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Functional Information on Meningiomas Through Perfusion Magnetic Resonance Imaging
intravenous (IV) catheters and higher injection rates (≥4ml/s), Applications of Perfusion Magnetic
coupled with repeated rapid cine imaging of a volume of interest Resonance Imaging in Meningiomas
while the contrast passes through the capillary network. To record There are two main types of brain tumour: primary brain tumours
the tracer concentration during this passage faithfully, one must start in the brain, while metastatic brain tumours start somewhere
acquire images at a faster rate than the time it takes the bolus to else in the body and move to the brain. Meningiomas account for
pass through the tissue, which is usually in the order of several 30.1% of all primary brain tumours, making them the most common
seconds. For DSC-MRI, this acquisition was commonly carried out by primary brain tumour.
14
using a T2 (spin echo [SE]) or T2*-weighted (gradient-enhanced [GE])
echo planar imaging (EPI) sequence. Brain tumours require a blood supply to grow and this in turn
requires angiogenesis. More recently, angiogenesis has been
Weisskoff and co-workers
6–8
found that SE measurements are mainly recognised as a key element in the pathophysiology of tumour
sensitive to vessel sizes comparable to the water diffusion length growth and metastasis.
15
Once tumours grow beyond a diameter of
during the time of echo (10µm), whereas GE measurements are 1–2mm, passive diffusion is no longer sufficient to support the
equally sensitive to all vessel sizes. In practice, perfusion imaging viability of malignant cells, and neovascularisation becomes a
performed using an SE approach requires twice the amount of necessity.
16
Therefore, tumours that grow beyond the occult stage
contrast agent (usually 0.2mmol/kg) compared with imaging with are capable of activating the ‘angiogenic switch’. The new blood
GE-EPI (0.1mmol/kg). Furthermore, preliminary studies suggest that, in vessels formed are generally less organised than the normal vessels
the brain, the microvascular CBV ‘visible’ by SE-EPI is roughly 45% and hence have altered perfusion characteristics with increased
of the ‘total’ CBV compared with measurements using GE-EPI.
9
blood flow and volume.
17–19
By detecting the arterial as well as the total tissue concentration as a Meningiomas are highly vascular neoplasms and often show higher
function of time during a single transit, CBV can be determined from rCBV than other primary and metastatic brain tumours. Previous
the ratio of the areas under the tissue and arterial concentration time studies suggested that for meningiomas with atypical conventional
curves.
10
As arterial measurements (due to limited spatial resolution) MRI findings, calculation of rCBV ratios and construction of signal
are not readily quantifiable, relative CBV values are usually reported.
Assuming uniform arterial concentration profiles in all arterial inputs,
relative CBV measurements are determined by simply integrating the In our results, from highest to lowest, the
area under the concentration–time curve.
11,12
maximal regional cerebral blood volumes
Quantification of CBF and MTT, which are time-dependent parameters, in tumour parenchyma were ranked as
is much more complex. The highest degree of quantification utilises
angiomatous, anaplastic, meningiothelial
the deconvolution method and requires knowledge of an AIF. One must
calculate the contrast concentration versus time curves from the and fibrous meningioma.
signal intensity data. The area under the contrast concentration curve
provides an estimate of CBV within the voxel, and the width of the
contrast bolus is used as an estimate of the MTT of blood through intensity–time curves may contribute to the differentiation of
the voxel. The regional CBF can then be calculated using the central meningiomas from intra-axial tumours.
20,21
Different meningioma
volume theorem: CBF/CBV = MTT. Unfortunately, this approach to the subtypes also show different vascular characters. A study by Kimura
measurement of CBF is subject to significant errors arising from a et al. illustrated that among different subtypes of meningioma,
number of sources. These errors have led to modifications of the perfusion values of angiomatous meningioma were the greatest and
analysis method in an attempt to produce a more accurate, lowest for fibrous meningioma,
22
and their results correspond to our
quantitative estimate of blood flow. experiences. By studying a group of 37 patients with newly diagnosed
meningiomas, we found that the maximal rCBVs in both tumour
Absolute MTT values cannot be calculated because there are parenchyma and peritumoral oedema showed statistical differences
variables such as the dispersion of the contrast material following IV between subtype meningiomas.
23
injection, cardiac output and the precise amount of contrast entering
and leaving a region of interest (ROI) at a given point in time that In our results, from highest to lowest, the maximal rCBVs in tumour
cannot be measured. The mean time to enhance (MTE) is related to parenchyma were ranked as angiomatous, anaplastic, meningiothelial
the time to peak and to the width of the peak of the time–signal curve; and fibrous meningioma. In the peri-tumoral region, the maximal rCBV
MTE is computed and displayed only for the images between the last of anaplastic meningioma was highest, followed by fibrous,
pre-enhancement image and the first post-enhancement image, meningiothelial and angiomatous meningioma.
equivalent to the bolus arrival time.
When comparing the mean rCBVs of the two subtypes, our results
Among various perfusion parameters, regional CBV (rCBV) appears to showed that the maximum rCBVs in tumour parenchyma of
represent regional variations in CBV accurately and is particularly angiomatous meningioma and in the peri-tumoral region of anaplastic
used in the study of tumours.
13
Some professional software can obtain meningioma were statistically greater (p<0.05) than those of other
half-quantified measurements of blood flow by using deconvolution subtypes. From these studies, we presumed that some common
techniques with an arterial input function; however, the intrinsic benign subtypes of meningioma such as meningiothelial and
potential problems with this technique and consequent potential fibrous meningiomas cannot be differentiated from atypical or
inaccuracies in quantitative measurements must also be considered. anaplastic meningiomas simply by evaluating their parenchyma rCBV
EUROPEAN NEUROLOGICAL REVIEW 89
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