Fundamentals of MRI Physics

Question 1

What is the precessional frequency constant of hydrogen

Answer 1

Gyromagnetic ratio

42.6

Question 2

In order for T1 relaxation to achieve a significant amplitude, it must reach a rate of ____%

Answer 2

63%

Question 3

Formula for Gradient Field Variation

Answer 3

STRONGER:
B(+)= B0 + (G x D/ 1,000)

WEAKER:
B(-)= B0 - (G x D/ 1,000)

Magnetic strength B0
Gradient strength G
Distance from the center of the magnet D

Question 4

What is the strongest magnetic field that can be measured in a 3 Tesla magnet, 6 meters from the center of the magnet when a 6 mT/m gradient pulse is applied?

Answer 4

3.036

B(+)= B0 + (G x D/ 1,000)

B+ = 3 + (6 x 6/1000)
B+ = 3 + 0.036
B+= 3.036

Question 5

An RF pulse can only flip the net magnetization of hydrogen from the longitudinal to the transverse direction if the __________ and __________ share the same exact energy value.

Answer 5

RF pulse application and precessional frequency

Question 6

An RF pulse would be considered

Answer 6

Low energy, non-ionizing radiation

Question 7

The longitudinal direction can also be referred to as:

Answer 7

• Net magnetization aligned with B0

- perpendicular direction to the transverse direction

Question 8

When applying an x - gradient pulse, there are ______ and ______ variations in the magnetic field along a sagittal plane.

Answer 8

Weak and strong

Question 9

The Y - gradient creates linear variations in an anterior and posterior direction resulting in _______ imaging capabilities.

Answer 9

Coronal

Question 10

The accumulated amount of low thermal energy protons that align with the external static magnetic field is known as:

Answer 10

Net magnetization vector

Question 11

What is the weaker magnetic field variation that can be measured in 1.5 Tesla magnet, 3 meters from the center of the magnet when a 6 mT/m gradient pulse is applied?

Answer 11

1.482

B(-)= B0 - (G x D/ 1,000) 
B-= 1.5 - (6 x3/1000)
B-= 1.5 - 0.018
B- = 1.482

Question 12

Gradient strength or amplitude are measured in:

Answer 12

MilliTesla/meter

mT/m

Question 13

When randomly arranged low energy protons enter the magnetic field they become static and _______ with the magnetic field direction or net magnetization.

Answer 13

Parallel

Question 14

On a T1 weighted scale of brightness, which combination will be correct from brightest to darkest?

Answer 14

Fat, muscle, CSF

Question 15

If the precessional frequency is 42.6 MHz, what were the magnetic strength of the magnet be?

Answer 15

1.0T

Question 16

True or false
The ability to pinpoint an exact location within a patient’s anatomy with the use of gradient variation coils is referred to as spacial localization.

Answer 16

True

Question 17

As different tissue such as fat and water begin to de-phase, or fall out of phase, spin-spin interactions must reach an amplitude of ____% to be considered T2 weighted.

Answer 17

37%

Question 18

True or false

During T1 relaxation fat relaxes faster than water.

Answer 18

True

Question 19

What would the net magnetizations precessional frequency of a hydrogen atom be in an MRI machine with a magnetic field strength of 3.0?

Answer 19

127. 8 MHz

42. 6 x 3