Physics Midterm

Question 1

Once a slice is selected, the signal is located or encoded along both axes of the image.

Answer 1

True

Question 2

Gradients alter the external magnetic field in a nonlinear fashion.

Answer 2

False

Question 3

Spatial encoding is achieved by:

Answer 3

Gradients

Question 4

The position of a nucleus along a gradient can be identified according to its precessional frequency.

Answer 4

True

Question 5

If the gradient field adds to the external magnetic field, the precessional frequency of nuclei slow down.

Answer 5

False

Question 6

In a typical super conducting machine, which gradient affects the long axis of the magnet?

Answer 6

Z gradient

Question 7

Permanent magnets have different axes than superconducting magnets.

Answer 7

True

Question 8

Steep gradient slopes alter the precessional frequency of nuclei between two points, more than shallow gradient slopes.

Answer 8

True

Question 9

Locating a slice within the scan plane is termed:

Answer 9

Slice selection

Question 10

Spatially locating signal along the short axis of anatomy is called:

Answer 10

Phase encoding

Question 11

Spatially locating signal along the long axis of anatomy is called:

Answer 11

Frequency encoding

Question 12

Typically, which gradient selects axial slices?

Answer 12

Z gradient

Question 13

Typically, which gradient selects sagittal slices?

Answer 13

X gradient

Question 14

Typically, which gradient selects coronal slices?

Answer 14

Y gradient

Question 15

To achieve thin slices, a shallow slice select slope and/or broad transmit bandwidth is applied.

Answer 15

False

Question 16

In coronal and sagittal images, the long axis of the anatomy lies along the
Z axis of the magnet and therefore, the Z gradient performs frequency encoding.

Answer 16

True

Question 17

The size of the anatomy covered during a scan is referred to as the:

Answer 17

Field of View (FOV)

Question 18

All things are made up of:

Answer 18

Atoms

Question 19

The most abundant atom in the body is:

Answer 19

Hydrogen

Question 20

Two or more molecules arranged together are known as an atom.

Answer 20

False

Question 21

The abundance of hydrogen in the human body is found in molecules of water and fat.

Answer 21

True

Question 22

The mass of an atom comes mostly from its:

Answer 22

Nucleons

Question 23

The mass number is the sum of the protons in the nucleus.

Answer 23

False

Question 24

Atoms of elements with the same number of protons but a different number of neutrons are called:

Answer 24

Isotopes

Question 25

_________________ spin around the nucleus.

Answer 25

Electrons

Question 26

The nucleus itself spinning about its own axis, in nuclei with an ____________ mass number.

Answer 26

Odd

Question 27

In nuclei with odd mass numbers, spin directions are equal and opposite.

Answer 27

False

Question 28

MR active nuclei have ________________ mass numbers.

Answer 28

Odd

Question 29

Faradays’s Law of induction states that if two of three forces (motion, magnetism, and charge) are present, then the third is automatically induced.

Answer 29

True

Question 30

The mass number of Hydrogen is:

Answer 30

1

Question 31

The isotope of the hydrogen nucleus that is the MR active nucleus used in clinical MRI is called:

Answer 31

Protium

Question 32

The magnet of each hydrogen nucleus has a North and a South Pole of equal strength.

Answer 32

True

Question 33

The direction of a vector designates the size of the magnetic moment and the length of the vector designates the direction of the magnetic moment.

Answer 33

False

Question 34

In the absence of an applied magnetic field, the magnetic moments of the hydrogen nuclei are randomly orientated.

Answer 34

True

Question 35

When placed in a strong static external magnetic field, the magnetic moments of the hydrogen nuclei align with this magnetic field, both parallel and anti-parallel.

Answer 35

True

Question 36

Low-energy nuclei align their magnetic moments parallel to the external field and are termed spin-down nuclei.

Answer 36

False

Question 37

It is the strength of the external magnetic field that determines the relative quantities of spin-up to spin-down nuclei.

Answer 37

True

Question 38

The secondary spin caused by the influence of an external magnetic field is called precession.

Answer 38

True

Question 39

1 MHz is equal to:

Answer 39

One Million Cycles per Second

Question 40

ω0 = B₀ץ is the:

Answer 40

Larmor Equation

Question 41

At 1.0 the precessional frequency of hydrogen is:

Answer 41

42.57 MHz

Question 42

________________ is a phenomenon that occurs when an object is exposed to an oscillating perturbation that has a frequency close to its own natural frequency of oscillation.

Answer 42

Resonance

Question 43

For resonance of hydrogen to occur, an RF pulse of energy at exactly the Larmor frequency of hydrogen must be applied.

Answer 43

True

Question 44

The application of an RF pulse that causes resonance to occur is termed:

Answer 44

Excitation

Question 45

The angle to which the NMV moves out of alignment is called the:

Answer 45

Flip Angle

Question 46

B₀ is termed the transverse plane and the plane at 90° to B₀ is termed the longitudinal plane.

Answer 46

False

Question 47

Frequency is the position of each magnetic moment on the precessional path around B₀

Answer 47

False

Question 48

The MR signal is produced when coherent (in phase) magnetization cuts across the coil.

Answer 48

True

Question 49

The process by which hydrogen loses this energy is called excitation.

Answer 49

False

Question 50

The induction of reduced signal in the receiver coil is called the free induction decay (FID) signal.

Answer 50

True

Question 51

The recovery of longitudinal magnetization is caused by a process termed T1 recovery and the decay of transverse magnetization is caused by a process termed T2 decay.

Answer 51

True

Question 52

T1 recovery is caused by the nuclei giving up their energy to the surrounding environment or lattice, and it is termed spin lattice relaxation.

Answer 52

True

Question 53

T2 relaxation time is the time it takes 63% of the transverse magnetization to be lost.

Answer 53

True

Question 54

TR is the time from the application of the RF pulse to the peak of the signal induced in the coil and is also measured in milliseconds.

Answer 54

False

Question 55

TE controls the amount of T2 relaxation that has occurred when the signal is read.

Answer 55

True

Question 56

Extrinsic contrast parameters are those that cannot be changed because they are inherent to the body’s tissues.

Answer 56

False

Question 57

T1 recovery time, T2 decay time, proton density, flow, and apparent diffusion coefficient (ADC) are examples of intrinsic contrast parameters.

Answer 57

True

Question 58

TR, TE, flip angle, T1, turbo factor/echo train length, and b value are examples of extrinsic contrast parameters.

Answer 58

True

Question 59

A tissue with high signal appears dark on an image.

Answer 59

False

Question 60

The lower the proton density of a tissue, the more signal available from that tissue.

Answer 60

False

Question 61

Generally, the two extremes of contrast in MRI are fat and water.

Answer 61

True

Question 62

Hydrogen in fat recovers more rapidly along the longitudinal axis than water and loses transverse magnetization faster than in water.

Answer 62

True

Question 63

The NMV of fat realigns rapidly with B₀ so the T1 time of fat is long.

Answer 63

False

Question 64

T2 decay in water is less efficient than in fat.

Answer 64

True

Question 65

On T1 weighted images, fat is bright and water is dark.

Answer 65

True

Question 66

On T2 weighted images, fat is dark and water is bright.

Answer 66

True

Question 67

PD weighted images are characterized by areas with high proton density (dark) and areas with low proton density (bright).

Answer 67

False

Question 68

To achieve T1 weighting, the TR must be short enough so that neither fat nor water has sufficient time to fully return to B₀

Answer 68

True

Question 69

The TE controls the amount of T2 decay that is allowed to occur before the signal is received.

Answer 69

True

Question 70

To achieve PD weighting, the effects of T1 and T2 contrast must be diminished so that PD weighting can dominate.

Answer 70

True

Question 71

Inhomogeneities are areas within the magnetic field that do not exactly match the external magnetic field strength.

Answer 71

True

Question 72

T2* decay happens in part because of dephasing due to magnetic field inhomogeneities.

Answer 72

True

Question 73

Sequences that use a 180° pulse to regenerate signal are called gradient echo pulse sequences; those that use a gradient are called spin echo pulse sequences.

Answer 73

False

Question 74

The spin echo pulse sequences commonly uses a 90° excitation pulse to flip the NMV into the transverse plane.

Answer 74

True

Question 75

In a spin echo sequence, TR is the time between each 90° excitation pulse for each slice and TE is the time between the 90° excitation and the peak of the spin echo.

Answer 75

True

Question 76

A gradient echo sequence flips the NMV through 90° angle.

Answer 76

False

Question 77

The middle of the axis of the gradients remains at the field strength of the main magnetic field, which is known as isocenter.

Answer 77

True

Question 78

Since gradients rephase slower than 180° RF pulses, the minimum TE is much shorter than in spin echo pulse sequences, and so the TR must be increased.

Answer 78

False

Question 79

Gradient echo pulse sequences are very susceptible to magnetic field homogeneities.

Answer 79

True

Question 80

In gradient echo sequences, the flip angle is an extrinsic contrast parameter that is changed to affect image contrast.

Answer 80

True

Question 81

The units are K space are:

Answer 81

Radians per cm

Question 82

Positive polarity gradients fill the _____________ half of K space.

Answer 82

Top

Question 83

Which lines are filled by the shallow slopes of K space?

Answer 83

Shallow

Question 84

Data acquired in the central lines contributes to?

Answer 84

Signal and Contrast

Question 85

Data acquired in the outer lines contribute to contrast.

Answer 85

False