This paper reviews the use of contrast-enhanced CT studies to provide needed information within a relevant time frame to tailor appropriate treatment for victims of cerebral vascular accidents.
received his medical degree from Emory University Medical School,
Atlanta, GA in 1998. He is currently a third-year Radiology
Resident at Emory University. He plans to begin a fellowship in
Neuroradiology at Emory in 2003.
First-pass perfusion computed tomography (CT) and CT
angiography (CTA) can evaluate brain ischemia and large vessel
patency rapidly using the same imaging equipment often used in
the initial evaluation of stroke. While magnetic resonance (MR)
diffusion and perfusion techniques hold great promise in the
setting of cerebral ischemia/infarction, this promise has not
been realized, due in part to a lack of widespread 24-hour
availability of MR equipment. This paper reviews the use of
contrast-enhanced CT studies to provide needed information within
a relevant time frame to tailor appropriate treatment for victims
of cerebral vascular accidents. Reviewed studies will demonstrate
that these techniques triage patients quickly for current
treatment regimens and soon may provide the basis for
thrombolytic treatment regimens outside of the 6-hour limit
Cerebral vascular disease is the second leading cause of death
and the leading cause of permanent disability, affecting more than
600,000 people each year in the United States alone.
In recent years, significant advances have been made in the
treatment of stoke. In 1996, intravenous (IV) tissue plasminogen
activator (t-Pa) became the first treatment approved for acute
stroke by the U.S. Food and Drug Administration. This approval was
based on the findings of the National Institutes of Neurological
Disorders and Stroke (NINDS) t-Pa Study Group. This large,
multicenter, placebo-controlled study showed long-term clinical
benefit if IV t-Pa was given within 3 hours of onset of ictus to
patients who were found not to have hemorrhagic stroke by a
noncontrast computed tomographic (NCCT) head scan.
There was a substantially increased risk of hemorrhagic
transformation in the treated group, however, and in practice the
criteria have proven very restrictive.
The International Stroke Trial Pilot Study of 984 patients found
that only 4% of patients presented to the emergency department
clearly within the 3-hour limit. Extending the cut-off to 6 hours
included no more than 16% of cases.
Another study indicated that up to 60% of cases present with an
uncertain time of onset.
The Prolyse in Acute Cerebral Thromboembolism (PROACT II) study
demonstrated a new role for imaging, while again illustrating the
limitations of current treatment.
It showed benefit for proven occlusion of the M1 or M2 branches of
the middle cerebral artery (MCA) with intra-arterial urokinase
within 6 hours of onset, but of 12,323 patients screened for
suspected stroke only 474 candidates underwent immediate
angiography. Of these, only 180 patients met all criteria for
Attempts to extend the proven effective treatment window for IV
t-Pa have yielded ambiguous data, and again imaging is central to
the issue. The European Cooperative Acute Stroke Studies (ECASS) I
and II failed to demonstrate benefit of IV thrombolysis within 6
However, a sub-group analysis by the ECASS CT review panel found
that 52 patients were given t-Pa inappropriately due to
"misinterpretation" of CT scans.
The review panel concluded these patients showed CT findings of
ischemic changes involving >33% of a single MCA territory, which
was a criterion for exclusion from the treatment group. When these
patients were excluded from the analysis, benefit within a 6-hour
window was shown.
CT perfusion and CTA techniques will be discussed that have
demonstrated both sensitivity and specificity for ischemic stroke.
These provide information in a clinically relevant time frame to
expand the pool of patients eligible for treatment protocols
within, and perhaps beyond, the 6-hour window.
If cerebral perfusion is gradually reduced in a region, the
first detectable threshold is the point at which the metabolic
needs of electrical activity are no longer met and that portion of
the brain becomes "silent" by electroencephalographic (EEG)
monitoring and symptomatic for the patient. Measurements using
O-labeled water positron emission tomography (PET), considered the
gold standard for absolute perfusion, and other modalities such as
xenon-enhanced CT (Xe CT) and single-photon emission computed
tomography (SPECT), have given consistent estimates of 15 to 25
mL/100 g tissue/min for this threshold.
If perfusion is not restored within approximately 6 hours, or if
perfusion falls to 10 to 15 mL/100 g/min, the neuron can no longer
maintain normal ATP-dependent Na+/K+ membrane ion pump activity and
dendritic and perivascular astrocytic end-foot swelling occurs.
This so-called "cytotoxic edema" can be detected readily by MRI and
is partially or completely reversible if perfusion is normalized
within 3 to 6 hours. Beyond this period, or if perfusion falls
below 10 mL/100 g/min for even 5 to 10 minutes, infarction is
inevitable and cytotoxic edema becomes marked. If perfusion is
reduced but still present for 4 to 6 hours, there is loss of
integrity of the blood-brain barrier, allowing a marked efflux of
water and proteins into the extracellular space from the capillary
bed. This phenomenon, termed vasogenic edema, is detected by both
MRI and NCCT and typically reaches a peak in 3 to 5 days.
The natural history of a stroke varies, and current thinking
holds that there are opportunities for effective interventions if
the pathophysiology can be better characterized.
Clinical progression of stroke occurs in as many as one third of
and enlargement of the actual territory of the infarction is very
common. One recent prospective study found that 46 of 49 untreated
stroke patients demonstrated growth of infarct volume on scans
performed within 24 hours of the event and on the second day after.
Other longitudinal studies
and animal models
support the theory that with an event, there is a core of infarcted
tissue that is nonviable, surrounded by hypoperfused but still
viable brain at risk for infarction by prolonged hypo-perfusion,
failure of collateral circulation, secondary embolic events,
further reduced perfusion secondary to parenchymal edema, or
excitatory neurotransmitter-mediated metabolism alteration and
oxygen-radical injury. The volume of nonviable tissue is strongly
correlated with the risk of hemorrhagic transformation.
The threatened tissue, or ischemic penumbra, is the target for
treatment. Dedicated MRI techniques image this threatened tissue
directly and changes of ischemia have been shown as early as 5
minutes after the onset of the insult using animal models.
Reperfusion treatments have proven benefit.
Neuro-protective agents have yet to show benefit in humans.
Imaging techniques and requirements
Helical CT scanners must be used for CTA in order to image the
cervical vessels through M3 branches prior to the venous phase, as
traditional axial CT scanners are unable to cover the required
territory of interest before the arterial bolus becomes venous.
Following the acquisition of a routine NCCT, CTA is performed,
followed by a CT perfusion scan after a minimum delay of 5 minutes.
Typically, 75 to 150 mL of 300 mg I/mL or 370 mg I/mL iodinated
(I) contrast is injected at rates of 3 to 4 mL/sec through an
18-gauge IV needle in an antecubital vein.
Depending upon the likely cardiovascular status of the patient,
standard delays between 18 and 24 seconds can be selected before
initiating scan in a caudal-cranial direction from either the
cervical vessels or the skull base through the Sylvian fissures 1.5
to 2.0 cm above the sella. A 10- to 15-mL timing bolus may be
helpful if the patient is suspected of having an abnormal cardiac
output that might delay the peak arterial contrast phase.
Proprietary software packages vary among vendors regarding the
specifics of a timing bolus technique. Beam collimations from 1 to
1.5 mm are used with a low pitch of 0.8 to 1.0 with 120 to 140 kV
and maximum mA typically 250 to 300. The raw data is reconstructed
with a low-noise algorithm with a small field of view (FOV) that
includes the Circle of Willis and the lateral M3 branches, using
50% overlapping thin slices. The images should be reviewed on a
workstation allowing multiplanar reformats, three-dimensional (3D)
reconstructions with easily manipulated display windows and levels.
Curved planar reformatting, maximum-intensity projection (MIP),
volume-rendering (VR), and shaded surface display (SSD) have been
showing an advantage for MIP when dense vessel calcifications are
present, and for VR when viewing complex anatomy.
CT perfusion techniques are evolving, and many recent advances
were presented at the 2001 annual meeting of the Radiological
Society of North America (RSNA 2001). Eastwood et al
reported on a scanning protocol that performs a continuous cine in
the transverse plane, with angulation of the gantry to minimize
imaging artifact from dental amalgam. The continuous acquisition
necessitates limiting the imaged territory to the greatest
composite slice thickness the CT scanner can perform. Therefore a
scanner with a single 1-cm detector could provide a single 10-mm
slice perfusion study coverage, whereas a scanner with four 5-mm
detectors could produce a total imaged territory of 2 cm. The
imaged territory should be chosen to include the basal ganglia as
well as cortical vascular territories of the anterior, middle, and
posterior cerebral arteries bilaterally. Alternate slice locations
may be chosen on the basis of clinical presentation and the
preliminary findings of the angiographic scan. A total of 40 to 50
mL of contrast, a 25-cm FOV, and 512 * 512 pixel reconstruction are
used. X-ray generation and contrast injection techniques vary. A
high injection rate technique using 10 to 20 mL/sec would be imaged
with a kV of 140 and 40 mA.
A lower injection rate technique using 3 to 6 mL/sec, such as that
recently validated by Eastwood et al and others, uses a lower
energy technique of 80 kV and 200 mAs to improve tissue contrast
while keeping contrast dose low.
Higher rate techniques require large-bore venous access, such as
14-gauge IV needles, which can be difficult to place in the older
patients, making the lower rate technique more feasible.
Uses, validation, and pitfalls
It is argued the value of noninvasive angiography should be
equal to that of conventional angiography for diagnosis of
large-vessel occlusion, without the 1% to 2% complication rate of
stroke or arterial injury.
The advantages of traditional angiography are: 1) it remains the
gold standard for diagnosis and is itself evolving with the use of
3D rotational acquisition for single injection depiction of
vascular anatomy; and 2) treatment of an identified large clot with
catheter-administered intra-arterial thrombolytics is an
immediately available option.
Conventional angiography has a proven and important role in the
diagnosis of stroke. It can define the etiology of an ischemic
event, directing both immediate and long-term treatment.
Carotid dissection and involvement of the cerebral vasculature by
aortic dissection and large-vessel high-grade stenosis/occlusion
are readily shown,
and ulcerated arterosclerotic plaque is well depicted.
Third, the conclusions of the PROACT II study support the use of
angiography to prove MCA occlusion for intra-arterial thrombolysis
up to 6 hours after the onset of ictus
(figures 1 and 2).
There is validation in the literature comparing CTA with
invasive methods on emergent patients. In one series of 44
patients, patients with abnormal findings on CTA were immediately
taken for conventional angiography and a comparative accuracy of
99% for CTA was found.
No patient with a normal CTA was found on clinical or imaging
follow-up to have had a large-vessel occlusion. In another series
of 42 patients, all 22 patients later shown to have large-vessel
events were correctly identified by CTA.
Multiple studies on nonemergent patients comparing CTA with digital
subtraction angiography (DSA) and magnetic resonance angiography
(MRA) have shown near 100% accuracy for occlusions. The literature
disagrees, however, on CTA's ability to differentiate between
stenoses of 50% to 69% and 70% to 99%.
A complete overview of the challenges of CTA is beyond the scope
of this article; however, the following examples illustrate common
problems and how they can be addressed.
One pitfall identified in the literature is the potential for a
false positive diagnosis of internal carotid artery (ICA) occlusion
due to slow flow proximal to a stenosis or occlusion of a large
branch vessel when using an early arterial phase bolus technique.
A brief delay of 2 to 3 minutes, long enough to review initial
images at the scanner monitor and to initiate a second scan, may
aid in these cases. A second pitfall to avoid is injecting the
contrast into a left arm vein. If the patient has a compromised
cardiovascular status, the minimal relative impediment to passage
of contrast through the brachiocephalic vein can cause relux into
subcutaneous, muscular, and epidural plexus veins, degrading the
study. This can be lessened or avoided altogether by a right arm
Another pitfall is that although imaging vessel calcification is
an advantage of CT, beam hardening artifacts remain difficulties,
especially dense medial calcifications found in diabetic patients.
MRA has been considered to have a decided advantage in these cases,
however, using VR and MIP displays for CTA of the posterior fossa
for vasospasm secondary to subarachnoid hemorrhage has shown
Continuing efforts to address the obscuration caused by bone,
aneurysm clips, dental amalgam, and other surgical metal are being
made. A complicating factor is that often functions labeled "VR"
and "MIP" can mean different renderings with different proprietary
software configurations, and the radiologist's experience with the
specific software package and workstation will prove important in
the diagnostic value of the study.
CT perfusion is based on tracer kinetic theory analysis using a
single-compartment model of first-pass of a bolus of iodinated
contrast material through the cerebral vasculature. The single
compartment is the vascular system, and it is assumed there is no
extravasation or stasis of contrast or alteration of the studied
organ caused by the contrast agent. As the contrast bolus passes
through the arterioles, capillary bed, and venules of the brain,
the brain parenchyma becomes homogeneously and diffusely more X-ray
attenuating. The entry and exit of the bolus can be seen directly
as opacification of the major arteries and veins, respectively.
The distribution of an IV contrast bolus leaving the heart and
entering the brain should follow a gamma-variate function, and a
curve can be readily generated showing an increase, peak, and
return to baseline of the X-ray attenuation by the brain as a
function of time (figure 3). From this curve, peak enhancement,
time to peak, and width at half-height--each proportional to blood
flow--can be calculated readily. Perfusion protocols generate a
contrast-enhancement curve for each pixel within the scanned slices
or commercially available software packages.
Regions-of-interest (ROIs) can be hand-drawn over one vessel for
arterial input and over another for a venous input, typically a
branch of the MCA and the superior sagittal sinus, respectively.
Taken altogether, this data is then analyzed to produce values for
three parameters: mean transit time (mTT), cerebral blood flow
(CBF), and cerebral blood volume (CBV). Mean transit time can be
defined either by the central volume principle as the ratio of CBV
to CBF. Cerebral blood volume can be calculated as either
proportional to the peak enhancement of a pixel, or from the
central volume principle using the other two values. These values
can be displayed as color images for interpretation. Interoperator
reliability for generation of these results by experienced
neuroradiologists has proven acceptable.
The data are analyzed by one of two algorithms, the maximum
or deconvolution method.
The difference between methods lies in the determination of CBF.
The maximum slope method assumes no venous contrast and calculates
CBF by finding the slope of the tissue-concentration curve versus
the integral of the arterial-concentration curve. This method
requires very high injection rates of 10 to 20 mL/sec in order to
obtain the needed arterial contrast concentration within the
typical minimum transit time of 4.5 to 6.5 seconds into the venous
The deconvolution technique compares the shape and height of the
time-attenuation curve of each pixel with the shape and height of
the arterial and venous time-attenuation curves to determine CBF.
Venous contrast is accounted for, and therefore contrast injection
rates of 3 to 6 mL/sec can be used. The resulting perfusion maps
are noisier but diagnostically equivalent.
A review of the literature finds that several small series of
acute cases have been published. Three studies included 22
and 32 patients
imaged within 6 hours of onset of symptoms, and one included 70
patients who were imaged within 12 hours of onset.
The reported sensitivities ranged from 89%
and specificities from 98%
for the detection of stroke.
MTT, CBV, and CBF
While it is agreed that tissue death is a direct result of time
subjected to blood flow below a viability threshold, CBF has not
proven to be a single-parameter predictor of tissue outcome.
The most sensitive and least specific indicator of ischemia is
With a stroke, this measure tends to be abnormal over the greatest
area of brain, and likely indicates the infarct, the penumbra, and
adjacent brain that is not at risk of infarction. An mTT below the
threshold of 6 seconds likely reflects delayed blood flow by
stenosed or collateral, circuitous routes.
This threshold agrees well with findings by MRI (figure 4).
CT perfusion-derived CBF has been validated in animals and
humans in comparison with Xe CT,
although the issue of quantification remains, and currently
O labeled-water PET is the gold standard for determining absolute
CBF values. Quantification is also an issue regarding MRI perfusion
studies, and, to date, all MRI perfusion studies have used relative
measures. Koenig et al
quantified flow by CT perfusion as relative to the contralateral
hemisphere--relative cerebral blood flow (rCBF) and relative
cerebral blood volume (rCBV)--while others give unit values. These
values are readily comparable and the results between groups
substantially agree. Eastwood et al
showed strokes detected by NCCT have mean CBF of 13.1 + 8.4 mL/100
g/min compared with values for the contralateral hemisphere of 31.6
+ 12.4 mL/100 g/min (roughly 40%). Mayer et al
showed that all of the patients with rCBF values below 30%
progressed to infarction, as did half of those whose values were
between 30% and 60%.
An rCBF cutoff value of 48% for prediction of infarction if left
untreated has been proposed by the authors of a third study in
which the lower range of normal perfusion was 55 mL/100 g/min in
the contralateral hemispheres. This value had an efficiency of
74.7% predicting the outcome of tissue.
These findings correlate well with the widely accepted values of 15
to 25 mL/100 g/min for infarction if prolonged (figure 5).
Cerebral blood volume abnormalities can vary between hyperemia,
mild oligemia, and profound hypovolemia.
There is vasodilatory autoregulation in the setting of acute
ischemia, and some have posited a protective effect of hypervolemia
in the setting of reduced flow.
However, as compensatory mechanisms fail, CBV falls, therefore it
has been argued that a markedly decreased CBV is the most specific
indication of infarction.
Eastwood et al
propose a cutoff CBV of 1.5 mg/100 g (roughly half the CBV of
controls), and showed a mean CBV of 0.9 ± 0.4 mg/100 g within areas
found to be abnormal on NCCT. A second study proposed an rCBV
cutoff of 60%,
finding this to be the best discriminator between infarct and
peri-infarct tissue, with an accuracy of 83.1% (figure 6).
The most exciting findings are from two studies by the same
group. The lowest values for rCBV and rCBF in tissue that did not
progress to infarction were 40% and 29%, respectively, and were
found in a subset of patients who received thrombolysis within 6
hours of onset.
An earlier study analyzed the CT perfusion studies of 38 patients
with ischemic stroke showing rCBF values between 20% and 35%.
Sixty-one percent of the areas of brain treated by intra-arterial
thrombolysis survived, compared with a 25% survival of areas of
brain with the same severity of ischemia treated only with heparin.
It is not established whether CBF or CBV will be the most
accurate measure of irreversible injury. Each clearly has
considerable predictive value. More investigation will be needed to
demonstrate conclusively the role each value should play.
A patient suspected of stroke could be scanned with a
comprehensive CT protocol, and might be found to have a small area
of the left MCA with rCBV and rCBF values below 40% and 30%,
respectively. This confirms the diagnosis of stroke and excludes a
number of frequently encountered clinical mimics, including
migraines, central nervous system trauma, seizures, and
hypoglycemia. Less severe derangements of rCBV, rCBF, and mTT of
the entire MCA territory would indicate the viable tissue still at
risk. If the CTA scan showed an MCA occlusion, the patient could be
confidently taken for intra-arterial catheter-directed thrombolysis
with a reasonable hope for substantial benefit at an acceptably low
risk for a complicating hemorrhage. If, on the other hand, more
than half the MCA territory showed rCBF and rCBV values below these
cut-offs, this patient could be excluded from thrombolysis despite
a normal NCCT.
Given tools such as these for the accurate and rapid evaluation
of perfusion, it will be possible to gather data that more clearly
define what volumes of infarct or what severity of derangements are
actually found in patients who hemorrhage. Thus far,
recommendations are based on large studies using the most
elementary information imaging has to offer, blind, as it were, to
what CT perfusion and CTA can safely and rapidly show.
One pitfall is technical. Lee et al
showed that the deconvolution algorithm must have an arterial input
with contrast enhancement prior to tissue enhancement. If the
selected artery is on the affected side distal to the occlusion,
the results will be erroneous if the uninvolved contralateral
hemisphere enhances before the affected vessel.
A second shortcoming may soon be remedied by advances in
hardware. Most published perfusion imaging techniques cover 1 or 2
adjacent centimeters of brain, usually through slices that include
the territories of all major intracranial vessels. This may lead to
false-negative findings due to limited coverage.
One group has used a table-toggling technique to cover a greater
area; however, temporal resolution was sacrificed.
One manufacturer is currently pioneering the develolpment of a
large flat panel detector system of 256 contiguous 0.5 mm
detectors, covering over 12 cm in the z-axis. This would allow
continuous cine acquisition of data through the entire brain.
A more fundamental pitfall regards time. CBF values may suggest
tissue viability of regions that have been ischemic for too long
for recovery, and it has not yet been shown that this would be
reflected by CBV values. Therefore, in cases where onset of ictus
is unknown, it may be difficult to differentiate the ischemic
penumbra from inevitable infarction by CT perfusion alone, thus
exposing a person with a large volume of dead tissue to the risk of
hemorrhagic transformation by thrombolytic therapy.
Comparative advantages and disadvantages
PET imaging using
O-labeled water is accepted as the gold standard for measuring
perfusion, but availability of this short-lived cyclotron-produced
tracer is a major impediment to its widespread use. SPECT imaging
may be more feasible than PET; however, spatial resolution is poor
in comparison with PET, CT, and MRI.
A significant limitation of nuclear studies is their complete
inability to exclude hemorrhage. Time is the most critical issue in
stroke, and a protocol that needs two studies before treatment
would not be warrented without some considerable and as yet
Stable xenon CT
This technique uses X-ray attenuation by inhaled xenon to image
hematogenous delivery of this highly lipophilic agent to the brain
as a reliable measure of cerebral blood flow. Neither spatial
resolution nor exclusion of hemorrhage would be problems with this
technique; however, the only parameter produced by this study is a
measure of cerebral blood flow.
CBV and mTT measures are not calculable. Furthermore, this would
require equipment for delivery of xenon to the patient, while CTA
and perfusion studies can be performed with the hardware and
software already in place in most imaging departments.
Although a detailed discussion of MR diffusion, perfusion, and
spectroscopy techniques is beyond the scope of this article, a
brief overview follows. Conventional MRI is relatively specific and
sensitive for subacute stroke, principally by detection of
vasogenic edema, but it has not been shown to be useful for the
acute presentation. More advanced MRI techniques for diffusion,
perfusion, and spectroscopy have been extensively investigated for
use in stroke. In 1990, Reith et al
demonstrated abnormal diffusion within 5 minutes of insult using an
animal model. Cytotoxic edema is detected reliably by diffusion
imaging techniques that show reduced Brownian motion of water as it
moves into the injured or dying neuron. A partial explanation is
that cellular structures impede movement relative to the simpler
interstitial spaces. Apparent diffusion coefficient (ADC) maps have
shown sensitivities of 88% to 100% and specificities of 86% to 100%
for ischemia in the clinical setting as early as 5 minutes after an
Attempts to demarcate the core infarct from the ischemic penumbra
by diffusion abnormalities, however, have not yet been successful.
Small studies suggest a reduction of ADC of approximately 20% may
prove a reliable time-independent indicator.
Less severe abnormalities of ADC are problematic, and similar to
CBF, it is both the degree of abnormality and the duration of
ischemia, often unknown, that determine reversibility. MRI
perfusion is very similar to CT perfusion, using the same models
and assumptions regarding first-pass imaging of intravascular
gadolinium contrast. Currently, the concept of the mismatch between
severe MR diffusion derangement and MR perfusion abnormality (most
commonly the mTT) is being investigated to distinguish between
infarct and penumbra.
MR spectroscopy does show promise in delineating viable from
nonviable brain by measuring biochemical markers.
Lactic acid accumulates in the ischemic tissue because of increased
reliance on anaerobic glycolysis or decreased clearance from the
region. This has not proven reliable in showing the duration of
ischemia. More interestingly, N-acetyl aspartate (NAA), one of the
most abundant amino acids within the brain, is readily measurable,
and initial findings show a progressive decline in NAA levels with
the length of insult.
This offers a possible measure of the surviving population of
neurons within the ischemic tissue independent of information
regarding the time of onset. This is not yet proven.
Some advantages of CT over MRI are substantial but probably
temporary. The length of time needed for MRI studies is constantly
being reduced by advances in fast imaging techniques, so this does
not appear to be a fundamental obstacle. In addition, FLAIR
sequences have been shown to be highly sensitive for hemorrhage,
but NCCT has the advantage of having a clearly defined role for
stroke. It is listed as a requirement for treatment in the package
insert for alteplase in order to exclude hemorrhage and is
recommended by the American Heart Association Thrombolysis Practice
Advisory Guidelines to exclude extensive infarct.
Further, adding perfusion and angiographic protocols for CT does
not significantly lengthen imaging time. The average time for the
performance of emergent NCCT, CT perfusion, and CTA for stroke in
one series of 73 patients was 12 minutes, including an appropriate
The major drawback of MR in the setting of stroke appears to be
an issue of availability. One study showed that urgent MR
evaluation of stroke patients in the emergency department occurred
more than twice as long after symptom onset than evaluation by CT.
It is telling that, although MR diffusion and perfusion imaging has
been investigated in the use of stroke for several years, to date
there has not been one large prospective study initiated using
these techniques as part of a standard protocol for emergent
stroke. The widespread availability of CT scanning, with 24-hour
staffing for emergent patients, in contrast to MRI, gives CT
imaging an immense advantage in the evaluation of stroke. Although
the demands for training CT technologists to perform high-quality
CTA and CT perfusion studies may prove substantial, well-composed
imaging recipes have proven manageable in many centers.
CTA and CT perfusion can provide information in a timely manner.
Not every issue regarding the modality is settled. However, it is
clear more can be offered to the patient than is now widely
available without any change in equipment and staffing. Current
treatment regimens may be improved by a better understanding of the
individual pathophysiology presenting to the emergency department.
A large prospective study using these techniques as standard
protocols for the evaluation of stroke needs to be initiated.
The author would like to thank Dr. Arthur Fountain and Dr. James
Eastwood for the use of the images featured in this article. I
would also like to thank Dr. Fountain and Dr. Srinivasan Mukundun
for their invaluable support in preparing this manuscript.