Imaging For Gamma Knife Treatment Using A Verio 3t MriRalph Mackintosh1, Michael Brant-Zawadzki1, Christopher Duma2, Marianne Plunkett1, Helmuth Schultze-Haakh3, Gerhard Laub31Hoag Memorial Hospital Presbyterian 2Newport Beach, United States 3 Siemens Medical Solutions USA Inc Keywords: image guidance, magnetic resonance imaging, Imaging, gamma knife, dose planning
MRI using 1.5T magnets for localization of brain lesions prior to Gamma Knife treatment has been a standard for some time. We recently acquired a 3T MRI (Siemens Magnetom Verio) that we now use for 96% of Gamma Knife patients. 3T MRI offers higher signal to noise but concerns are a higher SAR, a larger chemical shift, susceptibility effects and eddy current generation in the frame. Imaging protocols require careful balance between rf pulse bandwidths, receiver bandwidths, spatial resolution and scan time.
Our purpose was to optimize protocols, discover issues unique to 3T imaging and demonstrate the clinical utility of the Verio MRI for GK imaging.
Due to issues with the GK frame fitting in the Verio head coil we evaluated a custom coil setup designed by Siemens for the GK frame. Sequences were evaluated for spatial accuracy and distortions using a known target phantom (PTGR). Specific sequences were developed by Siemens for GK imaging. These formed the basis for our fine tuning and modifications. Studies were done with phantoms and clinical subjects to compare geometrical variances between 1.5T and 3T and CT images.
The Siemens custom coil configuration using a wooden framework coupled with a standard body coil was evaluated. It was found that the standard 12 channel coil w/o spacer blocks and straps could be utilized for most patients. Sequences were constructed to minimize distortions at the pin sites and adjacent to the base frame. Care must be taken in using localizer box registration data from points near the base frame ring. The phantom data between the 1.5T (GE) and 3T scanners was comparable with the 3T being equal or superior for most sequences. Clinical tumor location agreement was within 1.0 mm for SPGR and MPRAGE sequences and within 1.5-2.0 mm for the FLAIR sequences (4-5 mm thickness). Anatomical points were evaluated for the CT and MRI images and were within 1.0-1.5 mm.
This is a retrospective study.
A Verio 3T MRI for Gamma Knife imaging is clinically acceptable with careful selection of MRI parameters, validation of geometrical accuracy, and awareness of increased distortion regions.
Patients must be screened and alternate imaging modalities considered for selected regions. We have successfully scanned over 300 patients on a Magnetom Verio prior to Gamma Knife treatment. Project Roles:
R. Mackintosh (), M. Brant-Zawadzki (), C. Duma (), M. Plunkett (), H. Schultze-Haakh (), G. Laub ()