Magnetism - Gradient Coils

Question 1

Which of the following has been documented to cause muscle contractions, cardiac arrhythmias, mild cutaneous sensations and visual light flashes?

Answer 1

Time varying magnetic fields (gradient)

Question 2

Which of the following’s primary biological effect is tissue heating/deposition?

Answer 2

Oscillating magnetic fields (radiofrequency)

Question 3

The orientation of the main magnetic field in a high field, superconducting, short bore magnet is:

Answer 3

Horizontal

Right Hand Grip rule – Current passes through electrically induced coil of wire

Question 4

The ____________ is responsible for the knocking noise the system makes while the sequence is in progress.

Answer 4

Rapid change/switching of the magnetic field by the gradient coils

The rapid, successive switching of the gradient coils is the primary cause of the noise in the MR scan room.

Question 5

If a sagittal slice plane has been selected, the __________ is enabled to alter the magnetic field around the patient’s body.

Answer 5

X gradient

Question 6

If a coronal slice plane has been selected, the __________ is enabled to alter the magnetic field around the patient’s body.

Answer 6

Y gradient
Y gradient encodes coronal slice orientation

Question 7

If a transverse/axial slice plane has been selected, the __________ is enabled to alter the magnetic field around the patient’s body.

Answer 7

Z gradient

Z gradient is utilized to acquire axial/transverse images on a patient lying supine/prone in the magnet.

Question 8

The primary biological effect of radiofrequency fields is:

Answer 8

Tissue heating

Question 9

The measurement of radiofrequency absorption is delineated as:

Answer 9

Watts per kilogram

Question 10

The effects of time varying magnetic fields can include all of the following EXCEPT:

Answer 10

Warmth and/or increase in body temperature

The effects of time varying magnetic fields can include peripheral nerve stimulation, acoustic damage/hearing loss, magnetophosphenes (“seeing stars”).

Question 11

Current FDA limits on time varying magnetic fields are:

Answer 11

Once the patient experiences peripheral nerve stimulation

Current FDA guidance limits the Time Rate of Change of Magnetic Field (dB/dt) to levels which do not result in painful peripheral nerve stimulation.

Question 12

Which of the following sequences would be more at risk for the effects that time varying magnetic fields can cause?

Answer 12

EPI

EPI (Echo Planar Imaging) sequences can have more of a detrimental effect on patients with regards to time varying magnetic fields.

Question 13

The strength of the gradient magnetic fields are measured in:

Answer 13

A and D

Question 14

The gradient rise time is defined as the:

Answer 14

Time it takes for the gradient to reach its full amplitude

Question 15

The gradient slew rate is the:

Answer 15

Rate of speed of ascent or descent of a gradient from zero to its maximum amplitude

The gradient slew rate is defined as the rate of speed of ascent or descent of a gradient from zero to its maximum amplitude

Question 16

The duty cycle is defined as the:

Answer 16

Time the gradients are on during a TR period

The duty cycle is defined as the time the gradients are on during a TR period

Question 17

RF (radiofrequency) energy is:

Answer 17

Low energy non-ionizing radiation

Question 18

Magnetic field inhomogeneity is expressed in:

Answer 18

Parts per million

Magnetic field inhomogeneity is expressed in parts per million (ppm)

Question 19

A technique utilized to reduce the MRI scan time which requires the use of an array coil is:

Answer 19

Parallel imaging

Question 20

Utilization of surface coils yields all of the following EXCEPT:

Answer 20

Increased FOV capabilty

Question 21

Cables from RF coils and gating/trigger leads should be:

Answer 21

Braided and positioned straight in the bore

Cables from RF coils and gating leads should be braided and positioned straight in the bore, NEVER in direct contact with the patient’s skin

Question 22

RF heating is more of a concern in ________ sequences.

Answer 22

Fast spin echo

RF heating is more of a concern in fast spin echo sequences due to the multiple echo train lengths, leading to potential increases in tissue heating.

Question 23

Applying two gradients simultaneously during slice selection would:

Answer 23

Produce an oblique slice

Applying two gradients simultaneously during slice selection would produce an oblique slice.

Question 24

Multiple coil elements combined with multiple receiver channels make a:

Answer 24

Phased array coil

A phased array coil is comprised of multiple coil elements combined with multiple receiver channels

Question 25

The strength of the gradient over a specific distance is known as the:

Answer 25

Slew rate

Question 26

A coil that is not properly tuned to the correct magnetic field strength will result in:

Answer 26

Signal loss

A coil that is not properly tuned to the correct magnetic field strength will result in signal loss.

Question 27

The coil construction in an MR system, from the innermost aspect to the outer:

Answer 27

Radiofrequency coils, gradient coils, shim coils, main magnet

The coil construction in an MR system, from the innermost aspect to the outer: Radiofrequency coils, gradient coils, shim coils, main magnet.

Question 28

A 6 inch surface coil is able to receive signal:

Answer 28

3 inches deep into the patient

Question 29

When going from a linear coil to a quadrature coil:

Answer 29

SNR is increased by 40%

When going from a linear coil to a quadrature coil, SNR is increased by 40%.

Question 30

The ______________ is the speed rate of ascent or descent of a gradient from zero to its maximum amplitude, either positive or negative

Answer 30

Slew rate