Closed loop control of painful laser stimuli based on thermography and thermal modelling of the skin
Author
Frahm, Ken Steffen
Term
4. term
Publication year
2009
Pages
130
Abstract
This thesis investigates whether painful heat can be delivered and precisely regulated without skin contact by using a closed-loop controlled laser. The motivation is the need for temperature control in psychophysical pain research and the interest in offset analgesia, a phenomenon where a small reduction in an otherwise painful heat stimulus markedly decreases perceived pain. A non-contact, temperature-controlled system was developed in which a near-infrared laser heats the skin while an infrared camera measures surface temperature in real time. Laser power is adjusted by a PI controller using the camera feedback. To understand and predict the skin’s thermal response during laser stimulation, a detailed finite element model of heat transfer in skin was built and validated experimentally. The system relies on passive cooling, which limits how fast temperature can be reduced compared with actively cooled contact devices. In tests with eight volunteers, the system was able to evoke offset analgesia in all participants. The work shows that closed-loop control using thermography and thermal modelling enables precise temperature control of painful laser stimuli for psychophysical studies.
Dette speciale undersøger, om smertefulde varme-stimuli kan leveres og reguleres præcist uden hudkontakt ved hjælp af en laser styret i lukket kredsløb. Baggrunden er behovet for temperaturkontrol ved psykofysiske smerteforsøg og interessen for offset analgesi, et fænomen hvor en lille reduktion i en ellers smertefuld varmestimulering markant mindsker den oplevede smerte. Der blev udviklet et ikke-kontakt, temperaturkontrolleret system, hvor en nær-infrarød laser opvarmer huden, mens et infrarødt kamera måler hudtemperaturen i realtid. Laserens effekt reguleres af en PI-regulator baseret på kameradata. For at forstå og forudsige hudens varmerespons under laserstimulering blev der opbygget og eksperimentelt valideret en detaljeret Finite Element-model af varmetransport i huden. Systemet gør brug af passiv køling, hvilket begrænser, hvor hurtigt temperaturen kan sænkes sammenlignet med aktivt kølede kontaktstimulatorer. I forsøg med otte forsøgspersoner kunne systemet fremkalde offset analgesi hos samtlige deltagere. Arbejdet demonstrerer, at lukkede kredsløb med termografi og termisk modellering kan muliggøre præcis temperaturstyring af smertefulde laserstimuli til brug i psykofysiske studier.
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