Quantitative comparison of functional contrast from BOLD-weighted spin-echo and gradient-echo echoplanar imaging at 1.5 Tesla and H2 15O PET in the whole brain

Multi-study fMRI outlooks on subcortical BOLD responses in the stop-signal paradigm

This study investigates the functional network underlying response inhibition in the human brain, particularly the role of the basal ganglia in successful action cancellation. Functional magnetic resonance imaging (fMRI) approaches have frequently used the stop-signal task to examine this network. We merge five such datasets, using a novel aggregatory method allowing the unification of raw fMRI data across sites. This meta-analysis, along with other recent aggregatory fMRI studies, does not find evidence for the innervation of the hyperdirect or indirect cortico-basal-ganglia pathways in successful response inhibition. What we do find, is large subcortical activity profiles for failed stop trials. We discuss possible explanations for the mismatch of findings between the fMRI results presented here and results from other research modalities that have implicated nodes of the basal ganglia in successful inhibition. We also highlight the substantial effect smoothing can have on the conclusions drawn from task-specific general linear models. First and foremost, this study presents a proof of concept for meta-analytical methods that enable the merging of extensive, unprocessed, or unreduced datasets. It demonstrates the significant potential that open-access data sharing can offer to the research community. With an increasing number of datasets being shared publicly, researchers will have the ability to conduct meta-analyses on more than just summary data.

Optimization and validation of multi-echo, multi-contrast SAGE acquisition in fMRI

The purpose of this study was to optimize and validate a multi-contrast, multi-echo fMRI method using a combined spin- and gradient-echo (SAGE) acquisition. It was hypothesized that SAGE-based blood oxygen level-dependent (BOLD) functional MRI (fMRI) will improve sensitivity and spatial specificity while reducing signal dropout. SAGE-fMRI data were acquired with five echoes (2 gradient-echoes, 2 asymmetric spin-echoes, and 1 spin-echo) across 12 protocols with varying acceleration factors, and temporal SNR (tSNR) was assessed. The optimized protocol was then implemented in working memory and vision tasks in 15 healthy subjects. Task-based analysis was performed using individual echoes, quantitative dynamic relaxation times T2 * and T2, and echo time-dependent weighted combinations of dynamic signals. These methods were compared to determine the optimal analysis method for SAGE-fMRI. Implementation of a multiband factor of 2 and sensitivity encoding (SENSE) factor of 2.5 yielded adequate spatiotemporal resolution while minimizing artifacts and loss in tSNR. Higher BOLD contrast-to-noise ratio (CNR) and tSNR were observed for SAGE-fMRI relative to single-echo fMRI, especially in regions with large susceptibility effects and for T2-dominant analyses. Using a working memory task, the extent of activation was highest with T2 *-weighting, while smaller clusters were observed with quantitative T2 * and T2. SAGE-fMRI couples the high BOLD sensitivity from multi-gradient-echo acquisitions with improved spatial localization from spin-echo acquisitions, providing two contrasts for analysis. SAGE-fMRI provides substantial advantages, including improving CNR and tSNR for more accurate analysis.

A Joint Analysis of Multi-Paradigm fMRI Data With Its Application to Cognitive Study

With the development of neuroimaging techniques, a growing amount of multi-modal brain imaging data are collected, facilitating comprehensive study of the brain. In this paper, we jointly analyzed functional magnetic resonance imaging (fMRI) collected under different paradigms in order to understand cognitive behaviors of an individual. To this end, we proposed a novel multi-view learning algorithm called structure-enforced collaborative regression (SCoRe) to extract co-expressed discriminative brain regions under the guidance of anatomical structure of the brain. An advantage of SCoRe over its predecessor collaborative regression (CoRe) lies in its incorporation of group structures in the brain imaging data, which makes the model biologically more meaningful. Results from real data analysis has confirmed that by incorporating prior knowledge of brain structure, SCoRe can deliver better prediction performance and is less sensitive to hyper-parameters than CoRe. After validation with simulation experiments, we applied SCoRe to fMRI data collected from the Philadelphia Neurodevelopmental Cohort and adopted the scores from the wide range achievement test (WRAT) to evaluate an individual's cognitive skills. We located 14 relevant brain regions that can efficiently predict WRAT scores and these brain regions were further confirmed by other independent studies.

Reduction of BOLD interference in pseudo-continuous arterial spin labeling: towards quantitative fMRI

Fluctuations in blood-oxygenation level dependent (BOLD) signal and perfusion affect the quantification of changes in cerebral blood flow (CBF), coupled to neuronal activity, in arterial spin labeling (ASL). Subtraction methods for control and labeled MR images (i.e. pair-wise, surround subtraction, and subtraction of sinc-interpolated images), postulated to mitigate this interference in pseudo-continuous ASL (pCASL), were evaluated by comparison with quantitative ¹⁵O-water PET. At rest, a good agreement in the CBF values was found between PET and MRI for each of the subtraction methods. Stimulation of the visual system resulted in a regional CBF increase in the occipital lobe, which was detectable in both modalities. Bland-Altman analysis showed a systematic underestimation of the CBF values during activation in MRI. Evaluation of the relative CBF change induced by neuronal stimulation showed good inter-modality agreement for the three subtraction methods. Perfusion data obtained with each subtraction method followed the stimulation paradigm without significant differences in the correlation patterns or in the time lag between stimulation and perfusion response. Comparison to the gold standard confirmed the detectability of a neuronal stimulation pattern by pCASL. The results indicate that the combined use of background suppression and short TE reduces the BOLD-weighting in the pCASL signal.

Multiband multi-echo simultaneous ASL/BOLD for task-induced functional MRI

Typical simultaneous blood oxygenation-level dependent (BOLD) and arterial spin labeling (ASL) sequences acquire two echoes, one perfusion-sensitive and one BOLD-sensitive. However, for ASL, spatial resolution and brain coverage are limited due to the T1 decay of the labeled blood. This study applies a sequence combining a multiband acquisition with four echoes for simultaneous BOLD and pseudo-continuous ASL (pCASL) echo planar imaging (MBME ASL/BOLD) for block-design task-fMRI. A multiband acceleration of four was employed to increase brain coverage and reduce slice-timing effects on the ASL signal. Multi-echo independent component analysis (MEICA) was implemented to automatically denoise the BOLD signal by regressing non-BOLD components. This technique led to increased temporal signal-to-noise ratio (tSNR) and BOLD sensitivity. The MEICA technique was also modified to denoise the ASL signal by regressing artifact and BOLD signals from the first echo time-series. The MBME ASL/BOLD sequence was applied to a finger-tapping task functional MRI (fMRI) experiment. Signal characteristics and activation were evaluated using single echo BOLD, combined ME BOLD, combined ME BOLD after MEICA denoising, perfusion-weighted (PW), and perfusion-weighted after MEICA denoising time-series. The PW data was extracted using both surround subtraction and high-pass filtering followed by demodulation. In addition, the CBF/BOLD response ratio and CBF/BOLD coupling were analyzed. Results showed that the MEICA denoising procedure significantly improved the BOLD signal, leading to increased BOLD sensitivity, tSNR, and activation statistics compared to conventional single echo BOLD data. At the same time, the denoised PW data showed increased tSNR and activation statistics compared to the non-denoised PW data. CBF/BOLD coupling was also increased using the denoised ASL and BOLD data. Our preliminary data suggest that the MBME ASL/BOLD sequence can be employed to collect whole-brain task-fMRI with improved data quality for both BOLD and PW time series, thus improving the results of block-design task fMRI.

A comparison of dual gradient-echo and spin-echo fMRI of the inferior temporal lobe

Magnetic susceptibility differences at tissue interfaces lead to signal loss in conventional gradient-echo (GE) EPI. This poses a problem for fMRI in language and memory paradigms, which activate the most affected regions. Two methods proposed to overcome this are spin-echo EPI and dual GE EPI, where two EPI read-outs are serially collected at a short and longer echo time. The spin-echo method applies a refocusing pulse to recover dephased MR signal due to static field inhomogeneities, but is known to have a relatively low blood oxygenation level dependant (BOLD) sensitivity. In comparison, GE has superior BOLD sensitivity, and by employing an additional shorter echo, in a dual GE sequence, it can reduce signal loss due to spin dephasing. We directly compared dual GE and spin-echo fMRI during a semantic categorization task, which has been shown to activate the inferior temporal region-a region known to be affected by magnetic susceptibility. A whole brain analysis showed that the dual GE resulted in significantly higher activation within the left inferior temporal fusiform (ITF) cortex, compared to spin-echo. The inferior frontal gyrus (IFG) was activated for dual GE, but not spin-echo. Regions of interest analysis was carried out on the anterior and posterior ITF, left and right IFG, and part of the cerebellum. Dual GE outperformed spin-echo in the anterior and posterior ITF and bilateral IFG regions, whilst being equal in the cerebellum. Hence, dual GE should be the method of choice for fMRI studies of inferior temporal regions.

Oxygen-enhanced magnetic resonance imaging of the brain: a rodent model

Oxygen-enhanced MRI has been shown to be a viable alternative to hyperpolarized gases for pulmonary imaging. The changes in the relaxation times due to hyperoxic conditions in the blood pool induced by inhalation of pure oxygen have produced sufficient signal changes for imaging applications. This is a safe and low-cost alternative for contrast-enhanced imaging. The application of oxygen-enhanced MRI in brain imaging has been much less studied. In this study, we investigated the changes in the relaxation times in the brain due to inhalation of pure oxygen in a rodent model. We also assessed the effects of reduced blood flow due to hyperoxic conditions. Despite the reduced blood flow, significant changes in T1, T2, and T2* relaxation times were detected. We conclude that oxygen-enhanced MRI can be used in rodent models of disease.

Spatial location and strength of BOLD activation in high-spatial-resolution fMRI of the motor cortex: a comparison of spin echo and gradient echo fMRI at 7 T

The increased blood oxygenation level-dependent contrast-to-noise ratio at ultrahigh field (7 T) has been exploited in a comparison of the spatial location and strength of activation in high-resolution (1.5  mm isotropic) gradient echo (GE) and spin echo (SE), echo planar imaging data acquired during the execution of a simple motor task in five subjects. SE data were acquired at six echo times from 30 to 55  ms. Excellent fat suppression was achieved in the SE echo planar images using slice-selective gradient reversal. Threshold-free cluster enhancement was used to define regions of interest (ROIs) containing voxels showing significant stimulus-locked signal changes from the GE and average SE data. These were used to compare the signal changes and spatial locations of activated regions in SE and GE data. T(2) and T(2)* values were measured, with means of 48.3 ± 1.1  ms and 36.5 ± 3.4  ms in the SE ROI. In addition, we identified a dark band in SE images of the motor cortex corresponding to a region in which T(2) and T(2)* were significantly lower than in the surrounding grey matter. The fractional SE signal change in the ROI was found to vary linearly as a function of TE, with a slope that was dependent on the particular ROI assessed: the mean ΔR(2) value was found to be 0.85 ± 0.11  s(-1) for the SE ROI and -0.37 ± 0.05  s(-1) for the GE ROI. The fractional signal change relative to the shortest TE revealed that the largest signal change occurred at a TE of 45  ms outside of the dark band. At this TE, the ratio of the fractional signal change in GE and SE data was found to be 0.48 ± 0.05. Phase maps produced from high-resolution GE images spanning the right motor cortex were used to identify veins. The GE ROI was found to contain 18% more voxels overlying the venous mask than the SE ROI.

Functional exploration of the human spinal cord during voluntary movement and somatosensory stimulation

Demonstrations of the possibility of obtaining functional information from the spinal cord in humans using functional magnetic resonance imaging (fMRI) have been growing in number and sophistication, but the technique and the results that it provides are still perceived by the scientific community with a greater degree of scepticism than fMRI investigations of brain function. Here we review the literature on spinal fMRI in humans during voluntary movements and somatosensory stimulation. Particular attention is given to study design, acquisition and statistical analysis of the images, and to the agreement between the obtained results and existing knowledge regarding spinal cord anatomy and physiology. A striking weakness of many spinal fMRI studies is the use of small numbers of subjects and of time-points in the acquired functional image series. In addition, spinal fMRI is characterised by large physiological noise, while the recorded functional responses are poorly characterised. For all these reasons, spinal fMRI experiments risk having low statistical power, and few spinal fMRI studies have yielded physiologically relevant information. Thus, while available evidence indicates that spinal fMRI is feasible, we are only approaching the stage at which the technique can be considered to have been rigorously established as a viable means of noninvasively investigating spinal cord functioning in humans.

BOLD fMRI using a modified HASTE sequence

For more than a decade, turbo spin echo (TSE) pulse sequences have been suggested as an alternative to echo planar imaging (EPI) sequences for fMRI studies. Recent development in parallel imaging has renewed the interest in developing more robust TSE sequences for fMRI. In this study, a modified half Fourier acquisition single-shot TSE (mHASTE) sequence has been developed with a three-fold GRAPPA to improve temporal resolution as well as a preparation time to enhance BOLD sensitivity. Using a classical flashing checkerboard block design, the BOLD signal characteristics of this novel method have been systematically analyzed as a function of several sequence parameters and compared to those of gradient-echo and spin-echo EPI sequences. Experimental studies on visual cortex of five volunteers have provided evidence suggesting that mHASTE can be more sensitive to extra-vascular BOLD effects around microvascular networks, which leads to more accurate function localization. The studies also show that the activation cluster size in mHASTE increases with the refocusing RF flip angle and TE while decreasing with the echo number (n(center)) used to sample the k-space center. Compared to spin-echo EPI, mHASTE incurs an approximately 50% reduction in activation cluster size and an approximately 20% decrease in BOLD contrast. However a higher signal-to-noise ratio and a spatially more uniform temporal stability have been observed in mHASTE as compared to the EPI sequences when the scan times are held constant. With further refinement and optimization, mHASTE can become a viable alternative for fMRI in situations where the conventional EPI sequences are limited or prohibitive.

FMRI connectivity analysis of acupuncture effects on an amygdala-associated brain network

Background

Recently, increasing evidence has indicated that the primary acupuncture effects are mediated by the central nervous system. However, specific brain networks underpinning these effects remain unclear.

Results

In the present study using fMRI, we employed a within-condition interregional covariance analysis method to investigate functional connectivity of brain networks involved in acupuncture. The fMRI experiment was performed before, during and after acupuncture manipulations on healthy volunteers at an acupuncture point, which was previously implicated in a neural pathway for pain modulation. We first identified significant fMRI signal changes during acupuncture stimulation in the left amygdala, which was subsequently selected as a functional reference for connectivity analyses. Our results have demonstrated that there is a brain network associated with the amygdala during a resting condition. This network encompasses the brain structures that are implicated in both pain sensation and pain modulation. We also found that such a pain-related network could be modulated by both verum acupuncture and sham acupuncture. Furthermore, compared with a sham acupuncture, the verum acupuncture induced a higher level of correlations among the amygdala-associated network.

Conclusion

Our findings indicate that acupuncture may change this amygdala-specific brain network into a functional state that underlies pain perception and pain modulation.

Independent Vector Analysis (IVA) for Group fMRI Processing of Subcortical Area

During functional MRI (fMRI) studies, blood oxygenation-level dependent (BOLD) signal associated with neuronal activity acquired from multiple individuals are subject to the derivation of group-averaged brain activation patterns. Unlike other cortical areas, subcortical areas such as the thalamus and basal ganglia often manifest smaller, biphasic BOLD signal that are aberrant from signals originating from cortices. Independent component analysis (ICA) can offer session/individual specific brain activation maps without a priori assumptions regarding the timing or pattern of the signal responses. The small activation loci within the subcortical areas are sparsely distributed among the subjects, and a conventional group processing method based on the general linear model (GLM) or ICA may fail to characterize the activation loci. In this paper, we present an independent vector analysis (IVA) to overcome these limitations by offering an analysis of additional dependent components (compared to the ICA-based method) that are assigned for use in the automated grouping of dependent (i.e. similar) activation patterns across subjects. The proposed IVA algorithm was applied to simulated data, and its utility was confirmed from real fMRI data employing a trial-based hand motor task. A GLM and the group ICA of the fMRI toolbox (GIFT) were also applied for comparison. From the analysis of activation patterns within subcortical areas, in which the hemodynamic responses (HRs) often deviate from a canonical, model-driven HR, IVA detected task-related activation loci that were not detected through GLM and GIFT. IVA may offer a unique advantage for inferring group activation originating from subcortical areas.

Comparison of fMRI activation as measured with gradient- and spin-echo EPI during visual perception

In this study, we compared fMRI activation measured with gradient- and spin-echo-based fMRI during visual perception of faces, which is mediated by neural activation within a distributed cortical network. With both fMRI techniques, bilateral activation was observed in multiple regions including the inferior occipital gyrus, fusiform gyrus, superior temporal sulcus, amygdala, inferior frontal gyrus, and orbitofrontal cortex. When compared with the gradient-echo sequence, activation measured with the spin-echo sequence was significantly reduced. This decrease was manifested by smaller cluster size, lower statistical significance, smaller amplitude of the fMRI signal, and smaller number of subjects who showed activation in all face-responsive regions. In orbitofrontal cortex, a region prone to susceptibility-related signal dephasing, the spin-echo acquisition considerably restored the signal, but did not reveal stronger activation when compared with the gradient-echo acquisition. Our data indicate that optimized GE sequences that reduce susceptibility artefacts are sufficient to detect activation in regions such as the orbitofrontal cortex.

Media Violence Exposure and Frontal Lobe Activation Measured by Functional Magnetic Resonance Imaging in Aggressive and Nonaggressive Adolescents

OBJECTIVE

To understand better the relation between media violence exposure, brain functioning, and trait aggression, this study investigated the association between media violence exposure and brain activation as measured by functional magnetic resonance imaging (fMRI) in groups of normal adolescents and adolescents with disruptive behavior disorder (DBD) with aggressive features.

METHODS

Seventy-one participants underwent neuropsychologic evaluation and assessment of exposure to violent media. Subjects also were evaluated with fMRI while performing a counting Stroop (CS) task.

RESULTS

Frontal lobe activation was reduced in aggressive subjects compared with control subjects. In addition, differences in frontal lobe activation were associated with differences in media violence exposure. Specifically, activation during performance of the CS in control subjects with high media violence exposure resembled that seen in DBD subjects.

CONCLUSIONS

Our findings suggest that media violence exposure may be associated with alterations in brain functioning whether or not trait aggression is present.

Lesion-induced pseudo-dominance at functional magnetic resonance imaging: implications for preoperative assessments

OBJECTIVE

To illustrate how lesion-induced neurovascular uncoupling at functional magnetic resonance imaging (fMRI) can mimic hemispheric dominance opposite the side of a lesion preoperatively.

METHODS

We retrospectively reviewed preoperative fMRI mapping data from 50 patients with focal brain abnormalities to establish patterns of hemispheric dominance of language, speech, visual, or motor system functions. Abnormalities included gliomas (31 patients), arteriovenous malformations (AVMs) (11 patients), other congenital lesions (4 patients), encephalomalacia (3 patients), and tumefactive encephalitis (1 patient). A laterality ratio of fMRI hemispheric dominance was compared with actual hemispheric dominance as verified by electrocortical stimulation, Wada testing, postoperative and posttreatment deficits, and/or lesion-induced deficits. fMRI activation maps were generated with cross-correlation (P < 0.001) or t test (P < 0.001) analysis.

RESULTS

In 50 patients, a total of 85 functional areas were within 5 mm of the edge of a potentially resectable lesion. In 23 of these areas (27%), reduced fMRI signal in perilesional eloquent cortex in conjunction with preserved or increased signal in homologous contralateral brain areas revealed functional dominance opposite the side of the lesion. This suggested possible lesion-induced transhemispheric cortical reorganization to homologous brain regions (homotopic reorganization). In seven patients, however, the fMRI data were inconsistent with other methods of functional localization. In two patients with left inferior frontal gyrus gliomas and in one patient with focal tumefactive meningoencephalitis, fMRI incorrectly suggested strong right hemispheric speech dominance. In two patients with lateral precentral gyrus region gliomas and one patient with a left central sulcus AVM, the fMRI pattern incorrectly suggested primary corticobulbar motor dominance contralateral to the side of the lesion. In a patient with a right superior frontal gyrus AVM, fMRI revealed pronounced left dominant supplementary motor area activity in response to a bilateral complex motor task, but right superior frontal gyrus perilesional hemorrhage and edema subsequently caused left upper-extremity plegia. Pathophysiological factors that might have caused neurovascular uncoupling and facilitated pseudo-dominance at fMRI in these patients included direct tumor infiltration, neovascularity, cerebrovascular inflammation, and AVM-induced hemodynamic effects. Sixteen patients had proven (1 patient), probable (2 patients), or possible (13 patients) but unproven lesion-induced homotopic cortical reorganization.

CONCLUSION

Lesion-induced neurovascular uncoupling causing reduced fMRI signal in perilesional eloquent cortex, in conjunction with normal or increased activity in homologous brain regions, may simulate hemispheric dominance and lesion-induced homotopic cortical reorganization.

Cortical depth-dependent gradient-echo and spin-echo BOLD fMRI at 9.4T

To examine cortical depth-related spatial specificity and signal changes in gradient-echo (GE) and spin-echo (SE) blood oxygenation level-dependent (BOLD) fMRI signals, a well-established cat visual stimulation model was used at 9.4T. The GE BOLD signal percent change is the highest at the surface of the cortex containing pial vessels, and decreases as cortical depth increases. In contrast, the SE BOLD signal is more specific to parenchyma, showing the highest signal change in the middle cortical areas. The stimulation-induced DeltaR2* to DeltaR2 ratio is dependent on the vessel size, which is related to basal susceptibility effects. The averaged ratio of DeltaR2* to DeltaR2 in all active regions, including large vessels, is 3.3 +/- 0.5 (N = 6). The averaged ratio of DeltaR2* to DeltaR2 is 8.8 +/- 1.7 (N = 4) on the surface of the cortex with large pial draining vessels, and decreases to 1.9 +/- 0.1 on the middle cortical areas with parenchymal microvessels. DeltaR2*/DeltaR2 is closely related to basal susceptibility effects and can be used to differentiate tissue from vessel regions.

Clustered components analysis for functional MRI

A common method of increasing hemodynamic response (SNR) in functional magnetic resonance imaging (fMRI) is to average signal timecourses across voxels. This technique is potentially problematic because the hemodynamic response may vary across the brain. Such averaging may destroy significant features in the temporal evolution of the fMRI response that stem from either differences in vascular coupling to neural tissue or actual differences in the neural response between two averaged voxels. Two novel techniques are presented in this paper in order to aid in an improved SNR estimate of the hemodynamic response while preserving statistically significant voxel-wise differences. The first technique is signal subspace estimation for periodic stimulus paradigms that involves a simple thresholding method. This increases SNR via dimensionality reduction. The second technique that we call clustered components analysis is a novel amplitude-independent clustering method based upon an explicit statistical data model. It includes an unsupervised method for estimating the number of clusters. Our methods are applied to simulated data for verification and comparison to other techniques. A human experiment was also designed to stimulate different functional cortices. Our methods separated hemodynamic response signals into clusters that tended to be classified according to tissue characteristics.

Practical consideration for 3T imaging

In the past 10 to 15 years, 1.5T has been one of the most commonly used field strengths for day-to-day clinical operations. However, recent advances in high field technology and the increased availability of high field (> 1.5T) human scanners have opened the doors for a variety of exciting improvements in clinical and research applications of MR imaging. In particular, 3T has continued to gain wide acceptance as one of the main field strengths for clinical and research studies. Therefore, in this article the authors focus on the pros and cons of 3T imaging and comparisons between results obtained at 3T and 1.5T.

A cross-linguistic fMRI study of perception of intonation and emotion in Chinese

Conflicting data from neurobehavioral studies of the perception of intonation (linguistic) and emotion (affective) in spoken language highlight the need to further examine how functional attributes of prosodic stimuli are related to hemispheric differences in processing capacity. Because of similarities in their acoustic profiles, intonation and emotion permit us to assess to what extent hemispheric lateralization of speech prosody depends on functional instead of acoustical properties. To examine how the brain processes linguistic and affective prosody, an fMRI study was conducted using Chinese, a tone language in which both intonation and emotion may be signaled prosodically, in addition to lexical tones. Ten Chinese and 10 English subjects were asked to perform discrimination judgments of intonation (I: statement, question) and emotion (E: happy, angry, sad) presented in semantically neutral Chinese sentences. A baseline task required passive listening to the same speech stimuli (S). In direct between-group comparisons, the Chinese group showed left-sided frontoparietal activation for both intonation (I vs. S) and emotion (E vs. S) relative to baseline. When comparing intonation relative to emotion (I vs. E), the Chinese group demonstrated prefrontal activation bilaterally; parietal activation in the left hemisphere only. The reverse comparison (E vs. I), on the other hand, revealed that activation occurred in anterior and posterior prefrontal regions of the right hemisphere only. These findings show that some aspects of perceptual processing of emotion are dissociable from intonation, and, moreover, that they are mediated by the right hemisphere.

An investigation of the value of spin-echo-based fMRI using a Stroop color-word matching task and EPI at 3 T

This study examines the value of spin-echo-based fMRI for cognitive studies at the main magnetic field strength of 3 T using a spin-echo EPI (SE-EPI) sequence and a Stroop color-word matching task. SE-EPI has the potential advantage over conventional gradient-echo EPI (GE-EPI) that signal losses caused by dephasing through the slice are not present, and hence although image distortion will be the same as for an equivalent GE-EPI sequence, signal voids will be eliminated. The functional contrast in SE-EPI will be lower than for GE-EPI, as static dephasing effects do not contribute. As an auxiliary experiment interleaved diffusion-weighted and non-diffusion-weighted SE-EPI was performed in the visual cortex to further elucidate the mechanims of functional contrast. In the Stroop experiment activation was detected in all areas previously found using GE-EPI. Additional frontopolar and ventral frontomedian activations were also found, which could not be detected using GE-EPI. The experiments from visual cortex indicated that at 3 T the BOLD signal change has contributions from the extravascular space and larger blood vessels in roughly equal amounts. In comparison with GE-EPI the absence of static dephasing effects would seem to result in a superior intrinsic spatial resolution. In conclusion the sensitivity of SE-EPI at 3 T is sufficient to make it the method of choice for fMR studies that require a high degree of spatial localization or where the requirement is to detect activation in regions affected by strong susceptibility gradients.

Regional differences of fMR signal changes induced by hyperventilation: comparison between SE-EPI and GE-EPI at 3-T

PURPOSE

To evaluate whether reproducible signal change of brain tissues by hyperventilation (HV) can be seen on spin-echo (SE)-echo planar imaging (EPI) at 3-T and to examine the sensitivity of SE-EPI for measuring vascular reactivity in regions of the brain, such as the hippocampal formation, that are difficult to visualize with gradient-echo (GE)-EPI due to susceptibility artifacts.

MATERIALS AND METHODS

Six healthy human subjects performed a voluntary HV task. The task design was as follows: two minutes normal breathing (rest) followed by two minutes HV, giving a basic four-minute block that was repeated three times for a total scan time of 12 minutes for one run. Each subject performed the run both for SE-EPI and GE-EPI. Statistical analysis was performed to detect the area with significant cerebrovascular reactivity. The percentage signal change was also obtained for each cerebral region.

RESULTS

Both GE-EPI and SE-EPI showed globally significant signal decreases in the cerebral cortex. In GE-EPI, the frontal cortex showed a larger signal decrease than the other gray matter tissues (P < 0.05). In SE-EPI, the differences among gray matter tissues except for the hippocampal formation were not significant. The hippocampal formation showed the largest signal change (P < 0.05) in SE-EPI, but no significant signal change was observed in GE-EPI due to the presence of susceptibility artifacts.

CONCLUSION

HV using SE-EPI at 3-T provides robust and reproducible signal decreases and may make the evaluation of the vascular reactivity in hippocampal formation feasible.

Imaging function in the working brain with fMRI

The intrinsic flexibility of functional magnetic resonance imaging has allowed ever more innovative neuroscience applications. New acquisition and analysis techniques have contributed to improvements in detection sensitivity, as well as spatial and temporal resolution. Furthermore, by considering the dynamic evolution of the active brain areas in a network, computational models are making the first steps towards linking brain and mind.