Article

Effects of number of diffusion gradient directions on derived diffusion tensor imaging indices in human brain

Department of Radiology, University of Rochester Medical Center, Rochester, NY 14642, USA.
American Journal of Neuroradiology (Impact Factor: 3.68). 10/2006; 27(8):1776-81.
Source: PubMed

ABSTRACT The effects of a number of diffusion-encoding gradient directions (NDGD) on diffusion tensor imaging (DTI) indices have been studied previously with theoretic analysis and numeric simulations. In this study, we made in vivo measurements in the human brain to compare different clinical scan protocols and to evaluate their effects on the calculated DTI indices.
Fifteen healthy volunteers were scanned with a 1.5T MR scanner. Single-shot DTI images were acquired using 3 protocols different in NDGD and number of excitations (NEX) for each direction (NDGD/NEX = 6/10, 21/3, 31/2). Means and standard error of mean (SEM) were calculated and compared in 6 regions of interest (ROIs) for mean diffusivity (D), fractional anisotropy (FA), diffusion tensor eigenvalues (lambda(1), lambda(2), and lambda(3)), and correlation coefficients (r) of these indices among the 3 DTI protocols.
At the ROI level, no significant differences were found for the mean and SEM of D and FA among protocols (P > .05). The 6-NDGD protocol, however, yielded higher values for lambda(1) and lambda(2) and lower values for lambda(3) in most ROIs (P < .05) compared with the other protocols. At the voxel level, the correlation between the protocols r(21-31) were higher than r(6-21) and r(6-31) in most ROIs. The correlation of FA among 3 protocols also increased with increasing anisotropy.
For ROI analyses, different NDGDs lead to similar values of FA and D but different eigenvalues. However, different NDGDs at the voxel level provide varying values. The selection of the NDGD, therefore, should depend on the focus of different DTI applications.

Download full-text

Full-text

Available from: Sven Ekholm, Feb 27, 2014
0 Followers
 · 
242 Views
  • Source
    • "Single-shot echo planar imaging (EPI) is widely used in functional MRI [1] [2], dynamic MRI with contrast agent [3], diffusion MRI [4] [5] [6] and cardiac MRI [7] for collecting data of high temporal resolution. However, images obtained with single-shot EPI are also more sensitive to artifacts than those obtained with multi-shot modalities, due to its long acquisition period in which phase errors from a variety of off-resonance sources may accumulate [8] [9]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a phase evolution rewinding algorithm for correcting the geometric and intensity distortions in single-shot spatiotemporally encoded (SPEN) MRI with acquisition of asymmetric self-refocused echo trains. Using the field map calculated from the phase distribution of the source image, the off-resonance induced phase errors are successfully rewound through deconvolution. The alias-free partial Fourier transform reconstruction helps improve the signal-to-noise ratio of the field maps and the output images. The effectiveness of the proposed algorithm was validated through 7T MRI experiments on a lemon, a water phantom, and in vivo rat head. SPEN imaging was evaluated using rapid acquisition by sequential excitation and refocusing (RASER) which produces uniform T2 weighting. The results indicate that the new technique can more robustly deal with the cases in which the images obtained with conventional single-shot spin-echo EPI are difficult to be restored due to serious field variations. Copyright © 2015 Elsevier Inc. All rights reserved.
    Journal of magnetic resonance (San Diego, Calif.: 1997) 02/2015; 254. DOI:10.1016/j.jmr.2015.02.007
  • Source
    • "In order to achieve meaningful information for the calculation of the diffusion tensor, at least 6 diffusion-weighted (DW) images for each section are needed, however, depending on the focus of the different DTI applications, more directions (up to 128) may be needed (Ni et al., 2006). In order to minimize acquisition time and, subsequently, motion artifacts from the patient's movement, the most common technique is spin-echo planar imaging. "
    [Show abstract] [Hide abstract]
    ABSTRACT: BACKGROUND: Progress in neuroimaging has yielded new powerful tools which, potentially, can be applied to clinical populations, improve the diagnosis of neurological disorders and predict outcome. At present, the diagnosis of consciousness disorders is limited to subjective assessment and objective measurements of behavior, with an emerging role for neuroimaging techniques. In this review we focus on white matter alterations measured using Diffusion Tensor Imaging on patients with consciousness disorders, examining the most common diffusion imaging acquisition protocols and considering the main issues related to diffusion imaging analyses. We conclude by considering some of the remaining challenges to overcome, the existing knowledge gaps and the potential role of neuroimaging in understanding the pathogenesis and clinical features of disorders of consciousness.
    Frontiers in Human Neuroscience 01/2015; 8. DOI:10.3389/fnhum.2014.01028
  • Source
    • ", and 4 diffusion weighted runs were collected with 3 b0 (nondiffusion weighted) images per run. Previous research has shown that 20 diffusion gradient directions allow for calculating reliable FA measurements (Li et al., 2005; Ni et al., 2006). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Youth with family history of alcohol abuse have a greater risk of developing an alcohol use disorder (AUD). Brain and behavior differences may underlie this increased vulnerability. The current study examined delay discounting behavior and white matter microstructure in youth at high risk for alcohol abuse, as determined by a family history of alcoholism (FH+), and youth without such family history (FH-). Thirty-three healthy youth (FH+ = 15, FH- = 18), ages 11 to 15 years, completed a delay discounting task and underwent diffusion tensor imaging. Tract-based spatial statistics (Smith et al., 2006), as well as follow-up region-of-interest analyses, were performed to compare fractional anisotropy (FA) between FH+ and FH- youth. FH+ youth showed a trend toward increased discounting behavior and had significantly slower reaction times (RTs) on the delay discounting paradigm compared to FH- youth. Group differences in FA were seen in several white matter tracts. Furthermore, lower FA in the left inferior longitudinal fasciculus and the right optic radiation statistically mediated the relationship between FH status and slower RTs on the delay discounting task. Youth with a family history of substance abuse have disrupted white matter microstructure, which likely contributes to less efficient cortical processing and may act as an intrinsic risk factor contributing to an increased susceptibility of developing AUD. In addition, FHP youth showed a trend toward greater impulsive decision making, possibly representing an inherent personal characteristic that may facilitate substance use onset and abuse in high-risk youth.
    Alcoholism Clinical and Experimental Research 09/2010; 34(9):1590-602. DOI:10.1111/j.1530-0277.2010.01244.x
Show more