Type:
Educational Exhibit
Keywords:
CNS, Neuroradiology brain, Vascular, CT, Diagnostic procedure, Ischaemia / Infarction, Cancer
Authors:
L. Canales1, M. López Ramírez2, E. A. Torres1, P. Orellana1, G. A. Miranda2, L. Lopez1, J. de Grazia2, A. Salas1, B. Perez1; 1Santiago/CL, 2Santiago, RM/CL
DOI:
10.26044/ecr2019/C-1607
Background
The CTp is a technique that allows rapid qualitative and quantitative evaluation of cerebral perfusion by generating maps of cerebral blood flow (CBF),
cerebral blood volume (CBV),
and mean transit time (MTT).
The technique is based on the central volume principle (CBF=CBV/MTT) (Fig. 1,
Fig. 2).
There are some complementary parameters such as the permeability map of the blood-brain barrier (Fig. 3).
Perfusion studies are obtained by monitoring the first pass of an iodinated contrast agent bolus through the cerebral vasculature.
There is a linear relationship between contrast agent concentration and attenuation,
with the contrast agent causing a transient increase in attenuation proportional to its amount in a given region.
Contrast agent time - concentration curves are generated in an arterial region of interest (ROI),
a venous ROI,
and in each pixel.
Deconvolution of arterial and tissue enhancement curves,
a complex mathematic process,
gives the MTT.
The CBV is calculated as the area under the curve in a parenchymal pixel divided by the area under the curve in an arterial pixel.
The central volume equation can then be solved for CBF (Fig. 4).
Its main indication has been the study of acute cerebral infarction to determine ischemic penumbra susceptible to reperfusion treatment.
However,
there is evidence of its usefulness in other situations such as: hypo-hyperperfusion states,
tumor grading in gliomas,
trauma and others.
The advantages of CTp are its availability,
speed and possibility of performing associated with angiographic studies.
The main disadvantages are derived from the use of ionizing radiation and iodinated contrast agent.
The CTp scans at our institution are obtained using a 128-slice CT scanner.
After an unenhanced CT of the whole brain,
a perfusion acquisition is made that includes all the arterial territories in a maximum extension of 10 cm,
which can be reduced as necessary.
In our experience,
a reduction of the radiation dose is obtained by adjusting the parameters of mAs and kV to values of 180 and 70 respectively,
without impairing the quality of the study and obtaining DLP values close to 1500 mGycm.
Total DLP is also reduced by eliminating the additional pre and postcontrast phases in patients who already have other imaging techniques.