Relating Longitudinal and Cross-Sectional Analyses of Atrophy in Alzheimer's: BSI, SIENA and SIENAX

Brain volume loss measured with structural MRI is accepted as a pathology marker, e.g., for Alzheimer's disease (AD). Atrophy can be measured with a variety of methods, some of which are longitudinal (measuring atrophy rate, for example, % brain volume change (PBVC), using two or more temporally-separated scans) and others being cross-sectional (measuring atrophy state, for example, brain volume normalised for head size, with a single scan). Three validated analysis tools for measuring brain atrophy are BSI and SIENA for longitudinal, and SIENAX for cross-sectional. Previous work has shown BSI and SIENA to have similar accuracy around 0.2% error in PBVC, but no papers have compared the methods directly. Here we present a comparison using data from AD and controls. We focus on comparing BSI and SIENA longitudinal atrophy estimation, and on comparing SIENA longitudinal atrophy with SIENAX cross-sectional atrophy estimation (using the earliest scan taken from each subject). We find excellent correspondence between BSI and SIENA, and strong correspondence between SIENA longitudinal and SIENAX cross-sectional atrophy.