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PubMed2001

Three-dimensional conformal radiation treatment planning and delivery for low- and intermediate-grade gliomas.

Three-Dimensional conformal radiation treatment (3D-CRT) planning and delivery is an external beam radiation therapy modality that has the general goal of conforming the shape of a prescribed dose volume to the shape of a 3-dimensional target volume, simultaneously limiting dose to critical normal structures. 3-Dimensional conformal therapy should include at least one volumetric imaging study of the patient. This image should be obtained in the treatment position for visualizing the target and normal anatomic structures that are potentially within the irradiated volume. Most often, computed tomography (CT) and/or magnetic resonance imaging (MRI) are used; however, recently, other imaging modalities such as functional MRI, MR spectroscopy, and positron emission tomography (PET) scans have been used to visualize the clinically relevant volumes. This article will address the clinically relevant issues with regard to low- and intermediate-grade gliomas and the role of 3D-CRT planning. Specific issues that will be addressed will include normal tissue tolerance, target definition, treatment field design in regard to isodose curves and dose-volume histograms, and immobilization.

Brain Neoplasms↗
PubMed2005

Sign language: its history and contribution to the understanding of the biological nature of language.

CONCLUSION: The development of conceptualization of a biological basis of language during the 20th century has come about, in part, through the appreciation of the central nervous system's ability to utilize varied sensory inputs, and particularly vision, to develop language. OBJECTIVE: Sign language has been a part of the linguistic experience from prehistory to the present day. Data suggest that human language may have originated as a visual language and became primarily auditory with the later development of our voice/speech tract. Sign language may be categorized into two types. The first is used by individuals who have auditory/oral language and the signs are used for special situations, such as communication in a monastery in which there is a vow of silence. The second is used by those who do not have access to auditory/oral language, namely the deaf. MATERIAL AND METHODS: The history of the two forms of sign language and the development of the concept of the biological basis of language are reviewed from the fourth century BC to the present day. RESULTS: Sign languages of the deaf have been recognized since at least the fourth century BC. The codification of a monastic sign language occurred in the seventh to eighth centuries AD. Probable synergy between the two forms of sign language occurred in the 16th century. Among other developments, the Abbey de L'Epée introduced, in the 18th century, an oral syntax, French, into a sign language based upon indigenous signs of the deaf and newly created signs. During the 19th century, the concept of a "critical" period for the acquisition of language developed; this was an important stimulus for the exploration of the biological basis of language. The introduction of techniques, e.g. evoked potentials and functional MRI, during the 20th century allowed study of the brain functions associated with language.

Brain↗
PubMed2006

Structural and functional plasticity in the somatosensory cortex of chronic stroke patients.

Animal studies have demonstrated that motor recovery after hemiparetic stroke is associated with functional and structural brain plasticity. While studies in stroke patients have revealed functional plasticity in sensorimotor cortical areas in association with motor recovery, corresponding structural plasticity has not been shown. We sought to test the hypothesis that chronic hemiparetic stroke patients exhibit structural plasticity in the same sensorimotor cortical areas that exhibit functional plasticity. Functional MRI during unilateral tactile stimulation and structural MRI was conducted in chronic stroke patients and normal subjects. Using recently developed computational methods for high-resolution analysis of MRI data, we evaluated for between-group differences in functional activation responses, and cortical thickness of areas that showed an enhanced activation response in the patients. We found a significant (P < 0.005) increase in the activation response in areas of the ventral postcentral gyrus (POG) in the patients relative to controls. These same ventral POG areas showed a significant (P < 0.05) increase in cortical thickness in the patients. Control cortical areas did not show a significant between-group difference in thickness or activation response. These results provide the first evidence of structural plasticity co-localized with areas exhibiting functional plasticity in the human brain after stroke.

Adult↗
PubMed1994

[An introduction to fast and ultrafast sequences in magnetic resonance].

The main limitations of magnetic resonance imaging (MRI) are due to the long acquisition time needed for data sampling. Fast and ultrafast sequences, thanks to progress in hardware and software technology, allow the acquisition times to be dramatically reduced. Such improvements will definitely increase MR capabilities and make MRI a fast and dynamic technique no longer depending on patients' cooperation and limited by patients' conditions--e.g., trauma, pediatric, or claustrophobic patients--or even by the anatomic features of the region of interest. The latest experimental studies are aimed at increasing the clinical applications and the perspectives of clinical MRI and at such ambitious goals as MR-fluoroscopy, interventional MRI, total body examination in less than one minute and functional MRI. In this paper the technical principles and the main indications of this new kind of sequences are reported, with a special emphasis on Gradient-Echo (GE), Turbo Spin-Echo (turbo SE) or Fast Spin-Echo (fast SE), Turbo FLASH and Echo Planar (EP) sequence. A smaller flip angle (FA) and the substitution of the 180 degrees RF pulse with a gradient reversal are the main differences of GE from SE sequences. From GE sequences, several fast sequences are derived, such as angiographic and turbo FLASH sequences. The latter, thanks to 180 degrees preinversion RF pulse, using idoneous inversion times (IT), provide flexible contrast. Turbo SE sequences, which are directly derived from conventional SE sequence, allow the acquisition time to be markedly shortened, by acquiring several Fourier lines of K-space for each TR. The repetition of several 180 degrees pulses following the excitatory 90 degrees RF pulse does the trick through the creation of multiple echoes for a single TR. EP sequences are the fastest ones currently available: with them, an image can be acquired in 30-100 ms. However, the limited availability of the relative hardware and the need of both quality implementation and the definition of clinical indications are major obstacles to the widespread use of these sequences. The SE T2-weighted sequence, the main responsible for the long examination time, will be replaced soon. Further implementation of these sequences will make MRI a fast, flexible and adaptable method to any exam and patient disability.

Echo-Planar Imaging↗
PubMed1996

Magnetic Resonance in Schizophrenia.

In vivo magnetic resonance imaging (MRI) of schizophrenic patients permits the direct and noninvasive study of brain biochmeistry, structure, and function. During the last decade, a number of morphological abnormalities have been found in schizophrenic brains on the basis of qualitative and quantitative assessment of MRIs. Changes in ventricular volume, cortical volume, temporal lobe structures, and subcortical regions have been reported. The search for a precise and specific location underlying the pathophysiology of schizophrenia has led to the interpretation of imaging results in the context of interrelated systems of brain function, rather than isolated focal brain abnormalities. Furthermore, an important goal of imaging studies is to describe unusual features of schizophrenic brains that represent abnormalities central to the development of the disorder, including abnormalities that may represent vulnerabilities or risk factors, as well as those that are directly related to psychopathology. Identifying brain pathology that distinguishes schizophrenics' brains has proven difficult because it involves detecting rather subtle changes against a background of extensive normal variation. Application of powerful new magnetic resonance techniques continues to increase our understanding of these subtle changes. The importance of magnetic resonance spectroscopy is derived from the information it provides regarding the chemical content of the tissue being studied. Functional MRI provides a method for the assessment of functional architecture by measuring changes in oxidation and regional blood flow in discrete regions of the brain in response to challenge paradigms. These technologies promise to facilitate both the detection of cortical anomalies as well as provide the methods necessary for the systematic exploration of cortical structure and function needed to examine brain dysfunction from a network perspective.

Journal Article↗
PubMed2000

Neuroimaging: applications in disorders of early brain development.

Neuroimaging techniques have established new connections between etiological factors and disorders of early brain development. Neuroimaging has also strengthened the link between patterns of selective vulnerability in the developing brain and clinical syndromes, especially cerebral palsy. Both computed tomography (CT) and magnetic resonance imaging (MRI) identify early developmental malformations, including neural tube defects, callosal dysgenesis, neuronal migration disorders, posterior fossa malformations, and hydrocephalus. Periventricular white matter damage, most commonly seen in premature infants, is best visualized by cranial ultrasonography in the neonatal period and on MRI later in childhood. In term infants and children with genetic metabolic diseases, various applications of nuclear magnetic resonance, including MRI, have important diagnostic roles. The utility of diffusion-weighted imaging, MR spectroscopy, and functional MRI to further understanding of brain injury, biochemistry, and function is under active investigation. In summary, selecting the appropriate neuroimaging technique can improve diagnosis and management of childhood neurodevelopmental disorders.

Brain↗
PubMed2003

[Dystonia: contributions of functional imaging and magnetoencephalography].

Functional neuroimaging using positron emission tomography (PET), and more recently functional MRI (fMRI) and magnetoencephalography (MEG), is a valuable tool to study functional anomalies in dystonia. Activation studies have contributed to a better understanding of cerebral dysfunction in dystonia showing two main types of abnormalities: changes in activation levels during performance of sensory or motor tasks and disorganization of the selectivity of neuronal representations. In primary dystonia, most PET and fMRI studies have shown overactivity in premotor and prefrontal areas and underactivation of primary sensorimotor areas. In secondary dystonia, premotor and prefrontal areas are similarly overactive as well as primary sensorimotor areas. Altered selectivity of neuronal representations has been described more recently along cortico-subcortical circuits. The loss of neuronal selectivity may contribute to the loss of selectivity of muscular contractions observed in dystonia. Spectroscopic MRI may also be used to measure GABA levels, which are decreased in the cortex and basal ganglia in these patients.

Animals↗
PubMed2004

Dynamic field map estimation using a spiral-in/spiral-out acquisition.

The long readout times of single-shot acquisitions and the high field strengths desired for functional MRI (fMRI) using blood oxygenation level-dependent (BOLD) contrast make functional scans sensitive to magnetic field inhomogeneity. If it is not corrected during image reconstruction, field inhomogeneity can cause geometric distortions in the images when Cartesian k-space trajectories are used or blurring with spiral acquisitions. Many traditional methods to correct for field inhomogeneity distortions rely on a static field map measured with the use of images that are themselves distorted. In this work, we employ a regularized least-squares approach to jointly estimate both the undistorted image and field map at each acquisition using a spiral-in/spiral-out pulse sequence. Simulation and phantom studies show that this method is accurate and stable over a time series. Human functional studies show that the jointly estimated field map may be more accurate than standard field map estimates in the presence of respiration-induced phase oscillations, leading to better detection of functional activation. The proposed method measures a dynamic field map that accurately tracks magnetic field drift and respiration-induced phase oscillations during the course of a functional study.

Brain↗
PubMed2002

On the origin of respiratory artifacts in BOLD-EPI of the human brain.

BOLD-based functional MRI (fMRI) can be used to explicitly measure hemodynamic aspects and functions of human neuro-physiology. As fMRI measures changes in regional cerebral blood flow and volume as well as blood oxygenation, rather than neuronal brain activity directly, other processes that may change the above parameters have to be examined closely to assess sensitivity and specificity of fMRI results. Physiological processes that can cause artifacts include cardiac action, breathing and vasomotion. Although there has been substantial research on physiological artifacts and appropriate compensation methods, controversy still remains on the mechanisms that cause the fMRI signal fluctuations. Respiratory-correlated fluctuations may either be induced by changes of the magnetic field homogeneity due to moving organs, intra-thoracic pressure differences, respiration-dependent vasodilation or oxygenation differences. The aim of this study was to characterize the impact of different breathing patterns by varying respiration frequency and/or tidal volume on EPI time courses of the resting human brain. The amount of respiration-related oscillations during three respiration patterns was quantified, and statistically significant differences were obtained in white matter only: p < 0.03 between 6 vs. 12 ml/kg body weight end tidal volume at a respiration frequency of 15/min, p < 0.03 between 12 vs. 6 ml/kg body weight and 15 vs. 10 respiration cycles/min. There was no significant difference between 15 vs. 10 respiration cycles/min at an end tidal volume of 6 ml/kg body weight (p = 0.917). In addition, the respiration-affected brain regions were very similar with EPI readout in the a-p and l-r direction. Based on our results and published literature we hypothesize that venous oxygenation oscillations due to changing intra-thoracic pressure represent a major factor for respiration-related signal fluctuations and increase significantly with increasing end tidal volume in white matter only.

Adult↗
PubMed2002

Brain development and the onset of mood disorders.

Research in mood disorder pathophysiology has stimulated considerable interest in clinical and biologic aspects of mood disorders among children and adolescents. From the clinical perspective, developmental aspects of psychiatric disorders have crystallized in the relatively new theoretical school known as developmental psychopathology. This school attempts to understand the nature of developmental changes in behavior, with the goal of differentiating normal from abnormal stage-related behavior. This perspective has exerted major impact on conceptualizations of psychiatric disorders. From the basic science perspective, biologic findings in emotion have stimulated an integration of basic and clinical approaches to mood disorders. The term emotion is often used to refer to brain states elicited by stimuli for which an organism will extend effort to obtain (rewards) or avoid (punishments). Imaging studies suggest that brain regions engaged by rewarding and punishing stimuli in lower mammals are also implicated in mood disorders. Other studies suggest that environmental factors exert profound effects on the development of these brain regions. The impact of 4 areas of research on our understanding of depression pathophysiology is reviewed: (1) mood disorder onset, (2) structural magnetic resonance imaging (MRI), (3) behavioral or cognitive correlates of major depression, and (4) functional MRI of brain regions engaged across development. This is a US government work. There are no restrictions on its use.

Adolescent↗
PubMed1994

Diagnosis in adolescents and adults with congenital heart disease. Prospective assessment of individual and combined roles of magnetic resonance imaging and transesophageal echocardiography.

BACKGROUND: The inability to obtain complete diagnoses with transthoracic echocardiography in many adults with congenital heart disease provided the incentive to evaluate prospectively the individual and combined roles of magnetic resonance imaging (MRI) and transesophageal echocardiography (TEE) as "second-line" techniques for unresolved diagnostic problems. METHODS AND RESULTS: Eighty-five patients were studied; 81 had MRI with a 0.5-T magnet to obtain spin-echo images, cine-MRI, and flow-velocity maps. Seventy-nine patients had TEE (37 biplane). A simple score (range, 0 to 1) was used for quantification of the results of MRI and TEE alone, for their comparison (in the 75 patients who had both), and for assessment of their combination. MRI, TEE, or their combination achieved a score of at least 0.75 in 18 of 25 diagnostic categories. A summary of the scores showed that for intracardiac anatomy. MRI scored 0.34, TEE scored 0.71 (P < .0001), and MRI plus TEE scored 0.84 (P < .003); for extracardiac anatomy, MRI scored 0.76, TEE scored 0.23 (P < .0001), and MRI plus TEE scored 0.84 (P = NS); and for hemodynamics and function, MRI scored 0.58, TEE scored 0.41 (P < .05), and MRI plus TEE scored 0.67 (P = NS). Total scores were MRI, 0.52; TEE, 0.50 (P = NS); and MRI plus TEE, 0.80 (P < .0001). MRI and TEE were inadequate for collateral and coronary arteries and pulmonary vascular resistance. Cine-MRI and flow-velocity maps comprised 43% of the MRI scores. Biplane TEE was better than single plane (scores of 0.59 versus 0.42, P < .0001). CONCLUSIONS: MRI and TEE are important and complementary "second-line" investigations for congenital heart disease. Analysis of their performance in a wide range of diagnostic categories provides guidelines for their judicious application. Where both are available, diagnostic catheterizations are either obviated or simplified.

Adolescent↗
PubMed2006

Pathologic and physiologic function in the subcortical band of double cortex.

Double cortex is a neuronal migration disorder, associated with impaired cognitive function and seizures, and characterized by a subcortical band of neurons. Using functional MRI, we assessed the involvement of the subcortical band in language function and with interictal discharges. In both girls assessed, language-associated activation was in typical cortical areas, as well as in parts of the subcortical band. Interictal discharges were associated with deactivation in the subcortical band. This suggests involvement of the subcortical neurons in physiologic and pathologic functions.

Adolescent↗
PubMed2001

[Clinical applications of functional magnetic resonance imaging].

Despite its immediate success as a tool for basic research, the clinical application of functional MRI(fMRI) is still limited. FMRI has proven useful for presurgical functional mapping of the eloquent cortices. Localization of the sensorimotor cortex by fMRI may be of relatively limited value because the sensorimotor cortex can often be readily localized by means of anatomical methods. In contrast, the language cortices may not be localized anatomically and the language dominant hemisphere has been determined by invasive Wada test. Previous reports have shown that fMRI can be a promising alternative to the Wada test. A recent clinical trial has suggested that fMRI can be used to diagnose Alzheimer's disease in its earliest stage, detecting subclinical deterioration of the memory function. FMRI may be useful to predict the future decline of memory in people with genetic risks. Monitoring of the functional recovery of post-stroke brains may be another promising clinical application of fMRI. FMRI has demonstrated functional reorganization of the brain that may be related to the restoration of motor and language functions.

Brain Diseases↗
PubMed2001

[New MRI techniques in multiple sclerosis].

Early imaging investigations in multiple sclerosis (MS) described focal signs. Technological progress now suggests this concept should be revisited as more diffuse anomalies of the central nervous system are described, sometimes involving regions that appear normal with conventional imaging techniques. This integrative concept results largely from the contribution of magnetic resonance imaging techniques recently broadened to in vivo investigations. Technical developments in MRI now provide new contrast images (magnetization transfer, diffusion, anisotropic diffusion, functional MRI using the BOLD method) as well as new variants of conventional sequences designed to demonstrate specific aspects of the MS lesions: FLAIR sequence (a T2-weighted sequence), black holes (a particular aspect on T1-weighted images), cord atrophy (quantification of the axial section of the cord on T1-weighted sequences). Together these new methods should improve diagnostic sensitivity (FLAIR) or provide prognosis information not provided by conventional sequences (T2 or T2 weighted images with or without gadolinium injection).

Brain↗
PubMed1996

[Functional imaging of the sensorimotor cortex using an ultra-fast MR imaging method].

UNLABELLED: The aim of this study was to assess changes in brain activity during a motor task and variable sensory stimulation using echo planar imaging, which represents the fastest clinically usefull imaging technique available. MATERIALS AND METHODS: The subjects of this study were 11 healthy-volunteers, 4 males and 11 females, with an average of 26.4 years. The subjects were instructed to tap the fingers of one hand as the motor task. Compressed air was applied 5 times a second as "simple" sensory stimulation. Simple figures were drawn on the subjects palm as "complex" sensory stimulation. In all cases, functional imaging was performed by T2*-weighted echo planar imaging (TE = 53 msec, TR = 3000 msec, flip angle = 90 degrees, matrix 64 x 64, FOV = 205 mm, slice thickness = 8 mm) alternately at rest and during the task (intervals: 30 sec). A total of 60 images was collected in 3 minutes. Images obtained by subtracting images at rest and during the task were analyzed. RESULTS AND DISCUSSION: Almost all subjects showed a transient signal increase in the contralateral paracentral region during simple sensory stimulation. Continuous signal increases in the contra- and/or ipsi-lateral para-central region were observed during complex sensory stimulation. Some exhibited signal increases in the parietal or frontal association cortex, but they disappeared when subject's attention was distracted during stimulation. All subjects displayed signal increases in the contralateral para-central region during the motor task. Some of them exhibited signal increases in the medial frontal area (supplementary motor area) and ipsilateral para-central region. These results suggest that the signal increases of functional MRI reflect not only simple reactions to stimulation but higher cerebral function as well.

Adult↗
PubMed2003

Retinotopic mapping in cat visual cortex using high-field functional magnetic resonance imaging.

In the field of neuroscience, there has always been a need for imaging techniques that provide high-resolution, large field-of-view measurements of neural activity. Functional MRI has this capability, but the link between the blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal and neural activity is indirect. High magnetic field strengths (>3 T) improve the strength and specificity of the BOLD signal, but there are additional concerns about imaging artifacts at high field. We have tested the capabilities of ultra high field fMRI in the anesthetized juvenile cat, demonstrating rapid, non-invasive retinotopic mapping of early visual areas. Maps of topographic organization and measured cortical magnification factors are in good agreement with electrophysiological studies. Measurement precision was estimated at 1 mm. This mapping, performed with an MRI scanner at ultra high field (9.4 T), demonstrates the capabilities of high-resolution functional mapping of the visual system at ultra high field.

Animals↗
PubMed2004

MRI compatible EEG electrode system for routine use in the epilepsy monitoring unit and intensive care unit.

OBJECTIVE: We report on the development of an electroencephalographic (EEG) recording system that is Magnetic Resonance Imaging (MRI) compatible and can safely be left on the scalp during anatomical imaging or used to obtain simultaneous EEG and metabolic or hemodynamic data using functional imaging techniques such as functional MRI or MR spectroscopy. METHODS: We assembled a versatile EEG recording set-up with medically acceptable materials that contained no ferromagnetic components. It was tested for absence of excess heating and distortion of the image quality in a spherical phantom similar in size to average adult human head in a clinical 1.5 T GE scanner. After testing its safety in four volunteers, 100 consecutive patients from our epilepsy long-term monitoring unit were studied. RESULTS: There was no change in the temperature of the EEG electrode discs during the various anatomical MRI sequences used in our routine clinical studies (maximum temperature change was -0.45 degrees C with average head SAR<==1.6 W/Kg in the selected subjects) nor were there any reported complications in the others. The brain images were not distorted by the susceptibility artifact of the EEG electrodes. CONCLUSIONS: Our MRI compatible EEG set-up allows safe and artifact free brain imaging in 1.5T MR scanner with average SAR<==1.6 W/Kg. This EEG system can be used for EEG recording during anatomical MRI studies as well as functional imaging studies in patients requiring continuous EEG recordings.

Artifacts↗
PubMed2000

Evidence for adaptive functional changes in the cerebral cortex with axonal injury from multiple sclerosis.

Axonal injury occurs even in the earliest stages of multiple sclerosis. Magnetic resonance spectroscopic imaging (MRSI) measurements of brain N:-acetylaspartate (NAA), a marker of axonal integrity, show that this axonal injury can occur even in the absence of clinically evident functional impairments. To test whether cortical adaptive responses contribute to the maintenance of normal motor function in patients with multiple sclerosis, we performed MRSI and functional MRI (fMRI) examinations of nine multiple sclerosis patients who had unimpaired hand function. We found that activation of the ipsilateral sensorimotor cortex with simple hand movements was increased by a mean of fivefold relative to normal controls (n = 8) and that the extent of this increase was strongly correlated (sigma = -0.93, P = 0.001) with decreases in brain NAA. These results suggest that compensatory cortical adaptive responses may help to account for the limited relationship between conventional MRI measures of lesion burden and clinical measures of disability, and that therapies directed towards promoting cortical reorganization in response to brain injury could enhance recovery from relapses of multiple sclerosis.

Aspartic Acid↗