Chapter 3

Question 1

The gradient subsystem consists of

Answer 1

the gradient coils and gradient amplifiers which provide power to the coils

Question 2

Gradient

Answer 2

defined as a slope and also as a measure of change in a physical quantity over distance

Question 3

gradient magnetic field

Answer 3

a magnetic field that varies in intensity (or strength) over distance

Question 4

the gradient magnetic fields are produced by

Answer 4

the gradient coils superimposed over the main static magnetic field

Question 5

What is the primary purpose of gradient fields/coils?

Answer 5

to provide for the spatial encoding and localization of the MR signals

Question 6

There are how many sets of gradient coils?

Answer 6

3
-each coil produces a gradient magnetic field oriented along 1 of the 3 orthogonal axes of the body

Question 7

the gradient coil which produces a gradient field along the head to foot direction of the body is referred to as the

Answer 7

Z gradient coil

Question 8

the gradient coil which produces a gradient field along the anterior to posterior direction of the body is referred to as the

Answer 8

Y gradient coil

Question 9

the gradient coil which produces a gradient field along the right to left direction of the body is referred to as the

Answer 9

X gradient coil

Question 10

The gradient fields not only vary in strength over distance but also vary in

Answer 10

time.
they are switched on and off very rapidly during the imaging process and are responsible for the sounds heard during a scan

Question 11

whether the gradient is positive or negative is referred to

Answer 11

as it’s polarity

Question 12

What is maximum amplitude?

Answer 12

the maximum slope to which the gradient field rises

Question 13

High amplitude gradient magnetic fields are required for:

Answer 13

thin slices and small FOV

Question 14

What is rise time?

Answer 14

the time required for the gradient to reach its maximum amplitude

Question 15

What is Slew Rate?

Answer 15

a way to express both the maximum amplitude and the rise time is the slew rate which is the max amplitude divided by the rise time

Question 16

Slew Rate formula

Answer 16

Slew rate = max amp / rise time
(T/m/sec)

Question 17

rise time is expressed in

Answer 17

units of microseconds

Question 18

max amplitude is expressed in

Answer 18

units of millitesla per meter (mT/m)

Question 19

slew rate is expressed in

Answer 19

units of tesla per meter per second
T/m/sec (Tesla per metre per second)

Question 20

What is one of the loudest MRI sequences?

Answer 20

Echo Planar Imaging (EPI)
can easily reach and exceed levels of 120 dB

Question 21

Gradient acoustic noise is greater the ____the gradients switch

Answer 21

faster

Question 22

Faraday’s Law of Induction states

Answer 22

if you move or change a magnetic field over time in presence of a loop of conductive material you will induce a current in that conductive loop

Question 23

As the gradient magnetic fields change rapidly over time,

Answer 23

they can produce significant current in loops of conductive material.

Question 24

Care should be taken not to form ________ with surface coil wires or have the wire touch the patient

Answer 24

large loops

Question 25

The patient should be positioned so that they do not:

Answer 25

cross or hold their hands nor should they cross their ankles. this prevents skin to skin contact but will also eliminate the formation of loop. this is done to prevent peripheral nerve stimulation

Question 26

The faster the gradients switch, the ____possibility of PNS

Answer 26

greater

Question 27

True or false: FDA guidelines state: No painful nerve stimulation

Answer 27

True -avoid large conductive loops (surface coil wires or ECG leads) -avoid patient loops (grasping wrist/fingers, crossing ankles, or wires touching patients)