Elsevier

Magnetic Resonance Imaging

Volume 16, Issue 2, February 1998, Pages 105-113
Magnetic Resonance Imaging

Original Contribution
Within-Subject Reproducibility of Visual Activation Patterns With Functional Magnetic Resonance Imaging Using Multislice Echo Planar Imaging

https://doi.org/10.1016/S0730-725X(97)00253-1Get rights and content

Abstract

Within-subject reproducibility of visual brain activation using multislice echo planar functional magnetic resonance imaging (fMRI) was tested. Ten healthy subjects underwent fMRI with visual stimulation on three occasions: two studies in one scanning session (without repositioning); and a third study 1 h to 2 weeks later. Following a three-dimensional matching procedure, activation was measured and compared between sessions on a voxel-by-voxel basis. Data were filtered to full-width-at-half-maximum of 4.0 × 4.0 × 5.0 mm and a conservative Bonferroni-corrected significance threshold was applied to correlation maps. For reproducibility, change in centre of mass of the activated volume, a ratio of the number of pixels and a ratio of the number of overlapping pixels was calculated. Further, reproducibility was tested varying significance thresholds and at different filter widths. Average changes in centre of mass of the activated volume were 2.63 and 3.96 mm between Studies 1 and 2 and 1 and 3, respectively. The reproducibility of the number of activated voxels was 90% and 88% (Studies 1 and 2 and 1 and 3). The ratio of overlapping pixels was 74% between Studies 1 and 2 and 64% between Studies 1 and 3. Varying the significance threshold showed that at a certain range, the overlap reached a maximum, and increasing the filter widths increased reproducibility. It is concluded that fMRI with visual stimulation can be used to measure brain activity with reasonably good reproducibility on a routine clinical system equipped with echo planar imaging. Difficulties remain in separating the contribution of motion, repositioning errors, and true physiological changes.

Introduction

Several pioneer studies have used blood oxygen level-dependent[1] functional magnetic resonance imaging (fMRI) to measure human brain activation in the motor cortex,2, 3 in the visual cortex,3, 4, 5, 6 and in areas corresponding to higher cognitive functions.7, 8, 9 For interpretation of fMRI studies in individuals, knowledge of the reliability and sensitivity of the technique, and of inter- and intrasubject variation, is important. Recently, a few studies have focused on this topic by testing reproducibility of activity in motor areas using multislice echo planar imaging (EPI)10, 11 and a three-dimensional (3D) gradient echo sequence.[12] In an earlier paper, we reported on test-retest reliability of activity in the visual cortex, using a double slice fast low angle shot technique.[13] Studies of the visual system that describe reproducibility of EPI between different scanning sessions have not been reported. In this study, we investigate the reproducibility of visual activation patterns with multislice EPI. Our goal was to provide a measure of reproducibility of a study design comparable with the situation in which patients are studied during longitudinal follow-up. Activation patterns of different scanning sessions are compared, and a conservative significance threshold is applied. The results are compared with the situation where subjects undergo two studies within one scanning session. Further, to provide reference data in a more general context, results of reproducibility testing are shown for a range of significance thresholds, more and less stringent than our conservative threshold, and different levels of data filtering are applied.

Section snippets

Data Acquisition

Imaging was performed with a 1.5-T magnetic resonance scanner (Vision; Siemens, Erlangen, Germany) using the standard circularly polarised head coil. After inserting earplugs, subjects were positioned in the head coil, using foam padding, and in the centre of the bore of the scanner. After a T1-weighted localising scan in three orthogonal directions, 21 T1-weighted sagittal images were acquired to detect the calcarine fissure (spin echo, time to repetition (TR) = 650 ms, time to echo (TE) = 14

Results

Activation could be detected in all 30 studies in the 10 subjects. After matching, motion artifacts or repositioning errors between sessions were not seen for unfiltered data with the movie tool. Within sessions, changes in centre of mass (as function of time) of the EPI volumes caused by motion did not exceed 0.2 voxel in-plane and 0.05 voxel through-plane in any subject. Volumes showing a signal increase after visual stimulation were centred in and around the calcarine sulcus, extending

Discussion

We have performed an fMRI study of the reproducibility of brain activition during visual stimulation with multislice EPI. In all scanning sessions, significant positive signal change was found around the calcarine sulcus, extending throughout the cuneus and the precuneus. Reproducibility testing with the application of the standard filter (FWHM = 4.0 × 4.0 × 5.0 mm) and a conservative Bonferroni-corrected significance threshold showed that Roverlap was 74 ± 7% within one scanning session and 64

Acknowledgements

Acknowledgments—The work described herein was partly funded by the “Stichting Vrienden MS Research” (grant 93-156). S.A.R.B. is the recipient of a USF grant from the Vrije Universiteit, Amsterdam, The Netherlands.

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