RADR 1201- Exam 5

Magnetic susceptibility

how easily a material becomes magnetized and whether it is attracted to or repelled by a
magnetic field

Types of magnetism

diamagnetism, paramagnetism, ferromagnetic

Diamagnetism

weakly repelled by magnetic fields and have a small negative magnetic susceptibility; no permanent magnetism and lose all magnetism once the external field is removed

Diamagnetic materials

hydrogen, helium, gold, silver lead

Paramagnetism

weakly attracted to magnetic fields and have a small positive magnetic susceptibility; create a temporary magnetic moment. However, once the external field is removed, the electrons lose alignment, and the material no longer stays magnetized

Paramagnetic materials

calcium, oxygen, aluminum, titanium, platinum

Ferromagnetism

strong attraction to magnetic fields and a large positive magnetic susceptibility; magnetic domains allow them to stay magnetized even after the external field is removed

Ferromagnetic materials

iron, nickel, cobalt, gadolinium

MRI alignment

aligns hydrogen atoms in body

Static magnetic field (B0)

constant, unchanging magnetic field that does not vary over time; main magnetic field; exposure in zone 4

Time varying magnetic field

changes in strength or direction over time

RF field (B1)

an oscillating electromagnetic field used in MRI to excite hydrogen atoms (flips their alignment)

Zone 1

public area

Zone 2

patients are greeted, screened, and supervised

Zone 3

ferromagnetic objects and unscreened people not allowed; controlled area;

Zone 4

scanner room, highest level of restriction; “The magnet is on”

Non MRI personnel

patients, visitors, and staff without MRI training

Level 1 personnel

office staff and safety aides that have passed minimal MRI safety education

Level 2 personnel

MRI techs, radiologists and nursing staff that have been trained on MRI safety

Device safety identifications

interactions that may interact with electromagnetic field

MR safe

items that pose no known risks in any MRI environment

MR conditional

items that are safe only under specific MRI conditions (static magnetic strength, RF fields, SAR(heating))

MR unsafe

items that are dangerous in all MRI environments

Main MRI safety concerns

transient biological effects and projectile hazards

Common transient effects

metallic taste in mouth, vertigo, phosphenes (flashes of light); walking next to or going into magnet

Projectile hazards

field strength drops outside the bore creating a powerful pull; force depends on magnets field strength and steepness of spatial gradient

Bore entrance

field strength drops sharply

Credit cards

field will demagnetize

Woman that used radiation

Marie Curie

Radiation

kinetic energy that passes from one location to another and can have many manifestations

Ionizing

x rays, gamma rays, high energy UV

Non ionizing

visible light, infrared, radio waves

Natural ionizing

earth, cosmic rays

Man made ionizing

x rays, ct scans

Terrestrial radiation

naturally occurring radioactive materials (uranium, thorium, radon)

Cosmic radiation

energy from solar system (sun and stars)

Fate of x ray photon

penetrate, scatter, absorb

X ray interactions

coherent scattering, photoelectric interactions, compton scattering, pair production, photodisintergration

Photoelectric

within x ray energy range; photon is absorbed by collision with inner shell electron; pt exposure

Compton scattering

within x ray range; photon collides with outer shell electron; tech exposure

Photoelectric absorption

x rays absorbed into the body

Exposure (X)- ionization in air

coulombs per kilogram (C/kg)

Absorbed dose (D)- amount absorbed by tissue

Gray (Gy)

Effective dose (EfD)- occupational exposure

Sievert (Sv)

Radioactivity

Becquerel

Dose limit

worker = 50 msv avg person = 5msv

Acute radiation syndrome

large amount of radiation over short period of time

Somatic effects

effects individual exposed; cancer and cataracts

Genetic effects

effects individual’s offspring

ALARA

as low as reasonably achievable

Inverse square law

less radiation exposure by standing farther away

Acute radiation syndrome order

prodromal, latent, manifest, recovery or death