Image Processing Reference
In-Depth Information
TE
2
TE
2
TM
rf
G
z
G
y
G
x
Signal
0
10
20
Time (ms)
30
40
FIGURE 11.3
Scheme for the STEAM sequence. The refocusing gradients have to be
positioned before the second and after the third RF pulse.
almost unchanged at the time when the third 90
°
pulse is applied (
Figure 11.4e
).
The z components of the magnetization experience only T1 relaxation, which is
small in the usual time interval of a few milliseconds of the so-called TM interval.
After the last 90
°
pulse, the remaining part of the magnetization is again flipped
rf
rf
rf
Signal
Signal
Signal
0
10
20
Time (ms)
30
40
0
10
20
Time (ms)
30
40
0
10
20
Time (ms)
30
40
(a)
(b)
(c)
FIGURE 11.4
The orientation of the magnetization vectors of different parts within
a selected volume during a STEAM sequence at different times within the sequence.
In (e) - (i), the magnetization vectors with lower and larger resonance frequencies
than the adjusted frequency are shown in separate spheres. The last figure shows the
net magnetization in bold and the modified hypothetical length of the magnetization
vector for the assumed T2 decay only (thin line).
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