Muonium response to low oxygen levels in haemoglobin and other biological aqueous solutions and potential application towards monitoring hypoxia

Abstract

Low oxygen concentration or hypoxia plays a crucial role in the diagnosis and treatment of tumours and cancer. Although there are some existing techniques, such as proton magnetic resonance imaging (MRI), for the detection of molecular oxygen in tissues, new non-invasive techniques for directly measuring the extent and spatial distribution of hypoxia in cancerous or tumorous tissues are still needed. In this study, we propose a new non-invasive method using muons that are available in accelerator facilities, such as the Japan Proton Accelerator Research Complex in Japan and the Rutherford Appleton Laboratory in the UK. Unlike existing MRI methods, the proposed muon-based method can be applied without any external magnetic field. With the help of muonium response in solutions, we measured oxygen concentration in the aqueous solutions of various biological materials, such as haemoglobin, albumin, serum, and tris-buffered saline, under controlled molecular oxygen concentrations. The observed relaxation rate pattern of muonium through a fixed oxygen concentration sample and that with a sample concentration of less than 1% oxygen shows that this method may be applicable in detecting molecular oxygen levels in various tissues of the human body. Based on our experimental results, we have estimated the expected muonium spectra in normal physiological concentrations of haemoglobin in blood. Further systematic studies on other biological solutions are required before a potential clinical application of the method is devised.