Key Properties of D-Optimal Designs for Event-Related fMRI Experiments with Application to Nonlinear Models

• Activity Number: 177
• Type: Contributed
• Date/Time: Monday, July 30, 2012 : 10:30 AM to 12:20 PM
• Sponsor: Biometrics Section
• Author(s): Darcie Delzell*+ and Richard Gunst
• Companies: Wheaton College and Southern Methodist University
• Keywords: hemodynamic response function ; genetic algorithm ; probabilistic experimental design ; ISI selection ; stimulus timing ; maximin

Abstract

In order to properly formulate functional magnetic resonance imaging (fMRI) experiments, it is advantageous to permit great flexibility in the statistical components of the design of these studies. New and increasingly difficult issues relating to the modeling of hemodynamic responses and the detection of activated brain regions continue to arise. In this article, the D-optimality criterion is used in conjunction with a genetic algorithm to create probability-based design generators for the selection of designs in event-related fMRI experiments where the hemodynamic response function (HRF) is modeled with a function that is nonlinear in the parameters. The designs produced by these generators are shown to be well performing compared to locally D-optimal designs and provide insight into optimal design characteristics that investigators can utilize in the selection of interstimulus intervals (ISIs). Designs with these characteristics are shown to be applicable to fMRI studies involving one or two stimulus types. The designs are also shown to be robust with respect to misspecification of an AR(1) error autocorrelation and compare favorably with a maximin procedure.