The use of near infrared spectroscopy (NIRS) as a diagnostic tool to measure microvascular haemodynamics in bone tissue.

Abstract

Bone is a dynamic and highly vascular tissue, but measuring markers of microvascular haemodynamics within bone is currently difficult. There are logistical and technical limitations with existing tests based around MRI and radioisotope scans, in part due to bone’s high density and mineral content. This complicates studying bone diseases where microvascular dysfunction plays a pathogenic role. Near infrared spectroscopy (NIRS) has the potential to measure bone haemodynamic markers in real time and is safe and inexpensive. It also provides information on oxygen levels within bone, previously only possible with bone biopsy. NIRS utilises similar technology to a pulse oximeter, transmitting and receiving designated optical frequencies using non-invasive probes at a specific anatomical sight and measuring tissue depths of up to 4cms (Figure 1). NIRS takes advantage of the differences in attenuation caused by oxyhaemoglobin (O2Hb) and deoxyhaemoglobin (HHb). This provides haemodynamic markers such as: Total oxygenation index (TOI): The ratio of O2Hb to total haemoglobin (cHb); Normalised total haemoglobin index (nTHI): Real time percentage change in cHb concentration from an initial baseline measurement; and, Real time absolute concentration changes of HHb, O2Hb and cHb [1].