(Saturday, 4/7/2018)
Room: Foyer
Purpose: The purpose of this study was to investigate the effects of an HVAC unit on the thermal drift of our Optical Surface Monitoring System (OSMS).
Methods: An HVAC vent is situated behind the central OSMS camera. The OSMS was allowed to reach thermal equilibrium with the HVAC unit powered off before acquiring measurements. A reference image of an anthropomorphic phantom was then captured at time zero. OSMS reported phantom displacements from reference conditions and camera reported temperatures were recorded at 2-5 minute intervals while the HVAC system was manually cycled on, off, and back on again. Measurements were continued after installing an air deflector to direct airflow away from the OSMS camera with the ventilation system on.
Results: During HVAC operation OSMS falsely reported phantom 3D displacements from baseline of 0.6 mm - 0.7 mm. The majority of the displacement (0.5 mm – 0.6 mm) occurred over the first four minutes of HVAC operation, with stabilization occurring after eight minutes. The return to baseline occurred more gradually, with a total time to stabilization of eighteen minutes after powering off the HVAC. The longitudinal and vertical displacements ranged from 0.40 mm – 0.50 mm and 0.35 mm – 0.70 mm, respectively, with the HVAC on. The lateral displacement ranged between 0.00 mm – 0.05 mm. All temperature readings reported by the central camera indicated a decrease in temperature after the HVAC was turned on, and correlated well with the OSMS displacements. Installing an air deflector resulted in the total displacement decreasing from 0.6 mm to 0.3 mm.
Conclusion: Variations in temperature affect the OSMS stability. HVAC vent proximity to a camera exacerbates the thermal drift that is seen under normal conditions and could lead to false positive shifts during stereotactic treatments.
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