MRI-Guided Interventions

Introduction

The term interventional MRI is used to describe the use of magnetic resonance imaging (MRI) for rapid guidance and/or monitoring of a minimally invasive diagnosis or therapy where the entire procedure is interactively performed within an interventional MRI suite in a manner that is equivalent to standard fluoroscopic or ultrasound (US)-guided procedures. The term interventional MRI itself is relatively new as a description of a full clinical service of MRI-guided interventions integrated within the daily practice of interventional radiology. The idea of adapting MRI for interventional procedure guidance, however, dates back to the mid-1980s shortly after the introduction of MRI as a diagnostic imaging modality.

Continued growth of the field of interventional MRI (iMRI) is marked by the increasing number of academic institutions with added iMRI capabilities, the growing diversity of iMRI applications adopted at these institutions, and the expanding technologic innovations that back this growth.

iMRI Suite Setup

An iMRI suite is an interventional procedure room equivalent to other medical procedure rooms where the main interventional equipment may consist of an x-ray fluoroscopy unit, a computed tomography (CT) scanner, a US scanner, an endoscopy unit, and so forth. In this case the room activity revolves around an MRI scanner. This arrangement is a hybrid design that has to fulfill the requirements of both a regular diagnostic MRI scanner and an interventional radiology suite. Specifically the fundamental requirements for an iMRI suite include:

• (1)

  Adequate access to the patient within the scanner to perform an interventional procedure. Access to the patient is restricted within the regular narrow, long bores of standard scanners. Interventional solutions include use of an open-configuration scanner or adopting other workflow solutions as described in this chapter.

• (2)

  Availability of MRI-compatible anesthesia equipment, monitoring tools, and interventional devices. These are currently available from several vendors on a commercial basis.

• (3)

  Ability to achieve proper draping and to ensure a completely sterile field during interventions. This is a more challenging job compared to the customary draping of flat surfaces during traditional x-ray fluoroscopy, CT, or US-guided interventions.

• (4)

  Ability to implement rapid pulse sequences with reasonable signal-to-noise ratio to ensure adequate visualization of the interventional device and timely updates of its location to achieve safe device placement.

• (5)

  Ability to operate the scanner and to review updated images at the patient's bedside without having to remove the operator's hand at any time from the interventional setting.

iMRI System Design and Workflow Solutions

Designing an MRI scanner for interventional purposes is a technically and logistically complex endeavor. On the technical side, the environment suitable for adequate access to the patient and comfortable application of anesthesia equipment and monitoring devices is basically the opposite of that “closed magnet” environment suitable for producing high-quality diagnostic MRI scans. Logistically there will probably be a need—at least for the foreseeable future—to use an iMRI scanner for routine diagnostic imaging to maximize the revenue of the scanner and support the associated interventional programs. Several interventional solutions have been implemented over the past years that included both magnet design and workflow/combined-suite solutions ( Fig. 66-1 ).