T Thermometry for Deep Brain Stimulation Applications: A Comparison between Rapid Gradient Echo Sequences.

BACKGROUND

T thermometry is considered a straight method for the safety monitoring of patients with deep brain stimulation (DBS) electrodes against radiofrequency-induced heating during Magnetic Resonance Imaging (MRI), requiring different sequences and methods.

OBJECTIVE

This study aimed to compare two T thermometry methods and two low specific absorption rate (SAR) imaging sequences in terms of the output image quality.

MATERIAL AND METHODS

In this experimental study, a gel phantom was prepared, resembling the brain tissue properties with a copper wire inside. Two types of rapid gradient echo sequences, namely radiofrequency-spoiled and balanced steady-state free precession (bSSFP) sequences, were used. T thermometry was performed by either T-weighted images with a high SAR sequence to increase heating around the wire or T mapping methods.

RESULTS

The balanced steady-state free precession (bSSFP) sequence provided higher image quality in terms of spatial resolution (1×1×1.5 mm compared with 1×1×3 mm) at a shorter acquisition time. The susceptibility artifact was also less pronounced for the bSSFP sequence compared with the radiofrequency-spoiled sequence. A temperature increase, of up to 8 ℃, was estimated using a high SAR sequence. The estimated change in temperature was reduced when using the T mapping method.

CONCLUSION

Heating induced during MRI of implanted electrodes could be estimated using high-resolution T maps obtained from inversion recovery bSSFP sequence. Such a method gives a direct estimation of heating during the imaging sequence, which is highly desirable for safe MRI of DBS patients.