Digital Signal Processing Reference
In-Depth Information
8.1.2.6
Identification of brain tumors in children
The choline to NAA ratio is considered to be especially helpful in identifying
lowgrade neoplasms in children, in whom the choline concentration might be
low or normal within the tumor. Since active myelination is ongoing in the
normal parts of the brain, the choline to NAA ratio would be increased at the
tumor site [211]. High choline, low NAA together with a minimal lactate peak
on proton MRS were helpful in differentiating bilateral thalamic astrocytomas
from encephalitis and neurometabolic disorders in a study by Gudowius et
al. [212]. As noted, these disorders are di
cult to distinguish among children
on the basis of MRI. Similar findings were reported by MollerHartmann et
al. [239]: high choline with low creatine and NAA were characteristic of
brain tumors, whereas noncancerous lesions such as cerebral infarction and
brain abscesses showed decreased choline, creatine and NAA. However, high
choline in a noncancerous lesion also led to a false positive MRS finding of
malignancy in a child undergoing MRS for workup of brainstem lesions [224].
8.1.2.7
Metabolites that may help rule-out malignancy:
acetate
and succinate
Brain abscesses often show acetate (1.92 ppm) and succinate (2.4 ppm),
whereas this is generally not the case for brain neoplasms [113, 211, 214, 240].
The appearance of these metabolites is thus considered to distinguish brain
abscesses from cystic or necrotic tumors [211]. In an investigation of fifty
patients with intracranial cystic mass lesions, Lai et al. [241] reported iden
tifying acetate or succinate only in brain abscesses, but not in any of the
twentythree patients with brain neoplasms. Altogether, however, acetate or
succinate were present respectively in only seven and four of the twentyone
brain abscesses, suggesting that these metabolites were rather infrequently
detected in the pyogenic lesions.
8.1.3 Grading of primary brain tumors by MRS & MRSI
Complete surgical resection is the aim for successful treatment of brain tu
mors. Realization of this goal vitally depends upon the grade and histopatho
logic characteristics of the tumor and anatomical location. If accessible, low
grade astrocytomas are usually surgically resected with RT often also em
ployed. Protocols vary substantially across centers, and strategies also differ
greatly in relation to the clinical considerations. Since highgrade gliomas
only rarely have clearly defined margins, total surgical resection is not possi
ble in most cases. Partial resection to control mass effect is often performed,
as well as RT, chemotherapy and glucocorticoids. Overall survival is poor,
generally below 1 year. Total surgical resection represents a curative treat
ment for meningiomas. If the resection is subtotal, local RT is usually given
and reduces recurrence rates to fewer than 10%. If the meningioma is not
surgically accessible, targeted radio surgery with the gamma knife or heavy
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