fMRI Noise Variability Across Subjects and Trials: Insights For Noise Estimation Methods

Purdon, Patrick L.; Solo, Victor; Brown, Emery; Buckner, Randy L.; Rotte, Micheal; Weisskoff, Robert M.

doi:10.1016/s1053-8119(18)31450-2

Cited by 10 publications

(5 citation statements)

References 4 publications

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“…This observation also applies to the widely used cross-correlation analysis technique, as this is equivalent to t-test analysis for simple two-state experiments [Lange, 1996]. For a recent examination of the issue of intrasubject noise variation and estimation, see Purdon et al [1998a]. These results provided one of our motivations for examining the more globally dependent processing provided by SSM/FLDA.…”

Section: Effects Of Preprocessing On Reproducibilitymentioning

confidence: 84%

Reproducibility of BOLD-based functional MRI obtained at 4 T

et al. 1999

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The reproducibility of activation patterns in the whole brain obtained by functional magnetic resonance imaging (fMRI) experiments at 4 Tesla was studied with a simple finger-opposition task. Six subjects performed three runs in one session, and each run was analyzed separately with the t-test as a univariate method and Fisher's linear discriminant analysis as a multivariate method. Detrending with a first- and third-order polynomial as well as logarithmic transformation as preprocessing steps for the t-test were tested for their impact on reproducibility. Reproducibility across the whole brain was studied by using scatter plots of statistical values and calculating the correlation coefficient between pairs of activation maps. In order to compare reproducibility of "activated" voxels across runs, subjects and models, 2% of all voxels in the brain with the highest statistical values were classified as activated. The analysis of reproducible activated voxels was performed for the whole brain and within regions of interest. We found considerable variability in reproducibility across subjects, regions of interest, and analysis methods. The t-test on the linear detrended data yielded better reproducibility than Fisher's linear discriminant analysis, and therefore seems to be a robust although conservative method. Preliminary data indicate that these modeling results may be reversed by preprocessing to reduce respiratory and cardiac physiological noise effects. The reproducibility of both the position and number of activated voxels in the sensorimotor cortex was highest, while that of the supplementary motor area was much lower, with reproducibility of the cerebellum falling in between the other two areas.

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Section: Effects Of Preprocessing On Reproducibilitymentioning

confidence: 84%

Reproducibility of BOLD-based functional MRI obtained at 4 T

et al. 1999

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“…Although we matched the brains of all three studies, differences in the registration of the signal can still be present, especially between sessions. One study by Purdon et al [1998] concluded that there is a wide range of noise variance in the fMRI signal within and between subjects, which influences the determination of active voxels. Earlier research in our institute examined the influence of changing the significance thresholds on the reproducibility of activation maps [Rombouts et al, 1998b].…”

Section: Factors Of Variancementioning

confidence: 99%

fMRI of visual encoding: Reproducibility of activation

et al. 2000

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fMRI, a noninvasive technique to measure brain activation, is gaining clinical interest, because its sensitivity enables individual assessments. However, more insight in the reproducibility of these measurements during higher cognitive tasks is necessary. We performed an fMRI study involving withinand between-subject reproducibility during encoding of complex visual pictures. Ten healthy subjects were studied on three occasions: twice in the same scanning session (study 1 and 2), and a third time, 3-24 days later (study 3). On all 30 occasions but one, activation was found in areas expected on the basis of previous studies, including the fusiform and lingual gyri, occipital and parietal areas, the (para)hippocampal area, and the frontal inferior sulcus. The reproducibility of the number of activated voxels in the whole brain was 72% and 63% (respectively, studies 1 and 2, and 1 and 3). The reproducibility of anatomical identical pixels that supplement these results was 49% and 36%. These reproducibility measures increase about 5-15% when only areas of expected activation are included. The quantitative measurements indicate that there is substantial variation in the volume of activation. The recognition of pictures as tested afterward explains part of this variation between subjects. Our findings indicate that whereas consistent patterns of activation exist, more insight is needed into what determines the volume of activation, especially to assess cognitive alterations in patients over time. Hum. Brain Mapping 9:156 -164, 2000.

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“…Similar findings were reported by Duann et al [ 14 ], who demonstrated that the hemodynamic response varied substantially across trials as well as sessions, subjects, and brain areas. Purdon et al [ 15 ] concluded that there exists a wide range of noise variances in the BOLD signal within and between subjects, which could affect the determination of the spatial extent.…”

Section: Discussionmentioning

confidence: 99%

Effects of single-trial averaging on spatial extent of brain activation detected by fMRI are subject and task dependent

Fang¹,

Wang²,

Hsu³

et al. 2006

Biomed. Imaging Interv. J.

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AimThe effects of single-trial averaging on the spatial extent of event-related fMRI activation may vary between subjects and tasks. The purpose of this study was to evaluate this variability using a visual task and a word generation task.Patients, materials, and methodsFive Chinese right-handed male volunteers participated in the experiment. Experiments were conducted using a 1.5 T clinical MRI scanner with a T2*-weighted single-shot gradient-echo EPI sequence. Each task contained 150 trials that were separated into 5 runs. For each voxel, time courses averaged across different numbers of randomly selected trials, were obtained. They were applied for determining the voxels with significant activations, using a students’ t-test (p<0.001, uncorrected).ResultsConsistent with previous findings, the number of the activated voxels increased monotonically with the number of trials combined. The ascending rate and the maximum number of the activated voxels were different, however, between tasks and among subjects.ConclusionsThe effects of single-trial averaging were found to vary significantly between tasks and subjects. Therefore, we strongly advise to carefully consider such variability when using the spatial extent of activation as a measure in a group or a task comparison.

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fMRI Noise Variability Across Subjects and Trials: Insights For Noise Estimation Methods

Cited by 10 publications

References 4 publications

Reproducibility of BOLD-based functional MRI obtained at 4 T

Reproducibility of BOLD-based functional MRI obtained at 4 T

fMRI of visual encoding: Reproducibility of activation

Effects of single-trial averaging on spatial extent of brain activation detected by fMRI are subject and task dependent

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