T1 Thermometry for Deep Brain Stimulation Applications: A Comparison between Rapid Gradient Echo Sequences.

Background: T₁ 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 T₁ 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. T₁ thermometry was performed by either T₁-weighted images with a high SAR sequence to increase heating around the wire or T₁ mapping methods.

Results: The balanced steady-state free precession (bSSFP) sequence provided higher image quality in terms of spatial resolution (1×1×1.5 mm³ compared with 1×1×3 mm³) 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 T₁ mapping method.

Conclusion: Heating induced during MRI of implanted electrodes could be estimated using high-resolution T₁ 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.