Unit 10 - MRI Safety Flashcards
the rate that electromagnetic energy in the radiofrequency is absorbed by tissues during MR image acquisition represented as watts per kilogram
specific absorption rate
which Zone includes all areas that are freely accessible to the general public. No MRI hazard. All personnel are permitted.
Zone I
which Zone functions as interface between the publicly accessible, uncontrolled Zone I and the strictly controlled Zones III and IV. Patients are under MRI personnel where patients change into gowns and are unscreened/answer screening questions and medical history is taken
Zone II
Access to this zone is restricted to trained MR personnel and other individuals and equipment that have been fully screened. This area can be harmful to unscreen patients/other personnel. Area should be restricted by the use of locked doors. Area should be marked if the 5 Gauss field line falls in this zone
Zone III
This zone presents the due to the presence of the strong magnetic field; typically contains the 5 Gauss line. All ferromagnetic objects must be excluded from this area. The entrance to this area must be restricted and controlled by MRI personnel.
Zone IV
patients, visitors or facility staff who have not undergone formal safety training
Non MRI personnel
office staff and patient aides who have passed minimal safety education to ensure their own safety as they work in Zone III.
Level 1 personnel
include MRI technologists, radiologist, and nursing staff who have been extensively trained in MRI safety. Level 2 training for these staff includes issues relating to thermal loading, burns and neuromuscular excitation from rapidly changing gradients.
Level 2 personnel
The device or implant is completely nonmagnetic, nonelectrically conductive, and nonradiofrequency reactive, therefore eliminating all the primary risks during MRI scanning.
MR Safe
Objects that are significantly ferromagnetic and pose a clear and direct threat to persons and equipment within the magnet room
MR unsafe
The device or implant may contain magnetic, electrically conductive, or radiofrequency-reactive
components that are safe for operation in proximity to the MRI, provide the conditions for safe operation are defined and observed (both for the MR scanner and the device itself)
MR conditional
Describe what a technologist can do to alleviate effects from claustrophobia
talk to the patient in a calm, bedside manner, keeping an open line of communication. tech can show patient the MRI. give reassurance. let loved one inside room
Discuss the adverse, long-term biological effects to exposure to MR imaging
No biological effects in humans exposed to 2T
Describe when a ferrous object is near the MR scanner
object becomes a projectile and can potentially cause harm
Rotational force that causes the alignment of an object to the lines of the magnetic flux
torque
Name the 2 forces exerted by the main magnetic field on metallic objects and their potential hazardous effects
translational force and rotational force (torque)
What is magnetohydrodynamic effect?
Conductive fluid such as blood (iron) moving across a magnetic field will result in creation of an electrical current
How is an ECG tracing affected by MHD (magnetohydrodynamic) effect?
an increase in the amplitude of the ECG T Wave when patient is placed in the static magnetic field
List the hazards of RF
-Patient heating and burns
-The antenna effect (burns)
-Adverse effect on implant function due to induced currents
What are the three modes of MR scanning
Normal operating mode, first level operating mode, second level operating mode
Define Normal Operating Mode
routine scanning; defined as “the mode of operation in which none of the outputs have a value that would be anticipated to cause physiological stress.
Define First Level Operating Mode
one or more outputs may reach a value that may cause physiological stress - must be medically advised
Define Second Level Operating Mode
research only. outputs can produce significant risk-explicit ethical approval required.
Identify the interventions used to reduce RF deposition
reducing flip angle, slice numbers per sequence, reduce ETL in FSE, etc.
Define antenna effect and how to prevent burns caused by it
-any conductor acts as an antenna (radio aerial) if it happens to be of a certain critical length
-keep conductive wires away from patient’s skin surface, especially if patients are sedated. use insulating pads to separate wires from patient. use insulating pads to separate patient from the walls.
-avoid creating a loop with wires
Describe the effects of time-varying magnetic fields (TVMF) and the cause
-Nerve stimulation:
-Effect on implanted devices:
-Acoustic
What is magneto-phosphene?
visual effect when retinal phosphates are stimulated by induction from TVMF. patients complain of seeing “stars in one’s eyes” or “light flashes”
What causes the acoustic noise?
created by currents that pass through the gradient coils during image acquisition
What are the recommended noise levels by Occupational Safety and Health Administration?
exposure to noise to be maintained below 85 db over an 8 hour period. levels over 100 db to be reduced to 15 min per day
List the primary safety concerns associated with cryogens:
-Thermal sensitivity
-Asphyxia
-Quench
-Explosion
Describe a quench, the reason for occurrence, and the appropriate time to initiate:
-sudden loss of superconductivity of the magnet coils when its temperature is raised. loss of magnetic field in a superconductive magnet
-use in life-threatening situations
What is the rate of expansion of helium:
1:754
Define Lorentz force
sensation of moving along a curved trajectory
