Biomedical Engineering Reference
In-Depth Information
opted for the pigmented, “hooded”, Long-Evans strain of rats for
our visual experiments only. Preparation was similar to forepaw
and whisker studies with the exception that isoflurane was used
for induction (3-4%) and surgery (1.5-2%).
Male Sprague-Dawley rats were anesthetized with urethane (1.3
g/kg, intraperitoneal) with additional doses (0.13 g/kg, intra-
venous) administered if necessary depending on the duration of
the experiment. These rats were freely breathing (i.e., no tra-
cheotomy).
2.2.3. Olfactory Studies
2.3. Experimental
Setup for fMRI
Studies
We used a custom-designed cradle with a bite bar for head
immobilization during fMRI scans. All stimulus delivery items
were secured onto the holder with adhesive tape. In some cases,
to record the electroencephalogram (EEG) simultaneously with
fMRI, we used a pair of carbon fibers (WPI) placed bilaterally over
the parietal cortex between the scalp and the skull
(44)
. All fMRI
data were obtained on a modified 11.7 T Bruker horizontal-bore
spectrometer (Bruker AVANCE, Billerica, MA) using a
1
Hsur-
face coil (diameter of 14 mm) radio frequency probe. The cradle
was securely placed under the coil. The z axis position was depen-
dent on the stimulus used and distance between coil and head (y
axis) was minimized.
A voxel of
L, respectively, for the bulb and
brain was shimmed with fast, automatic shimming technique by
mapping along projections (FASTMAP)
(45)
utilizing first and
second order shim gradients. The static field inhomogeneity was
optimized until the half-height line width of water in the shim-
ming voxel was less than 15 and 20 Hz, respectively, for imaging
the bulb and brain. The neuroanatomy was imaged with either the
rapid acquisition relaxation enhanced (RARE)
(46)
or fast low-
angle single shot (FLASH)
(47)
contrast sequence. For all brain
studies, we used single-shot echo-planar imaging (EPI)
(48)
with
sequential sampling
(49)
and the following parameters: Recycle
time (TR)
∼
100 and
∼
300
μ
=
1000 ms; echo time (TE)
=
15 ms; field of view
2.56 cm
2
; image matrix
(FOV)
=
2.56
×
=
64
×
64; number of
slices
=
3or6;slicethickness
=
2 or 1 mm; voxel size
=
320
45-60
◦
. For olfactory studies, we used
FLASH contrast and the following parameters: TR
or 160 nL; flip angle
=
=
500 ms;
1.56 cm
2
; image matrix = 64
=
×
×
TE = 15 ms; FOV
1.56
64;
number of slices
=
20; slice thickness
=
250 or 500
μ
m; voxel
15-30
◦
.
size
=
15 or 30 nL; flip angle
=
2.4. Experimental
Setup for
Electrophysiology and
Laser Doppler
Flowmetry
The rat was placed in a stereotaxic holder (David Kopf Instru-
ments, Tujunga, CA) sitting on a vibration-free table in a Faraday
cage adjacent to the scanner. For all somatosensory region record-
ings, we developed a combined dual-probe consisting of a high
