Building out an imaging suite: shielding, power and cooling for MRI, CT and X-ray

An imaging room looks simple once it is finished: a scanner, a table, a control window. Most of what makes it work is hidden in the walls, the floor, the ceiling, and the equipment room next door: lead in the walls for CT and X-ray, a sealed metal room for MRI, a floor that can carry the machine, a path to get it inside, and power and cooling sized to the equipment. This guide walks through each one, so an imaging group, a hospital outpatient department, or a practice adding X-ray knows what to plan for. It applies whether the suite goes into a new building or a finish-out or renovation of existing space.

The equipment comes first

Every imaging room is designed around one specific machine. The manufacturer publishes site planning drawings for each model, and those drawings set the room size, the weight on the floor, the electrical service, the heat the machine gives off, and the inputs the shielding designer needs. A room drawn for one CT and then built for another often means torn-out walls and new conduit.

So the order matters. Choose the modality and the model, or at least narrow it to one manufacturer, before the architect finishes the floor plan. Then give the architect, the engineers, and the contractor the site planning package for that model, and tell everyone if the selection changes. The equipment delivery date belongs on the construction schedule from the start, because the room has to be ready before the machine arrives.

Lead shielding for CT and X-ray

CT, general X-ray, fluoroscopy, and mammography rooms need radiation shielding, usually lead-lined drywall, lead-lined doors and frames, and a leaded glass window at the control area. How much lead, and in which walls, is not a contractor's call. A qualified medical physicist prepares a shielding design for each room. Mammography uses low-energy X-rays, so those rooms often need much less, and the physicist may find that ordinary drywall is enough. The national reference for that work is NCRP Report No. 147, which covers structural shielding for medical X-ray imaging rooms.

The physicist looks at the machine, how many patients the room will see, where the tube points, and what is on the other side of every wall, the floor, and the ceiling. A wall next to a storage closet needs less than a wall next to a waiting room. In a multi-story building, the floor and ceiling can matter as much as the walls.

The contractor builds to that design, and the details are where shielding fails. Lead has to lap at every seam. Electrical boxes, pipes, and ducts that pass through a shielded wall need lead behind or around them. Door frames and the control window need lead that meets the wall lead with no gap. After the room is built, the physicist surveys it to confirm the shielding performs as designed, and the owner keeps that report.

The MRI room

MRI does not use X-rays, so it needs no lead. It needs a different kind of enclosure: radio frequency (RF) shielding, a continuous metal box of copper or steel panels around the scanner room that keeps outside radio signals from showing up in the images. A specialty shielding vendor normally furnishes and installs the RF room, including its door, its window, and the filter panel where wiring enters. The vendor tests the room when it is complete, and it is often tested again after the other trades finish, because one screw through the shield in the wrong place can ruin the result.

Several other items are particular to MRI:

1. Magnetic field. The magnet is always on. Its field reaches past the room walls, and the layout has to keep that field away from public areas, other equipment, and moving steel such as elevators and parked cars. Some sites need steel magnetic shielding in the walls.
2. Access zones. The American College of Radiology's MR safety guidance divides the area into four zones, from the public waiting room to the scanner room itself. The floor plan has to make that controlled path possible, with screening before anyone reaches the magnet.
3. Quench vent. Many magnets need a vent pipe to the outside, sized and routed to the manufacturer's requirements, to carry helium gas safely out of the building if the magnet is shut down quickly.
4. Vibration. Nearby mechanical equipment, traffic, and even foot traffic on a floor above can disturb the image. The manufacturer sets the limits, and the structural engineer checks them.

Structure and the delivery path

An MRI magnet and a CT gantry are heavy, and they are heavy in a small footprint. In a new building, the structural engineer designs the slab for the equipment from the site planning drawings. In an existing building, the engineer has to confirm that the floor can carry it, and an upper floor may need new steel or a thicker slab under the scanner.

Then the machine has to get in. A magnet often will not fit through a standard door or down a typical corridor, so the delivery path is planned during design. It may be a wall opening left open until the delivery, a removable panel, or a route through the roof. Every floor the equipment crosses on its way in has to carry the load. A rigging contractor makes the move, and the room has to meet the manufacturer's readiness checklist before the delivery date is firm. Plan the same path for the day the machine is replaced, years later.

Power and cooling

Imaging equipment draws a large amount of power, and CT in particular draws it in short, heavy bursts. Each machine usually needs its own feeder from the building service, sized to the manufacturer's requirements, and sometimes a dedicated transformer. In an existing building, the first question is whether the service can support the new load at all. Many groups add a battery backup unit so a power blip does not interrupt a scan.

The heat has to go somewhere. Scanners and their equipment rooms give off heat all day, and an MRI's cooling system runs around the clock, every day, because the magnet stays cold whether or not patients are scheduled. That usually means a dedicated chiller or cooling unit and an equipment room HVAC system that does not depend on the building system's schedule. Ask the mechanical engineer what happens to the magnet if cooling fails on a holiday weekend, and design an alarm for it.

Registration and the last steps

In Texas, machines that produce X-rays are regulated by the Department of State Health Services radiation control program. That includes CT, general X-ray, and fluoroscopy, and the same program covers dental and veterinary X-ray. The department says a facility must apply for a certificate of registration within 30 days of beginning use of radiation machines, and it sends shielding questions to the facility's medical physicist. The department does not regulate MRI or ultrasound machines. The owner, not the contractor, holds the registration, so assign someone on your team to it early.

The city's building permit and inspections, and the state accessibility review, apply to an imaging suite just as they do to any medical space. Our guide to building permits for a medical office covers that part.

We have built imaging space for Radiology Associates of Tarrant County, including the Cleburne imaging center, a finish-out with an MRI room, a CT room, and an imaging control desk, and the Fort Worth center with its MRI and CT rooms. The ground-up Fort Worth Heart North Clinic includes a hot lab and nuclear imaging, and new veterinary hospitals such as Urban Trails Animal Hospital include an X-ray room. See our radiology and imaging construction page for more of this work.

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