Robust respiration tracking in high-dynamic range scenes using mobile thermal imaging

Youngjun Cho, SJ Julier, Nicolai Marquardt, N Bianchi-Berthouze
in Journal article

Abstract

The importance of monitoring respiration, one of the vital signs, has
repeatedly been highlighted in medical treatments, healthcare and fitness
sectors. Current ubiquitous measurement systems require to wear respiration
belts or nasal probe to track respiration rates. At the same time, digital
image sensor based PPG requires support of ambient lighting sources, which does
not work properly in dark places and under varied lighting conditions. Recent
advancements in thermographic systems, shrinking their size, weight and cost,
open new possibilities for creating smart-phone based respiration rate
monitoring devices that do no suffer from lighting conditions. However, mobile
thermal imaging is challenged in scenes with high thermal dynamic ranges and,
as for PPG with noises amplified by combined motion artefacts and breathing
dynamics. In this paper, we propose a novel robust respiration tracking method
which compensates for the negative effects of variations of the ambient
temperature and the artefacts can accurately extract breathing rates from
controlled respiration exercises in highly dynamic thermal scenes. The method
introduces three main contributions. The first is a novel optimal quantization
technique which adaptively constructs a color mapping of absolute temperature
matrices. The second is Thermal Gradient Flow mainly based on the computation
of thermal gradient magnitude maps in order to enhance accuracy of nostril
region tracking. We also present a new concept of thermal voxel to amplify the
quality of respiration signals compared to the traditional averaging method. We
demonstrate the high robustness of our system in terms of nostril-and
respiration tracking by evaluating it in high thermal dynamic scenes (e.g.
strong correlation (r=0.9983)), and how our algorithm outperformed standard
algorithms in settings with different amount of human motion and thermal
changes.