Inter-Vendor Reproducibility of Myelin Water Imaging Using a 3D Gradient and Spin Echo Sequence

Myelin water imaging can be achieved using multicomponent T2 relaxation analysis to quantify in vivo measurement of myelin content, termed the myelin water fraction (MWF). Therefore, myelin water imaging can be a valuable tool to better understand the underlying white matter pathology in demyelinating diseases, such as multiple sclerosis. To apply myelin water imaging in multisite studies and clinical applications, it must be acquired in a clinically feasible scan time (less than 15 min) and be reproducible across sites and scanner vendors. Here, we assessed the reproducibility of MWF measurements in regional and global white matter in 10 healthy human brains across two sites with two different 3 T magnetic resonance imaging scanner vendors (Philips and Siemens), using a 32-echo gradient and spin echo (GRASE) sequence. A strong correlation was found between the MWF measurements in the global white matter (Pearson’s r = 0.91; p < 0.001) for all participants across the two sites. The mean intersite MWF coefficient of variation across participants was 2.77% in the global white matter and ranged from 4.47% (splenium of the corpus callosum) to 17.89% (genu of the corpus callosum) in white matter regions of interest. Bland-Altman analysis showed a good agreement in MWF measurements between the two sites with small bias of 0.002. Overall, MWF estimates were in good agreement across the two sites and scanner vendors. Our findings support the use of quantitative multi-echo T2 relaxation metrics, such as the MWF, in multicenter studies and clinical trials to gain deeper understanding about the pathological processes resulting from the underlying disease progression in neurodegenerative diseases

Multi-modal characterization of rapid anterior hippocampal volume increase associated with aerobic exercise.

The hippocampus has been shown to demonstrate a remarkable degree of plasticity in response to a variety of tasks and experiences. For example, the size of the human hippocampus has been shown to increase in response to aerobic exercise. However, it is currently unknown what underlies these changes. Here we scanned sedentary, young to middle-aged human adults before and after a six-week exercise intervention using nine different neuroimaging measures of brain structure, vasculature, and diffusion. We then tested two different hypotheses regarding the nature of the underlying changes in the tissue. Surprisingly, we found no evidence of a vascular change as has been previously reported. Rather, the pattern of changes is better explained by an increase in myelination. Finally, we show hippocampal volume increase is temporary, returning to baseline after an additional six weeks without aerobic exercise. This is the first demonstration of a change in hippocampal volume in early to middle adulthood suggesting that hippocampal volume is modulated by aerobic exercise throughout the lifespan rather than only in the presence of age related atrophy. It is also the first demonstration of hippocampal volume change over a period of only six weeks, suggesting gross morphometric hippocampal plasticity occurs faster than previously thought

Rapid Three-Dimensional Multicomponent Relaxation Imaging of the Cervical Spinal Cord

Currently, little is known about the pathology of myelin in spinal cord disease due to the technical challenges of specifically measuring myelin content noninvasively. Multicomponent relaxometry allows estimation of the myelin water fraction, which is related to myelin content. However, conventional multiple-echo spin-echo-based multicomponent relaxometry techniques require prohibitively long acquisition times, lack spatial coverage, and are sensitive to artifacts common in spinal cord imaging. Multicomponent driven equilibrium single pulse observation of T-1 and T-2 (mcDESPOT) offers a promising alternative to conventional multicomponent relaxometry techniques. The goal of this pilot study was to assess the efficacy of mcDESPOT for obtaining high spatial resolution spinal cord myelin water fraction data covering the entire cervical spinal cord. Myelin water fraction values were found to be highly reproducible between subjects and over time but varied considerably along the length of the cord. Other relaxation characteristics that relate to tissue structure and health were also reliably measured. Magn Reson Med 65:551-556, 2011. (C) 2010 Wiley-Liss, Inc

dGEMRIC and metal artifact at 3T

Objective. To evaluate the effect of metal artifact reduction techniques on dGEMRIC T₁ calculation with surgical hardware present. Materials and Methods. We examined the effect of stainless steel and titanium hardware on dGEMRIC T₁ maps. We tested two strategies to reduce metal artifact in dGEMRIC: 1) saturation recovery (SR) instead of inversion recovery (IR) and 2) applying the Metal Artifact Reduction Sequence (MARS), in a gadolinium-doped agarose gel phantom and in vivo with titanium hardware. T₁ maps were obtained using custom curve-fitting software and phantom ROIs were defined to compare conditions (metal, MARS, IR, SR). Results. A large area of artifact appeared in phantom IR images with metal when TI≤700ms. IR maps with metal had additional artifact both in vivo and in the phantom (shifted null points, increased mean T₁ (+151% IR ROIartifact) and decreased mean inversion efficiency (f; 0.45 ROIartifact, versus 2 for perfect inversion)) compared to the SR maps (ROIartifact: +13% T1 SR, 0.95 versus 1 for perfect excitation), however SR produced noisier T₁ maps than IR (phantom SNR: 118 SR, 212 IR). MARS subtly reduced the extent of artifact in the phantom (IR and SR). Conclusion. dGEMRIC measurement in the presence of surgical hardware at 3T is possible with appropriately applied strategies. Measurements may work best in the presence of titanium and are severely limited with stainless steel. For regions near hardware where IR produces large artifacts making dGEMRIC analysis impossible, SRMARS may allow dGEMRIC measurements. The position and size of the IR artifact is variable, and must be assessed for each implant/imaging set-up.Applied Science, Faculty ofMedicine, Faculty ofScience, Faculty ofOther UBCNon UBCMechanical Engineering, Department ofOrthopaedic Surgery, Department ofPhysics and Astronomy, Department ofReviewedFacultyGraduat

Quantifying visual pathway axonal and myelin loss in multiple sclerosis and neuromyelitis optica

AbstractBackgroundThe optic nerve is frequently injured in multiple sclerosis and neuromyelitis optica, resulting in visual dysfunction, which may be reflected by measures distant from the site of injury.ObjectiveTo determine how retinal nerve fiber layer as a measure of axonal health, and macular volume as a measure of neuronal health are related to changes in myelin water fraction in the optic radiations of multiple sclerosis and neuromyelitis optica participants with and without optic neuritis and compared to healthy controls.Methods12 healthy controls, 42 multiple sclerosis (16 with optic neuritis), and 10 neuromyelitis optica participants (8 with optic neuritis) were included in this study. Optical coherence tomography assessment involved measurements of the segmented macular layers (total macular, ganglion cell layer, inner plexiform layer, and inner nuclear layer volume) and paripapillary retinal nerve fiber layer thickness. The MRI protocol included a 32-echo T2-relaxation GRASE sequence. Average myelin water fraction values were calculated within the optic radiations as a measure of myelin density.ResultsMultiple sclerosis and neuromyelitis optica eyes with optic neuritis history had lower retinal nerve fiber layer thickness, total macular, ganglion cell and inner plexiform layer volumes compared to eyes without optic neuritis history and controls. Inner nuclear layer volume increased in multiple sclerosis with optic neuritis history (mean=0.99mm3, SD=0.06) compared to those without (mean=0.97mm3, SD=0.06; p=0.003). Mean myelin water fraction in the optic radiations was significantly lower in demyelinating diseases (neuromyelitis optica: mean=0.098, SD=0.01, multiple sclerosis with optic neuritis history: mean=0.096, SD=0.01, multiple sclerosis without optic neuritis history: mean=0.098, SD=0.02; F3,55=3.35, p=0.03) compared to controls. Positive correlations between MRI and optical coherence tomography measures were also apparent (retinal nerve fiber layer thickness and ganglion cell layer thickness: r=0.25, p=0.05, total macular volume and inner plexiform layer volume: r=0.27, p=0.04).ConclusionsThe relationship between reductions in OCT measures of neuro-axonal health in the anterior visual pathway and MRI-based measures of myelin health in the posterior visual pathway suggests that these measures may be linked through bidirectional axonal degeneration

Inter-Vendor Reproducibility of Myelin Water Imaging Using a 3D Gradient and Spin Echo Sequence

Myelin water imaging can be achieved using multicomponent T2 relaxation analysis to quantify in vivo measurement of myelin content, termed the myelin water fraction (MWF). Therefore, myelin water imaging can be a valuable tool to better understand the underlying white matter pathology in demyelinating diseases, such as multiple sclerosis. To apply myelin water imaging in multisite studies and clinical applications, it must be acquired in a clinically feasible scan time (less than 15 min) and be reproducible across sites and scanner vendors. Here, we assessed the reproducibility of MWF measurements in regional and global white matter in 10 healthy human brains across two sites with two different 3 T magnetic resonance imaging scanner vendors (Philips and Siemens), using a 32-echo gradient and spin echo (GRASE) sequence. A strong correlation was found between the MWF measurements in the global white matter (Pearson's r = 0.91; p < 0.001) for all participants across the two sites. The mean intersite MWF coefficient of variation across participants was 2.77% in the global white matter and ranged from 4.47% (splenium of the corpus callosum) to 17.89% (genu of the corpus callosum) in white matter regions of interest. Bland-Altman analysis showed a good agreement in MWF measurements between the two sites with small bias of 0.002. Overall, MWF estimates were in good agreement across the two sites and scanner vendors. Our findings support the use of quantitative multi-echo T2 relaxation metrics, such as the MWF, in multicenter studies and clinical trials to gain deeper understanding about the pathological processes resulting from the underlying disease progression in neurodegenerative diseases

MSJ770085_supplementary_appendix – Supplemental material for A 24-month advanced magnetic resonance imaging study of multiple sclerosis patients treated with alemtuzumab

<p>Supplemental material, MSJ770085_supplementary_appendix for A 24-month advanced magnetic resonance imaging study of multiple sclerosis patients treated with alemtuzumab by Irene M Vavasour, Roger Tam, David KB Li, Cornelia Laule, Carolyn Taylor, Shannon H Kolind, Alex L MacKay, Adil Javed and Anthony Traboulsee in Multiple Sclerosis Journal</p