Near infrared spectroscopy: a potential tool for assessing haemodynamic markers of the microvascular blood supply within bone tissue

Abstract

Background: Measuring microvascular blood supply within bone remains challenging with existing imaging modalities due to its high density and mineral content. Near Infrared Spectroscopy (NIRS) has the potential to measure microvascular haemodynamic markers within bone, including perfusion rates and blood volume. NIRS is safe, inexpensive and provides oxygenation levels in real time allowing continuous monitoring, unlike existing tests. Objectives: To investigate if NIRS can accurately measure microvascular haemodynamics exclusively in bone tissue and that these measurements are reproducible with different operators and across different participants. Methods: 15 healthy volunteers were recruited for a range of feasibility testing following local ethical approval. NIRS measurements were performed simultaneously at muscle (lateral head of the gastrocnemius) and bone (proximal tibia) sites on the leg. Baseline total oxygenation index (TOI) was measured followed by an arterial occlusion protocol of the distal femur. Reproducibility work was also performed to assess inter and intra operator precision of baseline TOI measurements using three different operators. Results: Baseline TOI was significantly different (p < 0.001) between bone (83.00 % (SD4.13)) and muscle (70.05 %(SD4.82)) sites. Upon arterial occlusion, the rate of deoxygenation was on average 2.51 times faster at the muscle site than S636 Osteoporos Int (2016) 27 (Suppl 2):S609–S685 the proximal tibia (p< 0.01). Upon occlusion release, muscle recovered on average 3.81 times faster than the proximal tibia (p < 0.01). When three operators measured TOI on the same participant, the standard deviation of measurements was comparable between both bone (SD3.03 % ± 1.97 %) and muscle (SD2.10 % ± 1.37 %), with the latter being an established measurement site for NIRS. Discussion: Results suggest NIRS can exclusively measure bone tissue based on the physiological differences observed between the bone and muscle sites measured. The next step to validate this application of NIRS is to correlate it with Dynamic Contrast Enhanced MRI results. If successful, further research using NIRS in more diverse populations where bone health may have been effected by microvascular pathophysiology would be justified. Conclusion: Initial feasibility work suggests NIRS has the potential to be a new diagnostic tool for haemodynamic measurements of microvascular supply within bone tissue.