Chapter 2 Questions

Front 1

In a vertical magnet which axis corresponds to the longitudinal direction, if the patient is in a head first supine position?

Back 1

Y

Front 2

The magnetization of protons A makes one revolution of its precessional motion every 0.030 microseconds. The magnetization of proton B makes one revolutoin of its precessional motion every 0.015 microseconds, Therefore the frequency of the magnetization of proton A is ____________ the frequency of proton B.

Back 2

One half

Front 3

In the standard pulse sequence described so far in this program, to completely phase encode a single slice, how many TR periods are required?

Back 3

As many TR periods as phase lines in the resulting image matrix.

*Note: The size of the image matrix along the FREQUENCY encoding direction is independent of the phase encoding process and is determined by the number of data points into which each echo is digitized after it is recorded during the frequency encoding process.

Front 4

During a six minute conventional scan, when is the data collected that is used to form the lower third of the image?

Back 4

Throughout the entire scan

Front 5

Using a traditional pulse sequence, which of the following is FALSE regarding a single echo?

Back 5

It contains the anatomical information from a specific line of the resulting image.

*It contributes to the entire image.

Front 6

Along what direction are motion artifacts always seen?

Back 6

Along the phase direction of the image

Front 7

Along what direction are chemical shift artifacts always seen?

Back 7

Along the frequency direction of the image.

Hint 7

Chemical shift is the inherent differences in precessional frequencies in fat-based vs. water based protons within the same magnetic field.

Front 8

In order to disturb the protons in a particular location of the body, what must the frequency of the RF energy be?

Back 8

Matched to the precessional frequency of the patient's protons at that location.

Front 9

What is the reason that chemical shift does not create phase error?

Back 9

In any imaging technique that uses a 180 degree RF rephasing pulse the phase errors induced by by chemical shift are negated and are not present in the image.

Front 10

Which physical gradient must be used for slice selection in order to produce a coronal image?

Back 10

Y

Front 11

Which physical gradient could be used for phase encoding in a sagittal image?

Back 11

X

Front 12

A positive change in frequency followed by an equal negative change in frequency, both for the same duration will ______ the net phase of stationary protons.

Back 12

Have no effect on

Hint 12

Change in frequency results in a change of the net phase.

Front 13

Which of the following is a linear varying magnetic field?

Back 13

A gradient

Front 14

Which of the following gradients is NOT balanced for phase?

Back 14

Phase encoding

Front 15

Which physical gradient must be used for slice selection in order to produce a sagittal image?

Back 15

X

Front 16

In a 1.0 T MR system which of the followig sttatements is FALSE regarding the RF energy if no gradient is applied while a 42.56 MHz 90 degree pulse is being transmitted?

Back 16

It will be absorbed by only the protons at the center of the magnet.

*If a 90 degree RF pulse is delievered, transverse magnetization will be created in this entire population of protons which are within range of the transmitting antenna. Such RF excitation therefore, is not limited to those protons only at the center of the magnet.

Front 17

The select slice gradient must be turned on during which of the following events?

Back 17

Application of the RF energy

Front 18

What happens during the frequency encoding gradient?

Back 18

Readout echo

Front 19

Phase encoding gradient is applied during:

Back 19

Phase encoding step

Front 20

Spin spin interactions begin to occur:

Back 20

Immediately after the application of the RF excitiation pulse is applied to that slice.

Front 21

Which of the following is NOT determined by the slice select process?

Back 21

Field of view

Front 22

Which of the following has an effect on the resulting slice thickness?

Back 22

The range of frequencies encoded in the echo.

Front 23

Slice position is determined by:

Back 23

The center precessional frequency of the RF excitation pulse in combination with the strength of the slice select gradient.

Front 24

Slice orientation is determined by:

Back 24

The axis of the physcial gradient that is applied.

Front 25

The slice thickness is determined by:

Back 25

The frequency content (bandwidth) of the RF excitation pulse in combination with the strength of the slice select gradient.

Front 26

To make an oblique image which is oriented at an angle between transverse and coronal, which of the following physical gradients must be applied for slice select selection?

Back 26

Y and Z together

Front 27

Given a sagittal image, which of the following statements is ALWAYS TRUE?

Back 27

Slice selection was accomplished with the X gradient

Front 28

The frequency encoding gradient must be turned on during which of the following events?

Back 28

Readout of the echo

Front 29

Gradients are responsible for ensuring that all of the protons in the body simultaneously receive the RF energy, T/F?

Back 29

False

*Gradients are responsible for ensuring that only selected protons in the body are excited by the RF energy.

Front 30

Which of the following is TRUE regarding the Fourier Transform?

Back 30

It separates the phase and frequency components corresponding to each point of anatomy in the image plane.

Front 31

Decreasing the slice gradient amplitude will have what affect on the resulting slice if the RF transmitter bandwidth is held constant?

Back 31

Increases the slice thickness

*Has an inverse relationship

Front 32

On a coronal image, if frequency encoding is accomplished with the z-gradient, which physical gradient is used for phase encoding?

Back 32

Y

Front 33

If the Z-gradient is applied, which of the following statements is TRUE regarding a patient's protons?

Back 33

Those is the patient's feet precess at the same frequency as those in the patient's head.

Front 34

On a sagittal image, which logical gradient is assigned to the x-gradient?

Back 34

Slice select

Hint 34

*During the application of RF energy

Front 35

The phase encoding gradient must be turned on during which of the following events?

Back 35

Prior to the echo collection, but the exact timing is not critical.

Front 36

What effect will an applied gradient have on a population of stationary, in-phase protons within a 10 cm sphere at the center of the magnet?

Back 36

It will increase the phase dispersion.

Front 37

Which of the following is contained within a single spin echo?

Back 37

Many frequencies

Hint 37

A single spin echo is recorded during the application of the readout, or frequency encoding gradient.

Front 38

If a population of protons move through some distance during the time the echo is being sampled, what will be the apperance of the resulting image, provided that the gradients are operating properly for a simple spin echo sequence?

Back 38

Artifacts will appear in the phase.

Front 39

If a proton moved along the direction of an increasing gradient, its rate of precession would:

Back 39

Increase

*Beacuse it is moving toward the stonger magnetic field

Front 40

A given MR system claims it maximum gradient amplitude is 30mT/meter. Imagine an ideal case in which the filed strength at all paints inside the magnet is 1.500 T. If a pulse sequence drives the z-gradient to its maximum amplitude, the field strength at the center of the magnet is _______ Telsa.

Back 40

1.500

Magnetic strength at the center of the magnet always remains the same.

Front 41

In an ideal 0.2 T magnet with perfect homogeneity, if the y-gradient amplitude is 7 mT/m and a proton's magnetization has a precessional frequency of 8.62 MHz, the proton's approximate displacement along the y-direction is ____ cm. (Assume to gyromagnetic ratio equals 42.56)

Back 41

36

Hint 41

f= (y/2n) x (Bo + (D x G / 1000))

Front 42

In regards to the Fourier Transform, determine if these statements are True or False:
>It shuttles the collected echoes into the raw data file where they may be post processed.
>It separates the phase and frequency components corresponding to each point of anatomy in the image.
>It calculates the amount of energy absorption experienced by each tissue and generates the final image.

Back 42

The SECOND statement is True.

*The purpose of the Fourier Transform is to perform a calculation on the MR echo, or raw data in order to create the phase and frequency "map" which we call the MR image. In the process of creating the image the Fourier Transform separates the phase and frequency components of the echo data and in the process enables us to view the contrast information which corresponds to each point of anatomy in the image.

Front 43

Which of the following is NOT an essential part of localizing the MR signal generated during an MR study?

Back 43

Moving the patient within the magnet to ensure only the center slice is imaged.

Front 44

A given MR system claims its maximum gradient amplitude is 30 mT/meter. Imagine and ideal case in which the field strength at all points inside the magnet is 1.500 T. If a pulse sequence drives the x-gradient to its maximum amplitude, the feild strength at a point which is centered along the x-direction and displaced one meter toward the positive z-direction is ___________ Telsa.

Back 44

1.530

Front 45

If a population of protons moves through some distance during the time the 90 degree RF pulse is applied, what will be the appearance of the resulting image, provided that the gradients are operating properly for a simple spin echo pulse sequence?

Back 45

Artifacts will appear in the phase encoding direction of the image.

Front 46

Which gradient will make the precessional frequency of the magnetization of protons in the patient's left eye different than that in the patient's right heel?

Back 46

x, y, or the z.

*The patient's left eye is in a differnt plane that the patient's right heel.

Front 47

In an ideal 1.0 T magnet with perfect homogeneity, if a proton experiences a magnetic field of 1.006 T and is positioned 0.5 meter along the positive z-direction and centered along the positive z-direction and amplitude is _______mT/m.

Back 47

12

* The effect of the gradient on the magnetic field strength experienced by the proton is 1.006 T - 1.000 T = 0.006 T or 6mT. If the proton experiences a gradient induced shift in magnetic field of 6 mT at 0.5 meters from center, then the gradient firld strength is: gradient strength = magnetic field strength divided by distance from center.

Front 48

In an ideal 1.5 T magnet with perfect homogeneity, if a proton experiences a magnetic field of 1.504 T and the x-gradient amplitude is 16mT/m, the displacement of the proton along the x-direction is _____ cm.

Back 48

25

*The effect of the gradient on the magnetic field strength experienced by the proton is 1.504 T - 1.500 T = 0.004 mT. If the gradient strength is 16mT/m and the proton experiences 4 mT, then we can calculate the proton's location as follows: 4mT/(proton's location) = 4 mT/16 mT * 1 meter.