MRI wk1 Safety & wk2 Intro

What is the difference between level 1 personnel and level 2

Level 1 may not escort non-MR trained persona into Zone III and IV

What is earth’s magnetic field

0.5 gauss

Fringe fields:

magnetic field extend around MRI scanner, even past the scan room

What are common bioeffects from induced voltages in tissues

flashes of light

metallic taste

feeling of vertigo

what type of metal is magnetic

ferromagnetic

What does MRI conditional mean?

no known hazards under specific conditions

-Tested at a specific condition

What color top do MRI save oxygen canisters have

orange top

What is Nephrogenic Systemic Fibrosis (NSF)

administration of gadolinium based contrast into patients with renal insufficiency

What glomerular filtration rate (GFN) is too low for contrast

less than 30

What are the different groups of contrast?

group 1: agents associated with greatest number of NSF cases

Group 2: agents associated with view, if any cases of NSF

Group 3: agent data remains limited regarding NSF (too new)

What is Specific Absorption Rate (SAR)

average energy (heat) dissipated in the body per unit mass and time

SAR normal mode

2 w/kg whole body heat

No psychological stress expected

SAR first level mode

4 w/kg whole body and 3.2 w/kg head imaging

Psychological stress is possible

What is B1-RMS?

Direct measure of RF electromagnetic field

Consistent across all vendors, which makes it easier to follow

What is Specific Energy Dose (SED)

heat specifically given to a body part or tissue

Too much will cause burns and that specific area

What is the limit manufacturers main limit the total SED to?

14,440 J/kg

What can cause burns?

electrodes

Medication patches

Monitoring leads

skin to skin

Touching the scanner wall

How much padding is required between the scanner wall and patient skin

1/2”

What is the conversion form T/m to G/cm

7.2 T/m to 720 G/cm

What is the spatial gradient at isocenter?

zero

the ACR requires hearing protection for levels above what decibel

99 decibels

What does the quench button do?

deactivate magnetic field, cryogen boil off rapidly

Who invented MRI

Dr. Raymond Damadian

What was the 1st MRI scanner

Indomitable 1977

What was MRI originally called

Nuclear Magnetic Resonance Imaging (NMR)

What is the first scanner approved by FDA

Fonar scanner 1983

What do you need to create a MR image

Magnet

RF

Hydrogen

What is the main magnet (B0)

Magnetize the proton spins in the same directions

Permanently Magnetized Material

Magnet always on

low field strength

vertical magnetic fields

Resistive magnet

Can be turned off

light weight

Low field strength

vertical or horizontal fields

Superconducting magnet

pump: super-cooled to remove resistance (Cryogens)

Always ON

high field strength

Horizontal field strengths

What does shimming homogeneity mean

equal equality throughout AOI

What is passive shim system

shim plates, no current

set at set up

What is active shim system

shim coils, requires current

able to change

Gradient coil system

Acoustic noise caused by vibrations of gradient set

In the gradient configuration what is the center of the 3

Isocenter

On the gradient system what axis does B0 run along

axis Z

What is the gradient rise time

time it takes for a gradient to reach max amplitude (microsec)

Slew rate

time a gradient reaches max amplitude and what is max (mT/m/s)

Duty cycle

% of time the gradient is permitted to work

What is the resonant frequency of hydrogen

42.58

What is the Larmor equation mean:

the frequency of the procession is directly proportional to the magnetic field strength (B0) and gyromagnetic ratio

What are transmitters

start the process, send RF waves with enough energy to flip spins from low energy to high

(body coils, head coils)

What are receivers?

receive resulting signal

(body coils, Local coils)

What are volume coils

transmit and receive (body and head)

low SNR

What are examples of surface coils

linear

quadrature

phase array (body coil)

multi coils

What is sensitivity profile

sensitive volume extends to the diameter of the coil and the depth of the patient equal to 75% of the diameter

Faraday’s Law of Induction

When a conductor is placed in a magnetic field, an electromotive force is induced

Magnetic moment

strength and orientation (spinning and how fast) of a magnet or object that produces a magnetic field

Precession:

the angle that the secondary spin is induced around B0

Precessional frequency

speed at which the magnetic moment is around B0

What is 1 Hz equal to in terms of rotation?

1 Hz = 1 rotation per second

Resonance

nucleus gains energy and resonates from force

RF pulse exactly at the frequency of H, which will cause resonance

T1 recovery

H nuclei gives up its energy to surrounding environment, relaxation

TR (repetition time)

time from one RF pulse to the next RF pulse for each slice

Determines T1 relaxation

TE (echo time)

time from the RF pulse to the peak signal