DOCUMENT NO. 920012 REV 2 EFFECTIVE 03-14-18 INFRASCAN CONFIDENTIAL PAGE 10 OF 35
conditions for the tissue, it is possible to draw conclusions from these levels. Figure 2-1
shows the simulated diffusion path through target tissue from source to detector. This
simulation shows the photon path density, not the overall transmission level.
The principle used in identifying intracranial hematomas with the Infrascanner is that
extravascular blood absorbs NIR light more than intravascular blood. This is because
there is a greater (usually 10-fold) concentration of hemoglobin in an acute hematoma than
in normal brain tissue where blood is
contained within vessels. The Infrascanner
compares left and right side of the brain in
four different areas. The absorbance of NIR
light is greater (and therefore the reflected
light less) on the side of the brain containing
a hematoma, than on the uninjured side.
The wavelength of 805nm is sensitive only to
blood volume, not to oxygen saturation in the
blood. The Infrascanner is placed
successively in the left and right frontal,
temporal, parietal, and occipital areas of the
head and the absorbance of light at 805 nm
is recorded and compared.
Frontal
Left/Right forehead, above the frontal sinus
Temporal
In the Left/Right temporal fossa in front of the top of the Left/Right ear
Parietal
Above the Left/Right ear, midway between the ear and the midline of the skull
Occipital
Behind the top of the Left/Right ear, midway between the ear and the occipital
protuberance
The difference in optical density (ΔOD) in the different areas is calculated from the
following formula:
(1)
Where
I
N
= the intensity of reflected light on the normal side,
I
H
= the intensity of reflected
light on the hematoma side.
LEFT SIDE
FRONT
RIGHT SIDE
Figure 2-3: Head locations of NIR measurement
=
H
N
I
I
OD
10
log
T
F
O
P
T
F
O
P
F
F
F
F
O
P
F
T
O
P
F
T
Figure 2-2: Absorption of light by hemoglobin
