Biology Reference
In-Depth Information
4. Computed
Tomography
Angiography
and Perfusion
Computed tomography angiography (CTA) and computed
tomography perfusion (CTP) have emerged as new modalities in
the evaluation of vasospasm. Both of these modalities rely on CT,
which combines X-rays with computerized data analysis to con-
struct a three-dimensional image. In CTA, the scan is performed
simultaneously with high-speed injection of a contrast agent
through a peripheral vein ( 16 ). In CTP, the scan is performed
simultaneously with administration of a diffusible inert gas indica-
tor (e.g., xenon) or a nondiffusible indicator (e.g., iodinated con-
trast agent) ( 16 ). These two modalities may be combined for
aggregate data collection ( 16 ).
These techniques have distinct advantages and disadvantages.
CTA is less invasive than angiography in evaluating intracranial ves-
sels ( 16 ). However, it is not as accurate as angiography in diagnos-
ing vasospasm ( 16 ). CTP is often coupled with CTA, and can
provide information about cerebrovascular hemodynamics, includ-
ing cerebral blood fl ow, cerebral blood volume, and mean transit
time ( 16 ). It is more accurate in diagnosing severe vasospasm, but
has less sensitivity in diagnosing mild or moderate vasospasm ( 16 ).
Studies using CTA and CTP in animal models are limited
( 22, 23 ). Laslo et al. ( 22 ) investigated whether CT perfusion-
derived hemodynamic parameters could predict the severity of
vasospasm in rabbits. CTP was performed before SAH and up to
16 days post-SAH ( 22 ). The vessel diameter was assessed by CTA,
and hemodynamic parameters were assessed by CTP ( 22 ). Contrast
was administered via the saphenous vein ( 22 ). They found that a
decrease in mean transit time of blood in the cerebral vessels within
2 days of SAH predicted severe vasospasm in these rabbits ( 22 ).
The same group studied the effects of nimodipine on improving
CT perfusion-derived hemodynamic parameters following SAH in
rabbits ( 23 ). As with the previous study, they used CTA to calcu-
late the diameter of the basilar artery and CTP to assess the hemo-
dynamic parameters ( 23 ). They found that rabbits treated with
nimodipine in the peri-SAH period had increased mean basilar
artery diameter, improved neurologic outcome, and increased
mean cerebral blood fl ow ( 23 ).
5. Magnetic
Resonance
Angiography,
Perfusion, and
Spectroscopy
The combination of MRI with angiography (MRA), perfusion
(MRP), or spectroscopy (MRS) are also new modalities that are
being used with increasing frequency to evaluate vasospasm in both
humans and animal models ( 16 ). MRI uses a strong magnetic fi eld
 
Search WWH ::




Custom Search