Contactless in vitro detection of carboxyhemoglobin using hyperspectral imaging (HSI)

Hyperspectral imaging (HSI) allows for the contactless analysis of the composition of substances based on the reflected light and is already used in various areas of medicine. The carboxyhemoglobin (CO-Hb) concentration in blood of suspected fire victims serves to prove vitality and the cause of death. However, this metric is usually determined by spectrophotometry in the laboratory. The present study provides the basis for the future development of methods for determining CO-Hb concentrations right at the scene of a corpse or at necropsy using mobile HSI. Human erythrocyte concentrate was mixed with gaseous carbon monoxide using an aerator to produce a series of samples, which were analyzed for their CO-Hb concentration (2.9; 9.7; 18; 27.9; 39.9; 51.9; 62.3; 73.4% CO-Hb) using established spectrophotometric blood gas analysis. These blood samples were stored in a cool place at 4 °C, dripped onto a spot plate every 7 days over a period of 6 weeks, and photographed under standardized conditions (ambient lighting, distance and angle of the camera to the sample, camera settings) using the HSI camera SPECIM IQ. This device analyzes each image in the wavelength range from 400 to 1000 nm in 204 spectral bands. The data sets were used to train a lasso regression model, which provides predicted values for the CO-Hb concentration of the blood sample based on their hyperspectral properties. The results were then compared with the results of spectrophotometric measurements. The lasso regression model allowed the prediction of the CO-Hb concentration of the samples with a mean prediction error of 4.46 percentage points, independent of the sample age. Further investigations regarding pre-analytical influencing factors such as variable ambient light and tissue scattering effects, are planned to validate the robustness of the method and realize practical implementations.