Physiological parameters of groups of bruises determined from single measurements at time of presentation

Knowledge of model parameters in bruise modeling is a prerequisite for accurate simulation of temporal bruise behavior, e.g. to obtain reliable age determination. So far 3 tissue specific model parameters (diffusivity of hemoglobin, concentration of the hemoglobin converting enzyme, and clearance time of bilirubin into the lymphatic system) were determined from area measurements of hemoglobin and bilirubin at multiple times. In clinical practice, it is not always possible to follow a bruise in time. This complication is circumvented if bruises on the same anatomical position would have the same or very similar parameters. Therefore, we explored if we could determine the group average of these 3 model parameters in three groups of bruises: (1) 30 medial arm bruises, (2) 42 lateral arm bruises, and (3) 51 lateral leg bruises. We measured the hemoglobin and bilirubin areas in each bruise once, at the time of presentation. The optimal set of the 3 parameters for each group is assessed from the highest correlation between simulated and measured areas of hemoglobin and bilirubin. We show that, within measurement uncertainty, there is no difference between these group averaged sets of parameters in medial and lateral arm bruises and lateral leg bruises. We believe this is an important step in the age determination of bruises using numerical modeling. When parameters are accurately known for groups of bruises, age determination of future bruises falling within a certain group may not require measurements as frequently as was done previously, which would greatly improve the clinical applicability of age determination of bruises.