Abstract
Diffusion weighted magnetic resonance imaging is increasingly being used for neonatal and young pediatric subjects. Our purpose was to investigate a) whether cardiac triggering was needed to reduce variability of diffusion (tensor) imaging data, b) how pulsation artifacts affect the fitted diffusion tensor when triggering is not used and c) the feasibility of triggered data acquisition in neonates and young children.Data were collected from 11 infants and 7 adults. In seven infants and seven adults, diffusion encoding was applied solely along the z gradient direction with and without cardiac triggering. Non-parametric bootstrap statistical methods were applied to investigate the dependence of variance on triggering. One infant and all adults served as test–retest controls. From the remaining three infants diffusion tensor imaging data were acquired with and without triggering.Our findings that used the repeated measurements in a single diffusion-encoding direction indicated that without triggering the variability in the data was increased significantly both in infants and adults. When collecting diffusion tensor data in infants, this increased variability results in erroneous fractional anisotropy values and artifactual fiber direction estimates. Contrary to previous reports but supported by our findings involving adults, pulsation artifacts were present in a larger extent of the brain in the infant population.In conclusion, triggering is feasible in young subjects and is preferred when acquiring diffusion MRI data. In doing so, the amount of erroneous estimations due to image artifacts will be minimized, which in turn will lead to more specific and less ambiguous interpretations. Although fitting the pulse-monitoring device requires additional set-up time, the total imaging time is usually shorter than acquiring multiple data sets to compile a single, artifact-free set.
Highlights
Magnetic resonance imaging (MRI) is increasingly being used for neonatal and young pediatric subjects (Barkovich et al, 1988; Rutherford, 2002; Woodward et al, 2006)
The aims of this paper were to (a) examine the presence and extent of pulsation artifacts in diffusion-weighted imaging (DWI) collected from young pediatric subjects; (b) investigate the effect of pulsation artifacts on the estimated diffusion measures; and (c) test feasibility of triggered acquisition in this patient group
The variance in the acquired data is higher when triggering is not used regardless of the investigated population. Often this can be identified upon visual inspection, bootstrap statistics help establishing the significance of differences
Summary
Magnetic resonance imaging (MRI) is increasingly being used for neonatal and young pediatric subjects (Barkovich et al, 1988; Rutherford, 2002; Woodward et al, 2006). Diffusion weighted images (DWIs) are susceptible to several types of image artifacts which can be Abbreviations: ADC, apparent diffusion coefficient; bpm, beats/min; DTI, diffusion tensor imaging; DWI, diffusion-weighted imaging/diffusion weighted image; ECG, electrocardiogram; FA, fractional anisotropy; FOV, field of view; MRI, magnetic resonance imaging; NLLS, non-linear least squares fit; OLLS, ordinary linear least squares fit; (i)RESTORE, (informed) robust estimation of tensors by outlier rejection; SENSE, sensitivity encoding; SNR, signal-to-noise ratio; TR, repetition time; WLLS, weighted linear least squares fit. Fitting sensors to detect heartbeats can take precious examination time. For these reasons diffusion-weighted imaging of neonatal subjects usually proceeds without triggering
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