Imaging temperature changes in an interventional 0.5 T magnet: in-vitro results

Area of Science:

• Medical Imaging
• Interventional Radiology
• Biomedical Engineering

Background:

• Monitoring laser-induced temperature changes is crucial for interventional procedures.
• Open, interventional 0.5 T MRI systems offer unique advantages for real-time guidance.
• Fast imaging sequences are necessary to capture dynamic thermal events.

Purpose of the Study:

• To evaluate the efficacy of fast T1-weighted sequences for monitoring laser-induced temperature changes.
• To assess the ability of magnetic resonance imaging (MRI) to visualize thermal effects in an interventional 0.5 T magnet.
• To correlate MRI signal intensity changes with fluorooptically measured temperatures.

Main Methods:

• Investigated fast gradient echo (FGRE) and fast spoiled gradient echo (FSPGR) sequences with 2.5-second image updates.
• Applied a 5 Watt laser to induce tissue effects and measured temperature using fluorooptics.
• Correlated MRI signal intensity (SI) changes with temperature and compared MRI-lesions with macroscopic findings.

Main Results:

• FGRE sequences showed earlier and more pronounced SI changes compared to FSPGR (p < .0001).
• Strong correlations were found between temperature and SI loss (r = 0.94 for FGRE, r = 0.92 for FSPGR).
• FGRE demonstrated higher sensitivity to temperature variations due to a steeper slope; MRI generally underestimated lesion size.

Conclusions:

• Real-time laser monitoring is feasible using fast gradient echo sequences in a 0.5 T interventional MRI setting.
• Rapid image acquisition enables visualization of laser-induced thermal effects.
• This technique holds promise for enhancing safety and precision in interventional procedures.