chapter 10 Flashcards
What is the primary reason for MRI screening forms?
To identify potential contraindications to MRI.
Which of the following is considered a contraindication for MRI?
Cochlear implants.
What is the fringe field in an MRI system?
The area outside the magnet where the magnetic field is still detectable.
What is the primary danger of ferromagnetic objects near an MRI scanner?
They can become projectiles.
Which zone in the MRI suite is considered the most restricted?
Zone IV.
The term ‘quench’ in MRI refers to:
The release of cryogens from the magnet.
What is the most common cause of burns during an MRI scan?
Skin-to-skin contact or loops of wires touching the skin.
Gadolinium-based contrast agents are contraindicated in patients with:
Severe renal impairment.
What is the FDA limit for the specific absorption rate (SAR) in whole-body MRI scans?
4 W/kg.
What should be done if a patient becomes claustrophobic during an MRI scan?
Provide reassurance and potentially offer sedation.
All MRI-compatible implants are safe for scanning at any field strength.
False.
Patients with pacemakers should never undergo an MRI scan.
False (conditional MRI-safe pacemakers exist).
A patient’s clothing should always be screened for metallic fibers before entering the scanner room.
True.
The static magnetic field is always on in an MRI scanner, even when the machine is not in use.
True.
Pregnant patients should avoid MRI scans entirely.
False (MRI may be used if clinically justified, especially after the first trimester).
What is the static magnetic field?
Always on, the source of the main magnetic field.
What are Radiofrequency (RF) Coils?
Produces images by transmitting and receiving signals.
What is Zone III?
Area requiring strict access control; adjacent to Zone IV.
What is Cryogen?
Liquid helium used to cool the superconducting magnet.
What is a Quench Pipe?
Vents cryogens safely outside in case of a quench.
During an MR examination, what is responsible for PNS?
TVMF (Time Varying Magnetic Fields).
The three levels of personnel in MRI are: Non-MRI Personnel, Level 1 Personnel, and Level 2 Personnel.
True.
Who is responsible for MR safety screening?
Level 2 trained MR technologist.
Who is responsible for training the custodial staff about MR safety?
All MRI technologists on staff.
A designated ‘Zone 4’ in an MRI facility includes:
Suitable for screened patients under direct supervision of MRI staff.
What is the most important safety consideration associated with a quench?
Displacement of oxygen.
What is the rotational force that causes alignment on an object to the lines of magnetic flux?
Torque effect.
Which of the following is always on in an MRI scanner?
B₀ (Static Magnetic Field).
Vertigo, headaches, nausea, and metallic taste are examples of:
Short-term effects of exposure to MR imaging.
Which MR scanning mode should a technologist consider a patient’s dissipation of heat before using?
First-level and second-level controlled operating modes.
What must be done for a patient who has taken oral sedation at home before their MRI scan?
At minimum, pulse oximetry.
Which MRI zones should all persons be supervised in?
Both Zone 3 & Zone 4.
Where should the warning sign with ‘Magnet is On’ be located?
Zone 3.
An object that has strong magnetic attraction is known to have:
Ferromagnetism.
The ideal location for the patient dressing room should be in:
Zone 2.
Which personnel level has passed minimal MRI safety education to ensure their own safety?
Level 1.
The ACR (American College of Radiology) prohibits anyone except the patient from being in Zone 4 during scanning.
False (Screened individuals may accompany anxious patients).
According to the ACR recommendations, what degree of training should the MRI technologist have?
Level 2.
What is a ‘quench’ in MRI?
Sudden loss of liquid helium and magnetic field.
How many colors of MR safety identifier labels are used?
3.
SAR (Specific Absorption Rate) is measured in:
W/kg.
SAR stands for:
Specific Absorption Rate.
Which force is responsible for ferromagnetic materials becoming attracted to the static magnetic field?
Translational force.
Who must be screened before entering the MR area?
All of the above (Patients, Visitors, Ancillary personnel).
A designated ‘Zone 1’ in an MRI facility includes:
All areas that are freely accessible to the general public.
The most commonly reported effect of exposure to RF fields is:
Increase in body temperature.
What is the best method for controlled access to the MR environment?
MR level 2 safety trained person.
Under what circumstances should a superconducting magnet be quenched?
In case of an emergency when life or limb is at risk.
How many zones are recommended for the MR area?
4.
What is the leading cause of accidents in the MRI environment?
Personnel not adhering to established safety guidelines.
‘MR Conditional’ means:
The item poses no known hazards in a specified MR environment with specific conditions of use.
What is the 5 Gauss line?
The magnetic field strength and distance that is safe for a person with any device.
If an implanted device is tested safe at 3T, then it is assumed safe at all other lower field strengths.
False.
Items that are ‘unsafe’ to go into the MRI scan room have a label that:
Is a red circle with a diagonal line and ‘MR’ inside of it.
What physical barriers should be used for the MR environment?
Controlled access to Zone 3.
What is PNS?
Peripheral Nerve Stimulation.
What is the main cause of acoustic noise in the scan room?
Time Varying Magnetic Fields (TVMF).
Which psychological effect is NOT associated with MRI-related anxiety?
Excitement.
What is the temperature of liquid helium in Fahrenheit?
-452°F.
The five factors impacting patient safety in MRI include:
- Psychological effects
- Spatially varying static magnetic fields
- Time varying gradient fields
- Radiofrequency (RF) effects
- Acoustic noise
All of the following are examples of projectiles EXCEPT:
Transmit coils.
The main biological effect of RF in MRI is:
Tissue heating.
What are the major factors used to calculate SAR?
All of the above (RF duration, patient weight, pulse sequence type).
What determines the amount of ferromagnetic reaction/attraction?
All of the above (Size, shape, material type).
What is the FDA SAR limit for the whole body in MRI?
4 W/kg.
What is the antenna effect in MRI?
Causes heating in conductive wires of critical length.
The greatest hazard of the main magnetic field is:
Ferromagnetic projectiles.
B₀, TVMF, and RF are examples of:
None of the above (They are not forms of ionizing radiation).
Why is MRI safety complex?
MRI safety is complex due to varying field strengths, machine configurations, rapidly switching gradients, diverse patient implants, and body jewelry.
Who is primarily responsible for MRI safety decisions?
The referring physician, radiology lead, and MRI practitioner are responsible for assessing MRI safety risks.
Why must MRI practitioners stay updated on safety?
New implanted devices and safety research emerge regularly, requiring updated knowledge on safety protocols.
What is the role of medical physicists in MRI safety?
They provide expert advice on device interactions, safety risks, and field strength compatibility.
What is Zone I in an MRI facility?
Zone I is freely accessible to the public and outside the controlled MRI environment.
What is Zone II in an MRI facility?
Zone II serves as a transition area where patient screening, history-taking, and supervision occur.
What is Zone III in an MRI facility?
Zone III is a restricted area where unscreened personnel and ferromagnetic objects pose serious risks.
What is Zone IV in an MRI facility?
Zone IV is the MRI scanner room itself, with a high static magnetic field that must be clearly marked as hazardous.
Who are Non-MRI Personnel?
Patients, visitors, and hospital staff who haven’t received MRI safety training in the past 12 months.
Who are Level 1 MRI Personnel?
Office staff and patient aides who have minimal MRI safety training to ensure their own safety in Zone III.
Who are Level 2 MRI Personnel?
MRI technologists, radiologists, and nurses trained extensively in thermal loading, burns, and neuromuscular risks.
What does MR Safe mean?
The item is nonmagnetic, nonmetallic, and nonconducting, posing no known hazards in any MRI environment.
What does MR Conditional mean?
The item is safe only under specific MRI conditions such as field strength limits, SAR restrictions, or lead routing.
What does MR Unsafe mean?
The item poses hazards in all MRI environments, such as ferromagnetic scissors or non-MRI-compatible implants.
What percentage of MRI patients require sedation due to anxiety?
14.3% of patients require sedation or anesthesia due to claustrophobia and anxiety.
Why are brain MRI scans more likely to cause anxiety?
Because the head is positioned at isocenter, with the bore and head coil creating a confined space.
What are common psychological concerns in MRI?
Claustrophobia, fear of suffocation, fear of fainting, panic attacks.
How do failed MRI scans affect hospital operations?
Delays diagnosis, wastes scanner time, increases costs and administrative workload.
How can scanner design improvements reduce anxiety?
Shorter, wider bore scanners with fans, lighting, and immersive video environments help patients relax.
What biological effects can occur at high magnetic fields (3T–7T)?
Metallic taste, vertigo and dizziness, optical phosphenes (flashing lights).
Why does vertigo occur at ultra-high-field MRI?
The Lorentz force affects ions in the inner ear’s vestibular system, leading to dizziness.
What is Faraday’s Law of Induction in MRI safety?
Moving a conductor (optic nerve) through a magnetic field can induce electrical currents, causing flashing lights (phosphenes).
What is the main safety concern for patients experiencing MRI-induced vertigo?
Patients may need to avoid driving or operating machinery for 15+ minutes post-scan.
What creates projectile hazards in MRI?
The spatially varying static field gradient exerts a strong force on ferromagnetic objects.
What types of objects are common MRI projectiles?
Oxygen tanks, wheelchairs, scissors, pens, coins, keys.
Why are modern actively shielded MRI scanners a double-edged sword?
They contain the fringe field, but projectiles accelerate suddenly near the bore.
What should be done immediately after a large projectile incident?
If life-threatening, quench the magnet to remove the object.
What is a quench, and why is it sometimes necessary?
A quench rapidly shuts down the magnet by releasing cryogens, but may damage the scanner.
What are the consequences of metallic foreign bodies in the scanner bore?
They can cause image distortion or damage scanner components.
How can MRI departments reduce projectile risks?
Strict screening protocols, ferromagnetic detectors, secured, locked magnet rooms.
What is the most common cause of projectile incidents in MRI?
Unscreened hospital staff or visitors entering the magnet room with ferromagnetic objects.
Why are oxygen tanks particularly dangerous in MRI?
They are heavy, metallic, and can accelerate toward the magnet, causing serious injury or damage.
How often should staff receive MRI safety training?
At least annually, per ACR safety recommendations.
What happened in reported projectile injuries involving hospital staff?
Staff have suffered fractured forearms, facial fractures, and pelvic injuries from oxygen tank incidents.
What safety measure prevents unauthorized access to MRI rooms?
Locked doors, card key access, and controlled entry points.
What is torque in MRI?
The rotational force exerted on ferromagnetic implants or objects in the magnetic field.
What types of implants can experience torque in MRI?
- Pacemakers
- Aneurysm clips
- Deep brain stimulators
Why is torque dangerous for implanted medical devices?
It can cause movement, heating, or malfunction, potentially leading to serious injury or death.
How can MRI technologists determine if an implant is MRI safe?
By consulting device documentation, manufacturer safety guidelines, and MRI safety databases.
What should be done before scanning a patient with an implant?
- Check implant safety conditions
- Use lowest necessary field strength
- Monitor for adverse reactions
Why are metallic foreign bodies a risk in MRI?
They can be dislodged, migrate, or heat up, causing serious injury.
What type of patients require extra screening for metallic foreign bodies?
Patients with a history of metallic injuries, welding, or metal shavings in the eyes.
How should suspected metallic foreign bodies in the eye be evaluated?
A screening X-ray should be performed before MRI.
Why should some tattoos be screened before MRI?
Tattoos with metallic ink can cause burns or irritation.
What is the risk of dermal piercings in MRI?
They can heat up, cause burns, or be pulled toward the magnet.
What are cryogens used for in MRI?
To supercool superconducting magnets, maintaining magnetic field stability.
What is a quench?
A sudden loss of cryogens, rapidly turning off the magnetic field.
Why is an uncontrolled quench dangerous?
It can cause asphyxiation (oxygen displacement) and frostbite due to rapid gas expansion.
When should a quench be manually activated?
Only in life-threatening emergencies, such as a trapped patient or projectile incident.
What safety measures prevent quench-related injuries?
- Proper room ventilation
- Emergency escape plans
- Regular maintenance of quench pipes
What is torque in MRI?
Torque is a rotational force that aligns ferromagnetic objects with the magnetic field lines.
Why is torque dangerous for implanted devices?
It can cause movement or twisting, potentially damaging soft tissues or blood vessels.
Which implants are most at risk of torque in MRI?
- Aneurysm clips
- Neurostimulators
- Pacemakers
- Cardiac defibrillators
How does implant shape affect torque risk?
Long, narrow implants (e.g., surgical clips) experience more torque than compact shapes.
What are the safest types of implants regarding torque?
Implants anchored to bone (e.g., hip replacements, orthopedic nails) are less affected.
What factors reduce torque risks in implants over time?
- Fibrosis (scar tissue forming around the implant)
- Proper anchoring in bone
What MRI precaution should be taken for unknown aneurysm clips?
Cancel or postpone the scan until implant safety is confirmed.
What fatal incident has been linked to torque effects?
A patient with an aneurysm clip suffered fatal vessel rupture due to MRI-induced movement.
Why are some newer cardiac implants MRI-conditional?
They contain less ferromagnetic material and can be programmed into an MRI-safe mode.
What safety measures are required for scanning patients with MRI-conditional pacemakers?
- Device must be set to MRI-safe mode
- MRI must be done under cardiology supervision
- Strict monitoring during the scan
What risks do ferromagnetic foreign bodies pose in MRI?
They can move, rotate, or heat up, causing serious injury.
Why are ocular foreign bodies particularly dangerous?
Movement can cause retinal damage, hemorrhage, or blindness.
What are two documented cases of MRI-induced blindness?
- One patient suffered irreversible vitreous hemorrhage.
- Another patient developed a lenticular cataract.
Why are metal workers at high risk for MRI-related eye injuries?
They may have small, unnoticed metal fragments in their eyes from past work.
What screening test is used for ocular metal foreign bodies?
A plain radiograph (X-ray) of the orbits.
Should verbal history alone be used to rule out metallic foreign bodies?
No. Radiographic confirmation is required if there’s a history of eye trauma.
What type of radiation does MRI use?
Non-ionizing electromagnetic radiation (RF waves).
What is the difference between ionizing and non-ionizing radiation?
- Ionizing radiation (e.g., X-rays) can damage DNA and cause cancer.
- Non-ionizing radiation (MRI RF waves) does not break chemical bonds.
What are the three major safety concerns with RF in MRI?
- Patient heating and burns
- Antenna effect (induced currents)
- Implant malfunctions due to RF currents
Why does RF cause heating in MRI?
RF waves induce currents in tissues, and resistance causes heat generation.
What does SAR stand for in MRI?
Specific Absorption Rate – the rate of RF energy absorption in the body.
What are the SAR limits for normal MRI operation?
- Whole body: 2 W/kg
- Head: 3.2 W/kg
- Extremities: 10 W/kg
What patient groups are more susceptible to RF heating?
- Elderly & neonates
- Obese patients
- Patients with fever or impaired thermoregulation
What is the maximum core temperature increase allowed in MRI?
- Normal mode: ≤0.5°C
- First-level controlled mode: ≤1°C
- Second-level mode: >1°C (research only)
What strategies reduce SAR and heating risks?
- Increase TR
- Lower flip angle
- Use a different RF coil
- Reduce the number of slices
What is the antenna effect in MRI?
A conductor (e.g., wires) resonates at RF frequencies, causing localized heating.
What medical devices are at risk of antenna effect burns?
- Pacemaker leads
- ECG electrodes
- Long metal implants
What is the temperature risk for pacemaker leads in MRI?
The lead tip temperature can reach 80°C, causing serious burns.
What patient positioning can cause heating loops?
- Hands touching thighs
- Heels resting together
- Knees pressed against each other
How can patient heating from the antenna effect be prevented?
- Proper padding between body parts
- Avoiding unnecessary conductive materials
What is the primary cause of RF burns in MRI?
RF energy induces currents in conductive materials, leading to localized heating and burns.
Where do RF burns typically occur?
- Skin-to-skin contact points (e.g., hands touching thighs, knees pressed together)
- Conductive materials in contact with the skin (e.g., ECG leads, jewelry)
Why do loose loops of ECG leads increase the risk of RF burns?
Loops act as an antenna, absorbing RF energy and generating excessive heat.
What precaution should be taken for ECG leads in MRI?
Position them straight and away from the body, avoiding loops.
What can patients wear to reduce RF burns?
MRI-safe clothing without metallic fibers.
Why is padding important in preventing RF burns?
Padding eliminates conductive loops and insulates skin-to-skin contact points.
What common household items pose RF burn risks in MRI?
- Tattoo ink with metallic particles
- Makeup containing metallic pigments
- Certain wound dressings with metallic coatings
Why are tattoos a potential RF safety risk?
Some inks contain iron oxide, which can heat up and cause burns or irritation.
What should be done if a patient has a large tattoo in the MRI scan area?
Monitor the patient closely for discomfort or heating during the scan.
How do thermal burns from RF energy differ from traditional burns?
They occur without an external heat source, often with no immediate pain, but result in delayed redness, blistering, or tissue damage.
What are time-varying gradient fields in MRI?
Rapidly changing magnetic fields used for spatial encoding and slice selection.
What is peripheral nerve stimulation (PNS) in MRI?
PNS occurs when time-varying gradients induce small electric currents, causing muscle twitching or tingling.
Why does PNS occur during MRI?
The rapid switching of gradient fields stimulates nerves and muscles.
Which MRI sequences increase the risk of PNS?
- Echo planar imaging (EPI)
- Diffusion-weighted imaging (DWI)
- Fast gradient-echo sequences
How can PNS be minimized in MRI?
- Lower gradient amplitude
- Increase rise time of gradients
- Use patient positioning techniques
Is PNS dangerous in MRI?
PNS is generally harmless but may cause patient discomfort.
What patient factors increase susceptibility to PNS?
- Low body fat (less insulation)
- Longer limbs (larger conductive loops)
What sensation do patients experience during PNS?
- Mild tingling
- Involuntary muscle twitching
What is the purpose of cryogens in MRI?
To keep superconducting magnets cold (typically using liquid helium).
What happens during an MRI quench?
The cryogen rapidly boils off, shutting down the superconducting magnet.
What is the primary safety risk during a quench?
Asphyxiation due to helium displacing oxygen.
Why must the MRI quench pipe be checked regularly?
To ensure proper ventilation of helium outside the building.
What happens if a quench pipe fails?
Helium disperses into the MRI room, creating an oxygen-deficient environment.
What should staff do during a quench?
Evacuate the MRI room immediately and ensure proper ventilation.
When is an emergency quench necessary?
- A life-threatening projectile incident
- Fire inside the MRI scanner
- Trapped patient or staff member
Why is MRI so loud?
The rapid switching of gradient coils generates loud vibrations.
What is the average noise level inside an MRI scanner?
Between 80-110 dB, comparable to a rock concert.
How can MRI noise be reduced for patients?
- Earplugs
- Noise-canceling headphones
- MRI-compatible music systems
What are long-term risks of MRI noise exposure?
Potential hearing damage in repeated exposures.
Which MRI sequences generate the loudest noise?
- Echo planar imaging (EPI)
- Fast gradient-echo sequences
Why should pregnant technologists avoid staying inside MRI rooms?
Uncertainty about the effects of prolonged RF exposure on fetal development.
Can pregnant patients safely undergo MRI?
Yes, but only if medically necessary, avoiding gadolinium contrast.
Why should patients with conductive implants be monitored closely?
Conductors can induce currents, heat up, or cause burns.
What happens if a patient has a seizure inside the MRI?
- Stop the scan immediately
- Remove the patient from the bore
- Provide medical assistance
Why are implanted devices a major MRI safety concern?
MRI’s strong magnetic field can move, heat, or interfere with electronic implants, causing potential injury or malfunction.
What does MRI Conditional mean for implanted devices?
The device is safe under specific MRI conditions, such as magnetic field strength, SAR limits, and gradient exposure.
Which implanted devices are most at risk in MRI?
- Aneurysm clips
- Cardiac pacemakers & defibrillators
- Cochlear implants
- Deep brain stimulators
- Neurostimulators with leads
What should be done before scanning a patient with an implant?
Obtain manufacturer documentation and check the MRI safety database to determine scan conditions.
Why are ferromagnetic aneurysm clips dangerous in MRI?
They may experience torque, causing vessel tearing, stroke, or hemorrhage.
What does Lenz’s law explain about metallic implants in MRI?
Nonferrous metals can still experience forces due to eddy currents, potentially affecting function.
How can pacemakers malfunction in an MRI scanner?
RF pulses and magnetic fields may cause inappropriate pacing, power loss, or lead heating.
Why are retained bullet fragments a concern for MRI safety?
They can be ferromagnetic, causing displacement, heating, or distortion.
Why is an MRI screening form alone insufficient?
Some patients may forget implants or not know their implant’s MRI compatibility.
Why should patients with orbital foreign bodies be screened carefully?
Metal fragments in the eye may move during MRI, causing serious injury or blindness.
What is the primary safety concern with RF fields in MRI?
RF pulses cause tissue heating, which can result in burns.
Why is skin-to-skin contact a risk for RF burns?
It creates a conductive loop, concentrating RF energy in a small area.
How can ECG leads cause burns in MRI?
Loops in the leads can act as antennas, absorbing RF energy and overheating.
What is the best way to position conductive wires to prevent burns?
Keep wires straight, not looped, and insulated from the skin.
Why are neonates and anesthetized patients at higher risk for RF burns?
They cannot report pain if heating occurs during the scan.
How can SAR levels be reduced to prevent RF burns?
- Lower flip angle
- Increase TR
- Use fewer slices
- Avoid fast spin-echo sequences
How does RF frequency change with MRI field strength?
Higher field strengths require higher RF frequencies, increasing SAR and heating risks.
What causes peripheral nerve stimulation (PNS) in MRI?
Rapid switching of gradient magnetic fields induces currents in tissues.
What sensations do patients feel during PNS?
- Tingling
- Muscle twitching
- Throbbing
Can MRI stimulate cardiac muscles?
No, diagnostic MRI does not reach the cardiac stimulation threshold.
What sequence types are most likely to cause PNS?
- Echo-planar imaging (EPI)
- Diffusion-weighted imaging (DWI)
- Fast gradient-echo sequences
What is the primary safety concern of cryogens in MRI?
Helium can cause asphyxiation, burns, or pressure buildup.
What happens during a quench?
The magnet loses superconductivity, rapidly boiling off helium.
What is the expansion ratio of liquid helium to gas?
1 liter of liquid helium expands to 754 liters of gas.
What should be done if helium leaks into the MRI room?
Evacuate immediately due to the risk of asphyxiation.
Why might a quench prevent MRI room door access?
Rapid helium release can cause a pressure differential, sealing the door shut.
Why is MRI so loud?
Rapid switching of gradients generates Lorentz forces, causing vibrations.
What is the average dB level inside an MRI scanner?
Typically 80–115 dB, similar to a rock concert.
What type of hearing protection should be used in MRI?
- Earplugs
- Noise-canceling headphones
- MRI-compatible music systems
Why are children and elderly patients more sensitive to MRI noise?
Their hearing is more sensitive, making noise-induced discomfort more likely.
Why should non-MRI staff be screened like patients?
They may unknowingly bring ferromagnetic objects into Zone III.
What is a common theme in projectile accidents?
Unauthorized personnel entering the MRI room with ferromagnetic objects.
What should never be assumed about an implant?
That it is MRI-safe without official documentation.
What is the purpose of MRI safety zones?
To restrict access and prevent unauthorized entry into hazardous areas near the MRI scanner.
What are the four MRI safety zones?
1️⃣ Zone I: General public area
2️⃣ Zone II: Patient prep & screening
3️⃣ Zone III: Restricted access (MRI personnel only)
4️⃣ Zone IV: MRI scanner room
Who qualifies as Level 2 MRI personnel?
MRI technologists, radiologists, and trained nurses who understand MRI hazards.
What should be clearly marked in Zone IV?
A red light & sign stating ‘The Magnet is On’ at all times.
What should MRI screening forms include?
- Implants & medical devices
- Past surgeries
- Metallic foreign bodies
- Claustrophobia history
What causes projectile accidents in MRI?
Ferromagnetic objects are rapidly pulled into the magnet due to its high spatial field gradient.
What common hospital equipment is a known projectile hazard?
- Oxygen tanks
- Scissors & clamps
- Wheelchairs & stretchers
What was the most famous MRI projectile accident?
A 6-year-old boy was fatally struck by an oxygen tank in 2001.
Why is magnetic shielding important in MRI?
It limits the fringe field, reducing accidental projectile risks.
What non-metallic materials should be used for MRI safety equipment?
Brass, titanium, plastic, or carbon fiber.
Why does MRI cause heating?
RF pulses cause eddy currents, leading to tissue heating.
What is SAR (Specific Absorption Rate)?
A measure of RF energy absorbed by the body per kilogram.
What are safe SAR limits in MRI?
Whole-body SAR should not exceed 4 W/kg in first-level controlled mode.
What patient positioning errors increase burn risks?
- Hands touching thighs
- Feet touching
- Looped cables & wires
How can burn risks be reduced in MRI?
Use insulating pads to break skin-to-skin contact.
What causes peripheral nerve stimulation in MRI?
Rapid gradient switching induces electric currents in nerves.
What does PNS feel like for patients?
- Tingling
- Muscle twitching
- Mild discomfort
How is PNS minimized in MRI?
Using slower gradient switching and adjusting pulse sequences.
Why is MRI so loud?
Gradient coils create Lorentz forces, causing vibrations.
What are MRI noise levels in dB?
Ranges from 80–115 dB, similar to a rock concert.
What type of hearing protection is recommended for MRI?
- Earplugs
- MRI-safe headphones
- Noise-canceling systems
What happens during an MRI quench?
Liquid helium rapidly boils off, releasing gas into the room.
What is the main danger of a quench?
Helium displaces oxygen, causing asphyxiation.
How should a quench pipe failure be handled?
Evacuate immediately due to risk of suffocation.
What does fMRI measure?
Changes in blood oxygen levels (BOLD contrast).
What is the primary use of fMRI?
To map brain activity and localize functions.
What is perfusion imaging used for?
To assess blood flow in tissues, often for stroke evaluation.
What contrast agent is commonly used in perfusion MRI?
Gadolinium-based contrast agents (GBCA).
What is the most common artifact in MRI?
Motion artifact caused by patient movement.
How can motion artifacts be reduced?
- Patient immobilization
- Breath-hold sequences
- Navigator echoes
What is a chemical shift artifact?
A misalignment of fat & water signals due to different Larmor frequencies.
How can aliasing (wrap-around) artifact be prevented?
Increase the FOV (field of view) or use anti-aliasing filters.
