Significance: Photoacoustic imaging (PAI) enables the detection of blood haemoglobin (HB) concentration and oxygenation (sO2) with high contrast and resolution. Despite the heavy use of photoacoustic total haemoglobin (THbMSOT) and sO2 biomarkers in PAI research, their relationship with underlying biochemical blood parameters and the impact of intra- and inter-species genetic variability have yet to be established.
Aim: To explore the relationship between THbMSOT and sO2 photoacoustic biomarkers and the underlying biochemical blood parameters in a species-specific manner.
Approach: Experiments were performed on blood 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 measured using sO2MSOT 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.
Conclusions: Our results demonstrate the high sensitivity of photoacoustically determined biomarkers towards species-specific variations in vitro.
