A Phantom Study of Using Structured Light to Measure Absolute Respiratory Amplitude

The respiratory amplitude (RA) is a crucial physiological index in cardio-respiratory monitoring. While most existing studies have focused on measuring tidal volume to assess respiratory amplitudes, there is a notable lack of methods for non-contact quantification of absolute respiratory amplitudes. In this study, we explored the feasibility of measuring RA using structured light illuminator with a camera. Structured light actively projects laser spots onto the object surface, which allows estimating the distance between laser spots to normalize the varying distance between camera and object. We conducted a phantom study with a fully controllable motor for generating respiratory signals with different amplitudes and frequencies to determine the RA calibration model. A linear fitting model was established to calculate absolute RA across different camera-phantom distances. Experimental results achieved a mean absolute error (MAE) of 0.78 mm and a standard deviation (SD) of 0.57 mm. These findings underscore the potential of using structured light with a camera to measure the absolute RA.