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SURREY MEMORIAL HOSPITAL

ImageTech Lab

Sound Camel had the privilege of visiting Simon Fraser University’s leading medical imaging research facility to identify methods of attenuating noise propagating from the MRI scanning room to adjacent office spaces. 

SFU ImageTech Lab

Date: September 30, 2024 

Location: Surrey Memorial Hospital, Building A, Level 1, 13750 – 96 Avenue, Surrey, BC, V3V 1Z2

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Sources of Noise

This section outlines the primary sources of noise in the MRI facility and its impact on the control room environment.

The MRI machine is the primary source of noise in the lab, emitting up to 73dB in the adjacent control room when performing the angiogram sequence and 42dB at rest. This 31dB difference is perceived as approximately eight times louder than baseline to the human ear.

The rapid switching of electromagnetic gradients and Lorentz Forces that cause the coils to vibrate create mechanical vibrations that transfer to the surrounding structures, including the MRI machine’s housing, leading to the emission of sound waves. This creates the knocking, banging and buzzing noises experienced by staff and patients.

Sound from the MRI machine reaches the control room through flanking paths like the scanning room door, conduits, waveguides and HVAC system in three categories:

Airborne Sound Leakage: Even when the door is closed, small gaps around the edges of the door create an imperfect seal which allows noise to escape, contributing to the sound reaching the control room.

Structure-Borne Transmission: Structure-borne noise travels through rigid materials like metal conduits, piping and wall framing, which act as pathways for vibration transmission. Conduits and waveguides transmit noise from the MRI room to the control room.

Duct-Borne Noise:The HVAC system transmits sound through the ducts, carrying noise from the MRI room into other areas like the lab offices and MEG room.

Our observations suggest that the primary sources of noise in the control room and adjacent offices are airborne and duct-borne. The following recommendations outline potential solutions to address these issues, along with rough cost estimates.

To reduce duct-borne noise transmission, consider rerouting existing HVAC ducts or installing dampers and sound attenuators within the ductwork. Additionally, selecting air diffusers designed for acoustic performance can further minimize noise levels in the control room and other sensitive areas.

HVAC Air Diffusers

To reduce duct-borne noise transmission, consider rerouting existing HVAC ducts or installing dampers and sound attenuators within the ductwork. Additionally, selecting air diffusers designed for acoustic performance can further minimize noise levels in the control room and other sensitive areas.
The thin copper door lacks acoustic insulation, allowing noise to escape into the control room. Installing an acoustic barn door inside the MRI room can significantly improve sound isolation by providing an additional barrier that reduces airborne noise leakage. This solution enhances acoustic performance while maintaining accessibility to the scanner room.

MRI Scanner Room Door

The thin copper door lacks acoustic insulation, allowing noise to escape into the control room. Installing an acoustic barn door inside the MRI room can significantly improve sound isolation by providing an additional barrier that reduces airborne noise leakage. This solution enhances acoustic performance while maintaining accessibility to the scanner room.
Installing a broadband sound-absorbing acoustic panel over the waveguide openings will help reduce the amount of sound that escapes, minimizing noise levels in the control room. The panel can be easily removed to maintain access when needed, providing a practical solution for noise control without compromising functionality.

MRI RF Waveguides

Installing a broadband sound-absorbing acoustic panel over the waveguide openings will help reduce the amount of sound that escapes, minimizing noise levels in the control room. The panel can be easily removed to maintain access when needed, providing a practical solution for noise control without compromising functionality.

Solutions:

1. Reroute HVAC

To reduce noise in the control room and adjacent hallway caused by the HVAC system shared with the MRI room, the best solution is to either relocate the ducts or install acoustical duct silencers or dampers. Below is an outline of both processes. 

Instructions: 
 
Relocating Ducts: Evaluate the current HVAC layout to determine if it’s possible to reroute the ducts. The goal is to isolate the airflow for the MRI room, so the noise doesn’t travel directly into adjacent spaces. 
 
  1. Plan a new duct path for the MRI room, routing them away from the control room and hallway. Ideally, ducts should have dedicated pathways and not serve multiple rooms. 
  2. If feasible, create separate HVAC zones for the MRI scanning room and the control room/hallway to contain noise and vibration from the MRI equipment within the scanning room. 
  3. Install the new ductwork and seal all joints and seams using acoustic sealant to prevent sound leakage. Add vibration isolation hangers to further reduce noise. 
Recommended Products:
 

OSI Green Series Acoustical Caulk: This sealant is designed to reduce sound transmission through gaps and cracks in walls and around conduits. It remains flexible and can be painted over once dry, making it ideal for sealing conduit penetrations in walls. 

Argo Air Duct Vibration Isolation V Bracket 3/8″ Threaded Rod for Square & Spiral: This vibration isolation bracket fits both square and spiral air ducts.

Cost:

HVAC contractor quote required.

Altering the existing ductwork layout to reduce the escape of sound generated by the MRI machine will create a more isolated environment. Redirecting ducts away from sensitive spaces, utilizing insulated duct materials and silencers will help to absorb sound. Ensuring airtight connections, will help maintain airflow efficiency while mitigating noise. This targeted approach will contribute to a more comfortable environment for both staff and patients.

Relocate Ducts

Altering the existing ductwork layout to reduce the escape of sound generated by the MRI machine will create a more isolated environment. Redirecting ducts away from sensitive spaces, utilizing insulated duct materials and silencers will help to absorb sound. Ensuring airtight connections, will help maintain airflow efficiency while mitigating noise. This targeted approach will contribute to a more comfortable environment for both staff and patients.
Minimizes vibration transmission to the building framework and noise from ductwork systems.

Air Duct Vibration Isolation

Minimizes vibration transmission to the building framework and noise from ductwork systems.

2. Insert Acoustical Duct Silencers or Dampers

Acoustical duct silencers are designed to reduce noise traveling through ducts (up to 30dB), improving the acoustic environment in the adjacent areas. If total duct isolation between spaces isn’t feasible, silencers should be installed in the ducts connecting the MRI room to the hallway and control room to absorb noise while maintaining airflow.

Instructions: 

Assessment of Duct Noise Pathways: 

  1. Identify the ducts where noise from the MRI room is escaping into adjacent spaces, particularly toward the hallway and control room.
  2. Determine duct sizes and existing noise levels. This will help in selecting the right silencer to achieve the desired noise reduction.
  3. Evaluate the airflow requirements to ensure the silencers will maintain sufficient airflow while reducing noise.

Selection of the Acoustical Silencer: 

  1. Choose a silencer based on the duct size and configuration (rectangular or round ducts) and the targeted noise reduction level. Ruskin offers various models, such as narrow, medium, and wide silencers, each with different insertion loss characteristics. Narrow silencers might be suitable where space is limited, while wide silencers provide greater noise reduction. For the MRI facility, consider a silencer model with high sound attenuation across a wide frequency range, including low frequencies.

Installation Guidelines:

  1. Locate the ducts to be treated, ideally close to the MRI room to maximize noise reduction before it propagates further.
  2. Cut a section of the duct to insert the silencer, ensuring the length of the silencer follows the manufacturer’s installation recommendations for positioning.
  3. Secure the silencer using appropriate methods such as clamps, screws, or welding, ensuring the connections are airtight to prevent any air leakage.
  4. Seal joints and edges using acoustic sealant or gaskets to maintain airtightness and improve acoustic performance.
  5. Perform a functional test to check both noise reduction and airflow after installation.
Recommended Products:
 
Ruskin Rectangular Reactive Silencers: Resonators to dissipate acoustical energy introduced via the airstream.

Cost:

HVAC contractor quote required.

Ruskin produces reactive silencers that capture sound energy within a series of tuned chambers, which are specifically designed to resonate at certain frequencies. When sound waves enter these chambers, the internal shape and size of each cavity cause a shift in the phase of the sound waves. This phase shift cancels out the tuned frequencies, weakening the sound as it moves through the silencer. Rather than absorbing the sound, they convert and neutralize it by manipulating how it moves through the air within the duct system. Minimizing cross-talk is important as sound can travel between rooms or spaces through shared ductwork. Duct silencers help block sound transmission between rooms, improving privacy and reducing distractions in settings like offices and hospitals. Suitable for clean room and hospital settings.

Rectangular Reactive Silencers

Ruskin produces reactive silencers that capture sound energy within a series of tuned chambers, which are specifically designed to resonate at certain frequencies. When sound waves enter these chambers, the internal shape and size of each cavity cause a shift in the phase of the sound waves. This phase shift cancels out the tuned frequencies, weakening the sound as it moves through the silencer. Rather than absorbing the sound, they convert and neutralize it by manipulating how it moves through the air within the duct system. Minimizing cross-talk is important as sound can travel between rooms or spaces through shared ductwork. Duct silencers help block sound transmission between rooms, improving privacy and reducing distractions in settings like offices and hospitals. Suitable for clean room and hospital settings.

3. Acoustic Ceiling Insulation

Install 3″ Rockwool Safe ‘n’ Sound on T-bar ceiling around the perimeter of the MR scanner room and fully in the adjacent hallway and control room to absorb broadband frequencies and attenuate noise.

Instructions: 

  1. Ensure Compatibility: Verify that the T-bar grid can support the weight of the Rockwool Safe ‘n’ Sound at 2.4 lb/ft³ (0.6 lb/ft²). 
  2. Check whether pot lights and recessed fluorescent troffer lights are IC-rated (insulation contact) or leave adequate space around them for heat dissipation. 
Recommended Products: 
 
Rockwool Safe’n’Sound Sound 24 inch: Stone wool insulation for use where superior fire resistance and acoustical performance are required. 


Costs: 

  • $96.34 per 60 ft² (5.58 m²) of stone wool batt (approximately 8 packages or $770.72 total)
  • $22 per installed batt (estimated 64 batts or $1408 total)
Installing 3" Rockwool Safe 'n' Sound

Installing 3" Rockwool Safe 'n' Sound

Placing stone wool batts above ceiling tiles can significantly enhance acoustic performance by absorbing sound waves that would otherwise reflect off hard surfaces, including the copper Faraday cage. This additional layer of insulation reduces the amount of sound traveling through the ceiling, effectively minimizing echoes and improving overall sound clarity in the space. Stone wool’s dense structure captures and dissipates sound energy, making it especially effective for controlling both airborne noise and reverberation. This installation approach is particularly beneficial in environments with existing drop ceilings with acoustic tiles to maintain a more comfortable, focused atmosphere.

Install stone wool insulation along the perimeter of the MRI scanning room to attenuate noise in adjacent spaces.

Perimeter of the MRI Scanning Room

Install stone wool insulation along the perimeter of the MRI scanning room to attenuate noise in adjacent spaces.

4. Acoustic Door

Install 76.5″ x 100.5″ X 6″ acoustic barn door in MRI scanning room to block sound from penetrating existing thin copper-lined door. 

Instructions: 

  1.  Install barn door hardware on the inside of the MRI scanning room by existing door opening.
  2. Mount the acoustic barn door panel on the heavy duty tracks. 

Recommended Products:

Sound Camel Acoustic Door Panel: Custom acoustic barn door to provide full coverage over the entire door frame to block noise from all angles.

Magic 2 Legno Sliding Door System: Wall-mount sliding system for doors weighing up to 176 lbs (80 kg). Model 1800.

6 Inch Recessed Finger Pulls: Four durable 304 stainless steel finger pulls for dual-sided access. 

Costs: 

  • $1350 acoustic barn door with pull handles
  • $741 heavy duty concealed door hardware
  • $125 installation
Ideal for reducing audio transmission between rooms.

Acoustic Door Panel

Ideal for reducing audio transmission between rooms.
In the open position the acoustic barn door would rest in the space between the window and door opening in the MRI scanning room.

Acoustic Barn Door Open Position

In the open position the acoustic barn door would rest in the space between the window and door opening in the MRI scanning room.

5. Broadband Acoustic Panels

Install 4″ broadband acoustic panels centered on the back wall of the MRI scanning room, aligned with the bore of the machine. This installation aims to minimize reflections towards the control room, enhancing acoustic performance and reducing noise interference in the nearby MEG room and offices.  Additionally install 1 horizontal acoustic panel over the RF waveguides access door in the control room (easily removable). 

Instructions: 

  1. Install 8 Camel Cleats on the back wall centered with the bore of the MRI machine and 2 cleats over the RF waveguides access panel in the control room.
  2. Vertically mount 8 48″ x 24″ x 4″ acoustic panels on the french cleats without gaps between the panels in the scanning room and one horizontal acoustic panel over the waveguides access panel in the control room.

Recommend Products:

Sound Camel Acoustic Panels: Wall or ceiling mountable in any orientation with included cleat-lock mounting system.

Costs: 

  • $162 x 9 acoustic panels ($1458 total)
  • $50 x 9 acoustic panel installation ($450 total)
  • $295 delivery
Sound Camel acoustic panels, or Camel Panels™️, come clad in acoustically transparent speaker grille cloth used in professional applications for over 40 years. Broadband sound-absorbing panels available in 96 Colors.

MRI Scanning Room Wall Acoustic Panels

Sound Camel acoustic panels, or Camel Panels™️, come clad in acoustically transparent speaker grille cloth used in professional applications for over 40 years. Broadband sound-absorbing panels available in 96 Colors.
Example acoustic panel installation without gaps in an office.

48" x 24" x 4" Acoustic Panels

Example acoustic panel installation without gaps in an office.

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