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Increased Frameless Stereotactic Accuracy With High-Field Intraoperative Magnetic Resonance Imaging

Tanaka, Shota MD*; Puffer, Ross C. BS*; Hoover, Jason M. MD*; Goerss, Stephan J.*; Haugen, Laura M.*; McGee, Kiaran PhD; Parney, Ian F. MD, PhD*

doi: 10.1227/NEU.0b013e31826a88a9
Instrumentation Assessment

BACKGROUND: Frameless stereotaxy commonly registers preoperative magnetic resonance imaging (MRI) to patients by using surface scalp anatomy or adhesive fiducial scalp markers. Patients' scalps may shift slightly between preoperative imaging and final surgical positioning with pinion placement, introducing error. This might be reduced when frameless stereotaxy is performed in a high-field intraoperative MRI (iMRI), as patients are positioned before imaging. This could potentially improve accuracy.

OBJECTIVE: To compare frameless stereotactic accuracy using a high-field iMRI with that using standard preoperative MRI.

METHODS: Data were obtained in 32 adult patients undergoing frameless stereotactic-guided brain tumor surgery. Stereotactic images were obtained with 1.5T MRI scanner either preoperatively (14 patients) or intraoperative (18 patients). System-generated accuracy measurements and distances from the actual center of each fiducial marker to that represented by neuronavigation were recorded. Finally, accuracy at multiple deep targets was assessed by using a life-sized human head stereotactic phantom in which fiducials were placed on deformable foam to mimic scalp.

RESULTS: System-generated accuracy measurements were significantly better for the iMRI group (mean ± SEM = 1.04 ± 0.05 mm) than for the standard group (1.82 ± 0.09 mm; P < .001). Measured distances from the actual center of scalp fiducial markers to that represented by neuronavigation were also significantly smaller for iMRI (1.72 ± 0.10 mm) in comparison with the standard group (3.17 ± 0.22 mm; P < .001). Deep accuracy in the phantom model was significantly better with iMRI (1.67 ± 0.12 mm) than standard imaging (2.28 ± 0.14 mm; P = .003).

CONCLUSION: Frameless stereotactic accuracy is increased by using high-field iMRI compared with standard preoperative imaging.

ABBREVIATIONS: iMRI, intraoperative magnetic resonance imaging

pMRI, preoperative magnetic resonance imaging

TLE, target localization error

*Department of Neurologic Surgery, Mayo Clinic College of Medicine, Rochester, Minnesota

Department of Radiology, Mayo Clinic College of Medicine, Rochester, Minnesota

Correspondence: Ian F. Parney, MD, PhD, Department of Neurological Surgery, Mayo Clinic, 200 First St SW, Rochester, MN 55905. E-mail:

Received November 22, 2011

Accepted July 05, 2012

Copyright © by the Congress of Neurological Surgeons