Instrumentation Flashcards
magnetic fields associated with MR imaging system include the
static magnetic field
RF field
gradient field
MR system component that produces the B(o) field is the
main magnet
the MR system component that produces the B(1) field is the
radiofrequencey system
there are various types of magnets that can be sued for MR imagers, these include
permanent magnet
resisteive
magnet
hybrid magnet
‘superconductive magnet
the MR system component that provieds a meads for alignment of proton spins is the
main magnet
the MR system component that provides a meands for excitation is the
radio frequency system
the MR system component that provides a means for spatial encoding is the
gradient system
the liquid cryogen commonly used to maintain the magnet coil at superconducting temperatures is
helium
nitrogen
some systems use only one cryogen in such systems the cryogen is
helium
faradays law of induction states that if a loop of wire is moved through a magnetic field____will be created in the wire
voltage
the equation associated with faradays law of induction is
ΔB/ΔT=ΔV
according to faradays law of induction the amount of current produced in a loop of wire moving through a magnetic field is proportional to the
strength of magnetic field
in a typical superconducting cylindrical bore magnet, the direction of the magnetic field is
horizontal
the direction of the magnetic field in a typical permanent magnet is
vertical
to maintain the magnetic field of a resisteive magnet which of the follwoing should be applied to the magnet coils
current
magnetic field strength is measured in units of Tesla (T) and Gauss (G) whereby 1 T equals
10000 G
1.5 T =(gauss)
15000 G
in a superconducitng magnet the magnetic field strength is increases by increasing the
turns of a wire
in a solenoid supierconducint magnet the direction of current flow affects the
direction of magnetic field
permanent magnets with a vertical magnetic field use surface coils taht are
solenoids
the transmit bandwidth of the RF pulse affects
spatial resolution
\slice thickness
in order to create a thin slice thickness a _______is used
steep slice selecting gradient
high amplitude slice select gradient
narrow transmit bandwidth
the receiver bandwidth affects
chemical shift artifacts
SNR
if a coil is improperly tuned it will result in
a decrease in SNR
gradient magnetic fields are
always on
the timing of RF pulses during an MR pulse sequence
controls image contrast
the B1 magnetic field is produced by a
RF coil
in an MRI system that uses shim coils the B(o) homogeniety is adjusted by
changing current in the shim coil
shimming in MRi is performed by all of the followoing
changing current in the shim coil
adding metal to different coils within the shim coil
adding current to the gradient coils
gradient strength (amplitude) is measured in units of
mT/M
G/cm
gradient speed (rise time) is measure in units of
µs
gradient speed and strength is measured in units of
T/m/s
the amount of time that a gradient is permitted to work is known as the duty cycle and is measured in units of
%
the gradient strength is measure in units of
amplitude
the gradient characteristic that reflects both strength and speed is known as the
slew rate
gradients can work for a period of time known as the
duty cycle
gradient characteristics for speed is known as the
rise time
RF coil configureations include
linear
quadrature
phase array
helmholtz
multichannel
RF coil configureations that use multiple coils with one single receiver include
helmholtz
RF coil configurations that use multiple coils with multiple receivers are
phase array
multichannel
the sensitivy profile for a given coil is known as the
pulse profile
RF coil configuration that use coils whereyby the coil is configured with wires or electronic components that are perpendicular to one another are known as
quadrature
