Document Type : Original Research
Authors
1 Department of Medical Physics and Biomedical Engineering, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran
2 Department of Neurosurgery, Hazrat Rasool Hospital, Iran University of Medical Sciences, Tehran, Iran
3 Department of Physical Medicine and Rehabilitation, Northwestern University, USA
Abstract
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.
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