Image Processing Reference
In-Depth Information
CBF
C
VOI
(t) =
−
k
VOI
In
TE
S (t)
S
0
tissue signal
tissue concentration
0.6
0.4
505
495
485
CBV
0.2
sec
sec
0.0
475
0
20
40
60
80
0
20
40
60
80
arterial signal
arterial concentration
505
480
455
3.5
2.8
2.1
DSC-MRI
1.4
430
MTT
405
0.7
sec
sec
0.0
380
0
20
40
60
80
0
20
40
60
80
k
AIF
S (t)
S
0
C
AIF
(t) =
−
In
TE
FIGURE 19.3
The quantification process of DSC-MRI image: from signal acquisition
(left) to parametric mapping generation (right) of CBF, CBV, and MTT.
to be constant across the brain and by assigning the mean relative CBF value in
white matter to a standard value of 22 ml/100 ml/min. The relative CBF values
from each of the tissue gray regions were then multiplied by this individualized
scaling factor to yield absolute CBF. The rationale for using normal cerebral
white matter as an internal reference standard for generating absolute MRI CBF
values is based on PET measurements that showed that in normal adult volunteers,
white matter has a relatively uniform age-independent blood flow of 22 ml/100
ml/min. A different approach was introduced in Reference 42 and Reference 43
where in order to convert relative MRI CBF values to absolute ones, a conversion
factor derived by comparison studies between relative MRI and absolute PET
CBF measurements was proposed. A similar approach, with some dissimilarities,
has been proposed in Reference 44 where CBF values were converted to absolute
values by calculating the ratio of the CBF value measured by PET to the mean
relative CBF measured by DSC-MRI in three subcortical white matter regions
and multiplying by this scaling factor the relative CBF from each gray tissue to
yield absolute MRI CBF values. However, even if this approach can provide a
good qualitative index of CBF for patients with chronic carotid occlusion, these
absolute CBF values are not accurate [44]. In summary, there is no gold-standard
method to use in order to obtain accurate absolute CBF values in normal as well
as in pathological subjects, and additional studies are needed in order to address
the problem concerning the correct absolute quantification of CFB by DSC-MRI
[23,45], especially in presence of pathologies such as chronic carotid occlusive
diseases, tumors, and strokes.
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