Measurement of absorption in scattering media using objective laser speckle: application to blood oximetry

Theoretical and experimental investigations of speckle features based on free-space surface scattering

Speckle is a significant challenge for laser imaging systems, as it degrades the image quality. In this study, an improved theoretical model is established to describe the speckle features in free-space optical path. The model quantitatively defines the relationship between speckle contrast and five parameters: wavelength, screen surface roughness, light-spot diameter, incidence angle, and observation angle. Subsequently, the theoretical results are experimentally verified. This study enhances the theory of speckle suppression in free-space optical path, and thus enriches the existing speckle suppression theory. The speckle features based on free-space surface-scattered fields have the potential for applications related to non-imaging optics.

Relying on pulse oximetry to avoid hypoxaemia and hyperoxia: A multicentre prospective cohort study in patients with circulatory failure

PURPOSE

The purpose of this study was to assess the predictive performance of pulse oximetry (SpO₂) to rule out hypoxaemia and hyperoxia in critically ill patients.

METHODS

SpO₂, arterial oxygenation (SaO₂), and arterial partial pressure of oxygen (PaO₂) were prospectively and simultaneously measured every 6 h during the first 24 h of intensive care unit admission in a multicentre cohort of critically ill patients suffering acute circulatory failure. Likelihood ratios associated with different cutoff values of SpO₂ to rule out hypoxaemia (SaO₂ < 90% or PaO₂ < 60 mmHg) or hyperoxia (SaO₂ > 95% or PaO₂ > 100 mmHg) and post-test probabilities were calculated. Mean bias between SpO₂ and SaO₂ and agreement interval were calculated. Area under the receiver operating characteristics associated with SpO₂ to predict different threshold values of SaO₂ and PaO₂ were calculated.

RESULTS

Five hundred seventy-one patients (mean [standard deviation] Simplified Acute Physiology Score II: 58.7 [20.1]; mechanically ventilated 75.6%) with 2643 available SaO₂ and PaO₂ samples and corresponding 2643 SpO₂ values were analysed. Mean bias between SpO₂ and SaO₂ was 1.1%, and its agreement interval ranged from -8.2 to +11.1%. SpO₂ cutoff values of 88%, 90%, and 92% left the possibility that 8%-13% of patients had hypoxaemia. SpO₂ < 95% left the possibility that 31% of patients had hyperoxia. All calculated areas under the receiver operating characteristics showed a lower limit of their 95% confidence interval below 0.85 CONCLUSION: In this cohort of patients with circulatory failure, SpO₂ had poor discriminative ability to rule out hypoxaemia and hyperoxia. Overconfidence upon SpO₂ monitoring may be dangerous.

Computational Optical Sensing and Imaging: feature issue introduction

This Feature Issue includes 19 articles that highlight advances in the field of Computational Optical Sensing and Imaging. Many of the articles were presented at the 2019 OSA Topical Meeting on Computational Optical Sensing and Imaging held in Munich, Germany, on June 24-27. Articles featured in the issue cover a broad array of topics ranging from imaging through scattering media, imaging round corners and compressive imaging to machine learning for recovery of images.