Principles of MR, Relaxation Time T1&T2, Spatial Encoding & K Space

Spin

Hydrogen nuclei have a magnetic moment because they have what properties?

Spin

Spin & Charge

Low Mass Number

Charge

Faraday's Law

The law that explains the relationship between a moving electrical field and the creation of a magnetic field is __________.

Mansfield's Law

Faraday's Law

Ohm's Law

Einstein's Law

Magnitude & Direction

To be a vector you need a __________.

Magnitude, Direction, & Time

Direction

Time

Magnitude & Direction

Net Magnetization Vector (NMV)

The difference between the number of parallel and anti-parallel spins is known as the __________.

Gyromagnetic Ratio

Frequency

Phase

Net Magnetization Vector (NMV)

Larmor Frequency

In order for resonance to occur for Hydrogen, the radio frequency (RF) excitation pulse must match the __________.

Gyromagnetic Ratio

Signal to Noise Ratio & Gyromagnetic Ratio

Larmor Frequency

Larmor Frequency & Gyromagnetic Ratio

Net Magnetization Vector (NMV)

The __________ is the loss or decay of the MRI signal after the excitation RF pulse is turned off.

Net Magnetization Vector (NMV)

Free Induction Decay (FID)

Larmor Frequency

Amplitude

has a specific value.

The gyromagnetic ratio for a given nucleus

has a specific value.

is determined by the magnetic field

varies with the frequency of precession

has units of tesla per megahertz

Bloch's Equations

Because the nucleus spins on an imaginary axis, has an associated magnetic field. This magnetic field is called MAGNETIC MOMENT

Mansfield's Law

Faraday's Law

Larmor Equation

Bloch's Equations

gyromagnetic ratio per Tesla

In the Larmor equation, gamma (g) is the

gyromagnetic ratio per Tesla

gyromagnetic ratio in megahertz per Tesla

gyromagnetic ratio in megahertz

frequency of precession in megahertz

magnetic intensity in Tesla

In the Larmor equation the B is the

gyromagnetic ratio in megahertz

magnetic intensity in Tesla

frequency of precession in megahertz

magnetic field intensity in megahertz per Tesla

42 MHz/T

The gyromagnetic ratio of hydrogen has a value of approximately

42 MHz/T

13 Mhz/T

21

w = g ß0

The Larmor equation is best stated as

w = g ß0

wg = B

wB = g

wgB = 1

be random.

In the absence of an external magnetic field, the direction of a nuclear magnetic moment will:

be random.

be straight up.

be straight down

Spin

63 megahertz

A 1.5 Tesla MR imager has an operating frequency of:

63 megahertz

11 megahertz

21megahertz

42 megahertz

align over time

When tissue is placed in an external magnetic field, individual nuclear magnetic moments:

align over time

align instantly

become unaligned.

are unaffected.

are arranged randomly

When NMV equals zero, this indicates that nuclear magnetic moments

are arranged randomly

are arranged parallel

are arranged opposite

have disappeared.

sum of nuclear magnetic moments

Net magnetization is defined as the

number of nuclei in a voxel

sum of nuclear magnetic moments

number of nuclei in a patient

total number of spins

value of zero

In the absence of an external magnetic field, net magnetization has a

value that varies.

maximum value

value of zero

minimum value

It is measurable

NET MAGNETIZATION VECTOR (NMV)

It is measurable

It aligns in the same direction as the main magnetic field.

It represents M0.

All above

A and B

PRECESSION is

Spinning of nuclei because of B0 force

is secondary spin of magnetic moment around B0.

A and B

NONE

nuclear magnetic moment

The magnetic field associated with nucleus of the hydrogen is termed:

gyromagnetic field

nuclear magnetic field

gyromagnetic moment

nuclear magnetic moment

a 90° RF pulse

The maximum MRI signal is produced following

a 0° RF pulse

a 90° RF pulse

an alpha RF pulse

a 180° RF pulse

deliver an RF pulse at the specific processional frequency

EXCITATION IS

Alignment to B0

deliver an RF pulse at the specific processional frequency

Flipping to Z

All above

absorb energy and precess in phase

An RF pulse causes individual spins to

absorb energy and precess in phase

release energy precess out of phase

release energy and precess in phase

absorb energy and preccess out of phase

A and B

THE RESULT OF EXCITATION IS

The NMV moves out of alignment.

All the spins precess in phase.

A and B

NONE

flip

An RF pulse causes net magnetization to:

flip

shrink

grow

disappear

the sum

Net magnetization is the result of ______ individual spins

the sum

the difference

the precession

the relaxation

remains at 0

90° RF pulse, Mz

relaxes to M0

remains at 0

remains at M0

relaxes to 0

RELAXATION

process by which H+ loses energy

EXCITATION

RELAXATION

ALIGNMENT

FID remains at 0

All above

what is the result of relaxation

NMV returns to realign (regrow) with B0 (longitudinal plane)

NMV returns to realign (regrow) with B0 (longitudinal plane)

Magnitude of Transverse coherent magnetization decreases

All above

precess in phase

Following 90° RF pulse, the net magnetization vector precess because individual spins:

precess out of phase

precess in phase

are partially saturated

are at equilibrium.

CSF

Which of the following tissue has the longest T1 relaxation time?

CSF

FAT

brain

muscle

rapidly at first, then slows down

T1 relaxation occurs

rapidly at first, then slows down

is contestant.

slowly at first, then speeds up

is discontinuous.

longitudinal relaxation

T1 relaxation time is also known as:

spin density

transverse relaxation

precession

longitudinal relaxation

M0 to return to equilibrium.

T1 relaxation time is related to the time required for:

M0 to return to equilibrium.

Mxy to return to equilibrium

transverse saturation

longitudinal saturation

T2 relaxation

Relaxation of transverse magnetization is controlled by:

precession

spin density

T1 relaxation

T2 relaxation

XY

Transverse relaxation occurs in the _______ plane

XZ

YZ

XY

ZO

Mxy

Transverse magnetization is symbolized by

Bo

Mxy

Mo

Mz

T1 relaxation

The time it takes for 63% of the longitudinal magnetization to recover in tissue

T2 relaxation

spin density

T1 relaxation

precession

T2 relaxation

The time it takes for 63% of the transverse magnetization to dephase

T2 relaxation

spin density

T1 relaxation

Precession

A and B

T2 caused by

the magnetic field of neighboring hydrogen nuclei interacting with each other

Inhomogeneities in the B0 field

A and B

NONE

seconds, hertz

When representation in the time domain is transformed into the frequency domain: units are transformed from _____ to ______

seconds, hertz

hertz, seconds

millimeters, millimeter -1

millimeter-1 , millimeters

inverse Fourier transform

the symbol FT stands for Fourier transform, the symbol

FT-1 stands for:

negative Fourier transform

inverse Fourier transform

imaginary Fourier transform

real Fourier transform

fast Fourier transform

The abbreviation FFT stands for

fudged Fourier transform.

final Fourier transform

first Fourier transform

fast Fourier transform

???

gradient coil use

Transform RF signal

Homogeneity of main magnet

To locate individual signals

None

True

Spatial encoding is a process in MRI that allows the creation of detailed images by spatially mapping the signals emanating from tissues

True

False

False

There are typically FORE gradient coils in an MRI system

True

False

A & B

k-space is

mathematical space

represent the spatial frequencies of the signals

NONE

A and B

special frequency domain

K space is

intensity domain

special frequency domain

time domain

phase domain

True

During the scan, data acquired and stored in k space

True

False

spatial frequency and phase

each point in k-space corresponds to

spatial frequency

spatial frequency and phase

phase encoding

NONE

the strength and duration of gradients

position in k-space is determined by

RF transmit

FID

NONE

the strength and duration of gradients

True

K space sampling can affect the image quality and acquisition time

True

False

Cartesian

The simple method of K space filling

radial

Cartesian

spiral

Cartesian and radial

Cartesian

K space fill in linear manner from top to bottom or bottom to top

radial

spiral

Cartesian and radial

Cartesian

False

The application of spatial encoding gradients causes no change in the MRI signal amplitude.

True

False

Fourier Transform

What technique is used to sort the MRI signals recorded in K-space to produce an MRI image?

Faraday's Law

Fourier Transform

Nyquist theorem

Larmor Equation

True

The number of phase encoding steps performed in a pulse sequence determines the number of lines of k-space that are filled.

True

False