Special consideration must be given to all items that penetrate the exterior of the RF shield into the MRI suite. Specialty shielded penetrations must be provided to maintain the RF shielding integrity. For example, HVAC must pass through HVAC wave guides and plumbing for fire sprinklers, if required, must also pass through a wave guide. Wave guides are designed to specifically limit the frequencies that could pass through the shielding. Wave guides designed for a 100 MHz RF enclosure, for example, will not allow frequencies below 100 MHz to pass through the shielding as some of those frequencies could interfere with the MRI system. Additionally, all electrical items including power for outlets, lighting and specific sensors required for an MRI installation, must pass through electrical filters. Most electrical filters are low pass filters that only allow signals below a "cutoff" frequency to pass through. For example, a filter with a 1 MHz cutoff will only allow signals at frequencies below 1 MHz to pass though the filter into the MRI suite via the wiring of the filter.


Additionally, special attention must be given to the ground isolation of the room. This is a critical, but often overlooked, consideration when site planning. The RF enclosure, when first constructed, should achieve a minimum of 1000 ohms of ground isolation. This is intended to prevent ground loops and other issues, including less than optimal MRI images, which will occur due to poor grounding of an enclosure.

In addition to specialty shielded penetrations, other important aspects of the shielding that should be considered are the doors and windows. The doors and windows are items that the MRI end users will see and use every day. Therefore, functionality should be considered a top priority when designing and specifying products for a site. Typical MRI doors, as an example, use friction to create the RF seal. This works well for creating the RF seal at the door, but can be quite difficult to operate as these doors require a reasonable amount of force to open and close. This raises other concerns and issues. These doors require maintenance and repair of the door's RF fingers to maintain performance. Without proper maintenance, the door can become unreliable. There are doors available that provide mechanical seals to create the RF seal at the door with simple "push button" entry and egress operation. These doors have the look and feel of a standard door adding to user comfort while the ease of operation expedites patient throughput. It is important to keep in mind windows and doors will often have limited acoustic performance. Careful attention should be used when specifying doors and windows if acoustics are a concern.

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