Fundamentals Of Mri

Front 1

An RF pulse of what flip angle will maximize the component of the net manetization projected into the transverse plane?

Back 1

90 degrees

Front 2

T1 relaxation refers to ___________ relaxation.

Back 2

longitudinal

Front 3

Which of the following statements are false?
a. T1 relaxation refers to the longitudinal recovery of manetization while T2 relaxation refers to the transverse decay of manetization.
b. T1 relaxation and T2 relaxation occur simultaneously.
c. echos collected in the transverse plane demonstrate only T2 relaxation differences.
d. T2 relaxation occurs much more quickly than T1 relaxation.

Back 3

c. echos collected in the transverse plane demonstrate only T2 relaxation differences.

Front 4

If the precessional frequency of the protons net magnetization is approximately 21 MHx a ___ Telsa magnetic field is being experienced by the patient's protons.

Back 4

0.5

Hint 4

* Use the Larmor Equation
f=(y/2n)B
f= resonant or Larmor frequency in MHz
y/2n= Gyromagnetic ratio in MHz/T
B= Magnetic field in Telsa

Front 5

Which of the following is the definition of T1 relaxation?

Back 5

The time it takes the net longiudinal magneization of protons to grow to 63% of its final amplitude.

Front 6

Based on the graph of longitudinal relaxation shown above, which of the following would have the brightes signal intensity on a T1 weighted image?

Back 6

bone marrow

Hint 6

Short T1, bright, highest amplitude

Front 7

Based on the graph of the longitudinal relaxation shown above, which of the following has the shortest T1 relaxation time?

Back 7

Bone marrow

Front 8

The edema associated with pathology in the brain has a much longer T2 relaxation time than surrounding normal brain tissue. On a T2-weighted image, what does this result in?

Back 8

High signal intensity in the area of edema

Front 9

After a 90 degree RF pulse, if three 180 degree pulses are applied to generate three echoes, which of the following is responsible for the third echo being smaller than the first echo?

Back 9

spin spin interactions

Front 10

Which of the following dephasing mechanisms affect the size of the resulting spin echo?

Back 10

spin spin interactions

Front 11

The MR echo is NOT:

Back 11

Collected only one time for given image.

Front 12

What is the time from the initial RF excitation pulse to the echo called?

Back 12

TE (Echo TIME)

Front 13

The proton's _____________ contributes to its magnetic properties.

Back 13

Spinning motion and positive charge

Front 14

Which of the following is TRUE regarding the hydrogen protons in a patient's body when placed in the magnet of an MR system?

Back 14

More protons align with the main magnetic field than against the main magnetic field.

Front 15

On a T2 weighted image, CSF appears bright because it has a ___________ relaxation time.

Back 15

Long T2

Front 16

The precessional frequency of the net magnetization of protons in a magnetic field is determined by which of the following?

Back 16

the gyromagnetic ratio and the field strength

Front 17

The RF pulse should be transmitted at a frequency of approximately _____ MHz in order to disturb protons experiencing a 4 telsa field.

Back 17

170

Hint 17

* 1 Telsa = 42.6

Front 18

Referring to the figure below, if the main magnetic field is aligned along the z-axis which of the following corresponds to the correct orientation of the transverse plane?

Back 18

x-y

Front 19

Which of the following is NOT a requirement for magnetic resonance imaging?

Back 19

ionizing radiation

Front 20

Referring to the image below, if the main magnetic field is aligned along the y axis , which of the following corresponds to the correct orientation of the transverse plane?

Back 20

x-z

Front 21

What is the phenomenon called in which one proton transfers energy to another?

Back 21

a spin spin interaction

Front 22

Which of the following parameters controls the amount of contrast seen in an image due to T2 relaxation?

Back 22

TE (echo time)

Front 23

What is the time from the initial RF excitation pulse to the next RF excitation pulse for a given slice called?

Back 23

TR *initial pulse

***TE *initial echo

Front 24

From a resting state in which the fully relaxed net magnetization is aligned along the longitudinal direction, what would the application of a single 45 degree RF pulse result in?

Back 24

Equal amounts of transverse and longitudinal magnetization

Front 25

Which of the following is the definition of T2 relaxation time?

Back 25

The time at which the transverse magnetization has decayed to 37% of its full value.

Front 26

By increasing the TE from 80ms to 120ms on a spin-echo pulse sequence, which of the following is the expected result?

Back 26

Better tissue contrast based on the tissues T2 characteristics.

Hint 26

Longer TE = higher contast

Front 27

By decreasing the TR from 1000ms to 500ms on a spin echo pulse sequence, which of the following is the expected result?

Back 27

Better tissue contrast based on the tissues T1 characteristics

Hint 27

Short T1= higher contrast

Front 28

If six successive 180 degree RF pulses are applied, following a 90 degree RF pulse, how many echos will be formed?

Back 28

Six

Front 29

If six sucessive 180 degree RF pulses are applied, following a 90 degree RF pulse, echo ______ will contain the GREATEST signal?

Back 29

One

Front 30

After dephasing that results following a 90 degree RF pulse, which of the following RF flip angles maximizes the component of the net magnetization in the transverse plane at the time of the spin echo?

Back 30

180 degree

Front 31

Using a spin echo pulse sequence which generates two echoes, imaging a hypothetical tissue in whch the protons never experience spin-spin interactions. How does thhe signal from the first echo compare to the signal from the second echo?

Back 31

It is the same size

Front 32

What is the time from the 180 degree RF pulse to the echo?

Back 32

0.5 x TE

*The 180 degree pulse is placed exactly half way between the time of the 90 degree pulse and the desired echo time.

Front 33

The time from the 90 degree pulse to the echo is the:

Back 33

TE

Front 34

The time from the 90 degree pulse to the next 90 degree pulse is:

Back 34

TR

Front 35

Which of the following dephasing mechanisms is NOT rephased by a 180 degree RF pulse?

Back 35

Spin spin interactions

*The 180 degree RF pulse rephases the signal losses caused by a number of dephasing mechanisms because it creates an equal but opposite effect on the spin behavior of protons. The 180 degree pulse cannot recover signal losses due to the dephasing mechanism that forms the basis of T2 weighted imaging.

Front 36

Which of the following parameters controls the amount of contrast seen in an image due to T2 relaxation?

Back 36

TE

Front 37

The effect of an IV administered paramagnetic contrast agent used in MRI is a shortening of the T1 relaxation time of the protons within any perfused tissue. A vascular lesion would appear ________________ on a T1 weighted contrast enhanced image as compared to its appearance on a T1 weighted unenhanced image.

Back 37

Brighter

*The introduction of a contrast agent which further shortens the T1 time of blood will make perfused tissues appear like shorter T1 tissues. Short T1 has higher contrast between tissues.

Front 38

In a given MR system, the magnetization of protons within a patient precesses at 63.83 MHz. Without the interference of any other system component, what is the expected result if RF energy is applied at a frequency of 63.83 MHz?

Back 38

All of fthe patient's protons within the range of the transmitting antenna will be disturbed by the external energy.

Hint 38

Since their are no other interference of any other system components... their are NO gradient pulses applied. The only source of energy is the MR system.

Front 39

If the field strength experienced by a patient within an MR magnet is increased, the precessional frequency of the magnetization of the patient's protons will:

Back 39

Increase

Front 40

The energy used to form MR images is _______________ the patient's tissues.

Back 40

Released from

Front 41

The image shown is an example of what type of contrast?

Back 41

T1

*These conditions are created by using a short TR which prevents the longitudinal magnetization to recover in tissues with long T1 times.

Hint 41

T1 fluid is dark
Tissues are intermediate shade of gray
Fat is bright

Front 42

As an MR technologist, which of the following occurs as you walk toward the MR magnet to position a patient?

Back 42

1. The net magnetization within your body increases
2. The precessional frequency of the protons magnetization within your body increases.

Front 43

T1 relaxation is also called:

Back 43

Spin lattice relaxation

*This is because the energy which is released by the protons is received by the surrounding molecular lattice.

Front 44

T2 relaxation is also called:

Back 44

Spin spin relaxation

*This is because the energy is released by a proton (or spin) as it interacts with another proton causing it ot lose some of its phase in the transverse plane.

Front 45

In the vast majority of tissues T2 time is shorter than the T1 time. T/F?

Back 45

True

Front 46

In a T1 weighted image the signal contributed by the tissue with the shortest T1 generally will be stronger than that contributed by the other tissue an will appear __________ on the reconstructed image..

Back 46

Brighter

Hint 46

*Bone marrow is fat based.

Front 47

The tissues which demonstrates the most rapid recovery of the longitudinal magnetization has the _________ T1 relaxation time.

Back 47

Shortest

Front 48

Substances with a long T2 relaxation time exhibit a lower rate of spin-spin interactions, and this results in a slower loss of transverse magnetization. The consequence of this is that the strength of the echo in the transverse plane persists at _______ TE times in substances which have _____ T2 relaxation times.

Back 48

Long

Front 49

The loss of signal due to the spin spin interaction cannot be prevented since the spin spin interaction is an inherent irreversable process which can be experienced by every proton. T/F?

Back 49

True

*In other words, the 180 degree RF pulse cannot revert the loss of signal caused by spin spin interactions.

Front 50

Magnetic suseptibility, phase effect of chemical shift, and field inhomogenities are present in gradient echo images but not is spin echo images because gradient echo pulse sequences do not enjoy the rephasing effects of:

Back 50

The 180 degree RF pulse.

Front 51

The number of echoes collected is equal to:

Back 51

The size of the acquisition matrix along the phase encoding direction.

Front 52

TI is:

Back 52

The time between the initial 180 degree RF pulse and the 90 degree excitation pulse in an INVERSION RECOVERY sequence.

Front 53

TE is:

Back 53

The time between the RF excitiation pulse and the center of the echo.

Front 54

TR is:

Back 54

The time between successive RF excitation pulses.