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.