Imaging of Hematoma and Perihematomal Edema in Experimental Intracerebral Hemorrhage - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 665

during the slicing process. Cryostat sections of formaldehyde-fi xed
tissue can omit this problem but do not reveal the details that can
be detected in paraffi n sections.

An alternative means of measuring the clot volume in small animals
is to determine the quantitative hemoglobin content of the brain
using spectrophotometry ( 11, 12 ). The animal is subjected to
complete transcardial perfusion to remove intravascular blood, and
then the brain is harvested. Often the hemispheres are separated
and investigated independently. Distilled water is added to the
brain sample to reach a predefi ned volume, followed by homogeni-
zation, sonifi cation to lyse the erythrocyte membrane, and cen-
trifugation to obtain the hemoglobin-containing supernatant. By
Drabkins reagent, which is added to the supernatant, hemoglobin
is converted to cyanohemoglobin with its typical absorbance peak
at 540 nm. The amount of cyanohemoglobin is then measured
with a spectrophotometer, allowing calculation of the blood vol-
ume in the brain sample by comparison with a standard curve. The
standard curve is obtained by measuring brain samples from ani-
mals without hematoma, to which incremental volumes of homol-
ogous blood plus PBS were added up to a predefi ned volume
followed by the above described process of homogenization, soni-
fi cation, centrifugation, and spectrophotometry.

2.1.1. Spectrophotometry

A third option for hematoma assessment is postmortem magnetic
resonance imaging (MRI). After fi xation of the brain, MRI using
T2-weighted and susceptibility-weighted sequences (SWI) can be
performed to evaluate the hematoma volume. Belayev and cowork-
ers showed that pre- and postmortem hematoma volumes in
T2-weighted images are almost identical, whereas the hematoma
volume on postmortem SWI images is consistently lower than in
premortem SWI images ( 13 ).

2.1.2. Post-mortem
Magnetic Resonance
Imaging

The postmortem assessment of the edema is done consistently by
measuring the brain water content. The brain is removed immedi-
ately after sacrifi cing the animal and weighed to obtain the wet
weight. Afterward the brain is dried at 100°C for 24-72 h and
weighed again to defi ne the dry weight. Water content is expressed
as percentage of wet weight using the formula: wet weight − dry
weight/wet weight × 100 ( 4 ).

2.2. Evaluation
of the Edema Volume

3. Investigations
In Vivo

3.1. Magnetic
Resonance Imaging

If hematoma and edema volumes are to be measured repeatedly in
long-term experiments, magnetic resonance imaging (MRI) is the
imaging modality of choice. In small animal models, mostly rats or
mice, dedicated small animal imagers with a small bore and