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An Optimized System for Interventional Magnetic Resonance Imaging-Guided Stereotactic Surgery: Preliminary Evaluation of Targeting Accuracy

Larson, Paul S. MD*; Starr, Philip A. MD, PhD*; Bates, Geoffrey BS; Tansey, Lisa BS; Richardson, R. Mark MD, PhD*; Martin, Alastair J. PhD§

doi: 10.1227/NEU.0b013e31822f4a91
Technique Assessment: Editor's Choice
Editor's Choice

BACKGROUND: Deep brain stimulation electrode placement with interventional magnetic resonance imaging (MRI) has previously been reported using a commercially available skull-mounted aiming device (Medtronic Nexframe MR) and native MRI scanner software. This first-generation method has technical limitations that are inherent to the hardware and software used. A novel system (SurgiVision ClearPoint) consisting of an aiming device (SMARTFrame) and software has been developed specifically for interventional MRI, including deep brain stimulation.

OBJECTIVE: To report a series of phantom and cadaver tests performed to determine the capability, preliminary accuracy, and workflow of the system.

METHODS: Eighteen experiments using a water phantom were used to determine the predictive accuracy of the software. Sixteen experiments using a gelatin-filled skull phantom were used to determine targeting accuracy of the aiming device. Six procedures in 3 cadaver heads were performed to compare the workflow and accuracy of ClearPoint with Nexframe MR.

RESULTS: Software prediction experiments showed an average error of 0.9 ± 0.5 mm in magnitude in pitch and roll (mean pitch error, −0.2 ± 0.7 mm; mean roll error, 0.2 ± 0.7 mm) and an average error of 0.7 ± 0.3 mm in X-Y translation with a slight anterior (0.5 ± 0.3 mm) and lateral (0.4 ± 0.3 mm) bias. Targeting accuracy experiments showed an average radial error of 0.5 ± 0.3 mm. Cadaver experiments showed a radial error of 0.2 ± 0.1 mm with the ClearPoint system (average procedure time, 88 ± 14 minutes) vs 0.6 ± 0.2 mm with the Nexframe MR (average procedure time, 92 ± 12 minutes).

CONCLUSION: This novel system provides the submillimetric accuracy required for stereotactic interventions, including deep brain stimulation placement. It also overcomes technical limitations inherent in the first-generation interventional MRI system.

Author Information

Departments of *Neurological Surgery

§Radiology, University of California, San Francisco, San Francisco, California

MRI Interventions, Inc. (formerly SurgiVision, Inc.), Irvine, California

Correspondence: Paul S. Larson, MD, Associate Professor, Department of Neurological Surgery, University of California, San Francisco, 505 Parnassus Ave, Box 0112, San Francisco, CA 94143-0112. E-mail:

Received June 12, 2010

Accepted May 17, 2011

Copyright © by the Congress of Neurological Surgeons