Image Processing Reference
In-Depth Information
T2
MRE
FIGURE 14.12 Bovine muscle specimen with three areas of thermal coagulation, per-
ceptible in the T2 image. MRE (superimposed on a T1-w image) indicates zones of
coagulation as areas of high shear stiffness (red).
14.6.7
C HARACTERIZATION OF T HERMALLY A BLATED T ISSUE
MR-guided focused ultrasound (FUS) tissue ablation is a procedure in which
FUS is used to treat tumors by heating the tumor tissue and coagulating it, while
sparing the surrounding normal tissue as much as possible. Existing methods for
assessing the spatial extent of tissue coagulation obtained with FUS have limi-
tations because it is difficult to assess the exact location actually being heated
and the extent to which the heating has coagulated the tissue during the procedure.
Studies have demonstrated that MRE delineates thermally coagulated tissues as
areas of increased shear stiffness (see Figure 14.12) [35,65]. Further work in
which elastography was performed at multiple times during heating and cooling
of bovine tissue revealed a gradual softening of tissue as the temperature was
raised from 20
C and then a large, irreversible increase in tissue shear
stiffness upon further heating that appears to correspond to tissue coagulation
°
C to 60
°
due to irreversible protein denaturation ( Figure 14.13 ). These results suggest that
MRE may be well suited to assess the results of tissue ablation procedures. In
addition, because the shear waves required by MRE can be generated by FUS
radiation pressure at the focal spot (as described earlier), it may be possible to
use MRE for guiding tissue ablation procedures in real time, using FUS for both
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