Diffusion magnetic resonance (MR) imaging is evolving into a potent tool in the examination of the central nervous system. Although it is often used for the detection of acute ischemia, evaluation of directionality in a diffusion measurement can be useful in white matter, which demonstrates strong diffusion anisotropy. Techniques such as diffusion-tensor imaging offer a glimpse into brain microstructure at a scale that is not easily accessible with other modalities, in some cases improving the detection and characterization of white matter abnormalities. Diffusion MR tractography offers an overall view of brain anatomy, including the degree of connectivity between different regions of the brain. However, optimal utilization of the wide range of data provided with directional diffusion MR measurements requires careful attention to acquisition and postprocessing. This article will review the principles of diffusion contrast and anisotropy, as well as clinical applications in psychiatric, developmental, neurodegenerative, neoplastic, demyelinating, and other types of disease.
"The first magnetic resonance sequence able to measure diffusion coefficient in structures was developed in the early 80's (Wesbey et al., 1984), paving the way for a new, well-established imaging contrast for in vivo quantification of molecular diffusivity. Although a variety of sequences are now used to acquire diffusion weighted (DW) images, all DW sequences include two equal and opposing motion-probing gradients (Nucifor et al., 2007). The acquired signal from a voxel will exponentially decay as function of a parameter b which determines the strength and duration of the diffusion gradients and essentially represents the measurement's sensitivity to water diffusion . "
[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 · 2.99 Impact Factor
"Further, diminished response speed can lead to disruption of tasks that require mental manipulation and control (Bartzokis et al. 2007; Lu et al. 2013). Furthermore, studies have shown that deterioration in myelinated networks occurs with advanced age (Guttman et al. 1998; Nucifora et al. 2007). Aging affects WM microstructure, leading to inefficient communication between distinct brain regions, and a concomitant reduction in performance on tasks of EF and CPS. "
[Show abstract][Hide abstract] ABSTRACT: Executive function (EF) and cognitive processing speed (CPS) are two cognitive performance domains that decline with advanced age. Reduced EF and CPS are known to correlate with age-related frontal-lobe volume loss. However, it remains unclear whether white matter microstructure in these regions is associated with age-related decline in EF and/or CPS. We utilized quantitative tractography metrics derived from diffusion-tensor MRI to investigate the relationship between the mean fiber bundle lengths (FBLs) projecting to different lobes, and EF/CPS performance in 73 healthy aging adults. We measured aspects of EF and CPS with the Trail Making Test (TMT), Color-Word Interference Test, Letter-Number Sequencing (L-N Seq), and Symbol Coding. Results revealed that parietal and occipital FBLs explained a significant portion of variance in EF. Frontal, temporal, and occipital FBLs explained a significant portion of variance in CPS. Shorter occipital FBLs were associated with poorer performance on the EF tests TMT-B and CWIT 3. Shorter frontal, parietal, and occipital FBLs were associated with poorer performance on L-N Seq and Symbol Coding. Shorter frontal and temporal FBLs were associated with lower performance on CPS tests TMT-A and CWIT 1. Shorter FBLs were also associated with increased age. Results suggest an age-related FBL shortening in specific brain regions related to poorer EF and CPS performance among older adults. Overall, results support both the frontal aging hypothesis and processing speed theory, suggesting that each mechanism is contributing to age-related cognitive decline.
Brain Imaging and Behavior 11/2014; DOI:10.1007/s11682-014-9334-8 · 4.60 Impact Factor
"These features have been attributed to the disruption of the underlying structures of neural networks [Ellison-Wright and Bullmore , 2009; Kubicki et al., 2007]. Diffusion MRI is a technique that is capable of detecting the microstructural integrities of the axonal fibers of the white matter [Basser et al., 2000; Nucifora et al., 2007] and has revealed disruptions of these networks in vivo [Kanaan et al., 2005]. Numerous diffusion MRI studies have reported abnormal white matter regions in patients with schizophrenia and also in first-episode, drug-na€ ıve, and high-risk patients [Lee et al., 2013; Peters et al., 2008; Samartzis et al., 2014]. "
Victor M. Tang, Donna J. Lang, Chantelle J. Giesbrecht, William J. Panenka, Taylor Willi, Ric M. Procyshyn, Fidel Vila-Rodriguez, Willough Jenkins, Tania Lecomte, Heidi N. Boyda, Ana Aleksic, G. William MacEwan, William G. Honer, Alasdair M. Barr
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