Oxygen saturation-dependent effects on blood transverse relaxation at low fields

Area of Science:

• Biomedical Engineering
• Magnetic Resonance Imaging
• Medical Device Development

Background:

• Blood oxygenation monitoring is crucial for patient care.
• Magnetic Resonance (MR) techniques utilize the paramagnetic effect of deoxyhemoglobin to measure blood oxygenation.
• Existing MR methods are well-characterized at high magnetic fields (1.5T and above), but less is known about low-field applications.

Purpose of the Study:

• To explore the feasibility of blood oximetry at low magnetic fields.
• To characterize T2 relaxation changes in blood due to oxygenation within a physiologically relevant range.
• To inform the design requirements for low-field permanent magnet-based monitoring devices.

Main Methods:

• A continuous flow circuit was employed to control blood oxygen saturation and temperature.
• Continuous Pulse Gradient Spin Echo (CPMG) experiments were conducted in a variable field magnet to measure blood T2 relaxation.
• An optical sensor was used for real-time monitoring of blood oxygen saturation, enabling comparison with T2 changes.

Main Results:

• A small but detectable change in blood T2 relaxation was observed at low magnetic fields (as low as 0.1T) due to oxygenation.
• The experimental data at low fields align with theoretical models describing the T2 oxygen-deoxyhemoglobin effect.
• The study demonstrates the principle of low-field blood oximetry based on T2 variations.

Conclusions:

• Blood oxygenation-induced T2 changes are observable at magnetic fields as low as 0.1 Tesla.
• These findings suggest that low-field Nuclear Magnetic Resonance (NMR) relaxometry devices, potentially around 0.3 Tesla, can be designed for effective blood oxygenation monitoring.
• The study supports the development of cost-effective and accessible blood oxygenation monitoring solutions using permanent magnet systems.