Biomedical Engineering Reference
In-Depth Information
tion, and
C
b
(t)
becomes a linear function of the inhalation time.
This is also evident in
Eq. (15.10)
in which the high-order terms
become negligible when
t
is short. Therefore, it is possible to use
the simplified model for determining and imaging CMRO
2
based
on a single and completely noninvasive
17
O spectroscopic imag-
ing measurement of
C
b
(t) (55, 86, 87)
.
Recently, we have further examined the simplified model for
determining CMRO
2
under varied physiological conditions
(86)
.
In this study , we compared the CMRO
2
results obtained with the
complete model versus the simplified model using linear fitting
of C
b
(t)
under normothermia (37
◦
C) condition and hypother-
mia (32
◦
C) condition, which is a well known factor leading to
significant suppression of both CBF and CMRO
2
.
Figure 15.6
demonstrates an excellent consistency of the CMRO
2
results
between the complete and simplified models for either the
voxel-wised comparison (
Fig. 15.6A
) or the averaged CMRO
2
comparison (
Fig. 15.6B
) at both brain temperatures
(86)
.The
comparison results reveal the validity of the simplified
17
O
approach for imaging CMRO
2
applicable at a wide physiological
range. Additional technical development which further advances
the in vivo
17
O methodology could ultimately provide the sim-
plest and completely noninvasively
17
O neuroimaging approach
for imaging CMRO
2
(in humans).
Another merit of the
17
OCMRO
2
imaging approach is its abil-
ity for performing repeated CMRO
2
imaging measurements with
a short interval between two measurements. This is due to the
fact that the cerebral H
2
17
O concentration can quickly reach
a new and steady level within a few minutes after the cessa-
3.3.2. Robustness and
Reliability
3.0
3.0
(A)
(B)
T
=
32
°C
T
=
37
°C
T
=
32
°C
2.5
2.5
T
=
37
°C
2.0
2.0
1.5
1.5
1.0
1.0
R
=
0.97
0.5
0.5
0.0
0.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Simplified Model
Completed Model
CMRO
2
[Simplified Model]
(
μ
mol/g/min)
Fig. 15.6. (
A
) Voxel based CMRO
2
calculation and comparison using the completed and simplified models from a rep-
resentative rat (total voxel number used was 224 for 32
◦
C and 254 for 37
◦
C, voxel size = 75μ). (
B
)AveragedCMRO
2
values in the same rat brain at normothermia (37
◦
C) and hypothermia (32
◦
C) conditions, calculated with simplified and
completed model, respectively. Adapted from Zhu et al of Ref.
(86)
.
