MRI - physical principles Flashcards
What 3 rooms is the MR system distributed
magnet room
air-conditioned technical room
control room
What 5 aspects does the MR system consist of
magnet RF coils magnetic field gradients computer system couch
What does a sudden loss of superconductivity mean
results in a magnet quench where the magnetic field rapidly decrease with large amounts of helium being boiling off as gas
accidental quenches = rare
to create a strong enough magnetic field ….
very large currents have go through the wires of the magnet
What is the problem with having to create such a strong magnetic field with such a large current
if a large current is sent along a “normal” thickness wire, the wires resistance tries to resist flow of the current, heats up and burns it - could use thicker wires however they would have to be extremely thick
What is the solution to needing a large current to provide a strong magnetic field
wires lose all resistance to electrical currents when at very cold temperatures, helium at low temperatures is a liquid so the wires are immersed in liquid helium, removing all resistance allowing massive amounts of current to be carried - “superconducting”
MR signals are produced ….
in the patients tissue in response to RF pulses generated by RF coils
Patient in the scanner has ….
a homogenous magnetic field, with all the protons spinning at the same rate (speed they rotate at is called the precession frequency which depends on the strength of the magnetic field) so they all give off the same frequencies
To examine a specific slice of anatomy, what must be done
a second magnetic field (gradient field), with differing strengths in varying locations, must be superimposed over the external magnetic field so the magnetic field is stronger/weaker in places
How is the additional gradient field produced
by 3 sets of gradient coils embedded within the bore of the magnet, an electrical current is applied through the coils in a carefully controlled pulse sequence
What is a consideration that must be taken into account with the gradient fields
creates loud tapping noise or clicking or a high pitched beeping sound so ear defenders are required
How is the MR system controlled
via an operators console situated in the control room
What additional measures are included in the MR experience that help aid the patients experience
Intercom - to communicate with patient
Handheld alarm/’panic’ button
CCTV for visual monitoring
non ferromagnetic wheelchairs and trolleys and drip stands
