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Slide Slam D3

A New Approach for Identifying Functionally Compromised Tissue in Individuals with Chronic Aphasia

Slide Slam Session D, Tuesday, October 5, 2021, 5:30 - 7:30 pm PDT Log In to set Timezone

Noelle Abbott1,2, Carolyn Baker1,2, Conan Chen2, Thomas Liu2, Tracy Love1,2; 1San Diego State University, 2University of California, San Diego

Introduction: Individuals with chronic aphasia (IWA) exhibit variable patterns of language impairment, which makes it difficult to identify structure-function brain relationships[1,2]. This variability may be due to underlying alterations in brain function. Prior research has demonstrated that IWA have reduced cerebral blood flow (CBF; hypoperfusion) in areas of the brain that are structurally intact[3,4]. However, across these studies there is little consensus on how to best define hypoperfusion. Though standard CBF threshold values exist (healthy≥50mL/100g/min, hypoperfused=12-20mL/100g/min, necrotic≤12mL/100g/min), they do not fully capture tissue functionality in IWA[5-7]. Further, group-level analyses may overshadow important individual differences. In this exploratory study, we defined an individualized metric for hypoperfusion and used it (vs. standard approaches) to investigate (1) when perilesional tissue (often functionally compromised) returned to “normal” CBF levels and (2) how well our metric correlated with auditory comprehension. Methods: Participants included 6 monolingual, right-handed (premorbid), chronic (>1 year) IWA who had a single, unilateral, left hemisphere stroke. Aphasia subtype and severity were based on the Boston Diagnostic Aphasia Examination-3 and the Western Aphasia Battery-Revised[8-9]. Auditory comprehension was measured through the comprehension subtests of these assessments. Neuroimaging Procedures: Anatomical and resting state CBF data were acquired using a 3T-GE scanner (pre-processing information can be found in Abbott et al. 2021[10]). All scans were co-registered and labeled using the Automated Anatomical Labeling Atlas[11]. To systematically define perilesional tissue, we created four 3mm perilesional bands (0-3mm, 3-6mm, 6-9mm, 9-12mm). Analyses: Group- and individual-level analyses were performed to demonstrate the importance of an individualized approach. Here, we defined “normal” brain tissue based on each participant’s right hemisphere average CBF (CBFRH) and “functionally compromised” tissue as anything less than 1.5 standard deviations below CBFRH. Hypoperfusion in LH-perilesional bands and specific regions of interest (ROIs) were identified to explore the relationship between hypoperfusion and language behavior. Results: Our individualized approach was more sensitive to differences in tissue functionality for each participant. While the group-level analysis showed no difference in the 0-3mm band from the calculated hypoperfusion threshold (t(5)=-1.18,p=0.15), individual-level analyses revealed additional information; there were differences if and when CBF values returned to “normal” in the remaining three bands. Our individualized approach also picked up on hypoperfusion in ROIs that remained structurally intact, suggesting that our metric is more sensitive to individual patterns of brain function. Correlations between the two CBF metrics (standard/individual) and language behavior revealed a correlation between auditory comprehension and multiple temporal regions, which did not exist with standard thresholding. These results suggests that our individualized metric may better identify functionally compromised tissue on an individual basis. Conclusions: We propose a new approach for measuring functionally compromised brain tissue in IWA. Standard cut-off values and group-level analyses often over- or under-estimate tissue functionality in IWA. These results underscore the necessity of considering not just the structural integrity of brain regions but also the functional integrity when investigating structure-function relationships. By adding in measures of functional integrity, researchers may be able to better account for some of the variability demonstrated by IWA.

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