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Raman Micr oscopy for Biomedical Applications 231

for the inelastic scattered light. An unfiltered probe which consisted of
a single fiber of 300 μm diameter was recently applied to collect
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Raman spectra from porcine brain tissue. Whereas the small diam-
eter allows inserting the probe into the working channel of an endo-
scope, the missing collimating optic gives lower lateral resolution in
the range of 300 μm and reduced collection efficiency. Another disad-
−1
vantage is the smaller wavelength range from 2000 to 3900 cm . As
the Raman bands of tumor tissue (Fig. 8.2, spectrum E) are very simi-
lar to the Raman bands of normal brain tissue (Fig. 8.2, spectrum B)
−1
in the high-wavenumber region from 2700 to 3550 cm , detection of
tumor cells would be more difficult in this spectral interval.
8.2.2 Human Brain Tumors
Tumors that originate from brain tissue are called primary brain
tumors. According to the recommendation of the World Health Orga-
nization (WHO) they are classified to the cell types from which they
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are derived. Among them are glial cells, meninges, pituitary cells,
and periphery nerves. Gliomas from different glial cells constitute the
largest group of primary brain tumors (50 percent). The histopatho-
logical assessment of H&E-stained tissue sections is the so called
golden standard for the distinction of gliomas into astrocytomas, oli-
godendrogliomas, ependymomas, and oligoastrocytomas as mixed
gliomas. The malignancy of the most frequent astrocytomas is divided
into grade II (low-grade astrocytoma), grade III (anaplastic astrocy-
toma), and grade IV (glioblastoma multiforme, GBM). Tumor staging
is difficult as a tumor mass may encompass different tumor grades.
The highest tumor grade is an indicator of the prognosis which is in the
order of 12 months survival for GBM patients. In spite of the medical
progress in tumor treatment in the last years, this value did not increase
significantly. GBMs are characterized by fast, diffuse, and infiltrative
growth making them to one of the greatest challenge in tumor research.
Meningiomas are tumors of the meninges. The meninges are a
system of connective tissues that consist of the dura mater, the arach-
noid mater, and the pia mater. The arachnoid and pia mater are some-
times together called the leptomeninges. Meningiomas form the
second largest group of primary brain tumors (20 percent). Most of
them are benign tumors (grade I) that means they show slow growth,
do not infiltrate brain tissue and do not form metastasis. Schwanno-
mas are the third largest group of primary brain tumors. They origi-
nate from Schwann cells that produce myelin which is an electrically
insulating phospholipid layer that surrounds brain or periphery
nerves. Most of them are acoustic neurinomas of grade I. Raman
imaging can contribute to brain tumor classification and staging. First,
Raman-based classification can complement on-site diagnosis of tis-
sue sections. Second, tumor margins can be determined during sur-
gery which is important to maximize tumor resection upon minimum
damage of brain functions. Raman images of tissue sections were