Image Processing Reference
In-Depth Information
understand the effect of partial-volume presence in C
AIF
(t) in the quantification
of DSC-MRI images.
In addition to the presence of partial-volume effect, C
AIF
(t) may undergo
dispersion during its passage from the point of measurement to more peripheral
VOI, especially in pathology. If d(t) denotes the dispersion function, the decon-
volved residue function does not represent CBF multiplied by the true residue
function R(t), i.e., R
R(t), but represents CBF multiplied by the con-
volution between the true residue function and the dispersion one, i.e.,
′
(t)
=
CBF
⋅
Rt
′
()
=
CBFRt
⋅
()
⊗
dt
()
(19.24)
0
0
Rd
with , and . Thus, in presence of
dispersion, the actual residue function has a different shape and properties
(Figure 19.2) in comparison with the true one. The measured C
AIF
(t) may also be
affected by a delay. Delay and dispersion presence modifies the shape of the
deconvolved curve and, in this case, CBF is usually estimated from the maximum
of the deconvolved curve [13,22] instead of from the deconvolved curve at time
t
∫
dd
()
ττ
=
1
R
(00
′
=
∫
′
()
ττ
=
FM T
⋅
0, which is zero in presence of delay and dispersion. In this way, an error in
quantification of CBF is introduced. In fact, recent studies have shown that delays
of 1 to 2 sec can introduce a 40% underestimation of CBF and a 60% overesti-
mation of MTT [23]. Of note is that these delays between the “measured” and
“true” AIF are common in cerebral regions affected by cerebrovascular disease.
Consequently, the quality of information provided by quantification of MRI
images is reduced in important pathologies such as cerebral ischemia and carotid
stenosis. As suggested in Reference 24 and Reference 25, C
AIF
(t) should be
measured as close as possible to the true feeding artery to the VOI in order to
minimize delay and dispersion effects on the CBF estimate. Although the use of
=
1
no dispersion
dispersion
0.8
0.6
0.4
0.2
0
0
10
20
30
time (sec)
FIGURE 19.2
Residue function R(t) in the absence (solid) or presence (dashed line) of
arterial dispersion.
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