
2017-10-02
Pages
98
Abstract
Smerte er en vigtig beskyttelsesmekanisme, der hjælper os med at undgå skader. I smerteforskning bruges lasere til at give ren varmestimulation og til selektivt at aktivere bestemte nervefibre (A-delta og C-fibre), der leder smertesignaler. Forskellige lasere trænger forskelligt dybt ned i huden; jo dybere lys trænger, desto sværere er det at forudsige, hvordan lyset fordeles, og hvordan varmen breder sig. En matematisk model kan gøre dette mere forudsigeligt og dermed støtte forskning og kliniske anvendelser. Denne afhandling bygger på et tidligere projekt, der udviklede en matematisk model for absorption af laserlys og varmeledning i hud. Modellen beskriver et tværsnit af huden i to dimensioner (radius r og dybde z), bruger en Monte Carlo-simulering til at beregne lysabsorption over et bredt bølgelængdeområde (250–10.600 nm) og anvender en finit element-metode til at beregne varmeudbredelse. Den tidligere model var verificeret, men ikke valideret mod målinger, hvilket gjorde dens praktiske anvendelighed usikker. Formålet her var derfor at gennemføre en eksperimentel validering. Valideringen blev udført med både kuldioxid (CO2)-laser og neodymium: yttrium-aluminium-perovskit (Nd: YAP)-laser på fem raske forsøgspersoner. Data kom fra termografiske optagelser af stimulationsstedet og deltagernes feedback. Laserindstillingerne blev justeret med henblik på nociceptiv aktivering af A-delta-smertefibre. For at øge chancen for en vellykket validering blev modellen tilpasset det konkrete stimulationssted på den volare (indersiden af) underarm og justeret efter kritiske observationer fra det tidligere projekt. Derefter blev modeldata og forsøgsdata sammenlignet som tidslige varmeprofiler i 7,5 sekunder ved tre positioner: (0,0), (5,0) og (10,0) mm fra centrum. Modellen blev med succes valideret for CO2-laseren. Validering for Nd: YAP-laseren var ikke vellykket og kræver yderligere justeringer, før den kan valideres. Derudover bør de anvendte stimulationsintensiteter til at nå A-delta-smertetærsklen sammenlignes med relevant litteratur for at sikre deres troværdighed.
Pain is a vital protective mechanism that helps us avoid harm. In pain research, lasers are used to deliver pure heat and to selectively activate specific nerve fibers (A-delta and C fibers) that carry pain signals. Different lasers penetrate the skin to different depths; the deeper the light goes, the harder it is to predict how it spreads and how heat moves through the tissue. A mathematical model can make these processes more predictable and support research and clinical applications. This thesis builds on an earlier project that developed a mathematical model of laser light absorption and heat transfer in skin. The model represents a two-dimensional cross-section (radius r and depth z), uses a Monte Carlo simulation to estimate light absorption over a wide range of wavelengths (250–10,600 nm), and applies a Finite Element method to compute heat diffusion. The previous work had verified the model’s implementation but had not validated it against measurements, leaving its practical usefulness uncertain. The aim here was therefore to carry out an experimental validation. Validation was performed with both a carbon dioxide (CO2) laser and a neodymium: yttrium-aluminum-perovskite (Nd: YAP) laser in five healthy volunteers. Data consisted of thermal imaging of the stimulation site and participant feedback. Laser settings were tuned for nociceptive activation of A-delta pain fibers. To improve the chance of success, the model was tailored to the specific stimulation site on the volar (inner) forearm and refined based on critical observations from the earlier project. Model predictions and experimental measurements were then compared as time-dependent heat spot profiles over 7.5 seconds at three positions: (0,0), (5,0), and (10,0) mm from the center. The model was successfully validated for the CO2 laser. Validation for the Nd: YAP laser was not successful and will require further adjustments before it can be validated. In addition, the stimulation intensities used to reach the A-delta pain threshold should be compared with relevant literature to confirm their reliability.
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