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high- to ultra-high fi eld strengths (2.35-11.4 T) are often
employed, whereas in pigs, 0.5, 1.5, or 3 T MR imagers and stan-
dard receiving-transmitting coils, suitable for patients investiga-
tions, can be used.
There is no clear standard as to how the experimental hematomas
should be imaged and quantifi ed with MRI. Standard multiplanar
T2-weighted images employing Turbospin-echo sequences (TSE)
can be used (
14
). Depending on the state of degradation of
visualized blood products, better visualization of the clot may be
obtained by T2*-weighted images acquired with a gradient echo
sequence (GRE) (Fig.
1
) (
3
), albeit the latter may overestimate the
clot size due to considerable blooming artifact. Susceptibility-
weighted imaging (SWI) is another, recently developed sequence,
that is extremely sensitive for venous blood or hemorrhage and
that highlights cellular constituents inducing local susceptibility
(
15-17
). This method is based on a fl ow compensated long-echo
GRE sequence and detects even small amounts of blood. However,
this increased sensitivity of SWI sequences comes at a prize: the
hematoma volume in SWI is consistently larger than in T2-weighted
TSE images, which raises the question which sequence more pre-
cisely quantifi es the hematoma. The same problem may occur with
diffusion-weighted imaging (DWI): In the hyperacute stage after
clot induction, this technique can be used to determine the volume
of the clot. However, DWI (employing echo-planar imaging
techniques) is also prone to overestimation of the clot size since
it is based on imaging of susceptibility artifacts that are more
3.1.1. Evaluation
of the Hematoma Volume
Fig. 1. (
a
) T2*-weighted magnetic resonance (MR) images acquired with a gradient
echo sequence (GRE) allow to visualize the experimental frontal hematoma in a pig.
(
b
) Photograph displaying the experimental hematoma shown in (
a
) .
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