Non-contact Oxygenation Assessment of Biological Tissues Based on a Time-of-Flight Method

Assessment of oxygen saturation for biological tissues is crucial in many medical applications. A non-contact oxygenation measurement is important in clinical scenarios, for example, emergency situations and imaging-guided surgery, because non-contact measurement will speed up the measurement preparation by eliminating the need for cleaning skin and sensor for hygrine and placement of sensor. Near-infrared spectroscopy stands out as a key technology for probing tissue oxygenation. Non-contact measurement requires precise estimation of the distance between the tissue and the probe. However, high precision light detection and ranging in the near-infrared region is challenging to achieve when targeting biological tissues due to the strong light scattering. This challenge limits the design of non-contact instruments for oxygenation assessment.

The aim is to utilize time-of-flight (ToF) sensors to accurately determine both oxygenation (optical properties (OP), i.e., absorption and scattering coefficients) of biological tissues and the distance to these tissues.

Model-based direct ToF (DToF) models were built with a focus on highly scattering objects. A simulation study was performed to determine the OPs and distances. Two simulation tests were performed for a scattering object placed at 30 cm and 62 cm away. To demonstrate that the ToF measurements are sensitive to the OPs of the scattering object, we placed a tissue-mimicking phantom at 62 cm from the measurement plane, formed by a pulsed laser coupled to a collimator and a pinhole, while a single photon avalanche camera next to the emission point captures the ToF signals at four different wavelengths.

In both cases, the retrieved OPs and distances were very close to the reference parameters with <0.5% average error, showing the accuracy of the optimization process. The multi-spectral ToF measurements confirmed the simulation.

We developed a model-based DToF approach for precise oxygenation measurement at a distance. This method holds great potential for non-contact oxygenation measurements, offering valuable insights for various clinical scenarios.