184 Chapter 7 Edema regional comparisons Edema volume pre-radiotherapy The relationship between the volume of edema (expressed as percentage of the total brain volume) and the average physiological parameters within the healthy appearing whole-brain pre-radiotherapy was calculated using Spearman’s Rank correlations for each MRI metric (Figure 3). There were no significant correlations between the pre-radiotherapy edema volume and average whole-brain OEF (r = .02, p = .982), CBF (r = .43, p = .250), CMRO2 (r = .62, p = .086), or CVR (r = -.45, p = .223). Post-radiotherapy changes To assess the influence of the presence of edema on the assessed MRI metric, the average values within edematous regions were compared before and after SRS (Figure 4). Within edematous tissue, a distinction was made between regions with edema at both T0 or T1 (i.e. edema), regions with edema exclusively at T1 (i.e. new edema) and regions with edema exclusively at T0 (i.e. old edema). Comparisons were made using Wilcoxon-signed rank tests. For OEF, CBF and CMRO2 values in old edema (T0 edema) regions, were higher post-radiotherapy than pre-radiotherapy (all p ≤ .04), while CVR did not change in old edema (T0 edema) regions over time. When the outliers as visible in Figure 4 were removed from the analyses, CBF in old edema regions (T0 edema) was no longer statistically significantly higher post-radiotherapy than pre-radiotherapy (p = .078). For OEF and CMRO2 pre-post radiotherapy differences in old edema (T0 edema) remained statistically significant after outlier removal. Healthy appearing brain tissue Global post-radiotherapy changes To assess whether there were global effects of the radiotherapy on the healthy appearing brain tissue, average MRI values were compared pre- and postradiotherapy using Wilcoxon signed rank tests (Figure 5). Only CBF values were significantly higher post-radiotherapy than pre-radiotherapy (p = .020). This indicates perfusion throughout healthy appearing brain tissue increased after radiotherapy. None of the other MRI metrics showed significant changes after radiotherapy.
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