A Review of Intra-operative Magnetic Resonance Systems

A Review of Intra-operative Magnetic Resonance Systems

Alastair J Martin, Elyakim Bosak, Josef Debbins, Michael Steckner, Stephen G Hushek
Published: US Neurological Disease 2007 - Issue II
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Magnetic resonance imaging (MRI) quickly became an important tool for the study of neuroanatomy and most scans were ordered for brain or spine diagnoses. Subsequently, image quality (IQ) has improved, yielding higherresolution images, faster scans, and/or additional types of information. The continuous improvements are revealing tractography information via diffusion tensor imaging and function localization via functional MRI (fMRI). Similarly, image processing and manipulation have also progressed significantly, yielding segmentation routines for automatic tissue classification, fusion algorithms for multimodality image combination, and registration techniques for aligning the images with the patient’s physical anatomy; this has expedited data synthesis, simplified data integration, and improved data utility.

Image-guided surgery (IGS) systems have brought both the raw and processed images into the operating room (OR) and clarified the relationship between the images and anatomy. Intra-operative MRI (iMRI) systems have integrated all of these functions and elevated the timeliness of the information to a new level, enabling intra-operative updates of all information for burr hole alignment, craniotomy extent reduction, resection control, eloquent tissue avoidance, subsurface visualization, and complication detection. Various iMRI systems have been designed to satisfy the surgical imperatives and provide timely, quality images while preserving surgical workflow. This article will examine the ability of the various systems to meet these objectives, consider other factors that influence the acceptance of the systems, and examine trends that indicate their utility. Developments in complementary systems and technology have accompanied the advances in iMRI system design, but these developments will not be discussed here. Readers interested in a broader review and analysis are invited to consult recently published general iMRI system reviews,1,2 along with general MR safety guidelines3,4 and iMRI-specific safety discussions.5,6

The relative characteristics of iMRI systems designed specifically to meet this developing surgical need are compared with those of diagnostic systems with ‘add-on’ iMRI packages in Table 1. The physics of MR dictate that optimal IQ is achieved when the magnet, gradients, and radiofrequency (RF) coils can surround the patient and get as close as possible to the anatomy of interest. This directly competes with the surgical access requirement, thus explaining the contrast between those features in Table 1. Some designs provided both access and IQ but at different times, which then made the ease and speed of transition between surgery and imaging a prime design objective. All designs provide some type of MR-compatible head frame for patient fixation.


Table 1: Comparison of Specialty Systems with Enhanced Diagnostic Systems

Comparison of Specialty Systems with Enhanced Diagnostic Systems



Specialized Systems
Three different specialized systems were designed with a vertical gap and low field magnets (0.12–0.5 Tesla (T)) with imaging capabilities less than that found on standard 1.5T cylindrical superconducting systems. The systems had widely differing siting requirements, which influenced their clinical acceptance.

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