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PubMed2006

Atypically diffuse functional connectivity between caudate nuclei and cerebral cortex in autism.

BACKGROUND: Autism is a neurodevelopmental disorder affecting sociocommunicative behavior, but also sensorimotor skill learning, oculomotor control, and executive functioning. Some of these impairments may be related to abnormalities of the caudate nuclei, which have been reported for autism. METHODS: Our sample was comprised of 8 high-functioning males with autism and 8 handedness, sex, and age-matched controls. Subjects underwent functional MRI scanning during performance on simple visuomotor coordination tasks. Functional connectivity MRI (fcMRI) effects were identified as interregional blood oxygenation level dependent (BOLD) signal cross-correlation, using the caudate nuclei as seed volumes. RESULTS: In the control group, fcMRI effects were found in circuits with known participation of the caudate nuclei (associative, orbitofrontal, oculomotor, motor circuits). Although in the autism group fcMRI effects within these circuits were less pronounced or absent, autistic subjects showed diffusely increased connectivity mostly in pericentral regions, but also in brain areas outside expected anatomical circuits (such as visual cortex). CONCLUSION: These atypical connectivity patterns may be linked to developmental brain growth disturbances recently reported in autism and suggest inefficiently organized functional connectivity between caudate nuclei and cerebral cortex, potentially accounting for stereotypic behaviors and executive impairments.

Journal Article↗
PubMed1998

[Integration of functional and morphologic MRI data for preoperative 3D visualization of tumors. Example: cervical carcinoma].

PURPOSE: The goal of this exemplary study was to integrate morphological and functional MRI to establish computer-based, pre-operative therapy planning for tumors, instancing cervical carcinoma. METHODS: For morphological representation T1-weighted, filtered 3D sequences were investigated within a hierarchical segmentation approach. Using a method for image registration, segmented structures were combined and overlaid with functional information of contrast medium-enhanced, dynamic MRI. After assigning colour attributes to the segmented structures, they were presented using a method for direct volume visualisation. RESULTS: Segmentation of organs and vessels as well as tissue differentiation yielded a morphological visualisation of anatomical structures that were overlaid with pharmacokinetic parameters derived from dynamic MRI, subsequently. Thereby, three-dimensional, arbitrary views on the functional data were displayed. CONCLUSIONS: Image analysis and visualisation of the acquired MR data establishes both a morphologic and functional evaluation of suspect lesions and adjacent organs. By integrating morphologic and functional MRI additional information can be gathered that possibly impinge on preoperative planning.

Data Interpretation, Statistical↗
PubMed2006

Mapping activation levels of skeletal muscle in healthy volunteers: an MRI study.

PURPOSE: To use muscle functional MRI (mfMRI) to compare activation levels within and among triceps surae (TS) muscles. MATERIALS AND METHODS: Seven healthy males performed five sets of 10 repetitions of a unilateral heel-raise exercise. T2-weighted images were obtained before and immediately after the exercise. Pixels that showed T2 greater than the mean +1 SD of the region of interest (ROI) in pre-exercise images and lower than the mean +1 SD of the ROI in post-exercise images were identified. The remaining T2 values in the post-exercise images were assigned to five categories indicated by color: red (highest level of activation), yellow, green, sky blue, and blue (lowest level of activation). The images were then used to construct three-dimensional (3D) images from which the volumes at each level of activation were determined. RESULTS: Within each of the TS muscles the % activated volumes with low and moderate levels of activation were larger than those with a high level of activation (P < 0.05). The % activated volumes with a high level of activation were larger in the medial gastrocnemius than the soleus (Sol; P < 0.05). The Sol had a larger % activated volume with a low level of activation than the lateral gastrocnemius (P < 0.05). Each activation level was nonuniformly distributed along the length within each TS muscle. CONCLUSION: There is substantial variation in the level of activation within and among the TS muscles; however, the activation level is mainly in the moderate to low range in all three muscles.

Adult↗
PubMed2005

Experimental design in brain activation MRI: cautionary tales.

The use of functional magnetic resonance imaging (fMRI) in cognitive neuroscience has expanded at an amazing rate in the past 10 years. Current research includes increasingly subtle and specific attempts to dissect the cognitive and emotional mechanisms called into play when humans make decisions. The present essay will briefly review some of the general considerations and domains of information needed when one designs fMRI-based experiments. However, the main theme will be the difficulties associated with designing, conducting, analyzing and interpreting such research. Functional MRI is an unusually complicated technique, and there are numerous ways for experiments to go wrong. As well as demanding exceptional care in maintaining the quality of one's own research, this makes the universal problem of evaluating other peoples' research particularly challenging.

Animals↗
PubMed1997

Manganese ion enhances T1-weighted MRI during brain activation: an approach to direct imaging of brain function.

Present techniques for functional MRI rely on detecting changes in hemodynamics that result as a consequence of brain activation. It would be useful if MRI techniques could be developed that enable imaging of a parameter directly related to neuronal activity. Influx of calcium into neurons is necessary for release of neurotransmitters. Divalent manganese ions (Mn2+) can enter cells through voltage-gated calcium channels and Mn2+ is paramagnetic. Mn2+ accumulation in brain due to activation should alter relaxation times offering an approach to sensitize MRI to calcium influx in the brain. To test this idea, T1-weighted MRI was obtained from the rat brain in the presence of a continuous intravenous infusion of 3.6 mumol/min MnCl2. In the anesthetized rat brain, signal enhancement was detected in regions corresponding to ventricles. Activation of the brain with glutamate led to increase in MRI signal intensity in the brain to 238 +/- 23% of the original. This increase in signal was dependent on the presence of MnCl2 and was not due to changes in blood flow. It was necessary to break the blood brain barrier with mannitol to make Mn2+ accessible to the active sites for efficient detection. Enhancement of MRI signal in the brain was also detected with decreasing anesthesia and with somatosensory stimulation. Due to the slow clearance of Mn2+ from the stimulated region of the brain, MRI enhancement could also be detected after stimulation that occurred on awake, behaving rats outside the magnet. These data indicate that MnCl2 shows potential as a MRI contrast agent that is directly sensitive to brain activation.

Animals↗
PubMed2002

Preoperative assessment of motor cortex and pyramidal tracts in central cavernoma employing functional and diffusion-weighted magnetic resonance imaging.

BACKGROUND: Functional MRI (fMRI) combines anatomic with functional information and has therefore been widely used for preoperative planning of patients with mass lesions affecting functionally important brain regions. However, the courses of functionally important fiber tracts are not visualized. We therefore propose to combine fMRI with diffusion-weighted MRI (DWI) that allows visualization of large fiber tracts and to implement this data in a neuronavigation system. METHODS: DWI was successfully performed at a field strength of 1.5 Tesla, employing a spin-echo sequence with gradient sensitivity in six noncollinear directions to visualize the course of the pyramidal tracts, and was combined with echo-planar T2* fMRI during a hand motor task in a patient with central cavernoma. RESULTS: Fusion of both data sets allowed visualization of the displacement of both the primary sensorimotor area (M1) and its large descending fiber tracts. Intraoperatively, these data were used to aid in neuronavigation. Confirmation was obtained by intraoperative electrical stimulation. Postoperative MRI revealed an undisrupted pyramidal tract in the neurologically intact patient. CONCLUSION: The combination of fMRI with DWI allows for assessment of functionally important cortical areas and additional visualization of large fiber tracts. Information about the orientation of fiber tracts in normal appearing white matter in patients with tumors within the cortical motor system cannot be obtained by other functional or conventional imaging methods and is vital for reducing operative morbidity as the information about functional cortex. This technique might, therefore, have the prospect of guiding neurosurgical interventions, especially when linked to a neuronavigation system.

Adult↗
PubMed2004

[Cortical response in age-related macular degeneration (part I). Methodology and subject specificities].

PURPOSE: To evaluate the cortical response to visual stimulation in patients with age-related macular degeneration (ARMD). MATERIAL AND METHODS: We conducted a prospective functional MRI study at 1.5 Testa in ten patients presenting with unilateral or bilateral ARMD and five age-matched controls. The visual stimulus was a sequence of resting phase (presentation of a fixation point on a black background) followed by an activation phase (flashes at 2 Hz). Functional data were recorded with anatomy; significant hemodynamic response secondary to neuronal activation was statistically determined using the SPM 99 software. RESULTS: The first objective was to estimate the feasibility of a functional study in the elderly. Controls and patients complained about the duration of the examination, although each of the two active functional sessions lasted only 4.5 min. The central point fixation was impaired for the patients; some deviated their gaze to center the fixation point on a perimacular retinal area. Because of substantial movement during MRI acquisitions, the data from two patients and one control were withdrawn from statistic processing. DISCUSSION AND CONCLUSION: This study is one of the few evaluations reported on functional MRI in the elderly, because of technical constraints, patient fragility and their ophthalmologic pathology. Optimizing the visual stimulus and the paradigm of stimulation, repeating patient information and support have helped demonstrate significant cortical hemodynamic response in most subjects, even in the most affected patients. Evaluation of the visual cortex by functional MRI appears feasible in the ophthalmologic pathology of the elderly, providing an adapted management of the subject's conditions.

Age Factors↗
PubMed1997

[MRI and cognition].

Many groups are trying out functional MRI (fMRI) to study normal and diseased brain function. FMRI is a technique that images intrinsic blood signal changes accompanying variations of cerebral blood flow (CBF), cerebral blood volume (CBV) and oxygenation during mental activity. The main advantages which account for fMRI's increasing popularity are its time resolution (less than 1 second), a fine spatial resolution (on the scale of 1 mm), and the ability to acquire, within the same individual, repeated, multiple scans in a non-invasive manner. While the basic design of most studies centers on comparison of baseline to an active (test) condition, as the Positron Emission Tomography (PET), fMRI allows an important departure from the single scan per condition study-design, into more flexible paradigms of multiple scans over varying time intervals and multiple conditions. Although the technique is only a few years old, a large volume of experimental data have already been published. In this presentation we would like to provide potential users with a short overview of the basic principles and the main applications in cognitive neuroscience, as well as potential clinical applications.

Arousal↗
PubMed2002

The functional significance of perinatal corpus callosum damage: an fMRI study in young adults.

We used functional MRI (fMRI) to establish the functional significance of corpus callosum damage in young adults who had been born very preterm. Seven subjects from a cohort of individuals who had been born at <33 weeks gestation and who had sustained callosal damage visualized on structural MRI were compared while they carried out auditory and visual tasks requiring callosal transfer with nine very preterm subjects with corpora callosa of normal appearance on structural MRI, and with seven full-term controls. The very preterm subjects with damaged corpora callosa had significantly different activation patterns compared with the two control groups. In the visual task, additional activity was seen in the right dorsolateral prefrontal cortex of the damaged callosum group, possibly because the task was accomplished by storing information in working memory. On the auditory task, a deficit of activity was seen in the right temporal lobe of the callosum group. The findings reveal a plasticity of function compensating for early damage to the corpus callosum.

Adolescent↗
PubMed2003

Functional magnetic resonance imaging (fMRI) and effects of L-dopa on visual function in normal and amblyopic subjects.

PURPOSE: To evaluate the effects of a single dose of levodopa on visual cortex, based on functional MRI (fMRI), and on visual function, based on psychophysical tests, in amblyopic and normal subjects. METHOD: A prospective, randomized trial of a single dose of levodopa (2 mg/kg body weight) was undertaken in an institutional setting in nine normal and six amblyopic subjects, who were assessed at baseline and 90 minutes after levodopa ingestion. fMRI of occipital visual cortex was undertaken with a 1.5T GE MRI scanner utilizing the BOLD contrast technique. fMRI stimuli were two gratings (0.5, 2.0 cycles/degree of visual angle) that counterphased at 4 Hz. fMRI parameters for analysis included AREA and LEVEL of activation and a SUMMED score (AREA x LEVEL). Psychophysical tests included visual acuity, contrast sensitivity, stereoacuity, and binocular fusion. RESULTS: At baseline, AREA of activation (P = .05) and SUMMED score (P = .05) were significantly less in the amblyopic compared to the dominant eyes. Psychophysically, visual acuity and contrast sensitivity were significantly worse in the amblyopic eye. Following levodopa ingestion, there was significant decrease in LEVEL of activation in the amblyopic eye, even though visual acuity showed significant improvement (P = .03). Also, amblyopes showed a significant increase and normals showed some decrease in interocular difference in LEVEL of activation (P = .04). CONCLUSION: Unique information was obtained when fMRI was utilized to assess visual cortical function. While levodopa improved visual acuity in the amblyopic eye, it decreased the LEVEL of activation based on fMRI, a counterintuitive finding. The results highlight the value of utilizing fMRI to assess amblyopia and provide new directions for research.

Adult↗
PubMed2004

Brain localization of attentional control in different age groups by combining functional and structural MRI.

The present study used functional and structural MRI to investigate differences in neuronal substrates underlying shifts of attention in young and old subjects, studied with dichotic listening. Two different consonant-vowel syllables were presented and the subjects were instructed to attend to and report from either the left or right ear stimulus. Typically, a right-ear advantage is observed when attending to the right-ear stimulus, and a left-ear advantage when attending to the left-ear stimulus. The behavioral results showed that the old group had difficulties with attentional modulation of the right-ear advantage in the attend left condition. This is interpreted as a failure of an important aspect of attentional control; the top-down biasing of attention for selection of task-relevant stimulus. The fMRI results showed that an area in the left middle frontal gyrus was more activated in the young group compared to the old group in the attend left condition. The structural MRI data showed reduced gray matter density of the same area in the old group. Based on these converging findings, we suggest that the left middle frontal gyrus plays an important role in top-down biasing of selecting task-relevant stimuli, and to inhibit processing of task-irrelevant stimuli. To our knowledge, this is one of the first studies addressing the question on how age-related changes in attentional processing is reflected in both functional and structural differences in the brain.

Adult↗
PubMed2004

[MRT of bronchial carcinomas].

Compared to computed tomography (CT), magnetic resonance imaging (MRI) only plays a minor role for the imaging of lung cancer. Among the reasons are technical limitations, such as longer acquisition times or inferior spatial resolution, as well as unfavourable tissue characteristics which cause a low signal-to-noise ratio of the lung parenchyma. However, MRI is a valuable tool for staging lung cancer and may in some cases even be considered the method of choice. The following review illustrates the role of MRI for the diagnosis of lung cancer using current MR-techniques. In particular, the potential of MRI for TNM-staging, new technical developments (e. g. parallel MRI), and the application of functional MRI of the chest are described.

Carcinoma, Bronchogenic↗
PubMed2003

MRI aspects of the "inflammatory phase" of multiple sclerosis.

In early relapsing-remitting (RR) multiple sclerosis (MS), conventional magnetic resonance imaging (MRI) has proved to be a valuable tool to assess disease activity over time. However, conventional MRI can only provide gross estimates of irreversible tissue damage within and outside such lesions. Other MR-based techniques, including magnetization transfer MRI, diffusion-weighted MRI, proton MR spectroscopy and functional MRI, have the potential to provide additional pieces of information about the nature and the extent of MS tissue damage since the early "inflammatory phase" of the disease. The application of these MR techniques to the study of early RRMS is likely to improve our understanding of the pathophysiology of MS and our ability to assess the efficacy of experimental treatments.

Brain↗