Chapter 5 - questions Flashcards
The external magnetic field is annotated as:
a. B1
b. B0
c. Z
d. B
b. B0
A field strength of 1.5 Tesla is equivalent to:
a. 10,000 G
b. 20,000 G
c. 15,000 mT
d. 15,000 G
d. 15,000 Gauss
Which of the following systems utilizes technology to create a magnetic field that cannot be removed (turned off)?
a. resistive
b. permanent
c. superconductive
b. permanent
Which of the following systems utilizes technology to create a magnetic field that can easily and routinely be removed (turned off)?
a. resistive
b. permanent
c. superconductive
a. resistive
Reducing the temperature of a conductor reduces
a. current
b. resistance
c. voltage
d. conductor life
b. resistance
The cryogen most commonly used to maintain the magnet coils at a superconducting temperature is
a. helium
b. hydrogen
c. oxygen
d. xenon
a. helium
the sudden loss of superconductivity and thus a loss of the magnetic field in a superconducting magnet is known as a
a. steady state
b. quench
c. ramp down
b. quench
which of the following is utilized to obtain very high magnetic fields
a. resistive
b. permanent
c. superconductive
c. superconductive
in a cylindrical magnet, the direction of the magnetic field is oriented along which axis of the patient’s body
a. X
b. Y
c. Z
c. Z
which of the following materials is commonly used for passive magnetic shielding within the walls of the MRI room
a. copper
b. iron
c. bismuth
d. lead
b. iron
For adults, what is current FDA guideline limit for exposure to a magnetic field?
a. 8 T
b. 4 T
c. 3 T
d. 7 T
a. 8 Tesla
The biologic effects which is seen as an elevation of the T-wave on ECG tracing when a patient is placed in 1.5 T cylindrical bore magnet is known as:
a. peripheral nerve stimulation
b. teratogenesis
c. magnetohydrodynamic effect
d. magnetophosphene stimulation
c. magnetohydrodynamic effect
rotation or torque forces are greatest
a. when one enters the scan room
b. at isocenter
c. at the foot of the table
b. at isocenter
which of the following materials is commonly used for RF shielding
a. lead
b. iron
c. bismuth
d. copper
d. copper
which of the following coil designs uses 2 elements to produce 2 waveforms 90 degress out of phase with each other
a. linear
b. quadrature
c. multi-channel (phased array)
b. quadrature
the FDA guideline limits SAR for the head to
a. 4.0 W/kg
b. 8.0 W/kg
c. 3.2 W/kg
d 2.0 W/kg
c. 3.2 W/kg
the FDA guideline limits SAR averaged over the whole body
a. 4.0 W/kg
b. 8.0 W/kg
c. 3.2 W/kg
d 2.0 W/kg
a. 4.0 W/kg
the normal operating mode with limit the whole-body SAR average to no greater than
a. 4.0 W/kg
b. 8.0 W/kg
c. 3.2 W/kg
d 2.0 W/kg
d 2.0 W/kg
increasing the flip angle from 45 degrees to 90 will increase SAR by a factor of
a. 2
b. 4
c. 6
d. 8
b. 4
which of the following sequences is of most concern with regard to SAR
a. fast spin echo
b. conventional spin echo
c. echo planar imaging (EPI)
a. fast spin echo
patients can receive burns if their arms are touching the sides of the magnet bore
true or false
true
the primary purpose of the gradient magnetic fields produced by the gradient fields is to
a. reduce SAR
b. reduce acoustic noise
c. spatial encode the MR signals
c. spatial encode the MR signals
the gradient coil which varies the magnetic field along the head to foot direction of the body is annotated
a. x
b. y
c. z
c. z
Slew rate is defined as
a. maximum amplitude plus rise time
b. maximum amplitude divided by rise time
c. rise time multiplied by max amplitude
b. maximum amplitude divided by rise time
