Site Planning for Medical centres

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DOTmedbusiness news I january 2010 www.dotmed.com42

Site-Planning for Medical

Imaging Equipment

Informed Advance Planning Simplies

a Potentally Complex installaton

By Joel Kellogg, ETS-Lindgren and Dave Jordan, West Physics



DOTmedbusiness news I january 2010 43

Designing space for medical imaging equipment

can be quite complex and involved as there are

many items that must be addressed in order to

successfully develop a site. Good site plan-

ning must thoroughly evaluate both the impact

of the imaging equipment on the surroundings (environmen-

tal concerns) and the impact of the space itself on the per-

formance of the imaging equipment and the personnel using

the equipment (performance concerns). Depending upon the

equipment, concerns may include radiation, magnetic and/or radio frequency (RF) shielding, electromagnetic interfer-

ence (EMI), vibration, and acoustic requirements. There may

also be concerns over co-siting medical imaging equipment

as one piece of equipment could have a negative impact on

another piece of equipment. As a result, it is critical to de-

velop a site plan and workow process well in advance that

is functional for users, patients, and the planned equipment.

Environmental ConcernsShielding (Magnetic, Radio Frequency and Radiation) and

Acoustics Magnetic Shielding

Shielding is critical to the proper development of a site for imaging equipment. Some imaging equipment will require ra-

diation shielding and other equipment, mainly Magnetic Reso-

nance Imaging (MRI) systems, will require Radio Frequency

(RF) and magnetic shielding. Careful planning that accounts for

workow and surrounding areas can also help reduce the level

of shielding required representing a cost savings to the owner

while providing a functional, efcient work environment.

When planning for MRI systems, there are some sim-

ple things that can be done to avoid excessive magnetic

shielding costs. While the majority of MRI systems re-

quire an RF shield, the magnetic shielding requirements

are driven by specic site selection. For example, in large

imaging suites with multiple MRI systems, placing MRI

systems side-by-side with limited spacing between MRI

suites will drive the requirements for magnetic shielding.

In some cases, this may also require expensive modica-

tions to the equipment itself. While many sites will only

be concerned with meeting FDA recommendations of

5-Gauss containment in public areas surrounding MRI

suites, placing MRI systems next to each other can cre-

ate a concern for crosstalk. Crosstalk results in MRI sys-

tems having an interactive impact on each other. Figure

1 shows crosstalk concerns which result in increased

magnetic shielding requirements. To avoid crosstalk in

a situation where MRI systems are placed in close prox-

imity, the magnetic shielding requirements may change.

For example, a magnet vendor may require that the 3

Gauss fringe elds do not intersect, which means that the

magnetic shielding will need to be designed to contain

3 Gauss rather than 5 Gauss. This will result in a heavier

magnetic shield and increased shielding costs. A simple solu-

tion may be to place the MRI equipment rooms, which house

the MRI’s electronic systems, between adjacent MRI systems.

This may provide enough spacing so that the 3 Gauss lines do

not intersect; however, even if the 3 Gauss lines intersect, the

amount of magnetic shielding required to separate the 3 Gauss

lines will cost much less than having the MRI systems located

side by side.

It is also important to consider the areas surrounding im-

aging equipment that will need radiation and MRI shielding.

There are many pieces of equipment that could be adversely

impacted by high static magnetic elds similar to those gener -

ated by an MRI system. Ultrasound equipment, computerized

tomography (CT), cathode ray tube (CRT) monitors, linear

accelerators, and electron microscopes are just a few exam-

ples of equipment that can be negatively impacted by the one

Gauss fringe eld. Magnetic shielding costs can be reduced by

Figure 1

Crosstalk concerns result in increased magnetic shielding

requirements due to MRI systems in close proximity.

Figure 2

Providing separation between adjacent MRI systems will reduce the

potential for crosstalk and decrease the amount of magnetic shielding

required.




placing equipment at distances that are

outside the maximum allowable static

magnetic eld as required by the OEM

specications. Figure 2 shows how

providing separation between adjacent

MRI systems will reduce the potential

for crosstalk and decrease the amount of

magnetic shielding required. It is pos-

sible to place equipment such as ultra-

sounds and CTs next to, above, or below

an MRI system, but it should be under-

stood that such a placement may change

magnetic shielding requirements and

increase shielding costs. However, there

may be workow reasons that make it

advantageous to place a piece of equip-

ment near an MRI.

Radio Frequency ShieldingUnlike magnetic shielding, Radio Fre-

quency (RF) shielding is required for

the majority of MRI applications and

consists of a highly conductive materialsuch as copper, aluminum, or galvanized

steel surrounding the MRI system. De-

termining RF shielding requirements is

fairly simple due to the fact that all RF

shields consist of a six sided structure

and the level of attenuation or shield-

ing effectiveness is determined by the

eld strength of the MRI system to be

installed. For example, MRI systems

with eld strengths of 1.5T or less re-

quire an RF shield that provides 100 dB

of attenuation at 100 MHz while 3.0T

MRI systems require a shielding system

that provides a 100 dB of attenuation at

150 MHz. As the eld strength of the

MRI systems increase, the performance

requirements of the RF shielding will

typically increase as well.

Special consideration must be giv-

en to all items that penetrate the exte-

rior 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 plumb-

ing for re sprinklers, if required, must

also pass through a wave guide. Wave

guides are designed to specically 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 assome of those frequencies could inter-

fere with the MRI system. Additionally,

all electrical items including power for

outlets, lighting and specic sensors

required for an MRI installation, must

pass through electrical lters. Most

electrical lters are low pass lters that

only allow signals below a “cutoff” fre-

quency to pass through. For example, a

lter with a 1 MHz cutoff will only al-

low signals at frequencies below 1 MHz

to pass though the lter into the MRIsuite via the wiring of the lter.

Additionally, special attention

must be given to the ground isolation

of the room. This is a critical, but of-

ten overlooked, consideration when site

planning. The RF enclosure, when rst

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. There-

fore, functionality should be considered

a top priority when designing and speci-

fying products for a site. Typical MRI

doors, as an example, use friction to cre-

ate the RF seal. This works well for cre-

ating the RF seal at the door, but can be

quite difcult to operate as these doors

require a reasonable amount of force to

open and close. This raises other con-

cerns and issues. These doors require

maintenance and repair of the door’s

RF ngers to maintain performance.

Without proper maintenance, the door

can become unreliable. There are doors

available that provide mechanical sealsto 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 opera-

tion 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 win-

dows if acoustics are a concern.

Another signicant issue to consid-er is the oor. All RF shielding systems

have a oor that is between 5/8” and

1-1/2” thick. In some applications, de-

pending upon the vibration and acoustic

requirements, the oors may be thicker

than 1-1/2”. This can create an Ameri-

cans with Disabilities Act (ADA) issue

requiring a ramp into the room; this may

be inconvenient and create logistical is-

sues for moving patients. Therefore,

when designing a new space, a oor de-

pression for the MRI suite should be in-cluded. This will allow the RF shielding

vendor to install the RF shielding sys-

tem with a at threshold or a threshold

that meets ADA requirements, eliminat-

ing the need for a ramp into the room.

For existing buildings, concrete should

be removed to depress the slab.

Radiation ShieldingImaging procedures that use ionizing

radiation pose a health risk to the clini-

cal staff and patients as well as to members of the public in spaces surrounding

the imaging suite. Unlike the patient,

who derives a medical benet from the

radiation used in the procedure, these

individuals must be carefully protected

from exposure. Medical radiation comes

from two types of sources: X-ray tubes,

such as in CT scanners, radiographic

rooms, and uoroscopy suites, and ra-

dioactive materials, which are used in

procedures such as nuclear medicine,

ETS-Lindgren’s Auto-Seal™ II Door offers me-

chanical seals and a push-button operation.




single-photon emission computed to-

mography (SPECT), and positron emis-

sion tomography (PET). There are also

hybrid imaging systems such as PET/CT and SPECT/CT which utilize both a

radioactive source and an X-ray source.

All sources of ionizing radiation

are generally shielded the same way –

with layers of lead sheeting applied to

the existing structural barriers. Other

materials may be used, such as concrete,

steel, or gypsum wallboard. A radiation

physicist, such as a medical physicist

or health physicist, should be consulted

to determine these shielding require-

ments; in many states this consultation

is required by law. There are some im-

portant differences in the design ap-

proach to facilities using X-ray systemsand those using radioactive materials.

Given the additional cost and weight

associated with lead-shielded building

systems, facility designers should take

prudent steps to reduce the amount of

lead needed.

For X-ray imaging systems, the ef-

fective radiation source is the machine

itself. Figure 3 shows a typical layout

while Figure 4 shows a better, more ef-

fective layout. Lead shielding require-

ments can be mitigated by placing

equipment in larger rooms, effectively

increasing the distance between the

source of radiation and other occupied

spaces. Care should be taken when lo-

cating the wall or chest bucky (the de-

vice used to hold lm cassettes for chest

X-rays taken in a standing position) in

a radiographic room, since X-rays will

strike this wall directly. In addition toincreasing the distance, rooms adjacent

to X-ray imaging systems of all kinds

should be chosen for low-occupancy

uses – storage rooms, janitor’s closets,

restrooms, and outdoor areas are all

good choices to situate next to X-ray

and CT rooms. Areas that have high

occupancy, such as ofces, nurses’ sta-

tions, and so forth will require more

shielding if placed in close proximity to

an X-ray source.

In imaging operations using ra-dioactive material, the patient actually

becomes the radiation source once in-

jected with the radiopharmaceutical.

This requires a different approach, as

the source of radiation moves, occu-

pies, and exposes different areas of the

human body. For SPECT and general

nuclear medicine imaging, this is less

of a concern because the emitted radia-

tion is not very penetrating. However,

for PET and PET/CT suites, the site

planner should consult closely with theradiation physicist at the layout stage.

For these suites, the PET/CT scan room

is typically not the most critical shield-

ing design element. Rather, the “up-

take” or “quiet” rooms, where the pa-

tients wait for 30-60 minutes between

the radiopharmaceutical injection and

the scanning procedure, are the major

shielding concern. In a facility not laid

out with this in mind, the uptake room

walls can require several inches of lead

thickness to provide adequate shieldingto an adjacent ofce or waiting room.

Of course, for a PET/CT suite, the scan

room must be analyzed and shielded as

a CT scanner room in addition to the

shielding required due to the PET radio-

active material.

In either case, care should be taken

to congure the imaging suite so that

the imaging technologist will have full

control to prevent members of the pub-

lic from inadvertently coming into con-

Figure 3

Figure 4




tact with sources of radiation. This can

mean simply conguring the direction

of a door swing so that a technologist

will have an unobstructed view of a

doorway when seated at his or her work-

station, or a more difcult approach in

providing for proper security of areas

where radioactive materials are stored.

AcousticsAcoustics is an important issue that

should be investigated when designing a

site for medical imaging systems. Unlike

EMI and vibration concerns, acoustic

issues are often created by the imaging

equipment itself. In particular, MRI sys-

tems can be quite disruptive to the sur-

rounding environment. MRI systems can

create airborne noise, which is the propa-

gation of acoustic noise through the air,

and structure-borne noise, which is the

propagation of acoustic noise through the building structure. As a result, acoustic

solutions typically need to address both

airborne and structure-borne noise in or-

der to be effective. Typical airborne

acoustic solutions involve detailed

wall, ceiling and oor construction

to meet predetermined acoustic cri-

teria. The solution should also de-

tail how penetrations, HVAC ducts,

and gaps in construction around the

imaging suite should be treated.

Recommended wall and ceilingconstruction usually involves some

combination of gypsum board, stud

placement, sound batt insulation,

air gaps, and isolation clips to ad-

dress both the transmission and re-

ection of acoustic noise.

Structure-borne acoustic

solutions can be more complicated.

Typically, a structure-borne solution in-

volves some combination of weight and

isolation material. For example, with

proper site planning, a vibration slab

that is isolated from the surrounding

structure and is placed on spring isola-

tors could also be a cost-effective solu-

tion for structure-borne acoustic noise.

Performance ConcernsElectromagnetic Interference (EMI)

Medical imaging systems can be sen-

sitive to electromagnetic interference

(EMI). EMI may be caused by electri-

cal equipment, motors, moving metal

objects such as cars, trucks and eleva-

tors, and by transportation systems that

run on electrical power such as subways

and trains. Proper site layout based upon

an awareness of the impact this existing

equipment may have on the medical im-

aging system can avoid many of these

issues. For example, avoiding the place-

ment of EMI sensitive imaging equip-

ment near electrical rooms, large trans-formers and motors, parking garages,

roadways, and elevators can aid in the

prevention of potential EMI issues (as

well as the signicant vibrations associ-

ated with many of these elements).

Unfortunately, EMI issues cannot

always be avoided especially in large

urban areas where an owner may have

limited placement options. This does not

mean that imaging equipment cannot be

installed in an EMI environment that

exceeds manufacturer specications. Infact, there are solutions to EMI issues.

EMI shielding consultants are available

that can survey existing buildings to

quantify the EMI environment to deter-

mine if a facility meets the equipment

EMI criteria. If the building is under

construction, a consultant can approxi-

mate the source(s) of EMI based upon

the electrical layouts and the proximityof EMI sensitive equipment to items

such as moving metal found in elevators

or subways or electrical sources. Ideally,

addressing performance considerations

prior to or during the construction pe-

riod results in the most cost effective

solution for optimal performance of the

medical imaging equipment.

EMI issues also may be endemic to

the facility itself in the case of a retro-

t of an MRI suite. MRI scanners can

permanently magnetize steel and other

ferromagnetic components within the

building structure, and the resulting

magnetic eld can cause EMI within the

room after the MRI system is removed.

Steel shielding from the old MRI sys-

tem, steel beams, and corrugated metal

deck and rebar inside concrete oors

and ceilings are common culprits when

this type of interference exists.In the event that a site does not or

will not meet the manufacturer’s re-

quirements for EMI, a shielding con-

sultant could propose shielding options

that will reduce the EMI in the area

around EMI sensitive equipment. These

solutions typically come in two forms;

passive shielding and active shielding.

Passive shielding involves using

materials with magnetic shielding prop-

erties. Common materials that are used

for passive shielding are aluminum, sili-con steel, and low carbon steel. Passive

shielding can be very effective in resolv-

ing 60 Hz and higher frequency EMI

issues, but has limited effectiveness

in resolving lower frequency distur-

bances that can be created by mov-

ing metal objects such as subways

and trains that operate on DC elec-

tric power. Passive shielding also

requires no maintenance after instal-

lation and can often be the most cost

effective solution for higher frequen-cy (frequencies of 50 Hz and greater)

EMI issues. However, this solution is

dependent upon the level of the EMI

and the amount of material required

to resolve the issue.

Active shielding, on the other

hand, utilizes electronics and coil sys-

tems to create a cancelling magnetic

eld over a predetermined volume. Ac-

tive shielding, unlike passive shielding,

can be very effective at lower frequen-

cies (frequencies below 100 Hz). Thereare several benets associated with ac-

tive shielding solutions. First, an active

system has the ability to respond to a

changing environment. Therefore, if

the EMI environment becomes worse,

a well designed active system will be

able to respond to those changes and

maintain an EMI environment that

meets manufacturer specications for

EMI sensitive equipment. Second, an

active system requires considerably

Transportation systems such as subway trains can

cause electromagnetic interference with medical

imaging systems.




less construction. An active system

typically requires the installation of

coils unlike passive shielding, which

often requires the installation of a six

sided structure that requires interior

nishes. Additionally, since passive

shielding is a much less effective solu-

tion for lower frequency applications,

active shielding is often a more cost

effective solution to EMI issues gener-

ated by subways and moving metal. In

the event that a particular site does or will experience EMI issues, solutions

should be evaluated based upon the ef-

fectiveness of the solution and the cost

to implement the solution.

VibrationImaging equipment, particularly CT

and MRI scanners, can be impacted by

building vibrations. Fortunately, most

vibration concerns can be addressed

through careful design and construc-

tion of the area to house sensitive piecesof equipment. In existing buildings, it

is critical to perform a vibration sur-

vey. A survey will quickly determine

whether the existing structure meets

the vibration requirements of the equip-

ment being sited. If the equipment does

not meet the vibration criteria, a good

survey will analyze the cause of the

vibration and provide general recom-

mendations to resolve vibration issues.

Many vibration issues can be resolved

through inexpensive solutions. For ex-

ample, a nearby mechanical room may

not include isolation pads or isolators

for mechanical equipment that induce

vibrations into the structure. This may

simply require placing vibration isola-

tors under such equipment. It may also

be possible to use vibration isolators on

some imaging equipment such as MRIs,

which would allow for the attenuation

of vibrations and decoupling of the

equipment from the structure due to the benets of the isolators. However, in

some situations, it may be necessary to

stiffen the structure under the imaging

equipment or build an isolated slab to

meet the equipment’s vibration criteria.

The unfortunate aspect is that isolated

slabs and modications to the structure

can be quite expensive. However, such

a building retrot is much less costly to

perform during the process of outtting

a space and installing imaging equip-

ment. Performing a retrot after imag-ing equipment has been installed and

found to be adversely affected by vibra-

tions can be extremely expensive.

In the case of new construction,

a vibration consultant can aid in the

development of the site by reviewing

equipment specications and site plans

to determine the vibration response of

the structure due to vibration sources

such as mechanical, other imaging

equipment, and trafc in the building.

Further, a vibration consultant can aid

in the development of isolated slabs as

necessary, which is much less expensive

to implement at the time of construc-

tion and can have the added benet of

providing structure-borne sound attenu-

ation due to high noise levels that are

produced by some pieces of imaging

equipment, in particular MRI systems.

SummaryInformed site planning when designing

space for medical imaging equipment,

especially prior to construction, results in

a cost effective and successful site – one

that is completed on time and on budget.

An experienced shielding design team

with an experienced acoustic and/or vi-

bration consultant will aid the user in

this often complex process. The upfront

investment in an experienced consultant

for site planning will result in construc-tion and operational savings that more

than return the initial investment. To pro-

tect your investment, ask any consultant

or rm you may hire for customer ref -

erences and a list of recently completed

projects. Follow up on the references and

visit the project if prossible to assess the

capability of the consultant and value-

added services provided to the customer.

AcknowledgementThe authors would like to acknowledgeand thank Rick Ottolino, AIA, of Ottoli-

no Winters Huebner for his invaluable

contributions to and review of this article.

About the AuthorsJoel Kellogg is Manager of Technical

Engineering and Consulting with ETS-

Lindgren in Glendale Height, IL. His ex-

perience includes design of MRI suites to

meet various acoustic, vibration, EMI, and

radio frequency shielding requirements.

He may be reached at 630-307-7200 or [email protected]

Dave Jordan is Senior Medical

Physicist with West Physics Consulting

in Atlanta, GA. His experience includes

acceptance, accreditation, and safety

evaluations of medical imaging systems

and design of radiation shielding. He

may be reached at (770) 435-9186 or

[email protected]

• Online: dotmed.com/dm11080

ETS-Lindgren uses isola-

tors under the magnet to

perform vibration surveys

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