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Preliminary Studies with Infrascanner
prototype
A dual wavelength reflectance spectrometer
(Runman) was used in the pilot studies. This monitor
is small (6.5 inches X 4.5 inches X 2
inches), battery-operated, and can be easily
transported into the emergency room or
intensive care unit. The probe consists of 2
small incandescent bulbs placed 4.5 cm on
either side of a 760 and 850 nm
photodetectors. The 4.5 cm separation of
light source and detector allows measurement
of NIR absorbance in a volume of tissue
approximately 2 cm wide by 2 to 3 cm deep.
Leakage of the light is minimized by the
presence of rubber dams between the light
emitter and detectors, and around the
circumference of the probe. The procedure
for a NIRS examination using the RUNMAN
equipment takes less than ten minutes.
In the pilot study, a NIRS examination was
obtained in the ER at the time of the
admission CT scan. The maximal ΔOD among the
various regions examined was recorded for
each patient and was correlated with the
admission CT scan.
Using the RUNMAN NIRS, serial measurements
of ΔOD have been obtained in 305
head-injured patients under previous
Baylor College of Medicine IRB protocols
(#H-1492 and #H-949). As shown in Fig. 1,
ΔOD on admission to the hospital was
significantly elevated (>0.05) in all but 4
(2%) patients with intracranial hematomas.
ΔOD was normal (0.00-0.05) in patients with
diffuse brain injury (DBI) (Fig. 1-bottom).
With extracerebral hematomas, where the
blood was in the configuration of a layer,
the thickness of the hematoma measured on
the initial CT scan was directly related to
the ΔOD (Fig. 2).
Fig. 1. Distribution of maximal ∆OD in 302
patients with various types of intracranial
injuries: EDH – Epidural Hematoma, SDH –
Subdural Hematoma, ICH – Intracerebral
Hematoma, DBI – Diffuse brain injury
Fig. 2. Relationship between maximal ∆OD and
the thickness of the hematoma on CT scan
A single NIRS examination therefore reliably
identified patients with an intracranial
hematoma (98% had a ΔOD > 0.05), and gave a
suggestion of whether the hematoma was
intracerebral (most had a ΔOD <0.6) or
extracerebral (most had a ΔOD >0.6). This
type of information would be useful in the
initial assessment of a head-injured patient
(1) in the field to triage patients likely
to require surgery directly to a hospital
having a neurosurgeon, (2) in emergency
rooms where CT scanning is not immediately
available, and (3) as a less expensive
screening exam than CT scan for patients
with mild head injury (who have an incidence
of hematomas of only 1%). Serial NIRS
examinations might be used in the ICU
setting to detect development of delayed or
postoperative intracranial hematomas.
In a pilot study of reproducibility, 10
patients were examined independently by two
different operators. The ΔOD was calculated
by the formula ΔOD = log (lright / Ileft) so
that a negative ΔOD indicated a greater
absorbance on the right, and a positive ΔOD
indicted a greater absorbance on the left.
The results show fairly good reproducibility
when there is no intracranial lesion. When
an intracranial lesion was present, the
variability of ΔOD values was greater
between the two operators. However, with
both operators the ΔOD was significantly
greater in the patients with a focal lesion
than with no focal lesion, and the side of
greatest absorbance of the NIR light
indicated the side of the focal lesion. |
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