Quantitative photoacoustic imaging study of tumours in vivo

Photoacoustic imaging (PAI) provides information on haemoglobin levels and blood oxygenation (sO2). To facilitate assessment of the variability in sO2 and haemoglobin in tumours, for example in response to a therapy, the intrinsic variability of these parameters was evaluated in subcutaneous head and neck tumours in mice, using a PAI system (MSOT-inVision 256TF). Tumours of anaesthetized animals (midazolam-fentanyl-medetomidine) were imaged for 75 minutes; in varying positions; and repeatedly over 6 days. An increasing linear trend for tumoural haemoglobin and blood sO2 was observed, when imaged over 75 minutes. There was no significant difference in variability of the parameters, when re-positioning tumours. A negative correlation was found between tumour growth rate and percentage decrease in blood sO2, over 6 days. This paper shows the potential of PAI to monitor intrinsic variation and reproducibility in estimating blood sO2 and haemoglobin, with an eventual aim of predicting and monitoring cancer treatment response.