Neonatal auditory activation detected by functional magnetic resonance imaging

The objective of this study was to detect auditory cortical activation in non-sedated neonates employing functional magnetic resonance imaging (fMRI). Using echo-planar functional brain imaging, subjects were presented with a frequency-modulated pure tone; the BOLD signal response was mapped in 5 mm-thick slices running parallel to the superior temporal gyrus. Twenty healthy neonates (13 term, 7 preterm) at term and 4 adult control subjects. Blood oxygen level-dependent (BOLD) signal in response to auditory stimulus was detected in all 4 adults and in 14 of the 20 neonates. FMRI studies of adult subjects demonstrated increased signal in the superior temporal regions during auditory stimulation. In contrast, signal decreases were detected during auditory stimulation in 9 of 14 newborns with BOLD response. fMRI can be used to detect brain activation with auditory stimulation in human infants.     

Quantitative estimation of brain white matter abnormalities in elderly subjects using magnetic resonance imaging

Twenty-five elderly subjects were examined with brain magnetic resonance imaging (MRI). The subjects were divided into two groups: those with Mini-Mental State Examination (MMSE) scores above 25, and those subjects with MMSE scores between 18 and 24. The degree of white matter abnormalities (WMA) (expressed as relative volumes) as well as the presence of cerebrovascular risk factors were evaluated in the two groups. We found that a) subjects with low MMSE scores had significantly larger relative volumes of WMA than the subjects with higher scores, b) a significant correlation (r_s = 0.53, p < 0.009) between MMSE scores and the relative volume of WMA was also established, and c) a weak significant correlation (r_s = −0.51, p < 0.05) between arterial blood pressure and WMA was found in the subjects with high MMSE scores. Besides these findings no other correlations between the presence of cerebrovascular risk factors and WMA were found in any of the groups.     

Ictal imaging using functional magnetic resonance

Magnetic resonance imaging (MRI) can now provide maps of human brain function with high spatial and temporal resolution. This noninvasive technique can also map the coritical activation that occurs during focal seizures, as demonstrated here by the results obtained using a conventional 1.5 T clinical MRI system for the investigation of a 4-year-old boy suffering from frequent partial motor seizures of his right side. FLASH images (TE = 60 ms) were acquired every 10 s over a period of 25 min, and activation images derived by subtracting baseline images from images obtained during clinical seizures. Functional MRI revealed sequential activation associated with specific gyri within the left hemisphere with each of five consecutive clinical seizures, and also during a period that was not associated with a detectable clinical seizure. The activated regions included gyri that were structurally abnormal. These results demonstrate (a) that functional MRI can potentially provide new insights into the dynamic events that occur in the epileptic brain and their relationship to brain structure; and (b) that there is the possibility of obtaining similar information in the absence of clinical seizures, suggesting the potential for studies in patients with interictal electrical disturbances.     

Maturation-dependent microstructure length scale in the corpus callosum of fixed rat brains by magnetic resonance diffusion-diffraction

Techniques capable of assessing microstructure length scale are potentially useful in probing the integrity of biologic tissue at the microscopic level. Although the magnetic resonance (MR) diffusion-diffraction technique has been proposed for years, its realization in an undissected brain has not been reported on. In this study, validation of this method in a phantom simulating a series of repeated sheets of water with regular spacing was first performed. The same technique was applied to the corpus callosum of fixed rat brains of different ages (range, 21-84 days). The phantom was constructed with a pile of transparencies immersed in water doped with Gd-DTPA. The measured signal showed diffraction-like coherence peaks, the modulation of which was influenced by the gap distance and the center-to-center distance of the adjacent gaps. The measured distances were consistent with the actual values. In five 84-day-old rats, the diffusion length scale derived from the diffractogram was highly reproducible. In the course of brain maturation, the measured size decreased with age. Electron microscopy showed that axons on day 21 were smaller in diameter and less myelinated as compared with those on day 84. Progressive decrease in the diffusion length scale observed during brain maturation might reflect a gradual decrease in transmembrane permeability due to myelination. In conclusion, MR diffusion-diffraction can be observed in the corpus callosum of fixed rat brains. This technique might be useful in probing the status of myelination in the development of disease.     

The magnetic resonance imaging subset of the mngu0 articulatory corpus

This paper announces the availability of the magnetic resonance imaging (MRI) subset of the mngu0 corpus, a collection of articulatory speech data from one speaker containing different modalities. This subset comprises volumetric MRI scans of the speaker's vocal tract during sustained production of vowels and consonants, as well as dynamic mid-sagittal scans of repetitive consonant-vowel (CV) syllable production. For reference, high-quality acoustic recordings of the speech material are also available. The raw data are made freely available for research purposes.     

Flexible statistical modelling detects clinical functional magnetic resonance imaging activation in partially compliant subjects

Clinical functional magnetic resonance imaging (fMRI) occasionally fails to detect significant activation, often due to variability in task performance. The present study seeks to test whether a more flexible statistical analysis can better detect activation, by accounting for variance associated with variable compliance to the task over time. Experimental results and simulated data both confirm that even at 80% compliance to the task, such a flexible model outperforms standard statistical analysis when assessed using the extent of activation (experimental data), goodness of fit (experimental data), and area under the operator characteristic curve (simulated data). Furthermore, retrospective examination of 14 clinical fMRI examinations reveals that in patients where the standard statistical approach yields activation, there is a measurable gain in model performance in adopting the flexible statistical model, with little or no penalty in lost sensitivity. This indicates that a flexible model should be considered, particularly for clinical patients who may have difficulty complying fully with the study task.     

Real-time functional magnetic resonance imaging: methods and applications

Functional magnetic resonance imaging (fMRI) has been limited by time-consuming data analysis and a low signal-to-noise ratio, impeding online analysis. Recent advances in acquisition techniques, computational power and algorithms increased the sensitivity and speed of fMRI significantly, making real-time analysis and display of fMRI data feasible. So far, most reports have focused on the technical aspects of real-time fMRI (rtfMRI). Here, we provide an overview of the different major areas of applications that became possible with rtfMRI: online analysis of single-subject data provides immediate quality assurance and functional localizers guiding the main fMRI experiment or surgical interventions. In teaching, rtfMRI naturally combines all essential parts of a neuroimaging experiment, such as experimental design, data acquisition and analysis, while adding a high level of interactivity. Thus, the learning of essential knowledge required to conduct functional imaging experiments is facilitated. rtfMRI allows for brain-computer interfaces (BCI) with a high spatial and temporal resolution and whole-brain coverage. Recent studies have shown that such BCI can be used to provide online feedback of the blood-oxygen-level-dependent signal and to learn the self-regulation of local brain activity. Preliminary evidence suggests that this local self-regulation can be used as a new paradigm in cognitive neuroscience to study brain plasticity and the functional relevance of brain areas, even being potentially applicable for psychophysiological treatment.     

Task-specific deactivation patterns in functional magnetic resonance imaging

In general, image analysis of cognitive experiments using functional magnetic resonance imaging techniques has emphasized those regions of the brain where increases in signal intensity, with regard to the reference state, are associated with activation. Nevertheless, a number of recent papers have shown that there are areas of deactivation as well. In this study, we have used a univariate analysis and echo-planar functional magnetic resonance imaging to address the relationship of the reference state to the deactivations. We employed two dichotomous covert tasks, orthographic lexical retrieval and pure visual retrieval, to contrast with the reference state (baseline) of silent counting. Our analysis yielded extensive, task-specific landscapes of regional incremental and decremental responses. We have specifically demonstrated that the decremental responses are not due to activation in the reference state. We have also demonstrated that they are not an artifact of a specific part of the image analysis, and propose that they represent a physiological, task specific signal that should be considered an integral component of neural networks representing brain function.     

Generalized relative entropy in functional magnetic resonance imaging

The generalized Kullback-Leibler distance D_q (q is the Tsallis parameter) is shown to be an useful measure for analysis of functional magnetic resonance imaging (fMRI) data series. This generalized form of entropy is used to evaluate the “distance” between the probability functions p₁ and p₂ of the signal levels related to periods of stimulus and non-stimulus in event-related fMRI experiments. The probability densities of the mean distance (averaged over the N epochs of the entire experiment) are obtained through numerical simulations for different values of signal-to-noise ratio (SNR) and found to be fitted very well by Gamma distributions (χ²<0.0008) for small values of N (N<30). These distributions allow us to determine the sensitivity and specificity of the method by construction of the receiver operating characteristic (ROC) curves. The performance of the method is also investigated in terms of the parameters q and L (number of signal levels) and our results indicate that the optimum choice is q=0.8 and L=3. The entropic index q is found to exert control on both sensitivity and specificity of the method. As q (q>0) is raised, sensitivity increases but specificity decreases. Finally, the method is applied in the analysis of a real event-related fMRI motor stimulus experiment and the resulting maps show activation in primary and secondary motor brain areas.     

Acoustic noise during functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) enables sites of brain activation to be localized in human subjects. For studies of the auditory system, acoustic noise generated during fMRI can interfere with assessments of this activation by introducing uncontrolled extraneous sounds. As a first step toward reducing the noise during fMRI, this paper describes the temporal and spectral characteristics of the noise present under typical fMRI study conditions for two imagers with different static magnetic field strengths. Peak noise levels were 123 and 138 dB re 20 microPa in a 1.5-tesla (T) and a 3-T imager, respectively. The noise spectrum (calculated over a 10-ms window coinciding with the highest-amplitude noise) showed a prominent maximum at 1 kHz for the 1.5-T imager (115 dB SPL) and at 1.4 kHz for the 3-T imager (131 dB SPL). The frequency content and timing of the most intense noise components indicated that the noise was primarily attributable to the readout gradients in the imaging pulse sequence. The noise persisted above background levels for 300-500 ms after gradient activity ceased, indicating that resonating structures in the imager or noise reverberating in the imager room were also factors. The gradient noise waveform was highly repeatable. In addition, the coolant pump for the imager's permanent magnet and the room air-handling system were sources of ongoing noise lower in both level and frequency than gradient coil noise. Knowledge of the sources and characteristics of the noise enabled the examination of general approaches to noise control that could be applied to reduce the unwanted noise during fMRI sessions.     

Percept-related activity in the human somatosensory system: functional magnetic resonance imaging studies

In this paper, we review blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) studies addressing the neural correlates of touch, thermosensation, pain and the mechanisms of their cognitive modulation in healthy human subjects. There is evidence that fMRI signal changes can be elicited in the parietal cortex by stimulation of single mechanoceptive afferent fibers at suprathreshold intensities for conscious perception. Positive linear relationships between the amplitude or the spatial extents of BOLD fMRI signal changes, stimulus intensity and the perceived touch or pain intensity have been described in different brain areas. Some recent fMRI studies addressed the role of cortical areas in somatosensory perception by comparing the time course of cortical activity evoked by different kinds of stimuli with the temporal features of touch, heat or pain perception. Moreover, parametric single-trial functional MRI designs have been adopted in order to disentangle subprocesses within the nociceptive system.

Available evidence suggest that studies that combine fMRI with psychophysical methods may provide a valuable approach for understanding complex perceptual mechanisms and top-down modulation of the somatosensory system by cognitive factors specifically related to selective attention and to anticipation. The brain networks underlying somatosensory perception are complex and highly distributed. A deeper understanding of perceptual-related brain mechanisms therefore requires new approaches suited to investigate the spatial and temporal dynamics of activation in different brain regions and their functional interaction.     

Detection of heterotopic gray matter in children by magnetic resonance imaging

Heterotopic gray matter results from abnormal brain development and is a recognized focus of seizures. It may be associated with mental retardation and/or severe malformations of the brain. Three patients with heterotopia of gray matter were identified by magnetic resonance imaging (MRI). CT failed to detect the heterotopic gray matter in each case. One child was referred for removal of a neoplasm based on CT studies until MRI demonstrated the developmental nature of his condition. One infant had severely dysplastic left cerebral hemisphere associated with heterotopic gray matter and the syndrome of Hypomelanosis of Ito. All three children suffered from seizures and/or mental retardation. MRI provided important information in the management of each case and appears to be the imaging method of choice in evaluating children with seizures or retardation for heterotopic gray matter in the brain.     

脑功能磁共振成像在人类嗅觉研究中的应用

在人类的5种主要感觉中,嗅觉是最广泛、古老、直接和内在的感觉.这些特性使人们对人类嗅觉的研究异常艰难,以致于直到今天人们对嗅觉的功能仍不清楚,而对大脑的功能机制所知更少.与其他基于物理原理的方法一样,磁共振成像技术的广泛应用极大地推动了整个生命科学的发展.脑功能磁共振成像的优势(高分辨率、高对比度、无损性和无放射性等)为人们研究嗅觉高级中枢以及与嗅觉相关行为的脑机制等提供了强有力的技术手段.文章在简单介绍嗅觉知识的基础上,着重讨论了近十年来,脑功能磁共振成像技术在人类嗅觉研究中所取得的成果.     

脑功能磁共振成像在人类嗅觉研究中的应用

在人类的5种主要感觉中,嗅觉是最广泛、古老、直接和内在的感觉.这些特性使人们对人类嗅觉的研究异常艰难,以致于直到今天人们对嗅觉的功能仍不清楚,而对大脑的功能机制所知更少.与其他基于物理原理的方法一样,磁共振成像技术的广泛应用极大地推动了整个生命科学的发展.脑功能磁共振成像的优势（高分辨率、高对比度、无损性和无放射性等）为人们研究嗅觉高级中枢以及与嗅觉相关行为的脑机制等提供了强有力的技术手段.文章在简单介绍嗅觉知识的基础上,着重讨论了近十年来,脑功能磁共振成像技术在人类嗅觉研究中所取得的成果.     

Influence of speech stimuli intensity on the activation of auditory cortex investigated with functional magnetic resonance imaging.

Understanding the impact of variations in the acoustic signal is critical for the development of auditory and language fMRI as an experimental tool. We describe the dependence of the BOLD signal and speech intelligibility on the intensity of auditory stimuli. Eighteen subjects were imaged on a 1.5-T MRI scanner. Speech stimuli were English monosyllabic words played at five intensity levels. Intrasubject reproducibility was measured on one subject by presenting the stimulus five times at the same intensity level. Intelligibility was measured during data acquisition as subjects signaled when hearing two targets. Each functional trial consisted of four cycles (30 s off-30 s on). Five oblique slices covering primary and association auditory areas were imaged. Activated voxels were identified by cross-correlation analysis and their percent signal change (delta S) was measured. Intersubject differences in activation extent, asymmetry, and dependence on intensity were striking. Volume of activation was significantly greater in the left than in the right hemisphere. Intrasubject reproducibility for delta S was higher than for volume of activation. delta S and intelligibility showed a similar dependence on intensity suggesting that not only intensity but also intelligibility affect the fMRI signal.     

A novel functional magnetic resonance imaging compatible search-coil eye-tracking system

Measuring eye movements (EMs) using the search-coil eye-tracking technique is superior to video-based infrared methods [Collewijn H, van der Mark F, Jansen TC. Precise recording of human eye movements. Vision Res 1975;15(3):447-50], which suffer from the instability of pupil size, blinking behavior and lower temporal resolution. However, no conventional functional magnetic resonance imaging (fMRI)-compatible search-coil eye tracker exists. The main problems for such a technique are the interaction between the transmitter coils and the magnetic gradients used for imaging as well as the limited amount of space in a scanner. Here we present an approach to overcome these problems and we demonstrate a method to record EMs in an MRI scanner using a search coil. The system described has a spatial resolution of 0.07 degrees (visual angle) and a high temporal resolution (22 kHz). The transmitter coils are integrated into the visual presentation system and the control/analysis unit is portable, which enables us to integrate the eye tracker with an MRI scanner. Our tests demonstrate low noise in the recorded eye traces and scanning with minimal artifact. Furthermore, the induced current in the search coil caused by the RF pulses does not lead to measurable heating. Altogether, this MR-compatible search-coil eye tracker can be used to precisely monitor EMs with high spatial and temporal resolution during fMRI. It can therefore be of great importance for studies requiring accurate fixation of a target, or measurement and study of the subject's oculomotor system.     

Multifractal analysis of white matter structural changes on 3D magnetic resonance imaging between normal aging and early Alzheimer's disease

Applications of multifractal analysis to white matter structure changes on magnetic resonance imaging(MRI) have recently received increasing attentions. Although some progresses have been made, there is no evident study on applying multifractal analysis to evaluate the white matter structural changes on MRI for Alzheimer's disease(AD) research. In this paper, to explore multifractal analysis of white matter structural changes on 3D MRI volumes between normal aging and early AD, we not only extend the traditional box-counting multifractal analysis(BCMA) into the 3D case, but also propose a modified integer ratio based BCMA(IRBCMA) algorithm to compensate for the rigid division rule in BCMA. We verify multifractal characteristics in 3D white matter MRI volumes. In addition to the previously well studied multifractal feature,△α, we also demonstrated △ f as an alternative and effective multifractal feature to distinguish NC from AD subjects.Both △α and △ f are found to have strong positive correlation with the clinical MMSE scores with statistical significance.Moreover, the proposed IRBCMA can be an alternative and more accurate algorithm for 3D volume analysis. Our findings highlight the potential usefulness of multifractal analysis, which may contribute to clarify some aspects of the etiology of AD through detection of structural changes in white matter.     

Rapid three-dimensional functional magnetic resonance imaging of the initial negative BOLD response

Functional MRI is most commonly used to study the local changes in blood flow that accompanies neuronal activity. In this work we introduce a new approach towards acquiring and analyzing fMRI data that instead provides the potential to study the initial oxygen consumption in the brain that accompanies activation. As the oxygen consumption is closer in timing to the underlying neuronal activity than the subsequent blood flow, this approach promises to provide more precise information about the location and timing of activity. Our approach is based on using a new single shot 3D echo-volumar imaging sequence which samples a small central region of 3D k-space every 100ms, thereby giving a low spatial resolution snapshot of the brain with extremely high temporal resolution. Explicit and simple rules for implementing the trajectory are provided, together with a straightforward reconstruction algorithm. Using our approach allows us to effectively study the behavior of the brain in the time immediately following activation through the initial negative BOLD response, and we discuss new techniques for detecting the presence of the negative response across the brain. The feasibility and efficiency of the approach is confirmed using data from a visual-motor task and an auditory-motor-visual task. The results of these experiments provide a proof of concept of our methodology, and indicate that rapid imaging of the initial negative BOLD response can serve an important role in studying cognition tasks involving rapid mental processing in more than one region.     

Inter-vender and test-retest reliabilities of resting-state functional magnetic resonance imaging: Implications for multi-center imaging studies

This prospective multi-center study aimed to evaluate the inter-vendor and test-retest reliabilities of resting-state functional magnetic resonance imaging (RS-fMRI) by assessing the temporal signal-to-noise ratio (tSNR) and functional connectivity. Study included 10 healthy subjects and each subject was scanned using three 3 T MR scanners (GE Signa HDxt, Siemens Skyra, and Philips Achieva) in two sessions. The tSNR was calculated from the time course data. Inter-vendor and test-retest reliabilities were assessed with intra-class correlation coefficients (ICCs) derived from variant component analysis. Independent component analysis was performed to identify the connectivity of the default-mode network (DMN). In result, the tSNR for the DMN was not significantly different among the GE, Philips, and Siemens scanners (P = 0.638). In terms of vendor differences, the inter-vendor reliability was good (ICC = 0.774). Regarding the test-retest reliability, the GE scanner showed excellent correlation (ICC = 0.961), while the Philips (ICC = 0.671) and Siemens (ICC = 0.726) scanners showed relatively good correlation. The DMN pattern of the subjects between the two sessions for each scanner and between three scanners showed the identical patterns of functional connectivity. The inter-vendor and test-retest reliabilities of RS-fMRI using different 3 T MR scanners are good. Thus, we suggest that RS-fMRI could be used in multicenter imaging studies as a reliable imaging marker.