Unit 10 - MRI Safety

Question 1

the rate that electromagnetic energy in the radiofrequency is absorbed by tissues during MR image acquisition represented as watts per kilogram

Answer 1

specific absorption rate

Question 2

which Zone includes all areas that are freely accessible to the general public. No MRI hazard. All personnel are permitted.

Answer 2

Zone I

Question 3

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

Answer 3

Zone II

Question 4

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

Answer 4

Zone III

Question 5

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.

Answer 5

Zone IV

Question 6

patients, visitors or facility staff who have not undergone formal safety training

Answer 6

Non MRI personnel

Question 7

office staff and patient aides who have passed minimal safety education to ensure their own safety as they work in Zone III.

Answer 7

Level 1 personnel

Question 8

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.

Answer 8

Level 2 personnel

Question 9

The device or implant is completely nonmagnetic, nonelectrically conductive, and nonradiofrequency reactive, therefore eliminating all the primary risks during MRI scanning.

Answer 9

MR Safe

Question 10

Objects that are significantly ferromagnetic and pose a clear and direct threat to persons and equipment within the magnet room

Answer 10

MR unsafe

Question 11

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)

Answer 11

MR conditional

Question 12

Describe what a technologist can do to alleviate effects from claustrophobia

Answer 12

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

Question 13

Discuss the adverse, long-term biological effects to exposure to MR imaging

Answer 13

No biological effects in humans exposed to 2T

Question 14

Describe when a ferrous object is near the MR scanner

Answer 14

object becomes a projectile and can potentially cause harm

Question 15

Rotational force that causes the alignment of an object to the lines of the magnetic flux

Answer 15

torque

Question 16

Name the 2 forces exerted by the main magnetic field on metallic objects and their potential hazardous effects

Answer 16

translational force and rotational force (torque)

Question 17

What is magnetohydrodynamic effect?

Answer 17

Conductive fluid such as blood (iron) moving across a magnetic field will result in creation of an electrical current

Question 18

How is an ECG tracing affected by MHD (magnetohydrodynamic) effect?

Answer 18

an increase in the amplitude of the ECG T Wave when patient is placed in the static magnetic field

Question 19

List the hazards of RF

Answer 19

-Patient heating and burns
-The antenna effect (burns)
-Adverse effect on implant function due to induced currents

Question 20

What are the three modes of MR scanning

Answer 20

Normal operating mode, first level operating mode, second level operating mode

Question 21

Define Normal Operating Mode

Answer 21

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.

Question 22

Define First Level Operating Mode

Answer 22

one or more outputs may reach a value that may cause physiological stress - must be medically advised

Question 23

Define Second Level Operating Mode

Answer 23

research only. outputs can produce significant risk-explicit ethical approval required.

Question 24

Identify the interventions used to reduce RF deposition

Answer 24

reducing flip angle, slice numbers per sequence, reduce ETL in FSE, etc.

Question 25

Define antenna effect and how to prevent burns caused by it

Answer 25

-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

Question 26

Describe the effects of time-varying magnetic fields (TVMF) and the cause

Answer 26

-Nerve stimulation:
-Effect on implanted devices:
-Acoustic

Question 27

What is magneto-phosphene?

Answer 27

visual effect when retinal phosphates are stimulated by induction from TVMF. patients complain of seeing “stars in one’s eyes” or “light flashes”

Question 28

What causes the acoustic noise?

Answer 28

created by currents that pass through the gradient coils during image acquisition

Question 29

What are the recommended noise levels by Occupational Safety and Health Administration?

Answer 29

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

Question 30

List the primary safety concerns associated with cryogens:

Answer 30

-Thermal sensitivity
-Asphyxia
-Quench
-Explosion

Question 31

Describe a quench, the reason for occurrence, and the appropriate time to initiate:

Answer 31

-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

Question 32

What is the rate of expansion of helium:

Answer 32

1:754

Question 33

Define Lorentz force

Answer 33

sensation of moving along a curved trajectory