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Results for “Structural MRI”

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At least 145 records · Page 8Linked to original sources
PubMed2001

Unfolding the human hippocampus with high resolution structural and functional MRI.

The hippocampus is a region of the brain that is crucial to memory function. Functional neuroimaging allows for the noninvasive investigation of the neurophysiology of human memory by observing changes in blood flow in the brain. We have developed a technique that employs high-resolution functional magnetic resonance imaging (fMRI) in combination with cortical unfolding to provide activation maps of the hippocampal region that surpass in anatomic and functional detail other methods of in vivo human brain mapping of the medial temporal lobe. We explain the principles behind this method and illustrate its application to a novelty-encoding paradigm.

Brain Mapping↗
PubMed2001

Does the trabecular bone structure depicted by high-resolution MRI of the calcaneus reflect the true bone structure?

RATIONALE AND OBJECTIVES: The purpose of this study was to compare trabecular bone structure parameters assessed with high-resolution magnetic resonance imaging (HR-MRI) with those determined in specimen sections. METHODS: High-resolution MR images were obtained for 30 calcaneus specimens with a three-dimensional, T1-weighted spin-echo sequence (spatial in-plane resolution 0.195 mm, slice thicknesses of 0.3 and 0.9 mm). Thirty-eight sections were obtained from the specimens, and contact radiography was performed. In the corresponding sections, structural parameters analogous to bone histomorphometry were determined. RESULTS: Significant correlations between MRI-derived structural parameters and those derived from macro pathological sections were found: r values of up to 0.75 were obtained (P < 0.01). The highest correlations were found for apparent bone volume/total volume and trabecular thickness. Image thresholding techniques showed a significant impact on these correlations (P < 0.01). The thinner MR sections were less susceptible to the different thresholding algorithms. CONCLUSIONS: Trabecular bone structure depicted by HR-MR images is significantly correlated with that shown in macro sections (P < 0.01); however, a number of limitations have to be considered, including the substantial impact of thresholding techniques and slice thickness.

Aged↗
PubMed2001

Inner ear fluid volumes and the resolving power of magnetic resonance imaging: can it differentiate endolymphatic structures?

Magnetic resonance imaging (MRI) can accurately recognize minute volumes as small as 1 mm3. The volumes of the utricle and saccule of the inner ear are within the resolving power of MRI, but these structures cannot be recognized because the endolymph and perilymph signals are identical. To clarify the interpretation and description of inner ear structures on MRI, we measured and calculated the volumes of the perilymphatic and endolymphatic spaces of the human ear. We found the total volume of the bony labyrinth to be approximately 192.5 mm3 (endolymph, 34.0 mm3; perilymph, 158.5 mm3).

Ear, Inner↗
PubMed1999

Parkinson's disease: a novel MRI method for determining structural changes in the substantia nigra.

OBJECTIVES: To use MRI in a novel way to image and quantify the changes occurring in the substantia nigra in Parkinson's disease. METHODS: Six patients with idiopathic Parkinson's disease were compared with six age matched control subjects. The subjects were imaged using a combination of pulse sequences hypothesised to be sensitive to cell loss. RESULTS: The images showed patterns of change in patients with Parkinson's disease. Highly significant differences between the patients and control population were found (p<0.001). CONCLUSIONS: This methodology suggests the possibility of detecting presymptomatic disease in those judged to be at risk, and also in confirming the diagnosis in patients with early disease. Furthermore, the technique seems to hold promise as a means for staging the disease, and possibly differentiating other forms of parkinsonism.

Adult↗
PubMedDate not supplied

Anatomical MRI findings in mood and anxiety disorders.

OBJECTIVE: In vivo structural magnetic resonance imaging (MRI) studies have evaluated the brain anatomy of various psychiatric disorders, allowing the investigation of putative abnormal brain circuits possibly involved in the patophysiology of psychiatric disorders. Here we reviewed the structural MRI literature in mood and anxiety disorders. METHODS: All anatomical MRI studies evaluating mood and anxiety disorder patients were identified through a comprehensive Medline search conducted for the period from 1966 to January 2002, and a manual search of bibliographic cross-referencing complemented the Medline search. RESULTS: Differential patterns of anatomical brain abnormalities appear to be involved in subtypes of mood disorders, with hippocampus and basal ganglia being abnormal in unipolar disorder, and amygdala and cerebellum in bipolar disorders, suggesting that these two mood disorders are biologically distinct. As for anxiety disorders, orbital frontal regions and basal ganglia have been reported to be anatomically abnormal in obsessive-compulsive disorder, temporal lobe was found to be abnormally reduced in panic disorder, and abnormal hippocampus shrinkage was shown in posttraumatic stress disorder. CONCLUSIONS: The structural MRI findings reviewed here suggest abnormalities in specific brain regions participating in proposed neuroanatomic models possibly involved in the pathophysiology of mood disorders and anxiety disorders. Nonetheless, available MRI studies have suffered from limitations related to relatively small patient samples and involvement of medicated patients, and were largely cross-sectional investigations. Therefore, longitudinal MRI studies involving more sizeable samples of drug-free patients, patients at first episode of illness or at high risk for mood or anxiety disorders, associated to genetic studies, are likely to be extremely valuable to separate state from trait brain abnormalities and to characterize further the pathophysiology of these disorders.

Anxiety Disorders↗
PubMed2002

Serial MRI evaluation of cardiac structure and function in mice after reperfused myocardial infarction.

This study evaluated the utility of cardiac MRI for assessing the impact of myocardial infarction (MI) on cardiac structure and function in mice following reperfused 1- or 2-hr occlusions of the left anterior descending coronary artery (LAD). When assessed 1 day after MI, the left ventricular ejection fraction (LVEF) had declined by more than half, and remained depressed for the duration of the study. Furthermore, MI initiated dramatic increases in both LV end-systolic volume (LVESV) and end-diastolic volume (LVEDV), with a greater than threefold increase in LVESV and a twofold increase in LVEDV by 4 weeks post-MI. Transmural LV wall thickening (WTh) analysis revealed that noninfarcted myocardium in the remote septal region exhibited an early deficit in contractile function after MI that transiently resolved by day 7, only to be followed by a late phase of dysfunction that became fully manifest by day 28 post-MI. In conclusion, MRI allows the serial assessment of cardiac structure and function after MI in mice, with a resolution adequate to document both regional and temporal changes. The application of these imaging techniques in transgenic and knock-out mice will greatly expedite research aimed at defining the functional roles of individual genes in the pathophysiology of LV remodeling (LVR) after reperfused MI.

Animals↗
PubMed2000

Functional MRI in children with congenital structural abnormalities of the occipital cortex.

Functional MRI techniques were used to map the position of visual cortex in an awake and a sedated child with congenital anomalies of the posterior hemispheres. In one subject with cortical heterotopia, an activated cortex was found distinct from the structurally abnormal area detected on conventional MRI. In a sedated patient with holoprosencephaly, activated cortical areas in the posterior-medial portions of the hemispheres were identified. This study demonstrates the utility of functional MRI in such patients, both awake and sedated.

Adolescent↗
PubMed2003

In vivo identification of human cortical areas using high-resolution MRI: an approach to cerebral structure-function correlation.

Understanding the relationship between the structural and functional organization of the human brain is one of the most important goals of neuroscience. Individual variability in brain structure means that it is essential to obtain this information from the same subject. To date, this has been almost impossible. Even though noninvasive functional imaging techniques such as functional MRI (fMRI) are now commonplace, there is no complementary noninvasive structural technique. We present an in vivo method of examining the detailed neuroanatomy of any individual, which can then be correlated with that individual's own functional results. This method utilizes high-resolution structural MRI to identify distinct cortical regions based on cortical lamination structure. We demonstrate that the observed MR lamination patterns relate to myeloarchitecture through a correlation of histology with MRI. In vivo high-resolution MRI studies identify striate cortex, as well as visual area V5, in four individuals, as defined by using fMRI. The anatomical identification of a cortical area (V5MT) outside of striate cortex is a significant advance, proving it possible to identify extra-striate cortical areas and demonstrating that in vivo structural mapping of the human cerebral cortex is possible.

Brain↗
PubMed2002

Volumetric structural magnetic resonance imaging (MRI) of the rat hippocampus following kainic acid (KA) treatment.

An in vivo MRI study employing a high field (7T) magnet and a T1- and T2-weighted imaging sequence with subsequent histopathological evaluations was undertaken to develop and evaluate MRI-based volumetric measurements in the rat. The brain structures considered were the hippocampus, the cingulate cortex, the retrosplenial granular cortex and the ventricles. Control (n=3) and kainic acid (KA; n=4) treated rats were scanned 10 days following the manifestation of stage four seizures. The MRI images exhibited anatomical details (125 microm in-plane resolution) that enabled volumetric analysis with high intra-rater reliability. Volumetric analysis revealed that KA-treated rats had significantly smaller hippocampi, and a significant increase in ventricular size. The cingulate cortex and the retrosplenial granular cortex did not differ in volume between the two groups. The histological observations supported the MRI data showing neuronal loss and neuronal degeneration in CA1 and CA3 of the hippocampus, which was accompanied by strong microglia activation. These data demonstrate a reliable and valid method for the measurement of the rat hippocampus in vivo using MRI with a high field magnet, thereby providing a useful tool for future studies of rodent models of neuro-degenerative diseases.

Animals↗
PubMed1997

The relation between quantitative MRI measures of hippocampal structure and the intracarotid amobarbital test.

PURPOSE: The increasing sophistication of quantitative magnetic resonance imaging (MRI) techniques has generated hopes that they may eventually supersede the intracarotid amobarbital procedure (IAP) in the presurgical screening for bilateral abnormalities in prospective candidates for temporal lobe epilepsy surgery. As the first step toward this aim, the purpose of this study was to examine the relationship between these measures of structural and functional integrity. METHODS: We examined the relation between memory performance and pass/fail rates on the IAP and two MRI measures of hippocampal integrity: hippocampal volumes, adjusted for intracranial volume (HCvol) and hippocampal T2 relaxometry (HCT2), in 48 patients with medically intractable temporal lobe epilepsy, who underwent the IAP as part of their presurgical evaluation for temporal lobectomy. RESULTS: The unilateral memory scores from the IAP were not significantly correlated with the corresponding HCvol or HCT2 measures in the right- and left-temporal-lobe groups. However, the MRI measures of hippocampal asymmetry (right minus left HCvol, right minus left HCT2) were significantly correlated with our measure of functional asymmetry, the right minus left hemisphere memory score from the IAP, supporting the role of the IAP in lateralising temporal lobe dysfunction. Forty-six patients with unilateral hippocampal sclerosis and concordant EEG studies passed the IAP. Two patients failed the memory component of the IAP. In both cases, other presurgical investigations suggested bilateral abnormalities. CONCLUSIONS: We conclude that patients with unilateral hippocampal sclerosis, established by a rigorous quantitative MRI protocol, and concordant ictal and interictal EEG findings may not be at risk for postoperative amnesia, despite baseline neuropsychological deficits suggestive of bilateral disturbance.

Adult↗
PubMed2001

Separate and interactive effects of cocaine and alcohol dependence on brain structures and metabolites: quantitative MRI and proton MR spectroscopic imaging.

The effects of chronic cocaine and alcohol abuse on human brain structure and metabolites are not fully known. We studied controls (n = 13) and abstinent subjects dependent on cocaine (8), alcohol (12), and cocaine and alcohol (17) using quantitative MRI and proton MR spectroscopic imaging. Talairach-based techniques yielded tissue and CSF volumes and gray- and white-matter concentrations of N-acetylaspartate (NAA), creatine and choline metabolites in multiple brain regions. Alcohol dependents had lower gray-matter NAA concentrations and more sulcal CSF than non-alcohol dependents throughout the brain. They also had less subcortical gray matter and (regionally) less white matter. Cocaine dependents compared with non-cocaine dependents had higher posterior parietal white-matter creatine concentration. They also had less gray and white matter in the prefrontal lobes and in a region encompassing the temporal lobes and cerebellum. Structural white-matter deficits in cocaine dependents were greater with longer duration of cocaine use. Subjects with concurrent cocaine and alcohol dependence had less prefrontal white matter, especially in the anterior cingulate, than subjects dependent on only one substance. Chronically abused cocaine and alcohol each leave multiple metabolic and structural brain defects after long-term abstinence. Concurrent dependence on both substances may aggravate white-matter structural defects, primarily in frontal brain.

Journal Article↗
PubMed1994

Volumetric MRI assessment of temporal lobe structures in schizophrenia.

This magnetic resonance imaging (MRI) study was designed to investigate whether patients with schizophrenia have focal or lateralized deficits in the volumes of temporal lobe structures. Estimated volumes of the temporal lobes, hippocampi, superior temporal gyri, lateral ventricles, third ventricle, temporal horns of the lateral ventricles, and a frontal-parietal reference area (FPRA) were quantified for each hemisphere. The schizophrenic group had less gray matter (GM) in the temporal lobes and the FPRA relative to controls. Ventricular volumes were significantly larger in the schizophrenic group, as was cerebrospinal fluid (CSF) volume for temporal lobe sulci. No significant differences in hippocampal volumes emerged between groups. The magnitude of GM deficit was not greater in the temporal lobes relative to the FPRA. These results confirm the presence of bilateral GM volume deficits of the temporal lobes in schizophrenia but do not support the hypothesis that structural changes preferentially affect the temporal lobes or the left cerebral hemisphere.

Adult↗
PubMed1990

MRI findings in medial temporal lobe structures in schizophrenia.

In an MRI volumetric study of 10 young male schizophrenics (DSM-III-R 295.9x) a temporal lobe segment, corresponding hippocampal formation and parahippocampal gyrus were found smaller as compared with healthy controls while temporal horn was enlarged. Temporal lobe segment and parahippocampal gyrus were larger on the right in patients and controls, reversed asymmetry was found for the hippocampus.

Adult↗
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↗
PubMed1987

Nitroxides as potential contrast enhancing agents for MRI application: influence of structure on the rate of reduction by rat hepatocytes, whole liver homogenate, subcellular fractions, and ascorbate.

With an eye toward the development of nitroxides as potential contrast enhancing agents for MRI applications, we have compared the rates of reduction of 24 nitroxides of diverse structures by rat whole liver homogenate, hepatocytes, subcellular fractions, and ascorbate (10 eq excess). Our results indicate that five-membered ring nitroxides and alpha-carboxy alpha-aryl tert-butyl nitroxides are significantly more resistant toward bioreduction than six-membered ring and heterocyclic-substituted nitroxides in all systems. In the case of six-membered ring nitroxides the presence of either negatively charged or positively charged groups increases the susceptibility toward ascorbate reduction. The presence of carboxylate groups tends to enhance the resistance of all the nitroxides toward reduction by liver homogenate, hepatocytes, and subcellular fractions. trans-Azethoxyl nitroxides exhibited the best overall resistance toward bioreduction. The T1 relaxants of selected nitroxides were measured and found to be similar.

Animals↗
PubMed1997

Age dependence of the T2-weighted MRI signal in brain structures of a prosimian primate (Microcebus murinus).

Mouse lemurs (Microcebus murinus) are prosimian primates described to be convenient models of brain aging. We observed very high correlations between the T2-weighted magnetic resonance imaging (MRI) signal decrease and the natural logarithm of age in the basal ganglia. The correlation coefficient was higher for the pallidum (r = 0.95, P < 0.0001) than for other structures. We suggest that the ratio of the pallidum intensity divided by the amygdala and temporal lobe intensity should be a valuable non-invasive marker of age and of cerebral aging. It should be particularly useful for the non-invasive assessment of interventions and drugs that affect the aging process.

Aging↗