Digital Signal Processing Reference
In-Depth Information
8.1.2.5
Other metabolites often seen in brain tumors:
Lactate,
lipids, glutamine - glutamate, myoinositol
Some other metabolites or metabolite ratios have also been helpful in detecting
brain tumors via MRS and MRSI. Due to the predominance of anaerobic
glycolysis, lactate is seen often in malignancy. Lactate appears as a doublet
due to Jcoupling, and is centered at 1.33 ppm [113]. Lactate is said to be
found in most pediatric brain tumors [211]. A lactate peak was detected
in three of ten patients with highgrade gliomas, as reported in a study by
Saindane et al. [233]. In another study, lactate was registered among eighteen
patients with gliomas and five patients with metastatic brain tumors, but was
totally absent from all the unaffected brain tissue investigated [219].
Depending upon the presence or absence of necrosis, lipids in the region
around 0.9 ppm to 1.3 ppm may or may not be detected in brain tumors.
Lipids are generally described as absent in normal brain tissue [207, 211]. In
a study by Tarnawski et al. [225] there was no detected lipid whatsoever
in brain MRS recordings from thirty healthy volunteers, and a significantly
higher lipid to NAA ratio was found in the tumor bed of fiftyone patients
compared to the contralateral, noninvolved lobe. Smith et al. [234] reported
that the lipid to creatine ratio was significantly lower among five healthy
volunteers compared to twenty patients with brainstem tumors. It has also
been suggested [232] that targeting the regions with highest lipid content could
improve the diagnostic yield of stereotactic biopsy [232].
In a study by Fan et al. [235] glutamine - glutamate at 2.3 ppm to 2.5
ppm was found significantly more often at the site of brain tumors (high
grade gliomas and metastases) among twentytwo patients compared to nor
mal parts of the brain. These authors observe that glutamate may act as
an excitotoxin associated with accelerated cell proliferation of brain tumors.
Myoinositol at around 3.56 ppm is involved in the activation of protein C
kinase, which leads to the generation of proteolytic enzymes seen in brain
neoplasms [113]. As a precursor in lipid metabolism, myoinositol also may
be elevated with cell proliferation [207]. A number of reports indicate that
myoinositol is elevated in various brain tumors [220, 225, 236, 237]. A my
oinositol to NAA ratio > 0.9 was also found to help distinguish malignant
from pseudotumorous lesions in the earlier cited study of eighty four patients
with solid brain masses [228]. However, Brandao and Domingues [211] state
just the opposite, namely, that intracerebral neoplasms are one of the condi
tions associated with decreased myoinositol, whereas increased myoinositol is
seen in multiple sclerosis, Alzheimer's and Pick's disease, inter alia. Further
elucidation has been provided in a recent study by Hattingen et al. [238] using
2D MRS with a short TE of 30 ms among fiftysix patients with glial brain
tumors. These investigators found that myoinositol concentrations were sig
nificantly higher in all tumor tissues compared to normal white matter, with
the highest concentrations found in association with marked astrogliosis.
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