Techniques for Interventional MRI Guidance in Closed-Bore Systems

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Efficient image guidance is the basis for minimally invasive interventions. In comparison with X-ray, computed tomography (CT), or ultrasound imaging, magnetic resonance imaging (MRI) provides the best soft tissue contrast without ionizing radiation and is therefore predestined for procedural control. But MRI is also characterized by spatial constraints, electromagnetic interactions, long imaging times, and resulting workflow issues. Although many technical requirements have been met over the years—most notably magnetic resonance (MR) compatibility of tools, interventional pulse sequences, and powerful processing hardware and software—there is still a large variety of stand-alone devices and systems for specific procedures only.Assistance and navigation techniques are not a prerequisite for MRI-guided interventions but often provide the means for refined targeting, better control, and improved performance, particularly for more complex access routes or less experienced operators. Open MRI systems have long been a preferred interventional platform because of their largely unrestricted access. Current developments focus on cylindrical wide-bore systems instead that will likely become the standard platform for MRI diagnostics.Stereotactic guidance with the table outside the magnet is common and relies on proper registration of the guiding grids or manipulators to the MR images. Instrument tracking, often by optical sensing, can be added to provide the physicians with proper eye-hand coordination during their navigated approach. Only in very short wide-bore systems, needles can be advanced at the extended arm under near real-time imaging. In standard magnets, control and workflow may be improved by remote operation using robotic or manual driving elements.This work highlights a number of devices and techniques for different interventional settings with a focus on percutaneous, interstitial procedures in different organ regions. The goal is to identify technical and procedural elements that might be relevant for interventional guidance in a broader context, independent of the clinical application given here. Key challenges remain the seamless integration into the interventional workflow, safe clinical translation, and proper cost effectiveness.

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