Timing Diagrams for Spin Echo - ismrm
Timing Diagrams for Spin Echo - ismrm
Timing Diagrams for Spin Echo - ismrm
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Outline<br />
5.1 Pulse Sequences & Image Contrast <strong>for</strong> MRI<br />
<strong>Timing</strong> <strong>Diagrams</strong> <strong>for</strong> <strong>Spin</strong> <strong>Echo</strong><br />
pulse sequences including: spin echo, fast spin echo,<br />
inversion recovery, gradient echo and echo planar imaging<br />
Carolyn Kaut Roth, RT (R)(MR)(CT)(M)(CV) FSMRT<br />
CEO Imaging Education Associates<br />
www.imaginged.com<br />
candi@imaginged.com<br />
• <strong>Timing</strong> diagrams<br />
• What is a pulse sequence?<br />
• What is a spin echo?<br />
• Review <strong>Spin</strong> <strong>Echo</strong> & Fast spin echo<br />
• Inversion Recovery & Fast IR<br />
• Gradient <strong>Echo</strong><br />
Slide # 2<br />
What contrast characteristics in MR?<br />
How are images acquired in MR?<br />
• What contrast is available on CT<br />
• What contrast is available on MRI<br />
–T1<br />
–T2<br />
–PD<br />
Axial CT<br />
T1 PD T2<br />
• Pulse Sequences<br />
–SE<br />
–FSE<br />
–IR<br />
–Fast IR<br />
–GE<br />
–EPI<br />
T2 CSE<br />
12 minute scan<br />
T2 TSE (FSE)<br />
3 minute scan<br />
T2* EPI<br />
30 second scan<br />
Slide # 3<br />
Slide # 4<br />
To create MR images<br />
<strong>Timing</strong> Diagram<br />
RF Pulse<br />
• The patient is placed in<br />
the magnetic field<br />
–to align the spins<br />
• The RF pulse is applied<br />
–to excite the spins<br />
–at the Larmor Frequency<br />
Slice<br />
selection gradient<br />
Phase<br />
Encoding gradient<br />
Frequency<br />
encoding gradient<br />
MR signal<br />
• A pulse sequence is… a sequence of pulses<br />
• A timing diagram is the order and timing of pulses<br />
Slide # 5<br />
Slide # 6<br />
1
ECG<br />
What is this?<br />
TR (Repetition Time)<br />
90 0<br />
90 0<br />
Slide # 7<br />
Slide # 8<br />
<strong>Timing</strong> Diagram<br />
Short TR & Long TR Imaging<br />
TR (Repetition Time)<br />
TR, is the time<br />
between 90 0<br />
RF pulses<br />
These<br />
lines<br />
represent<br />
gradient<br />
pulses<br />
MR signal<br />
induced in the<br />
receiver coil<br />
RF Pulse<br />
Slice<br />
selection gradient<br />
Phase<br />
Encoding gradient<br />
Frequency<br />
encoding gradient<br />
MR signal<br />
90 0 180 0<br />
Short TR<br />
90 0 180 0 Long TR<br />
Slide # 9<br />
Slide # 10<br />
<strong>Timing</strong> <strong>Diagrams</strong> - Gradients<br />
Slice Selection<br />
Gradients<br />
SS (Z)<br />
PE (Y)<br />
FE (X)<br />
RF Pulse<br />
Slice<br />
selection gradient<br />
Phase<br />
Encoding gradient<br />
Frequency<br />
encoding gradient<br />
MR signal<br />
• If the magnetic field is<br />
homogeneous, the<br />
frequency is the same<br />
… head to feet<br />
• If the RF is applied…<br />
in this case the entire<br />
body would be excited<br />
Homogeneous magnetic field<br />
The frequency is the same<br />
from the head to the feet<br />
Slide # 11<br />
Slide # 12<br />
2
Selective Excitation<br />
Phase & Frequency Encoding<br />
•To excite a location<br />
within the imager, within<br />
the body..<br />
• A magnetic field<br />
gradient is applied<br />
• The RF pulse is applied<br />
that matches a location<br />
Homogeneous magnetic field<br />
gradient<br />
• Once the slice is selected…<br />
• Encoding along the other<br />
axes,<br />
–With gradients<br />
•R to L<br />
•A to P<br />
–For encoding<br />
•Phase encoding<br />
•Frequency encoding<br />
Gradient<br />
R to L<br />
Gradient<br />
A to P<br />
Gradient<br />
S to I<br />
Axial slice selection<br />
Homogeneous magnetic field<br />
Slide # 13With a linear gradient field applied<br />
Axial slice<br />
Slide # 14<br />
<strong>Timing</strong> Diagram- Signal<br />
MR Excitation Relaxation<br />
RF Pulse<br />
Slice<br />
selection gradient<br />
Bo<br />
Z<br />
Mz<br />
90 0 RF Pulse<br />
Z<br />
Z<br />
Phase<br />
Encoding gradient<br />
Mxy<br />
MR signal<br />
Frequency<br />
encoding gradient<br />
MR signal<br />
Y<br />
Alignment<br />
X<br />
Y<br />
Excitation<br />
X<br />
RF<br />
Receiver<br />
coil<br />
MR Signal<br />
FID<br />
Relaxation<br />
Slide # 15<br />
Slide # 16<br />
<strong>Timing</strong> Diagram - TE<br />
T2* Decay<br />
TR (Repetition Time)<br />
RF pulse<br />
T2* decay<br />
Mxy<br />
coil<br />
Axial T2* Brain Image<br />
TE (<strong>Echo</strong> Time)<br />
In phase Partially dephased Completely dephased<br />
Image with artifact<br />
Cleaned up the “SIC”<br />
Mx,y = transverse magentization<br />
Slide # 17<br />
Slide # 18<br />
3
Runners on the Race<br />
<strong>Spin</strong> <strong>Echo</strong> - Runners on the Race<br />
90 0 180 0<br />
FID<br />
FID<br />
Susceptibility artifacts<br />
<strong>Echo</strong><br />
spin echo, less artifacts<br />
Start<br />
I’m the<br />
fast<br />
guy<br />
90 0 180 0 Phase #3 cross<br />
Start<br />
Thought<br />
I was<br />
winning<br />
I’m on<br />
your<br />
heels<br />
Gotcha!<br />
Inhomogenieties<br />
Phase #1 start together<br />
and get apart<br />
Runners turn 180’<br />
Slide # 19<br />
Phase #2 after the 180<br />
Turn around apart<br />
Phase #4 starting line, together<br />
get apart again<br />
Slide # 20<br />
T2* and T2 Decay<br />
Is Susceptibility artifact always a bad thing?<br />
T2*<br />
T2 decay<br />
T2*<br />
T2 decay<br />
FID<br />
echo<br />
FID<br />
echo<br />
Axial T2* Brain<br />
Axial T2 Brain<br />
Axial T2* Brain<br />
Axial T2 Brain<br />
Slide # 21<br />
Slide # 22<br />
Gradient <strong>Echo</strong> - Runners on the Race<br />
Long TE – <strong>Spin</strong> <strong>Echo</strong> Imaging<br />
Start<br />
45 0 FID<br />
I’m the<br />
fast<br />
guy<br />
Start<br />
90 0 180 0<br />
½TE<br />
½TE<br />
T2WI axial<br />
I’m on<br />
your<br />
heels<br />
Inhomogenieties<br />
Phase #1 start together<br />
and get apart<br />
Phase #2 runners<br />
change places<br />
Phase #3 cross finish<br />
line, together<br />
Phase #4<br />
get apart again<br />
FID<br />
echo<br />
Long TE<br />
Slide # 23<br />
Slide # 24<br />
4
Short TE – <strong>Spin</strong> <strong>Echo</strong> Imaging<br />
A Few Fun Facts about T1 & T2<br />
90 0 180 0<br />
½TE<br />
½TE<br />
We cannot<br />
change….<br />
T1 recovery<br />
T2 decay<br />
unless we<br />
change<br />
Field strength<br />
Temperature<br />
or Add contrast<br />
agents!<br />
FID<br />
echo<br />
Short TE<br />
Slide # 25<br />
Slide # 26<br />
A Few Fun Facts about TR & TE<br />
A Few Fun Facts about T1 recovery<br />
Long TR<br />
Long TE<br />
T1 recovery<br />
T1 times at<br />
1.5T<br />
Are in the<br />
neighborhood<br />
of …<br />
2000 ms <strong>for</strong><br />
water<br />
150 ms <strong>for</strong> fat<br />
Short TR<br />
We can change<br />
TR & TE<br />
And…<br />
TR goes with T1<br />
TE goes with T2<br />
Short TE<br />
TR<br />
Slide # 27<br />
Slide # 28<br />
A Few Fun Facts about T2 Decay<br />
A Few Fun Facts about Image Contrast<br />
T2 decay<br />
We cannot<br />
change….<br />
T1 recovery<br />
T2 decay<br />
unless we<br />
change<br />
Field strength<br />
Temperature<br />
or Add contrast<br />
agents!<br />
T1 times at<br />
1.5T<br />
Are in the<br />
neighborhood<br />
of …<br />
2000 ms <strong>for</strong><br />
water<br />
150 ms <strong>for</strong> fat<br />
TE<br />
T2 times at<br />
1.5T<br />
Are in the<br />
neighborhood<br />
of …<br />
200 ms <strong>for</strong><br />
water<br />
50 ms <strong>for</strong> fat<br />
We can change<br />
TR & TE<br />
And…<br />
TR goes with T1<br />
TE goes with T2<br />
T2 times at<br />
1.5T<br />
Are in the<br />
neighborhood<br />
of …<br />
200 ms <strong>for</strong><br />
water<br />
50 ms <strong>for</strong> fat<br />
Slide # 29<br />
Slide # 30<br />
5
Let’s make a T1 image<br />
Let’s make a T2 image<br />
T1WI<br />
Short TR (500 ms)<br />
Short TE (20 ms)<br />
Bright fat<br />
T1 times at<br />
1.5T<br />
Are in the<br />
neighborhood<br />
of …<br />
2000 ms <strong>for</strong><br />
water<br />
150 ms <strong>for</strong> fat<br />
T2WI<br />
Long TR (4000 ms)<br />
Long TE (100 ms)<br />
Bright water<br />
T1 times at<br />
1.5T<br />
Are in the<br />
neighborhood<br />
of …<br />
2000 ms <strong>for</strong><br />
water<br />
150 ms <strong>for</strong> fat<br />
We can change<br />
TR & TE<br />
And…<br />
TR goes with T1<br />
TE goes with T2<br />
Short TR<br />
Short TE<br />
T2 times at<br />
1.5T<br />
Are in the<br />
neighborhood<br />
of …<br />
200 ms <strong>for</strong><br />
water<br />
50 ms <strong>for</strong> fat<br />
We can change<br />
TR & TE<br />
And…<br />
TR goes with T1<br />
TE goes with T2<br />
Long TR<br />
Long TE<br />
T2 times at<br />
1.5T<br />
Are in the<br />
neighborhood<br />
of …<br />
200 ms <strong>for</strong><br />
water<br />
50 ms <strong>for</strong> fat<br />
Slide # 31<br />
Slide # 32<br />
Let’s make a PD image<br />
Image Contrast Parameters<br />
PDWI<br />
T1 times at<br />
1.5T<br />
Are in the<br />
neighborhood<br />
of …<br />
Long TR (4000 ms)<br />
Short TE (20 ms)<br />
Bright fat & water<br />
2000 ms <strong>for</strong><br />
water<br />
150 ms <strong>for</strong> fat<br />
We can change<br />
TR & TE<br />
And…<br />
TR goes with T1<br />
TE goes with T2<br />
Long TR<br />
T2 times at<br />
1.5T<br />
Are in the<br />
neighborhood<br />
of …<br />
200 ms <strong>for</strong><br />
water<br />
50 ms <strong>for</strong> fat<br />
T1WI<br />
Short TR<br />
Short TE<br />
Bright fat, short T1 time<br />
PDWI<br />
Long TR<br />
Short TE<br />
Bright fat & water<br />
T2WI<br />
Long TR<br />
Long TE<br />
Bright water, long T2 time<br />
Short TE<br />
Slide # 33<br />
Slide # 34<br />
<strong>Timing</strong> Diagram – RF and Gradient Pulses<br />
TR (Repetition Time)<br />
What is a Pulse Sequence?<br />
TR, is the time<br />
between 90 0<br />
RF pulses<br />
RF Pulse<br />
Slice<br />
selection gradient<br />
These<br />
lines<br />
represent<br />
gradient<br />
pulses<br />
Phase<br />
Encoding gradient<br />
Frequency<br />
encoding gradient<br />
<strong>Spin</strong> echo family<br />
Longer<br />
Scan<br />
times<br />
Better<br />
quality<br />
T1Weighted Image<br />
SE<br />
(TSE) FSE<br />
IR<br />
Fast IR<br />
PD Weighted Image<br />
SE<br />
(TSE) FSE<br />
FLAIR<br />
Fast FLAIR<br />
Looks like PD<br />
T2 Weighted Image<br />
SE<br />
FSE<br />
STIR<br />
Fast STIR<br />
Looks like T2<br />
MR signal<br />
induced in the<br />
receiver coil<br />
MR signal<br />
TE (<strong>Echo</strong> Time)<br />
Gradient echo family<br />
Faster<br />
Scan<br />
times<br />
lower<br />
quality<br />
(T1 FFE) GrE spoiled<br />
TOF MRA<br />
Enhanced MRA<br />
(PD FFE) GrE<br />
EPI Flair<br />
T2* Weighted Image<br />
(T2* FFE) GrE<br />
PC MRA<br />
EPI<br />
Perfusion<br />
Diffusion<br />
Slide # 35<br />
Slide # 36<br />
6
<strong>Timing</strong> Diagram – <strong>Spin</strong> <strong>Echo</strong><br />
Short TR & Long TR Imaging<br />
TR (Repetition Time)<br />
TR, is the time<br />
between 90 0<br />
RF pulses<br />
These<br />
lines<br />
represent<br />
gradient<br />
pulses<br />
TE is the time<br />
to the echo<br />
RF Pulse<br />
Slice<br />
selection gradient<br />
Phase<br />
Encoding gradient<br />
Frequency<br />
encoding gradient<br />
MR signal<br />
90 0 180 0<br />
Short TR<br />
90 0 180 0 Long TR<br />
TE (<strong>Echo</strong> Time)<br />
Slide # 37<br />
Slide # 38<br />
Long TE – <strong>Spin</strong> <strong>Echo</strong> Imaging<br />
Short TE – <strong>Spin</strong> <strong>Echo</strong> Imaging<br />
90 0 180 0<br />
90 0 180 0<br />
½TE<br />
½TE<br />
½TE<br />
½TE<br />
T2WI axial<br />
FID<br />
echo<br />
FID<br />
echo<br />
Long TE<br />
Short TE<br />
Slide # 39<br />
Slide # 40<br />
Dual <strong>Echo</strong> Imaging (2 <strong>for</strong> 1)<br />
Image Contrast Parameters<br />
90 0 180 0 180 0<br />
Proton density-TE1<br />
T2WI-TE2<br />
FID<br />
T2 decay<br />
echo echo<br />
TE 1<br />
TE 2<br />
T1WI<br />
@ 1.5T<br />
Short TR (500 ms)<br />
Short TE (20 ms or less)<br />
Bright fat<br />
Scan time about 2 minutes<br />
With 2 signal averages<br />
PDWI<br />
@ 1.5T<br />
Long TR (4000 ms = 4 seconds)<br />
Short TE (20 ms or less)<br />
Bright fat & water<br />
Scan time about 17 minutes<br />
With 2 signal averages<br />
T2WI<br />
@ 1.5T<br />
Long TR (4000 ms = 4 seconds)<br />
Long TE (100 ms)<br />
Bright water<br />
Scan time about 17 minutes<br />
With 2 signal averages<br />
Slide # 41<br />
Scan time <strong>for</strong> SE = TR * #PE’s * NSA<br />
Slide # 42<br />
7
Outline<br />
<strong>Spin</strong> <strong>Echo</strong> <strong>Timing</strong> Diagram & K-space<br />
TR<br />
• <strong>Timing</strong> diagrams<br />
• What is a pulse sequence?<br />
• What is a spin echo?<br />
• Review <strong>Spin</strong> <strong>Echo</strong> & Fast spin echo<br />
• Inversion Recovery & Fast IR<br />
• Gradient <strong>Echo</strong><br />
RF Pulse<br />
Slice selection<br />
gradient<br />
Phase<br />
encoding<br />
gradient<br />
Frequency<br />
encoding gradient<br />
MR signal<br />
TE<br />
p<br />
h<br />
a<br />
s<br />
e<br />
frequency<br />
K-space = raw data<br />
Scan time = TR x PE’s x NSA<br />
Slide # 43<br />
Slide # 44<br />
Dual <strong>Echo</strong> Imaging & K-space<br />
Fast <strong>Spin</strong> <strong>Echo</strong> Imaging & K-space (1 in ½ the time)<br />
90 0 180 0 180 0 K-space-TE1 K-space-TE2<br />
90 0 180 0 180 0 K-space (TSE)<br />
T2 decay<br />
FID echo echo<br />
FSE<br />
TE 2 image<br />
Twice as fast<br />
TE 1<br />
TE 2<br />
Proton density-TE1 T2WI-TE2<br />
Slide # 45<br />
Turbo spin echo (TSE)<br />
Fast <strong>Spin</strong> <strong>Echo</strong> (FSE) Rapid Acquisition<br />
Recalled <strong>Echo</strong> (RARE)<br />
Slide # 46<br />
Effective TE<br />
Target TE<br />
T2WI<br />
Fast <strong>Spin</strong> <strong>Echo</strong> Imaging <strong>for</strong> PDWI<br />
Fast <strong>Spin</strong> <strong>Echo</strong> Imaging <strong>for</strong> T2WI<br />
echo 3<br />
echo 1<br />
Phase<br />
Encoding<br />
Gradient<br />
echo 1<br />
Phase<br />
Encoding<br />
Gradient<br />
echo 3<br />
echo 4<br />
echo 2<br />
Frequency<br />
Encoding<br />
Gradient<br />
echo 1 echo 2 echo3 echo4<br />
echo 4<br />
20 ms 40ms 60 ms 80ms<br />
Frequency<br />
Encoding<br />
Gradient<br />
echo 2<br />
echo 1 echo 2 echo3 echo4<br />
20 ms 40ms 60 ms 80ms<br />
TR * #PE’s * NSA<br />
Scan time (FSE) =<br />
ETL<br />
TR * #PE’s * NSA<br />
Scan time (FSE) =<br />
ETL<br />
Slide # 47<br />
Slide # 48<br />
8
Single Shot Fast <strong>Spin</strong> <strong>Echo</strong> Imaging <strong>for</strong> T2WI (SSFSE)<br />
Image Contrast Parameters - fast spin echo<br />
Abnormalities seen on<br />
Ultrasound<br />
FDA OK <strong>for</strong> pregnancy<br />
if… benefit outweighs<br />
the risk<br />
If mommy fits<br />
Slide # 49<br />
Fetal MRI<br />
T1WI<br />
@ 1.5T<br />
Short TR (500 ms)<br />
Short TE (20 ms or less)<br />
Bright fat<br />
Scan time about 1 minute<br />
With 2 signal averages<br />
ETL of 2<br />
PDWI<br />
@ 1.5T<br />
Long TR (4000 ms = 4 seconds)<br />
Short TE (20 ms or less)<br />
Bright fat & water<br />
Scan time about 8.5 minutes<br />
With 2 signal averages<br />
ETL of 2<br />
Scan time <strong>for</strong> SE = TR * #PE’s * NSA<br />
Slide # 50<br />
T2WI<br />
@ 1.5T<br />
Long TR (4000 ms = 4 seconds)<br />
Long TE (100 ms)<br />
Bright water<br />
Scan time about 8.5 minutes<br />
With 2 signal averages<br />
ETL of 2<br />
ETL<br />
Outline<br />
• <strong>Timing</strong> diagrams<br />
• What is a pulse sequence?<br />
• What is a spin echo?<br />
• Review <strong>Spin</strong> <strong>Echo</strong> & Fast spin echo<br />
• Inversion Recovery & Fast IR<br />
• Gradient <strong>Echo</strong><br />
<strong>Spin</strong> <strong>Echo</strong> vs Inversion Recovery<br />
90 0 180 0 TR<br />
TI<br />
FID<br />
echo<br />
TR<br />
1800 180 0<br />
90 0<br />
FID<br />
echo<br />
Slide # 51<br />
Slide # 52<br />
Why an initializing 180 0 pulse<br />
T1 recovery from a 90 0 pulse<br />
90 0 180 0 TR<br />
Inversion Recovery – STIR (Short Tau Inversion Recovery)<br />
TI<br />
1800 180 0<br />
TR<br />
90 0<br />
TR<br />
T1 recovery from a 180 0 pulse<br />
Compared to the 90 0 pulse<br />
TI<br />
FID<br />
TR<br />
1800 180 0<br />
90 0<br />
echo<br />
FID<br />
TE<br />
echo<br />
TI<br />
FID<br />
echo<br />
T1 <strong>Spin</strong> <strong>Echo</strong><br />
lesion<br />
STIR<br />
Slide # 53<br />
Slide # 54<br />
9
Why an initializing 180 0 pulse<br />
STIR is NOT fatsat<br />
T1 recovery from a 90 0 pulse<br />
90 0 180 0 TR<br />
FID<br />
echo<br />
T1 recovery from a 180 0 pulse<br />
Compared to the 90 0 pulse<br />
TI<br />
180 0 180 0 TR<br />
90 0<br />
Bone contusion<br />
Short TI (fat crosses null point, suppressed)<br />
FID<br />
echo<br />
STIR will suppress gadolinium enhancing lesions<br />
Slide # 55<br />
Slide # 56<br />
FATSAT FSE vs STIR<br />
Inversion Recovery – FLAIR (Fluid Attenuated Inversion Recovery)<br />
TI<br />
180 0 TR<br />
90 0 180 0<br />
FID<br />
echo<br />
TE<br />
FSE<br />
STIR<br />
Slide # 57<br />
PD FLAIR Slide # 58 T1<br />
Why an initializing 180 0 pulse<br />
Fast Inversion Recovery – scan time<br />
T1 recovery from a 90 0 pulse<br />
90 0 180 0 TR<br />
echo 1<br />
echo 4<br />
Lymes disease<br />
T1SE<br />
T1 recovery from a 180 0 pulse<br />
Compared to the 90 0 pulse<br />
FLAIR<br />
Long TI (water crosses null point, suppressed)<br />
TI<br />
FID<br />
FID<br />
echo<br />
180 0 1800 180 0 1<br />
90 0<br />
90 0<br />
TR<br />
echo<br />
echo 3<br />
echo 2<br />
TR * #PE’s * NSA<br />
Scan time (FSE-IR) =<br />
ETL<br />
FLAIR<br />
T1SE<br />
Slide # 59<br />
Slide # 60<br />
10
Outline<br />
<strong>Spin</strong> <strong>Echo</strong> vs Gradient <strong>Echo</strong><br />
RF<br />
• <strong>Timing</strong> diagrams<br />
• What is a pulse sequence?<br />
• What is a spin echo?<br />
• Review <strong>Spin</strong> <strong>Echo</strong> & Fast spin echo<br />
• Inversion Recovery & Fast IR<br />
• Gradient <strong>Echo</strong><br />
Gz<br />
Gy<br />
Gx<br />
Signal<br />
90 0 180 0 Gz<br />
RF<br />
Flip angle<br />
Readout<br />
Gy<br />
Gx<br />
Signal<br />
Positive lobe<br />
Negative lobe<br />
Bipolar Gradient<br />
Slide # 61<br />
Slide # 62<br />
Gradient <strong>Echo</strong> – runners on the race<br />
Susceptibility Artifacts on Gradient <strong>Echo</strong><br />
Gx<br />
Readout<br />
Gradient<br />
Start<br />
45 0 FID<br />
I’m the<br />
fast<br />
guy<br />
Positive lobe<br />
Negative lobe<br />
Gradient echo<br />
Start<br />
I’m on<br />
your<br />
heels<br />
Inhomogenieties<br />
Phase #1 start together<br />
and get apart<br />
Phase #2 runners<br />
change places<br />
Phase #3 cross finish<br />
line, together<br />
Phase #4<br />
get apart again<br />
Axial T2* Brain<br />
Axial T2 Brain<br />
Slide # 63<br />
Slide # 64<br />
Flip Angle and Image Contrast<br />
Flip Angle and Signal Quality (SNR)<br />
Flip angle goes with TR<br />
TR goes with T1<br />
Big flip, more T1<br />
Little flip, less T1<br />
10 0 Flip<br />
30 0 Flip<br />
As Flip increases<br />
SNR increases<br />
To a point<br />
Ernst Angle<br />
angle <strong>for</strong> optimum SNR<br />
10 0 flip 20 0 flip 30 0 flip<br />
40 0 flip 50 0 flip 60 0 flip<br />
60 0 Flip 90 0 Flip<br />
70 0 flip 80 0 flip 90 0 flip<br />
Slide # 65<br />
Slide # 66<br />
11
Flip angle<br />
Steady State<br />
Bo<br />
Z<br />
RF<br />
Z<br />
Bo Z<br />
Mz<br />
RF<br />
Another<br />
RF<br />
Mz<br />
Y<br />
X<br />
Thermal<br />
Equilibrium<br />
Excitation<br />
45 0 flip angle<br />
A little<br />
relaxation<br />
occurs<br />
Another<br />
Excitation<br />
45 0 flip angle<br />
X<br />
X<br />
Steady State is the condition whereby<br />
Everything that relaxes is flipped again<br />
Y<br />
Y<br />
Transverse magnetization<br />
SS images demonstrate T2* effects<br />
Bright fluid<br />
Slide # 67<br />
Slide # 68<br />
Steady State Imaging<br />
Steady State VS Spoiled Gradient <strong>Echo</strong>es<br />
FIESTA – IAC’s<br />
Fast Imaging Employing a steady STAte<br />
Steady State images Shaded Surface Display 3D re<strong>for</strong>mats<br />
Steady State<br />
T2* FFE<br />
Coherent Gradient <strong>Echo</strong><br />
“Spoiled” (spoil away transverse)<br />
T1 FFE<br />
Incoherent Gradient <strong>Echo</strong><br />
Slide # 69<br />
Courtesy of Munich - Pasing<br />
Slide # 70<br />
3D Steady State vs 3D Spoiled Gradient <strong>Echo</strong>es<br />
Dynamic Enhanced (T1) Spoiled Gradient <strong>Echo</strong>es<br />
Pre gad<br />
3D Steady State<br />
T2* GrE images<br />
Spoiled Gradient <strong>Echo</strong>es<br />
T1 GrE images<br />
1st pass<br />
2nd pass<br />
3rd pass<br />
Slide # 71<br />
Slide # 72<br />
12
Chemical Shift Artifact on Gradient <strong>Echo</strong>es<br />
<strong>Spin</strong> <strong>Echo</strong> vs Gradient <strong>Echo</strong> (Flowing Blood)<br />
BO<br />
Gradient<br />
Induced<br />
in phase<br />
out of phase<br />
Gated <strong>Spin</strong> <strong>Echo</strong><br />
Gated Gradient <strong>Echo</strong><br />
Slide # 73<br />
Slide # 74<br />
Cardiac Perfusion<br />
Time of Flight (TOF) MR Angiography (MRA) – T1 Gradient <strong>Echo</strong><br />
3D Volume<br />
Source Images<br />
Source Images<br />
Re<strong>for</strong>matted<br />
MIP Image<br />
Collapsed Image<br />
Emory University, Atlanta, GA<br />
3D TOF<br />
Re<strong>for</strong>matted MIP Image<br />
2D TOF<br />
Slide # 75<br />
Subendocardial Defect<br />
Slide # 76<br />
Phase Contrast (PC) MR Angiography (MRA) – T2 Gradient <strong>Echo</strong><br />
Phase Contrast (PC) MR Angiography (MRA) – CSF Flow<br />
Diastole- dark flow<br />
Systole – white flow<br />
3D PC<br />
Axial Acquisition<br />
Sag 2D PC<br />
No flow 4 th vent - hydrocephalus<br />
Slow flow HA’s<br />
Slide # 77<br />
Slide # 78<br />
13
EPI Speed Compared to FSE<br />
Single-Shot vs. Multi Shot EPI<br />
FSE<br />
EPI<br />
90<br />
90<br />
180 echo<br />
180 echo<br />
180 echo<br />
180 echo<br />
180<br />
ESP = 5 - 20 ms<br />
echo<br />
Time < 500 Ms<br />
echo<br />
ESP = 0.5- 4 ms<br />
echo<br />
Time < 100 Ms<br />
echo<br />
echo<br />
echo<br />
echo<br />
•Single-Shot EPI fills all lines of<br />
k-space in a single TR period<br />
•Fastest Scan Times<br />
•Most useful <strong>for</strong> functional<br />
imaging techniques<br />
•Multi-Shot requires multiple<br />
passes through k-space to fill all<br />
phase lines<br />
•Reduced artifacts<br />
•Allows <strong>for</strong> higher spatial<br />
resolution<br />
•Longer scan times<br />
Multi-Shot:<br />
Whole brain<br />
acquired in<br />
90 Seconds<br />
512 x 256 matrix<br />
Single Shot:<br />
Whole brain<br />
acquired in<br />
4 seconds<br />
128 x 128 matrix<br />
Slide # 79<br />
6<br />
6<br />
Slide # 80<br />
Diffusion-Weighted Imaging<br />
b-value = 0<br />
Diffusion Gradients Sensitize the Image<br />
Contrast to the Molecular Motion of<br />
Extracelluar Water<br />
The greater the amount of motion, the darker the resultant MR signal<br />
Tissue Sample A<br />
Normal Diffusion<br />
Edema results in restricted diffusion<br />
Tissue Sample B<br />
Restricted Diffusion<br />
9<br />
0<br />
180<br />
T2-weighted Image<br />
(b-value = 0)<br />
Slide # 81<br />
Slide # 82<br />
b-value = 1000<br />
Diffusion Weighting and b-value<br />
b-value determines the strength of the diffusion gradients<br />
Increasing the b-value increased diffusion weighting<br />
9<br />
0<br />
180<br />
Diffusion-weighted Image<br />
(b-value = 1000)<br />
b-value = 0 b-value = 500 b-value = 1000<br />
Slide # 83<br />
Slide # 84<br />
14
Isotropic Diffusion<br />
Apparent Diffusion Coefficient (ADC)<br />
ADC expresses the amount of diffusion<br />
Individual Diffusion<br />
Measurements<br />
Mathematical<br />
Combination<br />
Isotropic<br />
Diffusion-Weighted<br />
Image<br />
Radiology 2001<br />
Creating an ADC image (or map) results<br />
in images where the pixel intensity<br />
represents abnormal ADC and<br />
eliminates high signal from<br />
"T2 shine-through"<br />
Mathematical<br />
Calculation<br />
b-value = 0<br />
T2-weighted<br />
b-value = 1000<br />
Diffusion-weighted + T2<br />
ADC map<br />
Reduced ADC = Reduced Signal<br />
Slide # 85<br />
Slide # 86<br />
Perfusion Acquisition<br />
Perfusion Contrast<br />
Time<br />
Series<br />
Gradient <strong>Echo</strong> EPI Acquisition<br />
repea<br />
repea<br />
repea<br />
. . . . . . t<br />
. . .<br />
t<br />
t<br />
Gd washes out of<br />
blood stream<br />
Brain Cell<br />
Small Magnetic<br />
Field Gradient<br />
Gd<br />
Gd<br />
Gd<br />
Gd<br />
Concentrated<br />
Gadolinium<br />
Results in a<br />
Larger Magnetic<br />
Field Gradient<br />
T2* shortening<br />
results in loss of<br />
MR signal<br />
Up to > 400<br />
images<br />
Gd changes<br />
T2* of blood<br />
Gradient <strong>Echo</strong> EPI<br />
TE = 60<br />
Gradient <strong>Echo</strong> EPI<br />
TE = 60<br />
Acquired at Peak Bolus<br />
Slide # 87<br />
Slide # 88<br />
Perfusion of Stroke<br />
BOLD (fMRI)<br />
Blood Oxygen Level Dependent<br />
•When neurons fire, blood flow is increased to that area<br />
of the brain<br />
•Oxygen level increases<br />
•Local magnetic field changes occur due to the<br />
paramagnetic characteristics of oxygenated blood<br />
•Slight change in MR signal<br />
•1% - 2% at 1.5 T<br />
•4% - 6% at 3.0 T<br />
•Area of signal change indicates area of activity<br />
•Images processed on workstation and data is<br />
superimposed over higher resolution anatomic image<br />
Bilateral Finger Tapping<br />
Normal<br />
Abnormal<br />
Image courtesy Stan<strong>for</strong>d University<br />
Slide # 89<br />
Slide # 90<br />
15
Outline<br />
5.1 Pulse Sequences & Image Contrast <strong>for</strong> MRI<br />
• <strong>Timing</strong> diagrams<br />
• What is a pulse sequence?<br />
• What is a spin echo?<br />
• Review <strong>Spin</strong> <strong>Echo</strong> & Fast spin echo<br />
• Inversion Recovery & Fast IR<br />
• Gradient <strong>Echo</strong><br />
<strong>Timing</strong> <strong>Diagrams</strong> <strong>for</strong> <strong>Spin</strong> <strong>Echo</strong><br />
pulse sequences including: spin echo, fast spin echo,<br />
inversion recovery, gradient echo and echo planar imaging<br />
Thank you <strong>for</strong> your attention!<br />
Click to take your post test and get your credits<br />
Carolyn Kaut Roth, RT (R)(MR)(CT)(M)(CV) FSMRT<br />
CEO Imaging Education Associates<br />
www.imaginged.com<br />
candi@imaginged.com<br />
Slide # 91<br />
16
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