206 Chapter 8 impairment in at least one domain at three months post-radiotherapy. Memory was particularly susceptible, as demonstrated both by patients with cognitive deficits and those who experienced a general decline in cognitive performance at shortterm follow-up. In the long-term, slowing of processing and psychomotor speed was most prominent. A decline in objective cognitive performance was observed in 97% of patients three months post-radiotherapy. Interestingly, 81% of these patients experienced concurrent improvement in a different cognitive domain. This pattern of both deterioration and improvement persisted in the long-term. No clear risk factors were identified for cognitive decline post-radiotherapy. PART II: USING IMAGING TECHNIQUES TO UNDERSTAND NEUROCOGNITIVE FUNCTIONING The presence of within-individual cognitive variation, coupled with the absence of clear risk factors (Chapter 3 and 4), suggests a need for further investigation of the underlying mechanisms of cognitive performance in patients with BMs. The location of the BMs in the brain may be a contributing factor to the observed variation. However, lesion-symptom mapping (LSM) studies in the BMs population are complicated by numerous factors, while the generalizability of previous LSM results from other populations remains unclear. Chapter 5 compared LSM results from patients with ischemic stroke and primary brain tumors. Even with large sample sizes (196 tumor and 147 stroke patients), the limited degree of lesion overlap between stroke and primary brain tumor patients hindered comparison. In brain areas with adequate lesion overlap, considerable differences between stroke and tumor patients were found regarding the regions associated with either verbal memory or verbal fluency performance. This confirms that the etiology of focal damage in the brain influences the cognitive consequences of this lesion. Thus, caution is required when generalizing brain-behavior associations from one patient population to another. In Chapter 6 we compared physiological imaging parameters derived from either hypercapnic blood oxygenation level-dependent (BOLD) or arterial spin labeling (ASL) imaging in 14 patients with BMs from the APRICOT study prior to radiotherapy. The study focused on cerebrovascular reactivity (CVR), hemodynamic lag, cerebral blood flow (CBF), and arterial arrival time (AAT). There was a positive correlation between BOLD and ASL parameters, whereby areas with higher CVR exhibited higher perfusion and longer hemodynamic lag was found in regions with prolonged AAT. However, these associations were observed only in areas with sufficient vascular reserve capacity. Thus, the relationship between these physiological BOLD and ASL
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