Functional Magnetic Resonance Studies of Brain Activation

Recent advances in functional magnetic resonance imaging (fMRI), have stimulated considerable interest in applying this noninvasive approach to investigate the human brain. From early investigations of the visual and the motor system, applications of fMRI have matured to the demonstration of subtle activations associated with complex neurological tasks involving language, memory, and other higher brain functions. On the other hand, it is clear that current enthusiasm for fMRI must be tempered with the realization that interpretation of findings entails a number of assumptions about image contrast mechanisms which necessitate a more pragmatic assessment of what is actually being measured and how to compare the results to those of more established functional imaging techniques like positron emission tomography. Metabolic changes associated with neuronal activation can now be measured by functional magnetic resonance spectroscopy (fMRS) and functional magnetic resonance spectroscopic imaging (fMRSI). Comination of these approaches with fMRI may help to provide a more complete picture of vascular and metabolic mechanisms associated with brain function.     

磁共振功能成像在胶质瘤外科治疗中的应用

目的探讨磁共振波谱分析（MRS）、血氧水平依赖成像（BOLDI）以及弥散张量成像（DTI）在脑胶质瘤外科治疗中的作用。方法23例脑胶质瘤患者术前行常规MRI、^1HMRS、DTI及BOLDI检查，根据术前影像学评估，设计手术方案切除肿瘤，并与术后病理及随访结果进行对比。结果①^1HMRS表现为NAA峰降低，Cho峰升高，Cho／Cr、Cho／NAA比值升高，NAA／Cr比值降低。高级别胶质瘤Cho／Cr、Cho／NAA、LL／Cr比值和Cho值均显著高于低级别胶质瘤（P〈0．01），且常出现Lip峰。②BOLDI表现为手运动功能区被肿瘤挤压、移位者5例，其中2例移向后方，2例移向外侧，1例移向前方。③DTI中表观弥散系数（ADC）和分数各向异性（FA）图可明确区分正常脑白质、水肿区和肿瘤边缘，并可在轴位像上观察白质纤维束被推移、浸润和破坏的程度。纤维束重建后，表现为浸润＋破坏者5例，推移＋破坏者4例，推移＋浸润者11例，单纯推移者3例。④肿瘤全切6例，近全切8例，大部切除9例，所有患者术后无新发神经功能缺失。出院时KPS评分除1例患者60分外，其余患者均在90分以上。结论综合运用多种磁共振功能成像技术可从解剖、代谢等多方面对胶质瘤进行术前评价，以此明确诊断，可指导外科治疗，提高手术疗效，减少术后并发疖，     

Functional Magnetic Resonance Imaging Signal Variability Is Associated With Neuromodulation in Fibromyalgia

ObjectivesAlthough primary motor cortex (M1) transcranial direct current stimulation (tDCS) has an analgesic effect in fibromyalgia (FM), its neural mechanism remains elusive. We investigated whether M1-tDCS modulates a regional temporal variability of blood-oxygenation-level-dependent (BOLD) signals, an indicator of the brain's flexibility and efficiency and if this change is associated with pain improvement.Materials and MethodsIn a within-subjects cross-over design, 12 female FM patients underwent sham and active tDCS on five consecutive days, respectively. Each session was performed with an anode placed on the left M1 and a cathode on the contralateral supraorbital region. The subjects also participated in resting-state functional magnetic resonance imaging (fMRI) at baseline and after sham and active tDCS. We compared the BOLD signal variability (SD_BOLD), defined as the standard deviation of the BOLD time-series, between the tDCS conditions. Baseline SD_BOLD was compared to 15 healthy female controls.ResultsAt baseline, FM patients showed reduced SD_BOLD in the ventromedial prefrontal cortex (vmPFC), lateral PFC, and anterior insula and increased SD_BOLD in the posterior insula compared to healthy controls. After active tDCS, compared to sham, we found an increased SD_BOLD in the left rostral anterior cingulate cortex (rACC), lateral PFC, and thalamus. After sham tDCS, compared to baseline, we found a decreased SD_BOLD in the dorsomedial PFC and posterior cingulate cortex/precuneus. Interestingly, after active tDCS compared to sham, pain reduction was correlated with an increased SD_BOLD in the rACC/vmPFC but with a decreased SD_BOLD in the posterior insula.ConclusionOur findings suggest that M1-tDCS might revert temporal variability of fMRI signals in the rACC/vmPFC and posterior insula linked to FM pain. Changes in neural variability would be part of the mechanisms underlying repetitive M1-tDCS analgesia in FM.     

Magnetic Resonance Imaging Functional Activation of Left Frontal Cortex During Covert Word Production

Six normal volunteers underwent 4-T functional magnetic resonance imaging while performing a covert letter fluency task. An echo planar imaging sequence was utilized to detect activation based on deoxyhemoglobin contrast. All 6 subjects showed consistent activation in the frontal operculum and premotor and primary motor cortices. Activation was also detected in the supramarginal gyrus and the posterior part of the superior temporal gyrus. These results show that magnetic resonance functional neuroimaging can be used to investigate cerebral activity noninvasively during performance of complex cognitive tasks.     

Test-Retest Reliability of Functional Magnetic Resonance Imaging Activation for a Vergence Eye Movement Task

Vergence eye movements are the inward and outward rotation of the eyes responsible for binocular coordination.While studies have mapped and investigated the neural substrates of vergence,it is not well understood whether vergence eye movements evoke the blood oxygen level-dependent signal reliably in separate experimental visits.The test-retest reliability of stimulus-induced vergence eye movement tasks during a functional magnetic resonance imaging(fMRI) experiment is important for future randomized clinical trials(RCTs).In this study,we established region of interest(ROI) masks for the vergence neural circuit.Twenty-seven binocularly normal young adults participated in two functional imaging sessions measured on different days on the same 3 T Siemens scanner.The fMRI experiments used a block design of sustained visual fixation and rest blocks interleaved between task blocks that stimulated eight or four vergence eye movements.The test-retest reliability of task-activation was assessed using the intraclass correlation coefficient(ICC),and that of spatial extent was assessed using the Dice coefficient.Functional activation during the vergence eye movement task of eight movements compared to rest was repeatable within the primary visual cortex(ICC=0.8),parietal eye fields(ICC=0.6),supplementary eye field(ICC=0.5),frontal eye fields(ICC=0.5),and oculomotor vermis(ICC=0.6).The results demonstrate significant test-retest reliability in the ROIs of the vergence neural substrates for functional activation magnitude and spatial extent using the stimulus protocol of a task block stimulating eight vergence eye movements compared to sustained fixation.These ROIs can be used in future longitudinal RCTs to study patient populations with vergence dysfunctions.     

Magnetic Resonance Imaging of the Post-Mortem Autistic Brain

Magnetic resonance imaging (MRI) is a valuable, noninvasive tool for understanding structural abnormalities in the brain. The M.I.N.D. Institute at UC Davis has developed a protocol utilizing MRI to investigate anatomical differences in the post-mortem brain by applying a proton density weighted imaging sequence for optimal differences in image intensity (contrast) between gray and white matter. Images of the brain obtained prior to distribution of tissue and further neuropathological examination provide a record of how the brain appeared prior to tissue processing. The virtual representation of the whole brain can also be subjected to additional analyses, such as measuring the volume of brain regions or area of the cortical surface. We describe our procedures for carrying out post-mortem MRI of the human brain.     

Automatic Magnetic Resonance Tissue Characterization for Three-Dimensional Magnetic Resonance Imaging of the Brain

Computer-assisted diagnostic systems enhance the mformation available from magnetic resonance imaging. Segmentations are the basis on which three-dimensional volume renderings are made. The application of a raw data-based, operator-Independent (automatic), magnetic resonance segmentation technique for tissue differentiation is demonstrated. Segmentation images of vasogenic edema with gross and histopathological correlation are presented for demonstration of the technique. A pixel was classified mto a tissue class based on a feature vector using unsupervised fuzzy clustering techniques as the pattern recognition method. Correlation of fuzzy segmentations and gross and histopathology were successfully performed. Based on the results of neuropathological correlation, the application of fuzzy magnetic resonance image segmentation to a patient with a brain tumor and extensive edema represents a viable technique for automatically displaying clinically Important tissue differentiation. With this pattern recognition technique, it is possible to generate automatic segmentation images that display diagnostically relevant neuroanatomical and neuropathological tissue contrast information from raw magnetic resonance data for use in three-dimensional volume reconstructions.     

Functional Magnetic Resonance Imaging in Partial Epilepsy

Summary: Functional magnetic resonance imaging (FMRI) detects signal changes in brain that accompany regional changes in neuronal activity. In normal human brain, FMRI shows changes in signal in the postcentral gyrus or superior temporal gyrus that correlate with voluntary motor activity or language processing, respectively. The model used to explain the changes in signal linked temporally with cerebral activity is a reduction in cerebral capillary deoxyhemoglobin concentration due to the increased blood flow that accompanies neuronal activity in the cerebrum. FMRI has been used in normal subjects but not extensively in patients. To determine the feasibility of using FMRI to map cerebral functions in patients with partial epilepsy syndromes, we performed a pilot study, using FMRI to identify signal changes in motor and language areas in response to tasks that activate those areas. Signal changes in epilepsy patients approximated those observed in volunteers. We conclude that FMRI can be developed as a method for functional cerebral mapping in partial epilepsies.     

Functional Magnetic Resonance Imaging Correlates of Ventral Striatal Deep Brain Stimulation for Poststroke Pain

ObjectiveDeep brain stimulation (DBS) for pain has largely been implemented in an uncontrolled manner to target the somatosensory component of pain, with research leading to mixed results. We have previously shown that patients with poststroke pain syndrome who were treated with DBS targeting the ventral striatum/anterior limb of the internal capsule (VS/ALIC) demonstrated a significant improvement in measures related to the affective sphere of pain. In this study, we sought to determine how DBS targeting the VS/ALIC modifies brain activation in response to pain.Materials and MethodsFive patients with poststroke pain syndrome who were blinded to DBS status (ON/OFF) and six age- and sex-matched healthy controls underwent functional magnetic resonance imaging (fMRI) measuring blood oxygen level-dependent activation in a block design. In this design, each participant received heat stimuli to the affected or unaffected wrist area. Statistical comparisons were performed using fMRI z-maps.ResultsIn response to pain, patients in the DBS OFF state showed significant activation (p < 0.001) in the same regions as healthy controls (thalamus, insula, and operculum) and in additional regions (orbitofrontal and superior convexity cortical areas). DBS significantly reduced activation of these additional regions and introduced foci of significant inhibitory activation (p < 0.001) in the hippocampi when painful stimulation was applied to the affected side.ConclusionsThese findings suggest that DBS of the VS/ALIC modulates affective neural networks.     

Brain Activation Evoked by Sensory Stimulation in Patients with Spinal Cord Injury : Functional Magnetic Resonance Imaging Correlations with Clinical Features

Objective

The purpose of this study is to determine whether the changes of contralateral sensorimotor cortical activation on functional magnetic resonance imaging (fMRI) can predict the neurological outcome among spinal cord injury (SCI) patients when the great toes are stimulated without notice.

Methods

This study enrolled a total of 49 patients with SCI and investigated each patient''s preoperative fMRI, postoperative fMRI, American Spinal Injury Association (ASIA) score, and neuropathic pain occurrence. Patients were classified into 3 groups according to the change of blood oxygenation level dependent (BOLD) response on perioperative fMRI during proprioceptive stimulation with repetitive passive toe movements : 1) patients with a response of contralateral sensorimotor cortical activation in fMRI were categorized; 2) patients with a response in other regions; and 3) patients with no response. Correlation between the result of fMRI and each parameter was analyzed.

Results

In fMRI data, ASIA score was likely to show greater improvement in patients in group A compared to those belonging to group B or C (p<0.001). No statistical significance was observed between the result of fMRI and neuropathic pain (p=0.709). However, increase in neuropathic pain in response to the signal change of the ipsilateral frontal lobe on fMRI was statistically significant (p=0.030).

Conclusion

When there was change of BOLD response at the contralateral sensorimotor cortex on perioperative fMRI after surgery, relief of neurological symptoms was highly likely for traumatic SCI patients. In addition, development of neuropathic pain was likely to occur when there was change of BOLD response at ipsilateral frontal lobe.     

Brain Abnormalities in Pontine Infarction: A Longitudinal Diffusion Tensor Imaging and Functional Magnetic Resonance Imaging study

ObjectivesThe aim of this study was to make a reasonable and accurate assessment of the prognosis of patients with pontine infarction. We assessed the changes in structure and function in the whole brain after pontine infarction from the acute to chronic phase using diffustion tensor imaging and functional magnetic resonance imaging.Materials and methodsSixteen individuals with a recent pontine infarction and sixteen healthy controls were recruited and underwent 3.0T DTI, resting-state fMRI and upper extremity Fugl-Myer (UE-FM) functional evaluation at five time points: within one week (T1), half a month (T2), one month (T3), three months (T4), and six months (T5) after onset. Tract-based spatial statistics was used to conduct a voxelwise analysis.ResultsThe fractional anisotropy (FA) values were significantly lower in the pontine infarction group than in the control group. Then, specific ROIs were analyzed. The FA values of 10 regions of interest were significantly increased at T2 compared with those at T1. The FA value of the corticospinal tract was significantly increased at T3 compared with that at T2. Regional brain activity results showed that the amplitude of low frequency fluctuations value of the frontal lobe decreased at T1, then increased. Finally, The UE-FM scores showed the same increased trend.ConclusionThese findings show that the microstructure changes most significantly within half a month after pontine infarction and stabilizes after one month. The recovery of motor function in the later period is mainly caused by changes in the cortex. This facilitates more treatment options.     

Magnetic Resonance Imaging of the Brain in Aicardi's Syndrome

Aicardi's syndrome consists of multiple anomalies of the eye, brain, and axial skeleton in females, and is associated with early-onset infantile spasms and severe developmental delay. For the present study, magnetic resonance images of 20 patients with Aicardi's syndrome were obtained and the neuroimaging findings catalogued. These were compared to previously reported results and the findings correlated with current theories of fetal brain development. The results revealed a high frequency of cortical migration defects (94%) and a wide variability in the callosal defect, migrational abnormalities, and other findings in Aicardi's syndrome.     

Magnetic Resonance Imaging Features of Solitary Inflammatory Brain Masses

Brain lesions in inflammatory diseases may present as solitary masses, prompting a biopsy. We present neuroimaging and histologic findings in five patients with solitary, inflammatory, demyelinating mass lesions located in the supratentorial white matter and gray–white junction. The patients presented with seizures, focal neurologic signs, and neuroimaging findings that indicated the possibility of a neoplasm. Computed tomography (CT) revealed enhancing, sing le hypodense lesions associated with mild or no mass effect. On MRI, the lesions were hypointense on T3–weighted images and hyperintense on T2–weighted images. Variable patterns of enhancement were noted on CT and MRI, including homogeneous/patchy (n = 3) and ring/nodular (n = 1) enhancement. There was no evidence of calcification or hemorrhage. Biopsies revea led a leukoencephalitis and demyelination, with varying degrees of demyelination among the cases. The syndrome, re lating to a solitary lesion, was corticosteroid–sensitive, and it ultimately stabilized. Extensive longitudinal evaluations fai led to reveal multiple sclerosis, infection, or neoplasm. Solitary inflammatory lesions add to the differential diagnosis of large, supratentorial, solitary spaceoccupying lesions noted on CT and MRI scans.