Maximal Accuracy and Precision of HRF Measurements in Rapid-Presentation ER-fMRI Experimental Designs

نویسندگان

  • X. Zong
  • J. Huang
چکیده

Introduction: In an event-related (ER) fMRI study of visual masking in humans [1], the measured V1 hemodynamic response functions (HRFs) to briefly displayed visual stimuli were found to be correlated with electrophysiological responses to similar stimuli in the monkey primary visual cortex [2]. This suggests a possible quantitative relationship between the HRFs and the corresponding neuronal firings. Determining this quantitative relationship requires an accurate and precise measurement of HRF. This type of measurement may be achieved by increasing the total number of stimuli in a periodic ER-fMRI experimental design with an adequate interstimulus interval (ISI) which ensures no overlap of the HRF between consecutive stimuli. However, due to the limited MRI scanning time and possible subjects’ attention decline in a lengthy fMRI session, such a design constrains the total number of repeated stimuli which results in a low precision. The low precision could be improved with a rapid presentation (RP) ER-fMRI design utilizing the approximate linearity of the HRF [3]. For a given length of MRI scanning time and a selected ISI value, the estimator variance of the HRF could be minimized, therefore maximizing the precision via an appropriate design matrix selection. This results in a maximized estimator efficiency [4,5]. The estimator efficiency increases with decreasing ISI and could be ten times greater than that which can be achieved by periodic ER-fMRI designs [3]. Nevertheless, hemodynamic response is non-linear and its corresponding effect on the estimated HRF increases with decreasing ISI, rendering the estimated HRF inaccurate for small ISI values. A 17-25% reduction in the amplitude of HRF was observed for the ISI of 5 s compared to that for the ISI of 20 s [6]. Accordingly, an optimal ER-fMRI design should maximize both accuracy and precision of HRF measurements. In this preliminary study we investigated optimizing the accuracy and precision of HRF measurements in RP ER-fMRI experimental designs.

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تاریخ انتشار 2009