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it has been shown to be at least as sensitive as CT ( 10 ). However,
FLAIR and T2* MRI has been reported to overestimate the SAH
or ICH volume while CT underestimates the lesion volume ( 21 ).
In vitro models have shown it more sensitive than CT ( 22 ), and
some animal models have shown FLAIR to be clearly better than
CT as CT was inadequate to detect SAH in the reported model
( 23 ). However, in animal studies some caution is required in com-
parison to human data due to the type of SAH or ICH model that
may change the visibility of lesions. An example is the study by
Küker et al. who were able to visualize the ICH and SAH lesions at
both 1.5 and 0.5 T on T2* and FLAIR with the authors reporting
that FLAIR was optimal for SAH. In this study, the model used
venous blood to induce the injury which could account for the
improved visualization on MRI at the hyperacute time points ( 24 ).
Other MRI modalities have been reported but are not widely used
either clinically or in basic research. These include the use of per-
fusion-weighted imaging (PWI), magnetic resonance spectroscopy
(MRS), and derived parameters including relative blood volume
maps. Spectroscopy for SAH injury markers from CSF of patients
has also been performed but these are typically not used routinely
in the clinic ( 3 ). A recent report of 31P MRS in patients receiving
hypermagnesium therapy for SAH reported an effective therapeu-
tic potential ( 25 ).
1.5. Other MRI
Modalities
More recently, the introduction of susceptibility-weighted imaging
(SWI) has vastly improved the ability to visualize extravascular
blood deposition within the brain (Figs. 1 and 2 ). The technical
and clinical applications relevant to adults have been recently
reviewed by Haacke and colleagues ( 26, 27 ). SWI applications to
pediatric cases have also been reviewed ( 28-30 ). While SWI is
uniquely sensitive to blood and blood products within the brain, it
has not been routinely used for SAH diagnosis nor clinical evalua-
tion. One of the potential reasons for this is that the complemen-
tary phase information that is essential for the dramatic SWI
contrast is problematic at air tissue interfaces, thus potentially mak-
ing SAH diagnosis more diffi cult, particularly at the base of the
skull. However, advances in phase mapping ( 31 ) and phase unwrap-
ping ( 32 ) may alleviate this issues.
A recent publication evaluating traumatic SAH using SWI
demonstrates the utility of this advanced technique for diagnosis
( 33 ). In 20 patients, the authors evaluated eight anatomical regions
within the subarachnoid space and reported that SWI was able to
identify fi ve additional patients with SAH that could not be diag-
nosed with conventional CT.
Animal studies have reported increased sensitivity to blood
products in experimental models ( 34, 35 ) (Fig. 3 ). In our own
studies, we have shown that SWI, even using only the magnitude
1.6. Susceptibility-
Weighted Imaging
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