international Society for Magnetic Resonance in Medicine
01 Jan 2010-
About: The article was published on 2010-01-01 and is currently open access. It has received 656 citations till now. The article focuses on the topics: Magnetic resonance imaging.
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TL;DR: A set of procedures for modifying the representation of the cortical surface to inflate it so that activity buried inside sulci may be visualized, cut and flatten an entire hemisphere, and transform a hemisphere into a simple parameterizable surface such as a sphere for the purpose of establishing a surface-based coordinate system are designed.
5,816 citations
TL;DR: A post-processing technique for fast denoising of diffusion-weighted MR images is introduced and it is demonstrated that the technique suppresses local signal fluctuations that solely originate from thermal noise rather than from other sources such as anatomical detail.
1,110 citations
TL;DR: The performance of quantitative anisotropy (QA) in facilitating deterministic fiber tracking may assist fiber tracking studies and facilitate the advancement of human connectomics.
Abstract: Diffusion MRI tractography has emerged as a useful and popular tool for mapping connections between brain regions. In this study, we examined the performance of quantitative anisotropy (QA) in facilitating deterministic fiber tracking. Two phantom studies were conducted. The first phantom study examined the susceptibility of fractional anisotropy (FA), generalized factional anisotropy (GFA), and QA to various partial volume effects. The second phantom study examined the spatial resolution of the FA-aided, GFA-aided, and QA-aided tractographies. An in vivo study was conducted to track the arcuate fasciculus, and two neurosurgeons blind to the acquisition and analysis settings were invited to identify false tracks. The performance of QA in assisting fiber tracking was compared with FA, GFA, and anatomical information from T1-weighted images. Our first phantom study showed that QA is less sensitive to the partial volume effects of crossing fibers and free water, suggesting that it is a robust index. The second phantom study showed that the QA-aided tractography has better resolution than the FA-aided and GFA-aided tractography. Our in vivo study further showed that the QA-aided tractography outperforms the FA-aided, GFA-aided, and anatomy-aided tractographies. In the shell scheme (HARDI), the FA-aided, GFA-aided, and anatomy-aided tractographies have 30.7%, 32.6%, and 24.45% of the false tracks, respectively, while the QA-aided tractography has 16.2%. In the grid scheme (DSI), the FA-aided, GFA-aided, and anatomy-aided tractographies have 12.3%, 9.0%, and 10.93% of the false tracks, respectively, while the QA-aided tractography has 4.43%. The QA-aided deterministic fiber tracking may assist fiber tracking studies and facilitate the advancement of human connectomics.
806 citations
Cites methods or result from "international Society for Magnetic ..."
...Last, the anatomyaided tractography used in our study is only a simplified version, compared with other anatomy-based approaches [20,21], and we did not implement track rejection or continuation to fully exploit its power....
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...However, to determine when the fiber tracking should be terminated, a lot of fiber tracking methods still use voxel-based index, such as fractional anisotropy (FA), generalized fractional anisotropy (GFA)[19], and anatomical information from T1-weighted images [20,21]....
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TL;DR: Findings indicate that high-resolution MRI with a 3-dimensional multiple overlapping thin slab angiography protocol is capable of distinguishing intact, thick fibrous caps from intact thin and disrupted caps in atherosclerotic human carotid arteries in vivo.
Abstract: Background—The results of studies of advanced lesions of atherosclerosis suggest that the thickness of the fibrous cap that overlies the necrotic core distinguishes the stable lesion from one that is at high risk for rupture and thromboembolic events. We have developed a high-resolution MRI technique that can identify the fine structure of the lesion, including the fibrous cap, in vivo. The aim of the present study was to determine the agreement between in vivo MRI and lesion architecture as seen on histology and gross tissue examination to identify fibrous cap thickness and rupture. Methods and Results—Twenty-two subjects who were scheduled for carotid endarterectomy underwent MRI with a 3-dimensional multiple overlapping thin slab angiography protocol. The appearance of the fibrous cap was categorized as (1) an intact, thick, (2) an intact, thin, or (3) a ruptured fibrous cap on MRI, gross, and histological sections. Thirty-six sites were available for comparison between MRI and histology. There was a h...
622 citations
TL;DR: The results suggest that, even with moderate smoothing, a large number of voxels within central white matter regions may have non-normally distributed residuals thus making valid statistical inferences with a parametric approach problematic in these areas.
609 citations
Cites background from "international Society for Magnetic ..."
...Furthermore, with one possible recent exception (Kumari et al., 2004), no theories explaining the observation of the uniformity of the trace of the diffusion tensor across brain parenchyma (Pierpaoli et al....
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...Furthermore, with one possible recent exception (Kumari et al., 2004), no theories explaining the observation of the uniformity of the trace of the diffusion tensor across brain parenchyma (Pierpaoli et al., 1996) currently exist....
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References
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TL;DR: In this representation, it is shown that isotropic diffusion, anisotropic diffusion from a single fiber, and anisotrop diffusion from multiple fiber directions fall into distinct and separable channels and can be determined for any voxel without any prior information by a spherical harmonic transform.
Abstract: The methods of group theory are applied to the problem of characterizing the diffusion measured in high angular resolution MR experiments. This leads to a natural representation of the local diffusion in terms of spherical harmonics. In this representation, it is shown that isotropic diffusion, anisotropic diffusion from a single fiber, and anisotropic diffusion from multiple fiber directions fall into distinct and separable channels. This decomposition can be determined for any voxel without any prior information by a spherical harmonic transform, and for special cases the magnitude and orientation of the local diffusion may be determined. Moreover, non-diffusion-related asymmetries produced by experimental artifacts fall into channels distinct from the fiber channels, thereby allowing their separation and a subsequent reduction in noise from the reconstructed fibers. In the case of a single fiber, the method reduces identically to the standard diffusion tensor method. The method is applied to normal volunteer brain data collected with a stimulated echo spiral high angular resolution diffusion-weighted (HARD) acquisition.
602 citations
TL;DR: The results suggest that the compensation method allows for the detection of activation in brain areas which are usually unavailable for BOLD studies, even in the case of acceptable image intensities.
249 citations
TL;DR: Using MRI, the observation of a transient decrease of the apparent diffusion coefficient of water in the human brain visual cortex during activation by a black and white 8-Hz-flickering checkerboard is reported.
Abstract: Using MRI, we report the observation of a transient decrease of the apparent diffusion coefficient (ADC) of water in the human brain visual cortex during activation by a black and white 8-Hz-flickering checkerboard. The ADC decrease was small (<1%), but significant and reproducible, and closely followed the time course of the activation paradigm. Based on the known sensitivity of diffusion MRI to cell size in tissues and on optical imaging studies that have revealed changes in the shape of neurons and glial cells during activation, the observed ADC findings have been tentatively ascribed to a transient swelling of cortical cells. These preliminary results suggest a new approach to produce images of brain activation with MRI from signals directly associated with neuronal activation, and not through changes in local blood flow.
184 citations
TL;DR: The results demonstrate that while fractional area (FA) does not provide a good measure of CBV, FA corrected for section thickness effects does, and a new independent correlative measure should enable efficient and accurate progress in the development of MRI methods to evaluate tumor angiogenesis.
Abstract: In an effort to develop MRI methods for the evaluation of tumor angiogenesis (new blood vessel formation), MRI-derived cerebral blood volume (CBV) information has been compared to histologic measures of microvessel density (MVD). Although MVD is a standard marker of angiogenesis, it is not a direct correlate of the volume measurements made with MRI, and therefore inappropriate for the development and validation of the MR techniques. Therefore, the goal of this study was to develop an approach by which MR measurements of CBV can be directly correlated. To this end, dynamic susceptibility contrast (DSC) MRI experiments were performed in six Fisher rats implanted with 9L gliosarcoma brain tumors. Subsequently, the circulation was perfused with a latex compound (Microfil), after which 50-microm tissue sections were analyzed for vessel count, diameter, and the fraction of area comprised of vessels. The results demonstrate that while fractional area (FA) does not provide a good measure of CBV, FA corrected for section thickness effects does. Whereas the FA in normal brain was found to be 13.03 +/- 1.83% the corrected FA, or fractional volume (FV), was 1.89 +/- 0.39%, a value in agreement with those reported in the literature for normal brain. Furthermore, while no significant difference was found between normal brain and tumor FA (P = 0.55), the difference was significant for FV (P = 0.036), as would be expected. And only with FV does a correlation with the MRI-derived CBV become apparent (r(S) = 0.74). There was strong correlation (r(s) = 0.886) between the tumor / normal blood volume ratios as estimated by each technique, although the MR-ratio (1.56 +/- 0.29) underestimated the histologic-ratio (2.35 +/- 0.75). Thus, the correlation of MRI CBV methods requires a measurement of fractional vessel area and correction of this area for section thickness effects. This new independent correlative measure should enable efficient and accurate progress in the development of MRI methods to evaluate tumor angiogenesis.
126 citations
TL;DR: Ktrans values for Gd‐DTPA uptake into tumours could be a useful non‐invasive indicator of blood flow changes induced by anti‐vascular agents such as combretastatin.
Abstract: The anti-vascular effects of the tubulin binding agent, disodium combretastatin A-4 3-O-phosphate (CA-4-P), have been investigated in the rat P22 carcinosarcoma by measurements of radiolabelled iodoantipyrine uptake and dynamic contrast-enhanced MRI. The iodoantipyrine estimates of absolute tumour blood flow showed a reduction from 0.35 to 0.04 ml g−1 min−1 6 h after 10 mg kg−1 CA-4-P and to <0.01 ml g−1 min−1 after 100 mg kg−1. Tumour blood flow recovered to control values 24 h after 10 mg kg−1 CA-4-P, but there was no recovery by 24 h after the higher dose. Dynamic contrast-enhanced MR images were obtained at 4.7 T, following injection of 0.1 mmol kg−1 Gd-DTPA and analysed assuming a model arterial input function. A parameter, Ktrans, which is related to blood flow rate and permeability of the tumour vasculature to Gd-DTPA, was calculated from the uptake data. Ktrans showed a reduction from 0.34 to 0.11 min−1 6 h after 10 mg kg−1 CA-4-P and to 0.07 min−1 after 100 mg kg−1. Although the magnitude of changes in Ktrans was smaller than that in tumour blood flow, the time course and dose-dependency patterns were very similar. The apparent extravascular extracellular volume fraction, νe, showed a four-fold reduction 6 h after 100 mg kg−1 CA-4-P, possibly associated with vascular shutdown within large regions of the tumour. These results suggest that Ktrans values for Gd-DTPA uptake into tumours could be a useful non-invasive indicator of blood flow changes induced by anti-vascular agents such as combretastatin. Copyright © 2002 John Wiley & Sons, Ltd.
111 citations