A Temporal Instability Measure for fMRI Quality Assurance

Abstract

BackgroundThere exist several fMRI quality assurance measures to assess scanner stability. Because they have practical and/or theoretical limitations, a different and more practical measure for instability would be desirable.PurposeTo develop and test a sensitive, reliable and widely applicable temporal instability measure (TIM) for fMRI quality assurance.Study TypeTechnical development.PhantomSpherical gel phantom.PopulationA total of 120 datasets from a local Philips scanner with two different receive‐only head coils (32ch and 8ch, 60 datasets per coil) were collected as well as 29 additional datasets with three different receive‐only head coils (20ch, 32ch, and 64ch) from two additional sites with GE (seven runs with 32ch) and Siemens scanners (seven runs with 32ch and Multiband imaging, five runs with 20ch, 32ch, and 64ch) were borrowed.Field Strength/Sequence2D Echo‐planar‐imaging (EPI).AssessmentA new TIM was proposed that is based on the eigenratio of the correlation coefficient matrix, where each entry of the matrix is a correlation coefficient between two time‐points of the time‐series.Statistical TestsNonparametric bootstrap resampling was used twice to estimate confidence intervals (CI) of the TIM values and to assess the improved sensitivity of this measure. Differences in coil performance were assessed via a nonparametric bootstrap two‐sample t‐test. P‐values <0.05 were considered significant.ResultsThe TIM values ranged between 60 parts‐per‐million and 10,780 parts‐per‐million across all 149 experiments. The mean CI was 2.96% and 2.16% for the 120 and 29 fMRI datasets, respectively (the repeated bootstrap analysis gave 2.9% and 2.19%, respectively). The 32ch coils of the local Philips data provided more stable measurements than the 8ch coil (observed two‐sample t‐values = 26.36, −0.2 and −6.2 for TIM, tSNR, and RDC, respectively. PtSNR = 0.58).Data ConclusionThe proposed TIM is particularly useful for multichannel coils with spatially nonuniform receive sensitivity and overcomes several limitations of other measures. As such, it provides a reliable test for ascertaining scanner stability for fMRI experiments.Evidence Level5.Technical EfficacyStage 1.