Photoacoustics resolves species-specific differences in haemoglobin concentration and oxygenation

Introduction Photoacoustic imaging (PAI) enables the detection of blood haemoglobin (HB) concentration and oxygenation (SO2) with high contrast and resolution. To date, the relationship between photoacoustically determined total Haemoglobin (THbMSOT) and oxygen saturation (SO2) biomarkers and the underlying biochemical blood parameters has yet to be established. We sought to explore these relationships in a species-specific manner.Methods Experiments were performed in vitro using tissue-mimicking agar phantoms. Blood was extracted from mouse, rat, human and naked mole-rat (Heterocephalus glaber), anticoagulated in EDTA and measured within 48 hours. THbMSOT and SO2MSOT were measured using a commercial photoacoustic tomography system (InVision 128, iThera Medical GmBH). Biochemical blood parameters such as haemoglobin concentration (HB, g/dL), haematocrit (HCT, %) and red blood cell count (RBC, μL-1) were assessed using a haematology analyser (Mythic 18 Vet, Woodley Equipment).Results A significant correlation was observed between THbMSOT and biochemical HB, HCT and RBC in mouse and rat blood. Moreover, PAI accurately recapitulated inter-species variations in HB and HCT between mouse and rat blood and resolved differences in the oxygen dissociation curves between human, mouse and rat. With these validation data in hand, we applied PAI to studies of blood obtained from naked mole-rats and could confirm the high oxygen affinity of this species in comparison to other rodents of similar size.Conclusion In summary, our results demonstrate the high sensitivity of photoacoustically determined biomarkers towards species-specific variations in vitro.Competing Interest StatementJB, IQG and SEB have previously received research support from iThera Medical GmbH and Cyberdyne Inc.View Full Text