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PubMed1996

NMR functional imaging using a tailored RF gradient echo sequence: a true susceptibility measurement technique.

The tailored radio frequency gradient echo (TRFGE) technique that has been used in venography (Cho et al., Magn. Reson. Med. 28, 25-38, 1992; Ro, Cho, Magn. Reson. Med. 28, 237, 1992) is applied to functional imaging. The TRFGE technique has the advantage that it is sensitive to the field gradient created by the susceptibility effect, thereby enhancing only the signals from the regions with local field gradient. In addition, the method is insensitive to the in-flow effect, especially from the arterial blood. The latter further simplifies the functional MRI data analysis. The TRFGE sequence is, therefore, suitable for functional MR imaging for which true susceptibility effect measurements are of prime importance. To examine the TRFGE functional imaging systematically, experiments with various imaging parameters such as flip angle alpha, repetition time, and echo time were performed and the results were compared with the data obtained from the conventional gradient echo functional MR imaging. The experimental results shown were all obtained from human volunteers with a 2.0T whole body MRI system.

Arousal↗

PubMed1999

BOLD MRI of the human cervical spinal cord at 3 tesla.

The feasibility of functional MRI of the spinal cord was investigated by carrying out blood oxygen-level dependent (BOLD) imaging of the human cervical spinal cord at a field of 3 T. BOLD imaging of the cervical spinal cord showed an average intensity increase of 7.0% during repeated exercise with the dominant hand with a return to baseline during rest periods. The areas of activation were predominantly on the same side of the spinal cord as the hand performing the exercise, between the levels of the sixth cervical and first thoracic spinal cord segments. The direct correspondence between these areas and those involved with the transmission of motor impulses to the hand, and reception of sensory information from the hand, demonstrates that spinal functional magnetic resonance imaging is feasible. Magn Reson Med 42:571-576, 1999.

Adult↗

PubMed2006

Representation of lateralization and tonotopy in primary versus secondary human auditory cortex.

Functional MRI was performed to investigate differences in the basic functional organization of the primary and secondary auditory cortex regarding preferred stimulus lateralization and frequency. A modified sparse acquisition scheme was used to spatially map the characteristics of the auditory cortex at the level of individual voxels. In the regions of Heschl's gyrus and sulcus that correspond with the primary auditory cortex, activation was systematically strongest in response to contralateral stimulation. Contrarily, in the surrounding secondary active regions including the planum polare and the planum temporale, large-scale preferences with respect to stimulus lateralization were absent. Regarding optimal stimulus frequency, low- to high-frequency spatial gradients were discernable along the Heschl's gyrus and sulcus in anterolateral to posteromedial direction, especially in the right hemisphere, consistent with the presence of a tonotopic organization in these primary areas. However, in the surrounding activated secondary areas frequency preferences were erratic. Lateralization preferences did not depend on stimulus frequency, and frequency preferences did not depend on stimulus lateralization. While the primary auditory cortex is topographically organized with respect to physical stimulus properties (i.e., lateralization and frequency), such organizational principles are no longer obvious in secondary and higher areas. This suggests a neural re-encoding of sound signals in the transition from primary to secondary areas, possibly in relation to auditory scene analysis and the processing of auditory objects.

Adult↗

PubMed2000

High-resolution segmented EPI in a motor task fMRI study.

A high-resolution gradient echo, multi-slice segmented echo planar imaging method was used for functional MRI (fMRI) using a motor task at 1.5 Tesla. Functional images with an in-plane resolution of 1 mm and slice thickness of 4 mm were obtained with good white-gray matter contrast. The multi-shot approach, combined with a short total readout period of 82 ms, limits blurring effects for short T(2)(*) tissues (such as gray matter), assuring truly high-resolution images. In all subjects, motor functions were clearly depicted in the contralateral central sulcus over several slices and sometimes activation was detected in the supplementary motor area and/or ipsilateral central sulcus. The average signal change of 11+/-3% was much higher than in standard low-resolution fMRI EPI experiments, as a result of larger relative blood fractions.

Adult↗

PubMedDate not supplied

Cortical activation and language task difficulty in aphasia.

BACKGROUND: Previous research using functional MRI (fMRI) suggests changes in cortical activation as a function of increased task difficulty. This relationship has not been explored in persons with aphasia even though it may have significant implications for pre- and post-treatment interpretation of fMRI data. AIMS: The purpose of this exploratory study was to investigate the relationship between changes in language task difficulty and cortical activation in persons with aphasia. METHODS #ENTITYSTARTX00026; PROCEDURES: Four persons with chronic anomic or Broca's aphasia and four matched control participants underwent fMRI while performing a picture-word matching task. OUTCOMES #ENTITYSTARTX00026; RESULTS: Compared to the more difficult task condition, all participants performed with greater accuracy on the easier condition. Moreover, greater mean blood oxygenated level dependent (BOLD) signal intensity and area recruitment were noted during the more difficult condition for three out of four persons with aphasia as well as three of the four controls. The increase in cortical activity was mainly noted in the superior temporal and posterior inferior frontal lobes. CONCLUSIONS: The present findings mirror those found in previous studies of normal subjects in that cortical activation increased in parallel to task difficulty for most of our participants. It is unclear what mechanism accounts for this effect; this phenomenon might need to be considered in future fMRI studies of neural plasticity associated with aphasia treatment.

Journal Article↗

PubMed2005

The functional anatomy of divided attention in amnestic mild cognitive impairment.

Recent neuroimaging studies have demonstrated changes in brain function in cognitively normal subjects at increased risk of developing Alzheimer's disease. Amnestic mild cognitive impairment (AMCI) carries a high risk of developing into Alzheimer's disease. In AMCI altered cortical activation has been demonstrated during memory tasks, using functional MRI (fMRI). Memory and attention are closely related cognitive functions. It is unclear whether the memory impairment of AMCI is associated with attentional deficits of the sort likely to be revealed by tasks requiring divided attention. Ten older adults (mean age 72 years, range 57-81 years) with AMCI were compared with healthy matched controls on divided attention and passive sensory processing tasks using fMRI. During the divided attention task both groups activated similar regions of left hemispheric prefrontal and extrastriate visual cortex. However, the AMCI group had attenuated prefrontal activation compared with age matched controls. On the passive sensory processing task there was no difference between the AMCI and control groups. We conclude that there are changes in the functional network subserving divided attention in patients with AMCI as reflected in the attenuation of prefrontal cortical activation. These findings have implications for evaluating cognition in AMCI and also for monitoring the effects of future treatments in AMCI.

Acoustic Stimulation↗

PubMed2006

Retinal thickness and subnormal retinal oxygenation response in experimental diabetic retinopathy.

PURPOSE: To test the hypothesis that subnormal retinal oxygenation response (DeltaPo2) found at 3 months of experimental diabetes is associated with cellular swelling and increased retinal thickness. METHODS: Two groups of animals were studied: control rats injected intraperitoneally with either 15% body weight of saline or distilled water (cellular swelling model) or with intravitreal N-methyl-D-aspartate (NMDA) and 3-month-old diabetic and age-matched control rats. Intraocular pressure and retinal thickness was assessed using an applanation tonometer or high-resolution MRI (23.4 microm2 in-plane). In separate studies, functional MRI was used to measure blood-retinal barrier (BRB) integrity after Gd-DTPA injection intravenously and retinal DeltaPo2 during carbogen provocation. RESULTS: Inner and total retinal thickness were lower (P < 0.05) after NMDA injection, not different (P > 0.05) between control, before and after saline injection and before distilled water injection, and supernormal (P < 0.05) after distilled water injection. In diabetic rats, thickness was normal (P > 0.05) at most distances from the optic nerve but was subnormal (P < 0.05) in superior retina (0.5 mm from the optic nerve). Intraocular pressure was not different (P > 0.05) between groups. BRB was intact (P > 0.05) after saline and distilled water injection. DeltaPo2 was normal (P > 0.05) after saline injection and over inferior hemiretina of the diabetic group but was subnormal (P < 0.05) after distilled water injection and over superior hemiretina of diabetic rats. CONCLUSIONS: The lack of increased thickness in 3-month-old diabetic rats in vivo raises the possibility that intracellular swelling is unlikely to underlie subnormal DeltaPo2 in experimental diabetes. In diabetic rats, the spatial disconnect between subnormal DeltaPo2 pansuperiorly and retinal thinning only superiorly to the optic nerve suggests that neurovascular coupling is perturbed.

Animals↗

PubMed2006

Bench to bedside: evidence for brain injury after concussion--looking beyond the computed tomography scan.

The emergency management of cerebral concussion typically centers on the decision to perform a head computed tomography (CT) scan, which only rarely detects hemorrhagic lesions requiring neurosurgery. The absence of hemorrhage on CT scan often is equated with a lack of brain injury. However, observational studies revealing poor long-term cognitive outcome after concussion suggest that brain injury may be present despite a normal CT scan. To explore this idea further, the authors reviewed the evidence for objective neurologic injury in humans after concussion, with particular emphasis on those with a normal brain CT. This evidence comes from studies involving brain tissue pathology, CT scanning, magnetic resonance image (MRI) scanning, serum biomarkers, formal cognitive and balance tests, functional MRI, positron emission tomography, and single-photon emission computed tomography scanning. Each section is accompanied by technical information to help the reader understand what these tests are, not to endorse their use clinically. The authors discuss the strengths and weaknesses of the evidence in each case. These reports make a compelling case for the existence of concussion as a clinically relevant disease with demonstrable neurologic pathology. Areas for future emergency medicine research are suggested.

Axons↗

PubMedDate not supplied

MR-based technology for in vivo detection, characterization, and quantification of pathology of relapsing-remitting multiple sclerosis.

In relapsing-remitting (RR) multiple sclerosis (MS), conventional magnetic resonance (MR) imaging (MRI) has proved to be a valuable tool to assess the lesion burden and activity over time. However, conventional MRI cannot characterize and quantify the tissue damage within and outside such lesions and only can provide some gross measures reflecting the presence of irreversible tissue damage, such as the load of T1 "black holes" and the severity of brain or cord atrophy. Other MR-based techniques, including cell-specific imaging, magnetization transfer (MT) MRI (MT-MRI), diffusion-weighted (DW) MRI (DW-MRI), proton magnetic resonance spectroscopy (1H-MRS), and functional MRI (fMRI), have the potential to overcome this limitation and, consequently, to provide additional information about the nature and the extent of MS tissue damage, which would inevitably remain undetected when only a conventional MRI is obtained. Cell-specific imaging should result in a better definition of the cellular mechanisms associated with MS inflammation. Metrics derived from MT- and DW-MRI can quantify the structural changes occurring within and outside lesions visible on conventional MRI scans. 1H-MRS could add information on the biochemical nature of such changes. fMRI is a promising technique to assess the mechanisms of cortical reorganization, which may limit the consequences of an MS-related injury. The application of these MR techniques to the study of RRMS is likely to provide useful insights into the pathophysiology of this disease and to improve our ability to assess the efficacy of experimental treatments.

Biopsy, Needle↗

PubMed1996

Activation of the hippocampal formation by vestibular stimulation: a functional magnetic resonance imaging study.

Functional MRI (f-MRI) is a non-invasive technique developed to permit functional mapping of the brain with a better temporal and spatial resolution than that offered by PET techniques. In our study, f-MRI was performed using blood oxygenation level dependent (BOLD) contrast imaging based on the magnetic properties of hemoglobin. This method relies on changes in the blood supply to the brain that accompany sensory stimulation or changes in cognitive state. All the images were obtained at 1.5 T on a Signa GEMS without ultrafast imaging. The vestibular stimulation was cold irrigation of the external auditory meatus (caloric stimulation). A population of normal healthy volunteers without a history of vestibular dysfunction was studied. The hippocampal formation as well as the retrosplenial cortex and the subiculum were activated by vestibular stimulation, suggesting that this activation may be related to spatial disorientation and a sensation of self-rotation experienced by the subjects during vestibular stimulation. The other results are similar to those obtained using PET.

Brain Mapping↗

PubMed2003

Brain anatomy and development in autism: review of structural MRI studies.

Autism is a neurodevelopmental disorder that severely disrupts social and cognitive functions. MRI is the method of choice for in vivo and non-invasively investigating human brain morphology in children and adolescents. The authors reviewed structural MRI studies that investigated structural brain anatomy and development in autistic patients. All original MRI research papers involving autistic patients, published from 1966 to May 2003, were reviewed in order to elucidate brain anatomy and development of autism and rated for completeness using a 12-item check-list. Increased total brain, parieto-temporal lobe, and cerebellar hemisphere volumes were the most replicated abnormalities in autism. Interestingly, recent findings suggested that the size of amygdala, hippocampus, and corpus callosum may also be abnormal. It is conceivable that abnormalities in neural network involving fronto-temporo-parietal cortex, limbic system, and cerebellum may underlie the pathophysiology of autism, and that such changes could result from abnormal brain development during early life. Nonetheless, available MRI studies were often conflicting and could have been limited by methodological issues. Future MRI investigations should include well-characterized groups of autistic and matched healthy individuals, while taking into consideration confounding factors such as IQ, and socioeconomic status.

Autistic Disorder↗

PubMed2004

Imaging of neurogenetic and neurometabolic disorders of childhood.

Magnetic resonance imaging (MRI) has emerged as a powerful tool in the study of normal and abnormal brain structure, function, and biochemistry. In particular, functional MRI has come into its own as a tool to study normal and abnormal brain functions such as learning, memory, and motor learning, as well as delineation of neurogenetic cognitive phenotypes. White matter microstructure can be studied using diffusion tensor imaging, which may allow abnormal white matter to be visualized prior to abnormalities on anatomic MRI. Magnetic resonance spectroscopy, a noninvasive method to study brain biochemistry, may allow for the delineation of regional metabolic changes as a result of disease progression and/or therapeutic intervention. With MRI techniques, one can investigate the relationship between structure, function, genes, and behavior. This report discusses the research applications of MRI to the study of neurogenetic disorders of childhood.

Child↗

PubMed1997

Imaging and epilepsy.

MRI has been applied to the investigation of epilepsy for 12 years. The principle role of MRI is in the definition of structural abnormalities that underly seizure disorders. Hippocampal sclerosis may be reliably identified, quantitative studies are useful for research and, in equivocal cases, for clinical purposes. A range of malformations of cortical development (MCD) may be determined. In patients with refractory partial seizures who are candidates for surgical treatment, a relevant abnormality is identifiable using MRI in 85%, it is likely that subtle MCD or gliosis accounts for the majority of the remainder. The proportion of cryptogenic cases will decrease with improvements in MRI hardware, signal acquisition techniques and post-processing methodologies. Functional MRI is used to identify the cerebral areas that are responsible for specific cognitive processes, and is of importance in planning resections close to eloquent cortical areas. Magnetic resonance spectroscopy (MRS) provides a means of investigating cerebral metabolites and some neurotransmitters, non-invasively. The concentrations of N-acetyl-aspartate (NAA), creatine and choline-containing compounds may be estimated using proton MRS. Reduction of the ratio of NAA/(creatine+choline) is a feature of cerebral regions that include epileptic foci. Cerebral concentrations of GABA and glutamate, and the effects of antiepileptic drugs on these, may be estimated. Concentrations of high energy phosphate compounds, inorganic phosphate and pH may be assessed using 31P-MRS. In general, epileptic foci are associated with an increase in pH, increased inorganic phosphate and decreased phosphate monoesters. Carbon-13 spectroscopy promises to be a useful method for investigating cerebral metabolism in vivo. PET may provide data on regional cerebral blood flow (rCBF), glucose metabolism and the binding of specific ligands to receptors. Correlation of functional and structural imaging data is necessary for adequate interpretation. The hallmark of an epileptic focus is an area of reduced glucose metabolism, identified using [18F]fluorodeoxyglucose (18FDG), that is commonly more extensive than the underlying anatomical abnormality. The clinical role of 18FDG-PET requires re-evaluation in the light of the advances in structural imaging with MRI. Specific ligands are used to investigate specific receptors. Benzodiazepine and opioid receptors have been studied most. Reduced benzodiazepine receptor binding is commonly seen at an epileptic focus, in a more restricted distribution than an area of hypometabolism. Focal increases and decreases in benzodiazepine receptor binding have been demonstrated in MCD in areas that appear normal on MRI, indicating the widespread nature of the abnormalities. It has been found that mu-opioid receptors are increased in temporal neocortex overlying mesial temporal epileptic foci. Dynamic studies of ligand-receptor binding are possible using PET, for example the release of cerebral endogenous opioids has been implied at the time of serial absences. The main use of single photon emission computed tomography (SPECT) is to produce images reflecting rCBF. Interictal studies alone are not reliable. A strength of SPECT is the ability to obtain images related to rCBF at the time of seizures. Concomitant video-EEG recording is necessary. Ictal scans need to be considered in comparison with an interictal scan and an MRI. Interpretation must be cautious, but may yield data that is useful in the investigation of patients for possible surgical treatment.

Cerebral Cortex↗

PubMed2003

Stereotaxic assembly and procedures for simultaneous electrophysiological and MRI study of conscious rat.

A stereotaxic restraining assembly was designed and developed for simultaneous electrophysiological recordings and functional MRI (fMRI) data acquisition from a conscious rat. The design of the nonmagnetic stereotaxic apparatus facilitated the restraining of head and body of the unanesthetized conscious animal during MRI experiments. The apparatus was made of Teflon and Perspex materials with an appropriate size and shape for a 4.7 T / 40 cm animal MRI scanner. Electrodes made from nonmagnetic silver wire were implanted on the skull for recording the electroencephalogram (EEG), the electro-oculogram (EOG), and the electromyogram (EMG), while polycarbonate screws were used for anchoring the electrode assembly. There were no major distortions or artifacts observed in the electrophysiological tracings and MR images. Electrophysiological recordings during fMRI acquisitions are useful to study different neurophysiological mechanisms of sleep and pathophysiology of seizure activity. Integration of electrophysiological recordings (with their good temporal resolution) and MRI (with its superior spatial resolution) is helpful in characterizing the functional state of different brain regions.

Animals↗

PubMed1996

Neuroimaging in pediatric epilepsy.

Neuroimaging techniques have advanced the diagnosis, management, and understanding of the pathophysiology underlying the epilepsies. High-resolution ultrasound is an important and useful technique in the investigation of prematures and neonates with seizures. Computed tomography (CT) scans have a diminishing role in the investigation of patients with epilepsy, but in the absence of magnetic resonance imaging (MRI), CT may detect gross structural pathology. MRI is the technique of choice for investigation of patients with seizure disorders. MRI provides excellent anatomic information and tissue contrast, resulting in high sensitivity. MRI studies should be customized to answer the appropriate clinical question. Functional imaging techniques including single photon emission computed tomography (SPECT), positron emission tomography (PET), magnetic resonance spectroscopy, and functional MRI are becoming increasingly important in the investigation and management of patients with seizures. These techniques permit noninvasive assessment of the epileptic substrate, functional status, ictal activity, blood flow changes, metabolism, and neuroreceptors. Application of these new techniques promises to advance our understanding and treatment of seizures in children.

Adult↗

PubMed2005

Bilateral neurostimulation systems used for deep brain stimulation: in vitro study of MRI-related heating at 1.5 T and implications for clinical imaging of the brain.

Deep brain stimulation (DBS) is used increasingly in the field of movement disorders. The implanted electrodes create not only a prior risk to patient safety during MRI, but also a unique opportunity in the collection of functional MRI data conditioned by direct neural stimulation. We evaluated MRI-related heating for bilateral neurostimulation systems used for DBS with an emphasis on assessing clinically relevant imaging parameters. Magnetic resonance imaging was performed using transmit body radiofrequency (RF) coil and receive-only head RF coil at various specific absorption rates (SARs) of RF power. In vitro testing was performed using a gel-filled phantom with temperatures recorded at the electrode tips. Each DBS electrode was positioned with a single extension loop around each pulse generator and a single loop at the "head" end of the phantom. Various pulse sequences were used for MRI including fast spin-echo, echo-planar imaging, magnetization transfer contrast and gradient-echo techniques. The MRI sequences had calculated whole-body averaged SARs and local head SARs ranging from 0.1 to 1.6 W/kg and 0.1 to 3.2 W/kg, respectively. Temperature elevations of less than 1.0 degrees C were found with the fast spin-echo, magnetization transfer contrast, gradient-echo and echo-planar clinical imaging sequences. Using the highest SAR levels, whole-body averaged, 1.6 W/kg, local exposed-body, 3.2 W/kg, and local head, 2.9 W/kg, the temperature increase was 2.1 degrees C. These results showed that temperature elevations associated with clinical sequences were within an acceptable physiologically safe range for the MR conditions used in this evaluation, especially for the use of relatively low SAR levels. Notably, these findings are highly specific to the neurostimulation systems, device positioning technique, MR system and imaging conditions used in this investigation.

Deep Brain Stimulation↗

PubMed2006

[Functional magnetic resonance imaging in clinical practice].

In the last decade, functional MRI (fMRI) has become one of the most widely used functional imaging technique in neurosciences. However, its clinical applications remain limited. Despite methodological and practical issues, fMRI data has been validated by different techniques (magnetoencephalography, Wada test, electrical and magnetic stimulations, and surgical resections). In neurosurgical practice, fMRI can identify eloquent areas involved in motor and language functions, and may evaluate characteristics of postoperative neurological deficit including its occurrence, clinical presentation and duration. This may help to inform patients and to prepare postoperative care. fMRI may also identify epileptic foci. In neurological practice, fMRI may help to determine prognosis of recovery after stroke, appropriate medication, and rehabilitation. fMRI may help to identify patients at risk of developing Alzheimer disease. Finally, cerebrovascular reactivity imaging is an interesting approach that might provide new radiological insights of vascular function.

Brain↗

PubMed2006

[Cerebral gliomas: imaging diagnosis and follow-up].

The management of gliomas evolves towards more aggressive strategies with a combination of surgery, radiotherapy and chemotherapy. Follow-up imaging based on morphological MRI, with simple and reproducible protocols, may be associated with functional MRI and spectroscopy. Baseline postsurgical MRI must be performed within the first three days. Follow-up examinations should be done 2 months after radiotherapy and during chemotherapy, usually after each cycle of two or three treatments. Continued follow-up after therapy is recommended to assess response and detect recurrences or therapeutic complications.

Aged↗