Week 5 Pt 3 , Ssfp, Balanced Ge, Fast Gradient Echo, K Space Filling In Fast Ge Sequences,epi

Front 1

Gradient echo sequences do not demonstrate true T2 weighting because:1.__________
2.__________

Back 1

1. the TE is never long enough;
2. gradient rephasing is so inefficient, that any echo is dominated by T2* effects .

Front 2

sequence that obtains images that have a sufficiently long TE and less T2* when using the this type of sequence than other gradient echo pulse sequences

Back 2

SSFP

Front 3

using a flip angle between 30° and 45° in conjunction with a TR of less than 50 ms. will produce what type of pulse sequence?

Back 3

SSFP

Front 4

Every TR an excitation pulse is applied. When the RF is switched off a 1. ___ is produced.
After the TR, another excitation pulse is applied which also produces its own 2. ___

Back 4

1. FID
2. FID

Front 5

Steady state free precession is also a method of MR excitation in which strings of RF pulses are applied rapidly and repeatedly with interpulse intervals short compared to bothT1 and T2.
However, the radio-waves within it that have an amplitude to rephase the previous FID and a spin echo results
Each RF pulse therefore not only produces its own FID, but also rephases the FID produced from the previous excitation.
T OR F

Back 5

TRUE

Front 6

In SSFP, there are usually two TEs:
- the actual TE (time between the echo and the next excitation pulse) and
- the effective TE time from the echo to the excitation pulse that created its FID. Therefore the effective TE = (2 * TR) - actual TE
T OR F

Back 6

TRUE

Front 7

Typical values for SSFP SEQUENCES;

Flip angle 1._______
TR 2. ________
Actual TE 3. _________

Back 7

1 30°–45°
2 Less than 50ms
3 7ms

Front 8

Rephasing has been initiated by an RF pulse rather than a gradient so that more T2 and less T2* information is present - THIS DESCRIBES WHAT TYPE OF PS ?

Back 8

SSFP

Front 9

This type of sequences are used to acquire images that demonstrate true T2 weighting rapidly. With the advent of fast spin echo, however, this sequence is not commonly used.

Back 9

SSFP

Front 10

These sequence is a modification of coherent gradient echo sequence, that uses a balanced gradient system to correct for phase errors in flowing blood and CSF.

Back 10

Balanced GE

Front 11

These measures ensure that the TE and TR are very short. TEs as low as 1 ms and TRs as low as 5 ms can be achieved in this manner enabling the whole abdomen to be imaged in a single breath-hold.

Back 11

Fast gradient echo

Front 12

very fast pulse sequences that can acquire several slices in a single breath-hold. These usually employ much faster versions of coherent and incoherent gradient echo sequences or combinations of both (hybrids). Faster scan times are achieved in the following ways:

Back 12

applying only a portion of the RF excitation pulse, so that it takes much less time to apply and switch off;
reading only a proportion of the echo (partial echo);
using asymmetric gradients which are faster to apply than conventional balanced gradients;
- sampling frequencies whilst the frequency encoding gradient is still rising (ramped sampling);
- filling K space in a single shot or in segments

Front 13

many ultrafast sequences use extra pulses applied before the pulse sequence begins to pre-magnetize the tissue. In this way a certain contrast can be obtained. Pre-magnetization is usually achieved in two ways, as follows.

Back 13

A180° pulse is applied before the pulse sequence begins. This inverts the NMV into full saturation and, at a specified delay time, the pulse sequence itself begins. This can be used to null signal from certain organs and tissues and is similar to inversion recovery. It is sometimes known as a Magnetization Prepared Sequence

Front 14

A 90°/180°/90° combination is applied before the pulse sequence begins. The first 90° pulse produces transverse magnetization. The 180° pulse rephases this, and at a specified time later the second 90° pulse is applied.
This drives the coherent transverse magnetization into the longitudinal plane, so that it is available to be flipped when the pulse sequence begins.
This is used to produce T2 contrast and is sometimes known as

Back 14

driven equilibrium.

Front 15

K space filling in fast GE sequences include
1
2
3

Back 15

1 Centric K space filling
Line by line; fills the central lines first (FGE)

2 Keyhole filling
Similarly to centric, only central lines are filled during a certain part of the sequence

3 Spiral k space filling

Front 16

an MR acquisition method that collects all the data required to fill all the lines of K space from a single echo train.

Back 16

EPI

Front 17

Echoes are generated either by 180° rephasing pulses (termed ,2 ______ )or by gradients (termed 3 ____________) ; what type of acuisition method is this?

Back 17

1 ( spin echo EPI)
2 (gradient echo EPI)
3 EPI

Front 18

which type of EPI rephasing is faster, Gradient or 180 RF pulse ?

Back 18

Gradient rephasing is much faster and involves no RF deposition to the patient but does require high speed gradients.

Front 19

Gradient rephasing is much faster and involves no RF deposition to the patient but does require high speed gradients. In order to fill all of K space in one repetition, the readout and phase encode gradients must rapidly switch on and off , which is known as What?

Back 19

blipping

Front 20

Time that takes for gradient to reach position is known as ?

Back 20

raise time

Front 21

This is used to produce T2 contrast and is sometimes known as driven equilibrium

Back 21

Fast gradient echo

Front 22

magnetization prepared sequence
is what?

Back 22

A180° pulse is applied before the pulse sequence begins. This inverts the NMV into full saturation and, at a specified delay time, the pulse sequence itself begins. This can be used to null signal from certain organs and tissues and is similar to inversion recovery