A Re-defined and Generalized Percent-Overlap-of-Activation Measure for Studies of fMRI Reproducibility and its Use in Identifying Outlier Activation Maps

TL;DR

This paper introduces a generalized and more intuitive percent-overlap measure for fMRI activation maps, along with a method to identify outlier studies, enhancing the reliability assessment of fMRI reproducibility.

Contribution

It proposes a new generalized overlap measure based on the Jaccard coefficient and a testing mechanism to detect anomalous fMRI studies, improving reproducibility analysis.

Findings

The new measure effectively summarizes reliability across multiple studies.

The outlier detection method successfully flagged anomalous activation maps.

Application to motor task studies demonstrated high reliability and outlier detection accuracy.

Abstract

Functional Magnetic Resonance Imaging~(fMRI) is a popular non-invasive modality to investigate activation in the human brain. The end result of most fMRI experiments is an activation map corresponding to the given paradigm. These maps can vary greatly from one study to the next, so quantifying the reliability of identified activation over several fMRI studies is important. The percent overlap of activation~\citep{romboutsetal98,machielsenetal00} is a global reliability measure between activation maps drawn from any two fMRI studies. A slightly modified but more intuitive measure is provided by the ~\citet{jaccard1901} coefficient of similarity, whose use we study in this paper. A generalization of these measures is also proposed to comprehensively summarize the reliability of multiple fMRI studies. Finally, a testing mechanism to flag potentially anomalous studies is developed. The methodology is illustrated on studies involving left- and right-hand motor task paradigms performed by a right-hand dominant male subject several times over a period of two months, with excellent results.