· Essential features of an interventional suite include interactive, real-time imaging, in-room displays, and a communication system.

· Most components of an interventional suite are commercially available.

· The availability of MR-safe interventional devices is limited, but it is an active area of development.

Clinicians and scientists who are planning to begin an interventional MRI program. Information will be presented on how to plan for a new facility or retrofit an existing one to enable MRI-guided procedures.Interventional MRI provides excellent soft tissue visualization without ionizing radiation (1), and is being used to guide a wide array of clinical procedures in areas including neurosurgery, oncology and cardiology (see ref. (2) for a recent review). An interventional MRI suite requires incremental hardware modifications plus real-time, interactive imaging sequences (3). The major scanner vendors all offer suitable real-time sequences, and some offer additional features such as thermometry or active device tracking. The purpose of this presentation is to describe the additional systems needed in an interventional MRI suite and discuss developing technologies in the field.

Display: In an interventional MRI procedure the real-time images need to be displayed to the operators inside the MRI suite using MR-safe LCD monitors or shielded projectors (Figure 1). Where operators and staff will be during procedures should be considered to determine the optimal placement of the displays. Displays may need to be mirrored to either side of the magnet bore. Multiple displays are often required in order to display additional information, such as previously acquired images and hemodynamics. In the control room, a video matrix switch may be used to dynamically change the display configuration for different procedures. Video signals in the control room should be converted to optical signals and passed into the MRI suite via fiber through a waveguide.

Communication: It is critical that staff in the MR suite and control room can communicate during a procedure. Additionally, staff in the room may need to communicate directly with the patient. Commercial systems are available which consist of multiple headsets and provide adequate sound suppression to enable communication during scanning. These systems are wireless, but may require fiber connections through a waveguide to processing units outside the MR suite.

Hemodynamics: Hemodynamic monitoring and recording requirements vary by procedure. MR-safe monitoring systems that measure ECG, non-invasive and invasive blood pressure, and SpO2 are commercially available. Cardiovascular procedures usually require high-fidelity hemodynamic recording capabilities, typically available in cardiac angiography suites. These systems have more ECG and invasive blood pressure channels, higher data sampling rates, and are usually connected to patient database systems. Systems for electrophysiology procedures may also require measurement of intracardiac electrograms. Measurement of high-fidelity ECG in MRI is challenging because of RF and gradient interference, but several groups have developed solutions (4,5). While an MR compatible hemodynamic recording system is not yet commercially available, efforts are ongoing.

Most interventional devices are made from metal and pose a heating risk and/or produce large artifacts in MRI. Some devices have been specifically designed for use in MRI, including needles made from non-ferrous materials and non-metallic guidewires. Commercial MRI compatible electrophysiology systems are also under development (6,7). Certain catheters contain no metallic braiding and have been shown to be safe in MRI. When using a device specifically designed for MRI, the instructions for use should be carefully reviewed for restrictions on magnetic field strength and other use conditions. Other off the shelf devices may be screened for metal with fluoroscopy.Special consideration should be given to workflow and safety in an interventional MR suite. Some suites may have adjoining X-ray angiography suites and specialized transfer systems to move patients between the two modalities (Figure 2). Staff which may typically work with X-ray angiography or CT should undergo MRI safety training, and all personnel should be carefully screened before entering the suite. It is recommended to run drills for patient transfer and emergency evacuation regularly. The interventional MR technologist assumes additional roles and responsibilities, including sterile draping of the scanner system, preparation of an MR-safe procedure table, and running real-time imaging to guide the procedure (8).The interventional MRI suite includes additional features to enable operators to conduct procedures in the suite during real-time imaging. Most of the equipment necessary for an interventional MRI suite is now available from commercial vendors. Procedures have been limited by a lack of MR compatible devices, but there are several off the shelf devices which are MR-safe, and there is active development in areas such as MRI guided electrophysiology which holds promise for clinical translation in the near future. MRI guided interventions have become routine clinical practice at several institutions, and demand for interventional MRI suites is expected to grow as more MR compatible devices become commercially available.