Module 1 Flashcards
Bore
Opening through the magnet
Isocenter
The middle of the magnet (sweet spot)
Inhomogeneities
When space is erratic and makes variations
Shimming
A means to make the field more homogenous
Lines of force/flux
A magnetic field surrounds a current moving through a conductor.
Active shims
Small coils that superimpose magnetic fields on the main magnet altering the flux density
Parts per million
What deviation from perfection is measured as
Passive shims
Used for permanent magnets. Curved iron poles on corners
Quench
Gas expanding rapidly most likely to happen during the initial ramping after installation and it can happen multiple times
Superconducting magnet
Utilizes a super cold liquid, cryogenic to chill an exotic conductor, niobium, to a temperature that allows the flow of electricity without resistance
Quench pipe
Removes he from the room as quickly as possible
Primary coil
Main magnet referred to as B sub zero
Gradient coils
3 sets which enable spatial location
Shim coils
Used for homogeneity
RF probe
The radio frequency emits pulses of energy that excite Hydrogen atoms in the body
Active shielding
Contains the periphery of the magnetic field called the fringe field to a smaller area
Aperture
Opening diameter
Nuclear magnetic resonance
Produces a spectrogram of energy released from protons after radio frequency excitation
Gradient magnetic fields
Field that increases in strength over the distance it covers. (At a linear slope)
Transceiver
Coils that can both transmit the RF pulse and receive the signal back
Z gradient
Longitudinal
Y gradient
Vertical
X gradient
Transverse
Proton density
Proportional to the strength of the MR signal
Protium
The isotope of H with a single proton
Precessional frequency
The frequency of rotation is dependent on the field of strength of the external field
Radio frequency
Has the same Larmor frequency as H, irradiates tissue
Mxy
The magnetization of the patient at equilibrium
Net magnetization vector
Magnetic moments of individual active protons must add flux lines together to create a magnetic field that is strong enough to extend beyond the patients body and be detected
Out of phase
Two protons processing in B sub zero. Each has a magnetic moment but their amplitude doesn’t add together.
Resonance
The absorption of energy by a body, due to its frequency of oscillation being the same the frequency of another body’s oscillating is perturbed
Resonant frequency
When there is a loss of amplitude but the frequency of the vibrations are still the same its called the
Magnetic domain
At the resonant frequency H all active magnetic moments move to the same position on the processional path
Free induction decay
After coming into phase the RF pulse terminates and this begins
Flip angle
Determined by the amplitude and duration of the RF pulse
Angular momentum
Net spin
Dipole
Bipolar
Helix
A wire conductor wrapped in coil
Solenoid
Electric current flowing through a helix
Spin quantum number
Each element has this and it signifies if it is active or not
1 tesla
10,000 gauss
1 tesla
10,000 gauss
