Technical note: A spiral fluid-attenuated inversion recovery magnetic resonance imaging technique for stereotactic radiosurgery treatment planning for trigeminal neuralgia.

PURPOSE

Magnetic resonance imaging (MRI) is commonly used in treatment planning for stereotactic radiosurgery (SRS) of trigeminal neuralgia (TN). With current MRI techniques, the delineation of the trigeminal nerve root entry zone (REZ) may be degraded due to poor contrast and artifacts. The purpose of this work is to develop an MRI technique with better delineation of the trigeminal nerve REZ to improve SRS treatment planning for TN.

METHODS

A spiral fluid-attenuated inversion recovery (FLAIR) MRI technique was developed to improve image quality by improving tissue contrast, fluid suppression, artifact reduction, and signal-to-noise ratio (SNR). A concomitant-phase compensation method based on spiral gradient waveforms was implemented to minimize artifacts due to magnetic field change induced by the metal frame used in Gamma Knife treatment planning. The image quality of spiral FLAIR was assessed in four healthy volunteers. The geometric accuracy was quantitatively evaluated by registering spiral FLAIR to computed tomography (CT) images and comparing it with existing MRI techniques.

RESULTS

The spiral FLAIR technique demonstrated better delineation of the trigeminal nerve REZ, improved tissue contrast of the brain stem, and minimized flow artifacts, compared to steady-state free precession (SSFP) MRI. Spiral FLAIR also improved fluid suppression, SNR, and artifacts, which contributed to better delineation of the trigeminal nerve REZ compared to conventional Cartesian FLAIR. The measured mean (± standard deviation) distance between spiral FLAIR and CT images is 0.98 ± 0.56 mm, comparable to 0.40 ± 0.26 mm in 3T T1 spoiled gradient echo (T1-SPGR), 0.59 ± 0.25 mm in 3T SSFP, 0.66 ± 0.38 mm in 1.5T T1-SPGR, and 0.61 ± 0.25 mm in 1.5T Cartesian FLAIR.

CONCLUSION

A spiral FLAIR technique with improved image quality and good geometric accuracy provides a potential alternative for treatment planning in SRS for TN patients.