Pattern Recognition Methods in 1H MRS Monitoring In Vivo of Normal Appearing Cerebellar Tissue After Treatment of Posterior Fossa Tumors

The objective of this study was to investigate the metabolic responses of normal appearing cerebellar tissue after posterior fossa tumor treatment, and to identify characteristics of the particular treatment method. Moreover, this work examined the metabolic alterations of normal appearing tissue induced by a particular tumor state including resection, stagnation, progression, and recurrence. The studied group consisted of 29 patients treated for posterior fossa tumors. All of them were irradiated with a total dose of 54 Gy at 1.8 Gy/fraction (median values). In addition, 13 underwent: chemotherapy, 25 underwent total tumor resection, 18 were tumor-free in control examinations, 5 had a stable disease, and tumor progression or recurrence was observed in 2 and 4 cases, respectively. The 69 spectra, acquired using a MRI/MRS 2T system, were analyzed using; Partial Least Squares Discriminant Analysis (PLS-DA) with orthogonal signal correction (OSC) spectral filtering. A significantly elevated spectral region (0.97-1.55 ppm) was observed in patients after total resection in comparison to non-operated subjects. Patients treated with chemotherapy showed an elevated band between 1.15-1.75 and 2.7-3.0 ppm and had decreases in the remaining parts of the spectra. Increases in lactate and decreases in the remaining metabolites were characteristic for the tumor progression/recurrence group. Pattern recognition methods coupled with MRS revealed significant treatment-dependent alterations in normal appearing cerebellar tissue, as well as metabolic changes induced by tumor progression/recurrence.