Magnetic resonance in neuro-oncology: Achievements and challenges - Signal Processing in MRS with Biomedical Applications - page 262

the proliferation index assessed via Ki67 immunochemistry. The presence of
lactate at 1.36 ppm and free lipids between 0.8 ppm and 1.2 ppm was found
to have a significant multivariate association with proliferation index (both
intermediate and high) [283]. Regions with choline to NAA ratios≥2 prior to
combination chemotherapy and RT were reported to be predictive of relapse in
a study of nine patients with newly diagnosed glioblastoma followed bimonthly
[284]. On the other hand, the metabolic characteristics of suprasellar tumors
assessed in forty patients by singlevoxel proton MRS were not found to predict
recurrence following initial surgical resection [285].

8.1.6.3 Prognostic indicators via MRS & MRSI for pediatric brain

tumors

Tzika and colleagues [286] suggest that in vivo MRSI can be used as a prognos
tic indicator for pediatric brain tumors. These authors examined twentyseven
children with neuroglial brain tumors, and found that the percent change in
choline to NAA ratio on MRSI, as well as relative tumor blood volume were
significant predictors of tumor progression. A more recent study from the
same center revealed that among seventysix children with tumors of the cen
tral nervous system, a combined index of choline and lactate provided better
prediction of survival than standard histopathology [287]. Similarly, increased
total choline was also found to precede clinical deterioration in the earlier cited
study of fourteen children with diffuse intrinsic brainstem gliomas [254]. In a
series of twentyseven children who were a icted with pilocytic astrocytomas,
those tumors that progressed were found to have initially lower myoinositol
levels and decreased levels over time [288]. This information is particularly
important because it can impact upon management strategies when tumors
occur in brain regions that are not amenable to surgery [270].

8.2 Major limitations and dilemmas in MRS & MRSI for

neuro-oncology due to FFT envelopes and fittings

As summarized thus far in this chapter, MRS and MRSI have shown great
promise in relation to various aspects of brain tumor diagnostics, and tremen
dous strides have been made in the most recent period with these molecular
imaging modalities. It is also clear that further improvements are still needed.
In this section we analyze many of the problems and dilemmas encountered
using MRS and MRSI in neurooncology and their relation to reliance upon
the conventional Fourierbased framework for data analysis.