MRSO STUDY GUIDE TEST PAPER
QUESTIONS WITH THOROUGH ANSWER
EXPLANATIONS
●● what is the term B0?
Answer: main magnetic field direction
●● what is the main magnetic field unit?
Answer: Tesla (T)
●● what are magnetic flux lines? iso, high, low?
Answer: lines of magnetic force that travel from the north to south pole
of a magnetic source
iso - uniform
high - lines closer together, near source
low - lines further apart, away from source
●● what is fringe field?
Answer: the area as we move away from isocenter that contains
magnetic fields that are not useful for imaging
,measured in G or mT
●● static magnetic field map/fringe field
Answer: visualization of the magnetic field strength at a given location
in space
(G or mT)
●● spatial gradient map
Answer: visualization of how the magnetic field is changing over
distance (T/m or G/cm)
spatial gradient (db/dx)
db: amplitude of change
dx: time
●● what is another term for isogauss plot?
Answer: static magnetic field map/fringe field
●● what are gauss lines?
Answer: common boundaries marked around an MRI scanner that define
the strength of the magnetic field
,●● what are the biological effects of the main static field?
Answer: - magnetophosphenes (seeing bright lights/flashes)
- magnetohydrodynamic effect/ECG perturbations (elevated T waves,
patient experiences voltage induced as blood moves
through lines of magnetic flux)
- electrogustatory effect (metallic taste)
- vertigo/dissiness/nausea, nystagmus from movement through static
field
●● what are the 3 mechanical forces of the main static magnetic field?
Answer: translational, torque/rotation, lenz's
●● what is translational force?
Answer: missile effect, "attractive force"
determined by size, shape, ferromagnetic properties/mag susceptibility,
shielding
strongest translational force at opening of bore
●● what is torque/rotational force?
Answer: object's long axis aligns with B0, maximum rotational force
occurs at isocenter
, ●● what is Lenz's force?
Answer: electrically conductive object moves into a mag field, another
opposing mag field is created (resistive force)
ex: potential consequences for large implanted metallic devices (non
ferrous ortho implants), do not pose projectile hazards, rapid motion of
the patient/implant in a direction
perpendicular to the static magnetic field orientation can result in forces
on the implant opposing this motion. If the patient were to complain of
tugging or pulling on the implant, this might lead to the patient or health
care personnel to erroneously conclude that the device has ferromagnetic
components and possibly canceling the examination. SLOWER
movement towards/into bore = less resistance than FAST
depends on static field, size/orientation/speed of conductor, and
conductivity of metal
●● what are current FDA cleared scanner strengths for human use?
Answer: 0.064T - 7T
●● what is the maximum magnetic field strength based on age?
Answer: greater than 1 month - 8T
less than 1 month - 4T
QUESTIONS WITH THOROUGH ANSWER
EXPLANATIONS
●● what is the term B0?
Answer: main magnetic field direction
●● what is the main magnetic field unit?
Answer: Tesla (T)
●● what are magnetic flux lines? iso, high, low?
Answer: lines of magnetic force that travel from the north to south pole
of a magnetic source
iso - uniform
high - lines closer together, near source
low - lines further apart, away from source
●● what is fringe field?
Answer: the area as we move away from isocenter that contains
magnetic fields that are not useful for imaging
,measured in G or mT
●● static magnetic field map/fringe field
Answer: visualization of the magnetic field strength at a given location
in space
(G or mT)
●● spatial gradient map
Answer: visualization of how the magnetic field is changing over
distance (T/m or G/cm)
spatial gradient (db/dx)
db: amplitude of change
dx: time
●● what is another term for isogauss plot?
Answer: static magnetic field map/fringe field
●● what are gauss lines?
Answer: common boundaries marked around an MRI scanner that define
the strength of the magnetic field
,●● what are the biological effects of the main static field?
Answer: - magnetophosphenes (seeing bright lights/flashes)
- magnetohydrodynamic effect/ECG perturbations (elevated T waves,
patient experiences voltage induced as blood moves
through lines of magnetic flux)
- electrogustatory effect (metallic taste)
- vertigo/dissiness/nausea, nystagmus from movement through static
field
●● what are the 3 mechanical forces of the main static magnetic field?
Answer: translational, torque/rotation, lenz's
●● what is translational force?
Answer: missile effect, "attractive force"
determined by size, shape, ferromagnetic properties/mag susceptibility,
shielding
strongest translational force at opening of bore
●● what is torque/rotational force?
Answer: object's long axis aligns with B0, maximum rotational force
occurs at isocenter
, ●● what is Lenz's force?
Answer: electrically conductive object moves into a mag field, another
opposing mag field is created (resistive force)
ex: potential consequences for large implanted metallic devices (non
ferrous ortho implants), do not pose projectile hazards, rapid motion of
the patient/implant in a direction
perpendicular to the static magnetic field orientation can result in forces
on the implant opposing this motion. If the patient were to complain of
tugging or pulling on the implant, this might lead to the patient or health
care personnel to erroneously conclude that the device has ferromagnetic
components and possibly canceling the examination. SLOWER
movement towards/into bore = less resistance than FAST
depends on static field, size/orientation/speed of conductor, and
conductivity of metal
●● what are current FDA cleared scanner strengths for human use?
Answer: 0.064T - 7T
●● what is the maximum magnetic field strength based on age?
Answer: greater than 1 month - 8T
less than 1 month - 4T
