Biology Reference
In-Depth Information
6. Positron
Emission
Tomography
PET is a nuclear imaging modality that captures the three-
dimensional functional processes in the body ( 16 ). A biologically
active molecule with a radiotracer is injected, and becomes con-
centrated in the tissue of interest ( 16 ). The radioisotope within
this tissue undergoes time and metabolic-related decay ( 16 ).
This decay leads to the production of gamma photons which are
detected by a scintillator ( 16 ). These processes are captured on
scans that are typically superimposed on CT or MRI images.
PET is an evolving technique that captures metabolic pro-
cesses in tissues. Metabolic changes can be an early indicator of
impending vasospasm ( 16 ). However, this modality is expensive,
time-intensive, and not readily available ( 16 ). Furthermore, PET
does not evaluate the cerebral vessels directly ( 16 ). This has lim-
ited its utility in both animal models and human studies of vasos-
pasm ( 16 ).
Animal studies using PET to evaluate vasospasm are lacking.
Yamamoto et al. ( 29 ) followed radiolabeled water molecules to
evaluate changes in cerebral blood fl ow after SAH. They found
that cerebral vasospasm led to altered cerebral blood fl ow ( 29 ).
This same group evaluated the role of a hydroxyl radical scavenger
in improving cerebral blood fl ow and metabolism following SAH
in rats ( 30 ). By tracing radiolabeled water and glucose molecules,
they found that the use of this scavenger improved cerebral blood
fl ow and metabolism at 48 h following SAH ( 30 ).
7. Conclusions
Cerebral vasospasm following aneurysmal SAH can lead to devas-
tating neurological sequelae. The pathophysiology of this phenom-
enon has yet to be fully elucidated. Animal models, which rely on
in vitro examination of the cerebral arteries, have conventionally
been the primary method for studying this condition. Imaging
technologies are evolving rapidly, most notably TCD, CT (includ-
ing CTA and CTP), MRI (including MRA, MRS, and MRP), and
PET. These imaging modalities are providing promising new
options for in vivo examination of vasospasm, in both animal and
human models.
 
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