Physics Basics From Book Mri In Practice Chapter 2

Front 1

Whether gradient field adds or subtracts from the main magnetic field depends on

Back 1

the direction of the current passing through gradient coils.

Front 2

the direction of the current passing through gradient coils is called -?-

Back 2

the polarity of the gradient.

Front 3

What are magnetic field gradients generated by?

Back 3

coils of wire situated within the bore of the magnet.

Front 4

sequences that use a gradient to reduce magnetic homogeneity effects, as opposed to a 180° RF pulse used in spin echo sequences are called ?

Back 4

Gradient echo pulse sequences

Front 5

FSE is ?

Back 5

Fast spin echo

Front 6

what is an Echo Train

Back 6

FSE employs a train of 180° rephasing pulses, each one producing a spin echo.

Front 7

What is a much faster version of conventional spin echo?

Back 7

Fast spin echo (FSE)

Front 8

Which sequences are considered the considered the "gold standard" in that the contrast they produce is understood and is predictable. ?

Back 8

Spin echo sequences

Front 9

Spin echo sequences produce Which type of images?

Back 9

They produce T1, T2 and PD weighted images of good quality and may be used in any part of the body for any indication.

Front 10

What are the 5 Advantages of Spin Echo sequencing?

Back 10

-1Good image quality
-2 Very versatile
- 3True T2 weighting
-4 Available on all systems
-5Gold standard for image contrast and weighting

Front 11

What is/are the Disadvantages of spin echo sequencing?

Back 11

- Long scan times

Front 12

A dual echo means what?

Back 12

A dual echo sequence consists of two 180° pulses applied to produce two spin echoes

Front 13

a sequence that provides two images per slice location; one that is proton density weighted and one that is T2 weighted is ?

Back 13

A dual echo sequence consists of two 180° pulses applied to produce two spin echoes

Front 14

The first echo of a dual echo sequence = ? TE and a -?- TR and results in what type of images?

Back 14

1.Short TE (TE1)
2. Long TR
3. Results in a set of Proton Density weighted images.

Front 15

The second echo of a dual echo sequence has a 1._____TE (TE2) and a 2. ______TR and results in a 3.____ weighted set of images.

Back 15

1. long TE (TE2)
2. long TE (TE2)
3. T2 weighted

Front 16

Timing parameters in spin echo

TR =

Back 16

time between each 90 degree excitation pulse

Front 17

Timing parameters in spin echo

TE =

Back 17

time between 90 degree excitation pulse and the peak of the spin echo.

Front 18

Timing parameters in spin echo

TE = + =

Back 18

TE = TAU + TAU = 2TAU

Front 19

After the application of the 90° RF pulse, spins

Back 19

lose precessional coherence.

Front 20

After the application of the 90° RF pulse, spins lose precessional coherence and what is created?

Back 20

FID is created.

Front 21

After the application of the 90° RF pulse, spins lose precessional coherence
FID is created
then _________occurs,

Back 21

T2* decay occurs

Front 22

After the application of the 90° RF pulse, spins lose precessional coherence
FID is created
T2* decay occurs and then - ? -

Back 22

A 180° RF pulse flips the dephased nuclei through 180°.

Front 23

After the application of the 90° RF pulse, spins lose precessional coherence
FID is created
T2* decay occurs
A 180° RF pulse flips the dephased nuclei through 180°.
WHAT IS THIS PROCESS CALLED ?

Back 23

This is called RE-PHASING.

Front 24

When does a spin echo occur?

Back 24

Whenever a 180° RF rephasing pulse is applied, a spin echo results

Front 25

Rephasing the NMV does what?

Back 25

Rephasing the NMV ;Eliminates the effect of the magnetic field inhomogeneities, (T2* Decay).

Front 26

This regenerated signal is called 1.__ ____ and, because an RF pulse has been used to generate it, it is specifically called a 2.___ ____ .

Back 26

1. an echo
2. spin echo.

Front 27

In a spin echo pulse sequence there is a 1.__ ______ _____ followed by a 2.____ _____ _____ followed by 3. __ ____ .

Back 27

1. 90° excitation pulse
2. 180° rephasing pulse
3. an echo.

Front 28

The spin echo pulse sequence is AKA what?

Back 28

Conventional spin echo pulse sequences

Front 29

Conventional spin echo pulse sequences are used to produce what types of images?

Back 29

T1
T2 or
Proton Density weighted images.

Front 30

One of the most basic pulse sequences used in MRI.

Back 30

Conventional spin echo pulse sequences aka The spin echo pulse sequence

Front 31

Spins are rephased in two ways:

Back 31

• by using a 180° RF pulse
• by using a gradient.

Front 32

The main purposes of pulse sequences are:

Back 32

to rephase spins and remove inhomogeneity effects and therefore produce a signal or echo that contains information on the decay characteristics of tissue;
• to enable manipulation of the TE and TR to produce different types of contrast.

Front 33

T2* decay = The rate of dephasing due to inhomogeneities.
Magnetic field inhomogeneities cause the NMV to dephase before intrinsic magnetic fields of the nuclei can produce dephasing, i.e. T2* happens before T2 ------- SO -------
T2* is faster than T2 decay since it is a combination of two effects:
1._____ _____ ____
2. _________ _____ ______ ______ ________ .

Back 33

1. T2 decay itself
2. Dephasing due to magnetic field inhomogenities.

Front 34

TR controls

Back 34

the amount of T1 contrast

Front 35

TE controls

Back 35

the amount of T2 contrast

Front 36

TR controls the amount of T1 contrast

TE controls the amount of T2 contrast

PD - TR controls the amount of T1 contrast

TE controls the amount of T2 contrast

PD - CONTROLS ?

Back 36

between T1 & T2