Gradient coils Flashcards
Which of the following has been documented to cause muscle contractions, cardiac arrhythmias, mild cutaneous sensations and visual light flashes
Time varying magnetic fields (gradient)
Which of the following’s primary biological effect is tissue heating/deposition
Oscillating magnetic fields (radiofrequency
The orientation of the main magnetic field in a high field, superconducting, short bore magnet is:
Horizontal
The ____________ is responsible for the knocking noise the system makes while the sequence is in progress.
Rapid change/switching of the magnetic field by the gradient coils
: If a sagittal slice plane has been selected, the __________ is enabled to alter the magnetic field around the patient’s body
X gradient
: If a coronal slice plane has been selected, the __________ is enabled to alter the magnetic field around the patient’s body.
Y gradient
: If a transverse/axial slice plane has been selected, the __________ is enabled to alter the magnetic field around the patient’s body.
Z gradient
The primary biological effect of radiofrequency fields is
Tissue heating
The measurement of radiofrequency absorption is delineated as:
Watts per kilogram
The effects of time varying magnetic fields can include all of the following EXCEPT:
Warmth and/or increase in body temperature
Current FDA limits on time varying magnetic fields are
Once the patient experiences peripheral nerve stimulation
: Which of the following sequences would be more at risk for the effects that time varying magnetic fields can cause
A. SE
B. FSE
C. GE
D. EPI
EPI
The strength of the gradient magnetic fields are measured in:
A. Gauss per centimeter
B. Tesla per echo
C. Watts per kilogram
D. Millitesla per meter
E. A and D
A and D
The gradient rise time is defined as the:
Time it takes for the gradient to reach its full amplitude
The gradient slew rate is the
Rate of speed of ascent or descent of a gradient from zero to its maximum amplitude
The duty cycle is defined as the:
Time the gradients are on during a TR period
RF (radiofrequency) energy is:
Low energy non-ionizing radiation
Magnetic field inhomogeneity is expressed in:
Parts per million
A technique utilized to reduce the MRI scan time which requires the use of an array
: Parallel imaging
Cables from RF coils and gating/trigger leads should be
Braided and positioned straight in the bore
RF heating is more of a concern in ________ sequences.
Fast spin echo
Applying two gradients simultaneously during slice selection would
Produce an oblique slice
Multiple coil elements combined with multiple receiver channels make a:
Phased array coil
The strength of the gradient over a specific distance is known as the:
Slew rate
A coil that is not properly tuned to the correct magnetic field strength will result in:
Signal loss
The coil construction in an MR system, from the innermost aspect to the outer:
: Radiofrequency coils, gradient coils, shim coils, main magnet
A 6 inch surface coil is able to receive signal:
3 inches deep into the patient
When going from a linear coil to a quadrature coil
SNR is increased by 40%
The ______________ is the speed rate of ascent or descent of a gradient from zero to its maximum amplitude, either positive or negative
Slew rate
Utilization of surface coils yields all of the following EXCEPT
Increased FOV capabilty
