RADR Final

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

MRI

combines strong magnets with radiofrequencies

Sonography

uses sounds waves and echoes like a submarine

Mammography

x-ray tube

CT

ionizing radiation from x ray tubes; images acquired in the z axis; cross sectional

4 requirements for x rays

vacuum, source of electrons, method to accelerate electrons, method to stop electrons

Vacuum

air is removed from the tubes

Source of electrons

cathode (-) filament in tubes

Method to accelerate

voltage; plugging machine up

Method to stop

target made of tungsten (anode +)

Primary radiation

x ray beam after it exits the tube and before it reaches the patient

3 fates of an x ray photon

penetrate, scatter, absorb

Photoelectric absorption

x rays are absorbed into the body (the white in an x ray)

Compton scattering

x rays scatter and affect image quality and exposure; biggest contributor to tech dose

Penetrate

x rays go through pt and absorbed in image receptor (black in x ray)

Grids

cover for image receptor; lead strips allow remnant radiation to pass through reduce scatter

Kilovoltage peak (kVp)

causes electrons to go through the cathode then through anode at very high speeds; produces x-radiation; increase kVp= increase penetration power

X ray tubes

produce heat and x-radiation

Control console

main power, kVp. mA, timer, rotor exposure switch

Main technical factors

mAs, kVp, and source to image distance (SID)

Milliampere-seconds (mAs)

quantity of x-rays; mA x time = mAs; double mAs = double patient exposure to radiation

SID

controlled by moving x ray tube (40” or 72”)

Distortion

misrepresentation of size/shape

Fog

undesired exposure

Density

darkening of the image

Contrast

various shades of gray

Resolution

recorded detail/sharpness

Detail

true representation of anatomy

Improper mAs settings

image comes out too dark or too light

X ray production

1% x rays and 99% heat

Order of image collection

set up equipment, position patient, brief review, acquire image, review image

X ray tube

cathode emits electrons (negative), anode directs electrons (positive)

Object to image distance (OID)

magnification or distortion

Collimator

controls size and shape of x ray field; helps reduce pt exposure

Image receptor location

table top, table bucky, wall bucky

Film

film/screen is outdated (analog)

Computed radiography

digital cassettes are exposed and ran through a processor

Digital radiography solid state detector

image appears on computer console right away

Alignment

x ray tube is penetrating the correct anatomy and lined up with image receptor

Angulation

foreshortening, elongation, perspective, compensation

Fluoroscopy machines

real time imaging

Bucky

holds image receptor

Cryogen

A cooling refrigerant that is used to reduce external temperatures to a very low level

Gantry

Term used to express the equipment component that contains major technological components
comprising a CT or MR scanner

Horizontal

along the long axis

RF coil

Radio-frequency (RF) antennae that are used to transmit and receive RF frequencies

Sequence

The choice of MR scanning protocols used in scanning patients. Sequences generally alter RF
signal pulse amplitude and duration.

Solenoid

cylindrical coil of wire acting as a magnetic when carrying an electric charge

Vertical

perpendicular to the plane of the horizon