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CT Perfusion - Xenon Comparison
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CT Perfusion Overview
The CT Perfusion Application affords a quantitative measurement of regional
cerebral blood flows, i.e. of blood flows in each pixel of the cerebral
parenchyma. A perfusion CT study involves sequential acquisition of stationary
cerebral CT sections during intravenous administration of an iodinated contrast
material bolus (using The LightSpeed CT Unit from GE Healthcare). Analysis
of the resultant contrast enhancement curves (figure 1) according to the central
volume principle allows a physician to calculate three parameters describing the
cerebral hemodynamics in each pixel of the cerebral CT section: the regional
cerebral blood volume (rCBV) (figure 2), the blood mean transit time (MTT)
(figure 3) through cerebral capillaries and the regional cerebral blood flow
(rCBF) (figure 4). The rCBF map deduced from perfusion CT studies leads to
quantitative results which closely relate to those of stable Xenon-CT studies
(figure 5) as illustrated by the following case report.
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Fig. 1: Contrast media evolution in Artery (curve 1) and Vein (curve 2) according to time / slice number. Curve 3 shows the evolution of the cerebral parenchyma contrast media |
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| Fig. 2: Regional Cerebral Blood Volume (rCBV) image |
Fig. 3: Regional Cerebral Mean Transit Time (MTT) image |
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History
A 50-year-old female patient was
admitted at our institution with a right face-arm-leg hemisyndrome. Hemiparesis was
preponderant. A perfusion CT study performed in this patient depicts low rCBF values
in an area including the anterior parts of the left lenticulate nucleus and of the
left internal capsula, as well as the head of the left caudate nucleus (figure 4).
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| Fig. 4: Regional Cerebral Blood Flow (rCBF) image |
Fig 5: Xenon Perfusion Image |
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Xenon Comparison
Stable Xenon-CT obtained a few minutes before the perfusion CT displays exactly the same ischemic region (see ROI on the images). Perfusion CT also discloses a low rCBV (figure 2) and a slightly increased MTT in the ischemic cerebral area (figure 3), thus demonstrating it as an irretrievable cerebral infarct, with subsequent consequences on the patient's care. This stroke related to a post-herpetic cerebral vasculitis.
Stable Xenon-CT was validated as an accurate technique in the rCBF measurement (figure 5), but involves inhalation of stable Xenon by the patient, with possible side effects, and necessitates expensive and complex equipment, available only in few medical centers.
On the contrary, perfusion CT studies are easy to perform, and do not necessitate any special devices other than those present in every CT unit. Acquisition is realized in less than one minute, perfusion CT being thus very well tolerated by patients. Multidetector array technology allows a physician to evaluate a 20-mm-thick cerebral volume.
Perfusion CT studies can thus be achieved in the emergency setting, for instance after the conventional CT evaluation in the initial care of acute stroke patients. In the future, perfusion CT studies will perhaps modify acute stroke patients' management, for instance with respect to inclusion criteria in thrombolysis protocols.
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Protocol
Technical Parameters
Scan Type - cine (axial)
Rotation Time - 1.0 sec
Prospective Thickness - 10 mm
SFOV - 25 cm
kVp - 80
mAs - 200
Recon Type
Total Acquisition time - 50 sec
Coverage - 20 mm
Total of images - 2 x 50
Contrast Parameters
Rate - 5 ml/sec
Total Contrast Amount - 40 ml
Type of contrast - iohexol 300 mg/ml
(Accupaque 300, Nycomed, Oslo, Norway)
Acquisition beginning 2 seconds after intravenous administration.
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CT Perfusion is compatible with the following scanners/scanner series:
- LightSpeed Series (AW optional)
- HiSpeed CT/i *
- HiSpeed X/i *
- HiSpeed NX/i
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| * Advantage Windows Workstation required |
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Check out
the CT software packages currently available to eFlexTrial, at no cost, for 30 days.
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