Abnormal brain function in neuromyelitis optica: A fMRI investigation of mPASAT

PurposeCognitive impairment with the Neuromyelitis Optica (NMO) patients is debated. The present study is to study patterns of brain activation in NMO patients during a pair of task-related fMRI.Materials and methodsWe studied 20 patients with NMO and 20 control subjects matched for age, gender, education and handedness. All patients with NMO met the 2006 Wingerchuk diagnostic criteria. The fMRI paradigm included an auditory attention monitoring task and a modified version of the Paced Auditory Serial Addition Task (mPASAT). Both tasks were temporally and spatially balanced, with the exception of task difficulty.ResultsIn mPASAT, Activation regions in control subjects included bilateral superior temporal gyri (BA22), left inferior frontal gyrus (BA45), bilateral inferior parietal lobule (BA7), left cingulate gyrus (BA32), left insula (BA13), and cerebellum. Activation regions in NMO patients included bilateral superior temporal gyri (BA22), left inferior frontal gyrus (BA9), right cingulate gyrus (BA32), right inferior parietal gyrus (BA40), left insula (BA13) and cerebellum. Some dispersed cognition related regions are greater in the patients.ConclusionsThe present study showed altered cerebral activation during mPASAT in patients with NMO relative to healthy controls. These results are speculated to provide further evidence for brain plasticity in patients with NMO.     

Detection of the early negative response in fMRI at 1.5 Tesla.

Recent experimental studies have revealed an initial decrease in magnetic resonance (MR) signal that is consistent with optical imaging results. This initial response, thought to arise from a transient increase in deoxyhemoglobin concentration, is probably more localized to the site of neuronal activation. However, with MR imaging, this early response has only been demonstrated at high fields. In this paper, the observation of the initial response at 1.5 T is reported. Compared with results obtained at 4 T, the present study reveals that the initial response grows more rapidly with the field strength than the late positive response, suggesting a more microvascular origin of the initial response.     

Spatial/temporal correlation of BOLD and optical intrinsic signals in humans.

Comparing the BOLD signal with electrophysiological maps and other perfusion-dependent signals, such as the optical intrinsic signal (OIS), within subjects should provide insight into the etiology of the BOLD signal. Tongue activations were compared in five human subjects using BOLD fMRI, 610-nm OIS, and the electrocortical stimulation map (ESM). Robust fMRI activations centered on the lateral inferior aspect of the central sulcus and extended into pre- and post-central gyri, adjacent to ESM tongue loci. OIS and fMRI maps colocalized, although optical responses were spatially larger (P <.001 across multiple thresholds) and contained more gyral components. The timecourses of the fMRI and OIS signals were similar, appearing within 2.5 s and peaking 6-8 s after task onset. Although many processes contribute to increased 610-nm reflectance, optical spectroscopy and fluorescent dye imaging suggest that a significant part of this signal is due to a concomitant decrease in deoxyhemoglobin and increase in oxyhemoglobin concentrations. The spatial/temporal correlation of BOLD and the positive 610-nm response within subjects suggests that the two signals may share similar etiologies. The OIS/fMRI inconsistencies may be due to cell swelling and light-scattering contributions to OIS and fMRI sensitivity. This study also demonstrates that fMRI maps do not precisely colocalize with ESM, rather they emphasize changes in adjacent venous/sulcal structures.     

fMRI of the lumbar spinal cord during a lower limb motor task.

This study applied spinal fMRI to the lumbar spinal cord during lower limb motor activity. During active ankle movement, activity was detected in the lumbar spinal cord motor areas and sensory areas bilaterally. During passive ankle movement, activity was detected in the motor and sensory areas in lower lumbar spinal cord segments and motor activity in higher lumbar spinal cord segments. Spinal fMRI detects patterns of activity consistent with known physiology and can be used to reliably assess activity in the lumbar spinal cord during lower limb motor stimulation. This study affirms spinal fMRI as an effective tool for assessing spinal cord function and increases its potential as a clinical tool.     

Sensitivity-encoded single-shot spiral imaging for reduced susceptibility artifacts in BOLD fMRI.

Sensitivity encoding (SENSE) with iterative image reconstruction was used to shorten the readout duration in single-shot spiral imaging by a factor of 2. This enabled susceptibility-related blurring and signal loss artifacts to be reduced and spatial resolution to be improved. As a beneficial side effect, the gradient duty cycle was also reduced. The spiral SENSE technique was applied to functional MRI (fMRI) with blood oxygen level-dependent (BOLD) contrast and compared to a conventional spiral acquisition. Stimulation experiments were performed in seven volunteers using motor, visual, and taste paradigms. The signal-to-noise ratio (SNR) and signal-to-fluctuation-noise ratio (SFNR) of the SENSE acquisitions were reduced by 20% and 13%, respectively, with respect to the longer readout. The overall activation detected was comparable to that of the conventional spiral acquisition, even though difficulties in reproducing the stimulation response hampered the evaluation. In some cases, the application of SENSE enabled recovery of activation in regions affected by signal loss due to field inhomogeneity.     

Utilizing hemodynamic delay and dispersion to detect fMRI signal change without auditory interference: the behavior interleaved gradients technique.

A major problem associated with the use of functional magnetic resonance imaging (fMRI) is the attendant gradient noise, which causes undesirable auditory system stimulation. A method is presented here that delays data acquisition to a period immediately after task completion, utilizing the physiological delay and dispersion between neuronal activity and its resulting hemodynamic lag. Subjects performed finger movements with the gradients off, followed by a rest period with the gradients on. This resulted in task-related signals comparable to those obtained with concurrent task performance and image data acquisition. This behavior interleaved gradients technique may be particularly useful for the studies involving auditory stimulation or overt verbal responses.     

Differences in the BOLD fMRI response to direct and indirect cortical stimulation in the rat.

Functional MRI (fMRI) exploits a relationship between neuronal activity, metabolism, and cerebral blood flow to functionally map the brain. We have developed a model of direct cortical stimulation in the rat that can be combined with fMRI and used to compare the hemodynamic responses to direct and indirect cortical stimulation. Unilateral electrical stimulation of the rat hindpaw motor cortex, via stereotaxically positioned carbon-fiber electrodes, yielded blood oxygenation level-dependent (BOLD) fMRI signal changes in both the stimulated and homotypic contralateral motor cortices. The maximal signal intensity change in both cortices was similar (stimulated = 3.7 +/- 1.7%; contralateral = 3.2 +/- 1.0%), although the response duration in the directly stimulated cortex was significantly longer (48.1 +/- 5.7 sec vs. 19.0 +/- 5.3 sec). Activation of the contralateral cortex is likely to occur via stimulation of corticocortical pathways, as distinct from direct electrical stimulation, and the response profile is similar to that observed in remote (e.g., forepaw) stimulation fMRI studies. Differences in the neuronal pool activated, or neurovascular mediators released, may account for the more prolonged BOLD response observed in the directly stimulated cortex. This work demonstrates the combination of direct cortical stimulation in the rat with fMRI and thus extends the scope of rodent fMRI into brain regions inaccessible to peripheral stimulation techniques.     

BOLD contrast sensitivity enhancement and artifact reduction with multiecho EPI: parallel-acquired inhomogeneity-desensitized fMRI.

Functional MRI (fMRI) generally employs gradient-echo echo-planar imaging (GE-EPI) to measure blood oxygen level-dependent (BOLD) signal changes that result from changes in tissue relaxation time T(*) (2) between activation and rest. Since T(*) (2) strongly varies across the brain and BOLD contrast is maximal only where the echo time (TE) equals the local T(*) (2), imaging at a single TE is a compromise in terms of overall sensitivity. Furthermore, the long echo train makes EPI very sensitive to main field inhomogeneities, causing strong image distortion. A method is presented that uses accelerated parallel imaging to reduce image artifacts and acquire images at multiple TEs following a single excitation, with no need to increase TR. Sensitivity gains from the broadened T(*) (2) coverage are optimized by pixelwise weighted echo summation based on local T(*) (2) or contrast-to-noise ratio (CNR) measurements. The method was evaluated using an approach that allows differential BOLD CNR to be calculated without stimulation, as well as with a Stroop experiment. Results obtained at 3 T showed that BOLD sensitivity improved by 11% or more in all brain regions, with larger gains in areas typically affected by strong susceptibility artifacts. The use of parallel imaging markedly reduces image distortion, and hence the method should find widespread application in functional brain imaging.     

Parsing local signal evolution directly from a single-shot MRI signal: a new approach for fMRI.

In this work a new single-shot MRI method, single-shot parameter assessment by retrieval from signal encoding (SS-PARSE), is introduced. This method abandons a fundamental simplifying assumption that is used in conventional MRI methods. Established MRI methods implicitly assume that the local intrinsic signal does not change its amplitude or phase during signal acquisition, even though these changes may be substantial, especially during the relatively long signals used in single-shot image acquisitions. SS-PARSE, on the other hand, acknowledges local decay and phase evolution, and models each signal datum as a sample from (k,t)-space rather than k-space. Because of this more accurate signal model, SS-PARSE promises improved performance in terms of accuracy and robustness, but requires more intensive reconstruction computations. The theoretical properties of the method are discussed, and simulation results are presented that demonstrate more robust and accurate measurements of relaxation rate changes associated with brain activation in functional MRI (fMRI), freedom from geometric errors due to off-resonance frequencies, and better tolerance of the large susceptibility gradients that occur naturally in parts of the brain. In addition, this technique has the potential to assess nonexponential relaxation behavior during a single-shot signal.     

Evaluation of the early response in fMRI in individual subjects using short stimulus duration

Optical imaging studies have provided evidence of an initial increase in deoxyhemoglobin following the onset of neuronal stimulation/activation and demonstrated that this initial increase could be spatially more specific to the site of neuronal activity. These studies also raised the possibility of improving the specificity of fMRI by selective mapping of this early response. Previous MR studies reported the observation of this early response but were limited in scope and not in full agreement. This paper presents a more extensive study that (a) demonstrates the initial signal decrease in individual subjects and (b) examines its dependence on stimulus duration and subject. Binocular visual stimulation experiments were performed on 14 subjects using echo-planar imaging (EPI) with high temporal resolution. An initial signal decrease was consistently observed in regions that were more localized than those displaying the delayed positive response. In agreement with previous fMRI and optical imaging findings, the maximum signal decrease was 1–2% and occurred at approximately 2 s after the onset of the stimulus, depending on the subject. For stimulus longer than 3.0 s, the temporal dynamics and the amount of signal change of the early response was essentially independent of the stimulus duration, while the delayed response and the post-stimulus undershoot increased both in terms of magnitude and rise time as the duration of the stimulus increased; this observation is concordant with the recent optical imaging study.     

Visual analysis of variance: A tool for quantitative assessment of fMRI data processing and analysis

Analysis of variance (ANOVA) is widely used for the study of experimental data. Here, the reach of this tool is extended to cover the preprocessing of functional magnetic resonance imaging (fMRI) data. This technique, termed visual ANOVA (VANOVA), provides both numerical and pictorial information to aid the user in understanding the effects of various parts of the data analysis. Unlike a formal ANOVA, this method does not depend on the mathematics of orthogonal projections or strictly additive decompositions. An illustrative example is presented and the application of the method to a large number of fMRI experiments is discussed. Magn Reson Med 46:1202–1208, 2001. © 2001 Wiley‐Liss, Inc.     

Coupling of neural activity and BOLD fMRI response: new insights by combination of fMRI and VEP experiments in transition from single events to continuous stimulation.

Functional magnetic resonance imaging (fMRI) measures the correlation between the fMRI response and stimulus properties. A linear relationship between neural activity and fMRI response is commonly assumed. However, the response to repetitive stimulation cannot be explained by a simple superposition of single-event responses. This might be due to neural adaptation or the hemodynamic changes underlying the fMRI BOLD response. To assess the influence of adaptation, the BOLD responses and visual evoked potentials (VEPs) to identical stimuli were recorded. To achieve different adaptation levels, 2-s stimulus epochs alternated with different interstimulus intervals (ISI = 0.0, 0.4, 0.8, 2.0, and 12 s) were presented. Neural adaptation during the checkerboard reversal paradigm used for fMRI measurements is demonstrated. Even if the measured VEP amplitude is used as the weighting function for a linear model, the measured BOLD fMRI signal time-course is not adequately predicted.     

Recordings of eye movements for stimulus control during fMRI by means of electro-oculographic methods

A method for monitoring eye movements in humans during functional MRI is presented. It is based on the acquisition of electro-oculographic (EOG) signals near one eye. EOG potentials were amplified and converted into an optical signal just outside the head coil. An optical fiber was used for signal transmission from inside the magnet bore to the control room. The EOG sensor was tested during EPI sequences at 1.5 Tesla without contamination of the MR signal. Some flow related artifacts on the EOG were observed inside the magnet, but no additional interactions from the MR sequence. An analysis of the latency, direction, and amplitude of the saccadic eye movements was possible.     

单肺通气对心功能和血流动力学的影响

 目的 探讨胸外科手术中单肺通气对患者心功能及血流动力学的影响。方法 选择美国麻醉医师协会(American of society anesthesiologists,ASA)分级Ⅰ~Ⅱ级,择期全身麻醉下侧卧位行双腔气管插管手术患者101例。应用FloTrac/Vigileo系统监测患者各项血流动力学参数。记录时间点分别为患者入室后(T₀)、插管后仰卧位双肺5 min(T₁)、侧卧位双肺5 min(T₂)、侧卧位单肺5 min(T₃)、侧卧位单肺10 min(T₄)、侧卧位单肺30 min(T₅)、侧卧位单肺60 min(T₆)、鼓肺后(T₇)、平卧位双肺5 min(T₈)。结果 T₀时MAP、HR高于T₂(P<0.05);T₁时SVR高于T₆(P<0.05);T₁、T₂时MAP、HR、CO、CI低于T₃(P<0.05);T₃时MAP高于T₄,HR低于T₄(P<0.05);T₅时SpO₂最低(P<0.05);T₆时HR高于T₇,MAP、SV低于T₇(P<0.05),余比较无统计学差异。结论 单肺通气后,患者出现短暂的血流动力学不稳,与双肺通气时比较MAP、HR、CO、CI增高,SpO₂、SVR减低,但随着单肺通气时间延长,各指标逐渐达到平稳状态。     

Sensitivity comparison of multiple vs. single inversion time pulsed arterial spin labeling fMRI

PURPOSE: To study the sensitivity for detection of activation for multiple vs. single inversion time (TI) pulsed arterial spin labeling (PASL). MATERIALS AND METHODS: The number of activated voxels and the mean t-statistic over activated voxels was measured by means of multiple and single TI PASL sequences in five volunteers during visual stimulation by means of an alternating checkerboard. Acquisition was performed by means of the transfer insensitive labeling technique (TILT) and TURBO-TILT. RESULTS: It was found that the sensitivity for the detection of activation was lower for an individual TI out of a multiple TI sequence than for the corresponding single TI acquisition of equal duration. After averaging over all TIs between and including 600 and 1400 msec, the number of activated voxels and mean t-statistic were no longer statistically lower for the multiple TI sequence than for the single TI experiment. CONCLUSION: Multiple TI PASL can be used for functional MRI (fMRI) studies, when performing the detection of activated brain regions on data that is averaged over all TIs between 600 and 1400 msec. Subsequently the multi-TI data can be used to quantify cerebral blood flow (CBF) changes upon activation. Additionally, we have shown that single TI PASL fMRI overestimates the CBF changes upon activation due to transit time changes.     

老年人与青年人皮肤血流量比较研究

目的 判定增龄对皮肤血流量的影响。方法 用PIM2-LDPI检测皮肤血流量。结果 老年组前额、左手指背、命门穴部位皮肤血流量分别为:(1.94±0.86)V,(1.92±0.52)V和(0.71±0.19)V,与青年组比较差异无显著性。但是,老年男性在命门穴的皮肤血流量明显高于青年男性(P<0.05),老年女性前额的皮肤血流量明显降低(P<0.01)。男性比女性的皮肤血流量高。结论 皮肤血流量的差异无年龄相关性,男性组的皮肤血流量比女性组高。     

Influence of gradient acoustic noise on fMRI response in the human visual cortex.

A paired-stimuli paradigm combined with fMRI was utilized to study the effect of gradient acoustic noise on fMRI response in the human primary visual cortex (V1) in terms of the auditory-visual cross-modal neural interaction. The gradient noise generated during the fMRI acquisition was used as the primary stimulus, and a single flashing light was used as the secondary stimulus. An interstimulus interval (ISI) separated the two. Six tasks were designed with different ISIs ranging from 50 to 700 ms. Both BOLD signal intensity and the number of activated pixels in V1 were analyzed and examined, and they showed a significant reduction when the gradient noise preceded the flashing light by approximately 300 ms. These results indicate that the gradient acoustic noise generated during fMRI acquisitions does interfere with neural behavior and the BOLD signal in the human visual cortex. This interference is modulated by the delay between the gradient noise and visual stimulation, and it can be studied quantitatively when the stimulation paradigm is designed appropriately. This study provides evidence of the auditory-visual interaction during fMRI studies, and the results should have an impact on fMRI applications.     

Application of parallel imaging to fMRI at 7 Tesla utilizing a high 1D reduction factor.

Gradient-echo EPI, blood oxygenation level-dependent (BOLD) functional MRI (fMRI) using parallel imaging (PI) is demonstrated at 7 Tesla with 16 channels, a fourfold 1D reduction factor (R), and fourfold maximal aliasing. The resultant activation detection in finger-tapping fMRI studies was robust, in full agreement with expected activation patterns based on prior knowledge, and with functional maps generated from full field of view (FOV) coverage of k-space using segmented acquisition. In all aspects the functional maps acquired with PI outperformed segmented coverage of full k-space. With a 1D R of 4, fMRI activation based on PI had higher statistical significance, up to 1.6-fold in an individual case and 1.25+/-.25 (SD) fold when averaged over six studies, compared to four-segment/full-FOV data in which the square root R reduction in the image signal-to-noise ratio (SNR) due to k-space undersampling was compensated for by acquiring additional repetitions of the undersampled k-space. When this compensation for loss in SNR was not performed, the effect of PI was determined by the ratio of physiologically induced vs. intrinsic (thermal) noise in the fMRI time series and the extent to which physiological "noise" was amplified by the use of segmentation in the full-FOV data. The results demonstrate that PI is particularly beneficial at this ultrahigh field strength, where both the intrinsic image SNR and temporal signal fluctuations due to physiological processes are large.