instrumentation Flashcards
Magnetic fields associated with MR imaging systems include the
1. static MF B0
2. RF field B1
3. Gradient field
4. Gantry field
A) 1 only
B) 1 and 2 only
C) 1, 2 and 3
D) 1,2,3,4
C
the MR system component that produces the B0 field is the
A) main magnet
B) RF system
C) gradient system
D) shim system
a
the MR system component that produces the B1 field is the
A) main magnet
B) RF systems
C) gradient system
D) shim system
B
there are various types of magnets that can be used for MR images
1. permanent magnet
2. resistive magnet
3. hybrid maget
4. superconducting magnet
A) 1
B) 1 and 2
C) 1, 2 and 3
D) 1, 2 ,3 ,4
d
The MR system component that provides a means for alignment (magnetisation of proton spins) is the
A) main magnet
B) RF system
C) gradient system
D) shim system
A
the MRI system component that provides a means for excitation is the
A) main magnet
B) RF system
C) gradient system
D)shim system
b
the MR system that provides a means for spatial encoding
A) main magnet
B) RF system
C) gradient system
D) shim system
c
what are the characteristics of a permanent magnet
- low field 0.3 T
- open configuration
- vertical field direction
- always on
what are the characteristics of a resistive magnet
- lighter in weight
- low field strength 0.3 T
- open or tubular configuration
- vertical or horizontal field direction
- can be turned off and on
- requires a large current
what are the characteristics of a superconducting magnet
- between weight of a resistive and permanent magnet
- high field strength (1T, 1.5T, 3T)
- tubular configuration
- horizontal field direction
- always on
requires cryogens to cool
what are the characteristics of a hybrid magnet
- combination of resistive and permanent
- or a combination of permanent and superconducting
what gradient system is Z
superior inferior
what gradient system is y
anterior to posterior
what gradient system is x
left to right
what gradient is usually used for an axial slice selection
z
what is the general direction to phase an axial head scan
R-L
what is the general direction to phase an axial abdomen scan
A-P
the liquid cryogen commonly used to maintain the magnet coil at superconducting temperatures is
A) helium
B) hydrogen
C) nitrogen
D) a and c
a
some systems only use one cryogen, which is
A) nitrogen
B) hydrogen
C) helium
D) oxygen
C
faradays law of induction states that if a loop of wire is moving through a magnetic field ______ will be created
A) a magnetic wave
B) a voltage
C) torque
D) resonance
b
the equation associated with faradays law of induction is
A) w/kg
B) w(0)= BoY
C) ∆B/∆T=∆V
D) Ppm
c
according the faradays law of induction, the amount of current produced in a loop of wire moving through a MF is proportional to the
A) length of the wire
B) strength of the MF
C) spin density of the wire
D) time it takes for the MF to reach its full potential
b
in a typical superconductive magnet, the direction of the MF is
A) vertical
B) horizontal
C) around the flux lines
D) hard to measure
b
the direction of the MF in a permanent magnet
A) vertical
B) horizontal
C) around the flux lines
D) hard to measure
a
to maintain MF strength of a resistive magnet which of the following should be applied to the magnet coils
A) water
B) heat
C) current
D) cooling
c
MF strength is measured in T or G. what does 1T=
A) 1G
B) 1000 G
C) 10 000 G
D) 100 000 G
c
1.5T=?
A) 10 000 G
B) 15 000 G
C) 30 000 G
D) 3000 G
b
in a superconducting magnet. the MF strength is increased by
A) amount of cryogens
B) temperature
C) internal pressure
D) turns of wire
d. this can also be done by reducing the space between the wire turns
in a solenoid superconducting magnet the direction of the current flow affects the
A) strength of the MF
B) direction of the MF
C) intensity of the MF
D) homogeneity of the MF
b
permanent magnets with a vertical MF use surface coils that are
A) solenoids
B) linear
C) quadrature
D) flat
a. this is because the B1 or RF must be perpendicular to the orientation of B0
the transmit BW of the RF pulse affects the
A) spatial resolution
B) slice thickness
C) image contrast
D) a and b
d. ∆ the slice thickness in turn ∆’s the voxel volume and the spatial resolution
in order to create a thin slice thickness, a ______ is used
1. steep gradient
2. high amplitude slice selection gradient
3. narrow transmit BW
4. Narrow receive BW
A) 1
B) 1 and 2
C) 1, 2 ,3
D) 1, 2, 3 ,4
c
the receiver BW affects
A) chemical shift artefact
B) slice thickness
C) SNR
D) a and c
d. this is the range of frequencies being sampled. decreasing receiver BW increases SNR but increases the chemical shift artifact
if a coil is improperly tuned it will result in
A) a decrease in SNR
B) a reduction in voxel size
C) patient burns
D) resonance artifacts
a
the gradient MF are
A) always on
B) superimposed over the main MF
C) used for contrast control
D) controlled by RF pulses
B
timing of the RF pulses
A) controls the image contrast
B) spatially encodes the data
C) shims the static MF
D) a and b
a
B1 field is produced by a
A) gradient coil
B) shim coil
C) RF coil
D) magnet coil
C
in an mri system that uses shim coils, the B0 homogeneity is adjusted by
A) changing the current in the shim coil
B) adding metal to different coils within the shim coil
C) adding current to the gradient coils
D) turning the shim on and off rapidly
A
shimming in MRI is performed by all of the following except
A) changing the current in the shim coil
B) adding metal to different coils within the shim coil
C) adding current to the gradient coils
D) turning the shim coil on and of very rapidly
d
what can be used for passive shimming
metal plates being strategically placed within the magnet system
what can be used for active shimming
using current applied within the shim coils
gradient strength is measured in units of
1. mT/M
2. G/cm
3. T/m/s
4. µs
5. %
A) 1
B) 1 and 2
C) 3
D) 4
E) 5
b
Gradient speed is measued as (rise time)
1. mT/M
2. G/cm
3. T/m/s
4. µs
5. %
A) 1
B) 1 and 2
C) 3
D) 4
E) 5
d
Gradient speed and strength is measured units of
1. mT/M
2. G/cm
3. T/m/s
4. µs
5. %
A) 1
B) 1 and 2
C) 3
D) 4
E) 5
c
the amount of time that the gradient is permitted to work is known as the duty cycle. units of this is
1. mT/M
2. G/cm
3. T/m/s
4. µs
5. %
A) 1
B) 1 and 2
C) 3
D) 4
E) 5
E
gradient strength is measured in units of
A) amplitude
B) slew rate
C) duty cycle
D) rise time
A
gradient characteristic reflecting both strength and speed is known as
A) amplitude
B) slew rate
C) duty cycle
D) rise time
B
gradients can work for a period of time known as
A) amplitude
B) slew rate
C) duty cycle
D) rise time
c
gradient characteristic for speed is known as the
A) amplitude
B) slew rate
C) duty cycle
D) rise time
d
RF coil configurations include
1. linear
2. quadrature
3. phase array
4. helmholtz
5. multichannel
A) 1
B) 1 and 2
C) 1, 2, 3
D) 1, 2, 3, 4
E) 1, 2, 3 , 4, 5
E
RF coil configurations that use multiple coils with one single receiver include
1. linear
2. quadrature
3. phase array
4. helmholtz
5. multichannel
A) 1
B) 1, 2
C) 3, 5
D) 4
d
RF coil configurations that use multiple coils with multiple receivers include
1. linear
2. quadrature
3. phase array
4. helmholtz
5. multichannel
A) 1
B) 1, 2
C) 3, 5
D) 4
c
the sensitivity profile for a given coil is known as the
A) pulse profile
B) spectrum
C) FID
D) echo
a
RF coil configurations that use coils configured with wires that are perpendicular to one another are known as
1. linear
2. quadrature
3. phase array
4. helmholtz
5. multichannel
A) 1, 2
B) 2
C) 3, 5
D) 4
b
linear coil
one wire configured into a loop- flat coil
quadrature coil
configured with wires that are perpendicular to one another
Helmholtz pair
linear coils coupled or paired with a single receiver
phase array/multichannel coils
coils coupled or paired with one multi receiver
