Abstract
Objective
Blood oxygenation can be measured using magnetic resonance using the paramagnetic effect of deoxy-haemoglobin, which decreases the
T
2
relaxation time of blood. This
T
2
contrast has been well characterised at the
B
0
fields used in MRI (1.5 T and above). However, few studies have characterised this effect at lower magnetic fields. Here, the feasibility of blood oximetry at low field based on
T
2
changes that are within a physiological relevant range is explored. This study could be used for specifying requirements for construction of a monitoring device based on low field permanent magnet systems.
Methods
A continuous flow circuit was used to control parameters such as oxygen saturation and temperature in a sample of blood. It flowed through a variable field magnet, where CPMG experiments were performed to measure its
T
2
. In addition, the oxygen saturation was monitored by an optical sensor for comparison with the
T
2
changes.
Results
These results show that at low
B
0
fields, the change in blood
T
2
due to oxygenation is small, but still detectable. The data measured at low fields are also in agreement with theoretical models for the oxy-deoxy
T
2
effect.
Conclusion
T
2
changes in blood due to oxygenation were observed at fields as low as 0.1 T. These results suggest that low field NMR relaxometry devices around 0.3 T could be designed to detect changes in blood oxygenation.