NeuroImage
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Blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) has been recently used to quantify cerebral blood volume (CBV) and oxygen extraction ratio (OER). In the present study, we have exploited the intravascular BOLD model to assess gray matter (GM) OER at hemispheric level using parenchymal T(2) and CBV data at 1.5 T, obtained by single spin echo and dynamic susceptibility contrast (DSC) perfusion MRI, respectively. An OER of 0.40 +/- 0.07 was determined in gray matter for control subjects. ⋯ We also found three cases with ipsilateral gray matter CBV below 2 SD of the control value, two of these with >70% stenosis. Gray matter OER ipsilateral to the stenosis was above 2 SD of the control range in eight CS patients, three of these showing also high CBV. Use of the present approach to determine OER for the assessment of hemodynamic adaptations in CS patients is discussed in the light of documented hemodynamic adaptations to carotid stenosis.
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Our aim was to quantify with functional magnetic resonance imaging (fMRI) changes in brain activity in concussed athletes and compare the results with those of normal control subjects. Regional brain activations associated with a working memory task were obtained from a group of concussed athletes (15 symptomatic, 1 asymptomatic) and eight matched control subjects, using blood oxygen level dependent (BOLD) fMRI. The average percent signal change from baseline to working memory condition in each region of interest was computed. ⋯ On the first study, when he was still symptomatic, less task-related activations were observed. On follow-up, once his symptoms had disappeared, the task-related activations became comparable to those of the control group. These results demonstrate the potential of fMRI, in conjunction with the working memory task, to identify an underlying pathology in symptomatic concussed individuals with normal structural imaging results.
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Comparative Study
Evaluation of atlas selection strategies for atlas-based image segmentation with application to confocal microscopy images of bee brains.
This paper evaluates strategies for atlas selection in atlas-based segmentation of three-dimensional biomedical images. Segmentation by intensity-based nonrigid registration to atlas images is applied to confocal microscopy images acquired from the brains of 20 bees. This paper evaluates and compares four different approaches for atlas image selection: registration to an individual atlas image (IND), registration to an average-shape atlas image (AVG), registration to the most similar image from a database of individual atlas images (SIM), and registration to all images from a database of individual atlas images with subsequent multi-classifier decision fusion (MUL). ⋯ The superiority of the MUL strategy over the other three methods is statistically significant (two-sided paired t test, P < 0.001). Both the MUL and AVG strategies performed better than the best possible SIM and IND strategies with optimal a posteriori atlas selection (mean similarity index for optimal SIM, 0.83; for optimal IND, 0.81). Our findings show that atlas selection is an important issue in atlas-based segmentation and that, in particular, multi-classifier techniques can substantially increase the segmentation accuracy.
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Blood oxygenation level dependent contrast functional MRI (BOLD-fMRI) has been used to define the functional cortices of the brain in preoperative planning for tumor removal. However, some studies have demonstrated false-negative activations in such patients. We compared the evoked-cerebral blood oxygenation (CBO) changes measured by near-infrared spectroscopy (NIRS) and activation mapping of BOLD-fMRI in 12 patients with brain tumors who had no paresis of the upper extremities. ⋯ However, in the Deoxy-increase group, BOLD-fMRI revealed only a small activation area or no activation on the lesion side. Intraoperative brain mapping identified the PSMC on the lesion side that was not demonstrated by BOLD-fMRI. The false-negative activations might have been caused by the atypical evoked-CBO changes (i.e. increases in Deoxy-Hb) and the software employed to calculate the activation maps, which does not regard an increase of Deoxy-Hb (i.e., a decrease in BOLD-fMRI signal) as neuronal activation.
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The contingent negative variation (CNV) is a long-latency electroencephalography (EEG) surface negative potential with cognitive and motor components, observed during response anticipation. CNV is an index of cortical arousal during orienting and attention, yet its functional neuroanatomical basis is poorly understood. We used functional magnetic resonance imaging (fMRI) with simultaneous EEG and recording of galvanic skin response (GSR) to investigate CNV-related central neural activity and its relationship to peripheral autonomic arousal. ⋯ In a subset of subjects in whom we acquired simultaneous EEG and fMRI data, we observed activity in bilateral thalamus, anterior cingulate, and supplementary motor cortex that was modulated by trial-by-trial amplitude of CNV. These findings provide a likely functional neuroanatomical substrate for the CNV and demonstrate modulation of components of this neural circuitry by peripheral autonomic arousal. Moreover, these data suggest a mechanistic model whereby thalamocortical interactions regulate CNV amplitude.