MRI safety Flashcards
What are the main difference between CT & MRI?
Imaging technique: MRIs use radio waves and strong magnetic fields, while CT scans use X-rays.
Image quality: MRIs produce more detailed images of soft tissues and organs than CT scans.
Speed: CT scans are usually faster than MRIs, taking about five minutes, while MRIs can take 15 minutes to two hours.
Cost: CT scans are generally less expensive than MRIs.
Radiation exposure: CT scans expose patients to radiation, while MRIs do not.
Patient preparation: Patients must remain still during an MRI, while movement is less of an issue during a CT scan.
Patient safety: MRIs can interact with metal in the body, such as medical devices, shrapnel, and some tattoo inks. Patients are asked about their medical history and must fill out a safety form before an MRI.
Uses: CT scans are often the first choice for imaging and are ideal for emergency situations. They can spot bone fractures, blood clots, and organ injuries. MRIs are useful for detecting certain diseases that CT scans cannot, such as sports injuries and musculoskeletal conditions
MRI Magnetic field strength
The most common magnet strengths are;
1.5t – cardiac imaging - heart
3t – used for ligaments, tendons and cartilage to assess the stability of joints - knee
7t – small veins and lesions such as in the brain
As the number of Tesla’s increase so does the magnetic field strength. A 7t is stronger than a 1.5t. The stronger the magnet, the more spatial resolution (more detailed the images) and the less time patients spend inside the scanner.
The choice of magnetic is dependant on the patient and clinical details. The strength of the MRI magnet’s field is important because it determines the signal strength. Stronger fields can produce better signal-to-noise ratio.
However, the stronger the magnet field the louder the gradient noise and increase in body temperature or tissue heating in a patient’s body. This could cause cause more distortion from movement artifacts or even foreign objects in the body, which can decrease image quality.
Misconceptions: metal
There are some metal that are MRI Safe such as titanium, aluminum and brass
In theatre during surgery a surgeon will insert titanium.
A heart valve or stent
Dental implants
Other safety mechanism put in place
Auditory damage:
Patients will be given headphones
Or ear plugs if they don’t want to listen to music
To protect their hearing
Patient anxiety:
Patients will be given an emergency buzzer
The scan can be stop straight away once pressed
To support anxious patients
Emergency stop button:
Located In scan room
Will turn off electrics
MRI burn prevention
Screen patients for implants, devices, and other metallic objects.
Assume anything unknown is MR Unsafe.
Screen objects to ensure that anything entering the scan room is
MR Conditional or MR Safe. Match conditions on MR Conditional devices with your scanner. All metals, even non-ferromagnetic ones, have the potential to heat up and cause burns.
Have patients change out of street clothes whenever possible.
Position patients to avoid skin-to-skin contact (e.g., no hands on hips, no crossed arms, no crossed legs, etc.).
Always use the manufacturer-provided padding to insulate the patient. Sheets and blankets may be added for patient comfort but are not a substitute for manufacturer-provided padding.
Route cables out of the scanner in a straight Don’t coil cables or allow them to touch the patient.
Use only Normal Operating Mode and Lowest SAR whenever possible.
Keep your ears and eyes on the patient at all times. Stay in communication with patients to identify warming. Monitor sedated patients using
MR Conditional monitoring equipment.
What happens when it all goes wrong?
Thermal burns and blisters caused by heating
Patient thermal injuries are the most frequently reported adverse event, accounting for 59% of MRI incidents.
Missile effect – strong magnetic force pulling patient into scanner
Auditory damage due to the noise
What is MRI quenching?
When the MRI magnet loses its superconductivity (its ability to conduct electricity when cooled) this is because the liquid helium which is used to cool down the magnets is released into the air.
Quenching is considered an MRI ‘safety emergency procedure’ when it’s necessary to quickly shut down the magnetic field. The quench button should only be used in a state of emergency e.g. when a person is stuck and decreasing the magnetic field strength is the only safe way to avoid further injury.
During a quench, the quench pipe above the magnet vents the helium gas safely out of the building.
Quenching can be dangerous and expensive. The magnet may also need to be down for one to two months after regenerating, or several months if it needs repair.
