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At least 1,639 records · Page 91Linked to original sources
PubMed2006

High-field diffusion tensor imaging of mouse brain in vivo using single-shot STEAM MRI.

Information about the microstructural organization of cerebral white matter that is accessible by magnetic resonance diffusion tensor imaging (DTI) gains increasing importance for studies of animal brain. Particular challenges occur for in vivo conditions as well as at high magnetic fields. Here, we have employed a diffusion-weighted (DW) single-shot STEAM MRI sequence for DTI of mouse brain in vivo at 7 T. The approach exploits the increased longitudinal magnetization and prolonged T1 relaxation times of water protons at higher magnetic field strengths without suffering from susceptibility-induced artifacts. When compared to studies at 2.35 T, half Fourier DW STEAM MRI at 7 T yielded a substantial gain in signal-to-noise ratio (SNR) that could be invested either in a reduction of the measurement time or an increase of the spatial resolution. Thus, for a measurement time of 3h, DTI with a voxel size of 117 microm x 117 microm x 720 microm not only resulted in high-quality maps of the fractional anisotropy and main diffusion direction (MDD), but also allowed for fiber tracking of major mouse brain structures in vivo.

Animals↗
PubMed2005

Magnetic resonance restricted diffusion resolution correlates with clinical improvement and response to treatment in herpes simplex encephalitis.

INTRODUCTION: A 34-year-old man presented with herpes simplex encephalitis (HSE), with magnetic resonance imaging (MRI) showing dense foci of restricted diffusion in the temporal lobe. CASE REPORT: With treatment and clinical improvement, follow-up MRI done 8 days later showed complete resolution of the restricted diffusion abnormalities, whereas other MRI sequences suggested interval progression. DISCUSSION: Restricted diffusion abnormalities on MRI in patients with HSE may be more sensitive to and correlate better with disease activity in HSE.

Adult↗
PubMed2002

Cerebral grey matter pathology and fatigue in patients with multiple sclerosis: a preliminary study.

In patients with multiple sclerosis (MS), we investigated whether the extent of cerebral grey matter (GM) pathology is associated with the presence and severity of fatigue. We quantified cerebral GM pathology in 28 MS patients (14 with fatigue and 14 without fatigue) using magnetization transfer (MT) and diffusion tensor (DT) magnetic resonance imaging (MRI). The average MT ratio and mean diffusivity from cerebral GM did not differ between fatigued and non-fatigued patients. Fatigued and non-fatigued patients also did not differ in terms of GM pathology of the cerebral cortex of the frontal lobe and basal ganglia. No correlations were found between the fatigue severity scale scores and any of the MT- and DT-MRI quantities. These preliminary results suggest that structural GM pathology is not a major contributing factor to the development of fatigue in patients with MS.

Adult↗
PubMedDate not supplied

Cardiac amyloidosis: typical imaging findings and diffuse myocardial damage demonstrated by delayed contrast-enhanced MRI.

Amyloidosis is a rare systemic disease. However, involvement of the heart is a common finding and is the most frequent cause of death in amyloidosis. We report the sonographic, scintigraphic, and MRI features of a pathologically proven case of cardiac amyloidosis. Delayed contrast-enhanced MR images, using an inversion recovery prepped gradient-echo sequence, revealed diffuse enhancement in the wall of both left and right ventricles. This enhancement suggested expansion of the extracellular space of the myocardium caused by diffuse myocardial necrosis secondary to deposition of amyloid.

Aged↗
PubMed2006

Time related changes in reversible MRI findings after prolonged hypoglycemia.

Diffusion weighted magnetic resonance images (DWI) in hypoglycemic coma show more definite and earlier findings than do T1-weighted images, or even fluid-attenuated inversion recovery (FLAIR). However, there has been limited information on the time related changes of such MRI images. We report here the time related changes of MRI findings after prolonged hypoglycemia in a diabetic 62-year-old man without hypoxia. We found in the patient that hyperintensities in DWI, T2-weighted and FLAIR images disappeared on the 14th day along with normalization of the apparent diffusion coefficient (ADC). Single photon emission computed tomography (SPECT) showed no low perfusion findings throughout the course. Since the day when the hyperintensities disappeared, the patient became to open his eyes in response to verbal command. This paper demonstrates serial alterations in reversible DWI findings after prolonged hypoglycemia and we need to define its mechanisms in the future.

Brain↗
PubMed2005

Simultaneous recording of task-induced changes in blood oxygenation, volume, and flow using diffuse optical imaging and arterial spin-labeling MRI.

Increased neural activity in brain tissue is accompanied by an array of supporting physiological processes, including increases in blood flow and the rates at which glucose and oxygen are consumed. These responses lead to secondary effects such as alterations in blood oxygenation and blood volume, and are ultimately the primary determinants of the amplitude and temporal signature of the blood oxygenation level-dependent (BOLD) signal used prevalently to map brain function. We have performed experiments using a combination of optical and MRI-based imaging methods to develop a more comprehensive picture of the physiological events accompanying activation of primary motor cortex during a finger apposition task. Temporal profiles for changes in tissue hemoglobin concentrations were qualitatively similar to those observed for MRI-based flow and oxygenation signals. Quantitative analysis of these signals revealed peak changes of +16 +/- 2% for HbO, -13 +/- 2% for HbR, +8 +/- 3% for total Hb, +83 +/- 9% for cerebral blood flow, and +1.4 +/- 0.1% for the BOLD MRI signal. A mass balance model was used to estimate the change in rate of oxidative metabolism implied by the optical and flow measurements, leading to a computed value of +47 +/- 5%. It should be noted that the optical and MRI observations may in general reflect changes over different volumes of tissue. The ratio of fractional changes in oxidative metabolism to fractional change in blood flow was found to be 0.56 +/- 0.08, in general agreement with previous studies of flow-metabolism coupling.

Arousal↗
PubMed2001

[Intracranial occlusion of the internal carotid artery after minor closed head injury].

Thrombosis of the extracranial portion of the internal carotid artery as a result of nonpenetrating head and neck injury is not uncommon. However, intracranial occlusion of the internal carotid artery after minor head and neck injury without skull fracture is rare. We report a case of 14-year-old male who suffered a minor head injury during an athletic meeting of his school and developed a right hemiparesis and a lethargy state resulting from thrombosis of the supraclinoid portion of the left internal carotid artery. On admission, skull films and a CT scan revealed no abnormality. One hour later, he fully recovered. One day later, no definite lesions were detected on T1-weighted and T2-weighted image of MRI, but an abnormal high signal lesion in the left frontal lobe was detected on diffusion-weighted image of MRI. On additional MR angiography, intracranial occlusion of the internal carotid artery due to dissection was demonstrated.

Adolescent↗
PubMedDate not supplied

[Reversible posterior leucoencephalopathy syndrome: a case report and review of its physiopathology based on neuroradiological findings].

INTRODUCTION: Reversible posterior leucoencephalopathy is a clinico radiological syndrome first described in the last decade. The physiopathological mechanism governing it is not very well known. The currently accepted hypotheses are the generation of a vasogenic edema caused by failure of the mechanism that allows self regulation of the cerebral blood flow, and the production of a cytotoxic edema due to ischemia. Both experimental studies carried out in rats and the use of magnetic resonance imaging (MRI) to evaluate the diffusion of cerebral water support the first hypothesis. We report the case of a patient with reversible posterior leucoencephalopathy syndrome that was complicated by areas of cerebral infarction and we review the physiopathological mechanisms involved, basing our analysis on the findings obtained with MRI. CASE REPORT: A female patient was admitted to our hospital because of bilateral transient amaurosis, headaches, vomiting and arterial hypertension. MRI brain scans showed bilateral cortico subcortical lesions in the occipital parietal regions, frontal and right cerebellar hemisphere convexity, with hyperintense signal in T2 and diffusion weighted imaging. Some occipital parietal regions present a diminished signal on the apparent diffusion coefficient map. The patient was treated with intravenous antihypertensive drugs and full recovery was accomplished within 10 days. A month later, according to MRI scans, there were still hyperintense areas in T2 on both occipital lobes, which were compatible with cerebral infarcts. DISCUSSION: The mechanism that is most frequently involved in this entity is probably vasogenic edema. In our case there were, at the same time, areas of cytotoxic edema that progressed to cerebral infarcts. MRI with sequences that evaluate the diffusion of cerebral water is useful in distinguishing between the two mechanisms.

Animals↗
PubMed2003

High field functional MRI.

Functional magnetic resonance imaging (fMRI) has become the most widely used approach for studying brain functions in humans. The rapid and widespread diffusion of fMRI has been favoured by the properties this technique presents, and particularly by its sensitivity in analysing brain functional phenomena and by the lack of biological invasiveness, resulting in an unprecedented and unparalleled flexibility of use. These properties of fMRI brought the functional examination of the brain within the reach of the whole neuroscience community and have appreciably stimulated the research on the functional processes of the living brain. Among the main features of fMRI, its spatial and temporal resolution represents clear advantages compared with the other methods of functional neuroimaging. In fact, the high spatial resolution of fMRI permits to produce more precise and better localised information, and its temporal resolution provides the potential of a better understanding of neural dynamics at the level of single functional areas and of the neural constituents of functional patterns. A fundamental possibility of improving spatial and temporal resolution without excessively degrading signal-to-noise ratio consists in the use of high magnetic field intensity fMRI units. Besides, high field units make the use of more demanding fMRI paradigms, like single trial event related studies, much more compatible with the need of a solid statistical evaluation. This has notably promoted the diffusion of high field MRI units for human studies throughout the world, with very high field MRI units, up to 8 T, working in a few research centres, and a larger number of MRI units with field intensity ranging between 3 and 5 T.

Brain↗
PubMed2001

Neuroimaging studies in Rett syndrome.

Neuroimaging is a key instrument for determining structural and in vivo functional status of the brain, non-invasively. Multiple approaches can now determine aspects of anatomic and neurochemical changes in brain, and have been utilized effectively in Rett Syndrome patients to understand the biological basis of this neurodevelopmental disorder. Studies performed at our institute include volumetric analyses of MRI, magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), cerebral blood flow measurements with MRI, and positron emission tomography scans (PET). These studies have provided considerable insight into mechanisms underlying the clinical features of this disease. Volumetric analyses suggest that decreased brain volume in RS results from global reductions in both gray and white matter of the brain. A selective vulnerability of the frontal lobes is evidenced by the preferential reduction of blood flow, increased choline and reduced n-acetyl aspartate (NAA) by MRS, and increased glucose uptake in these same regions as shown by ((18)F)-fluorodeoxyglucose (FDG) PET scans. We hypothesize that the increased glucose uptake relates to increased glutamate cycling in synapses. The resulting neuroexcitotoxic injury to the developing brain contributes to the seizures, behavioral disturbance and respiratory irregularities commonly seen in phases 1 and 2 of this disorder.

Adolescent↗
PubMed2004

Brain edema in neurooncology: radiological assessment and management.

Vasogenic brain edema is a common diagnostic and management problem in brain tumor patients. Molecular mechanisms play a role in the pathophysiology, including abnormalities of tumor endothelium, vascular endothelial growth factor and leukotriene synthase. Edema diagnosis is facilitated by the development of neuroradiological imaging techniques, with diffusion-weighted imaging (DW-MRI) differentiating tumor grades or abscesses and tumors, and diffusion tensor imaging representing an advanced technique to potentially differentiate malignant glioma from metastasis or facilitate preoperative planning. Edema is a prognostic factor for meningioma and metastases but not for glioma. Therapy includes, amongst others, tumor-directed measures such as debulking surgery, radio- and chemotherapy. However, local therapeutic approaches might also induce or exacerbate edema formation. Peritumoral edema can usually be managed with corticosteroids. However, patients on corticosteroids are at greater risk of metabolic changes, Pneumocystis carinii pneumonia, and thromboembolism. More recently, inhibitors of cyclooxygenase-2 as well as boswellic acids have been explored as antiedema agents in patients with brain tumors.

Brain Edema↗
PubMed2005

Magnetic resonance imaging advances in multiple sclerosis.

Magnetic resonance imaging (MRI) has become a core component of clinical management and scientific research in multiple sclerosis (MS), providing essential information about tissue structure and function. MRI is now the most important laboratory diagnostic and longitudinal monitoring technology. A number of conventional MRI techniques, which include T2-weighted, T1-weighted, and gadolinium-enhanced imaging, are used to identify overt lesions and quantify tissue atrophy. MRI is highly sensitive in detecting brain and spinal cord involvement in MS and can visualize multifocal lesions, occult disease, and macroscopic atrophy. Advanced MRI techniques, such as magnetization transfer imaging, spectroscopy, diffusion-weighted imaging, and functional MRI, have added to our understanding of the pathogenesis of the disease. The precise role of these newer imaging approaches continues to be defined. In this supplement to the Journal of Neuroimaging, the authors review the role of conventional and advanced MRI techniques in detecting tissue changes in MS, diagnosing and monitoring patients, and charting the progression of disease in new and established patients.

Atrophy↗
PubMed2003

Imaging-based decision making in thrombolytic therapy for ischemic stroke: present status.

BACKGROUND: Thrombolysis is the treatment of choice for acute stroke within 3 hours after symptom onset. Treatment beyond the 3-hour time window has not been shown to be effective in any single trial; however, meta-analyses suggest a somewhat lesser but still significant effect within 3 to 6 hours after stroke. It seems reasonable to apply improved selection criteria that allow differentiation between patients with and without a relevant indication for thrombolytic therapy. SUMMARY OF REVIEW: The present literature on imaging in stroke has been thoroughly reviewed, covering Doppler ultrasound (DU), arteriography, CT, and MRI and including modern techniques such as perfusion CT, diffusion- and perfusion-weighted MRI (DWI, PWI), CT angiography and MR angiography (CTA, MRA), and CTA source image analysis (CTA-SI). The authors present their view of a comprehensive diagnostic approach to acute stroke, which challenges the concept of a rigid therapeutic time window. CONCLUSIONS: Information about the presence or absence of a vessel occlusion, whether by means of DU, CTA, or MRA, is essential before recombinant tissue plasminogen activator is given in the 3- to 6-hour time window. Clear demarcation of the irreversibly damaged infarct core and the ischemic but still viable and thus salvageable tissue at risk of infarction as seen on DWI/PWI/MRA or alternatively CT/CTA/CTA-SI should be obtained before thrombolysis is initiated within 3 to 6 hours. Once these advanced techniques are used, the therapeutic time window can be extended with acceptable safety. However, comprehensive informed consent is mandatory, especially when thrombolytic therapy is considered beyond established time windows.

Angiography, Digital Subtraction↗
PubMed1995

Diffusion in Fe(II/III) radiation dosimetry gels measured by magnetic resonance imaging.

We analyse the diffusion problem in the traditional Fe(II/III) agarose gel system employed in MRI studies of radiation dosimetry. The diffusion coefficient is measured using an inversion recovery null-point imaging method in a model gel/water phantom. The diffusion coefficient of Fe(III) in 1% agarose gel at pH 1.1 is D = 2.7 +/- 0.3 x 10(-6) cm2 s-1. The diffusion coefficient of Fe(II) is D = 3.3 +/- 0.5 x 10(-6) cm2 s-1. Measurement of the diffusion coefficients permits simulation of the MRI signal intensity from phantoms with model radiation dose distributions. We allow for diffusion of both Fe(II) and Fe(III) in our simulations as well as the effect of both relaxation agents on the local spin-lattice relaxation time T1. We also analyse the effects of the physical penumbra on the diffusion problem.

Gels↗
PubMed2001

CT and MRI findings in gliomatosis cerebri: a neuroradiologic and neuropathologic review of diffuse infiltrating brain neoplasms.

The aim of the study was to develop objective criteria that might be helpful for the diagnosis of gliomatosis cerebri (GC) with the highest possible probability based on both the neuroradiological and histopathological findings. Imaging findings in 14 patients with diffuse infiltrating brain neoplasms were studied by two neuroradiologists. Computed tomography and MRI scans were compared with each other side by side. The extent and kind of disease were graded on a scale of 1-5. Interexamination agreement between the two methods was calculated using a kappa analysis. Neither of the neuroradiologists performed the examinations and both were blinded to the histopathological findings, which were also available for all patients, based on biopsy as well as follow-up CT and MRI studies. A neuroradiological-neuropathological correlation was performed. A score system helped to differentiate the findings in three categories: 1 = suggestive of GC; 2 = GC cannot be excluded; and 3 = others. Both CT and MRI were performed in 14 patients with clinical signs and symptoms of an intracerebral tumor. All examinations had diagnostic quality and showed the involvement of at least two brain lobes. Stereotactic biopsy was carried out in all patients. In 2 patients the neuropathological diagnosis was suggestive of GC, in 1 patient glioblastoma, in 2 patients astrocytoma, and in 5 patients nonspecific astrogliotic proliferation. In the remaining 4 cases anaplastic tumor infiltration was diagnosed. The neuroradiological findings in 5 cases were suggestive of GC; in 6 cases a GC could not excluded; and in 3 patients only a slight probability of GC was found. In 2 cases was the neuropathological and the neuroradiological diagnosis of GC concordant. Magnetic resonance imaging is significantly more sensitive than CT in the diagnosis of GC. However, even with multiple, MRI-guided stereotactic biopsies in correlation with intraoperative analysis of the sample by smear preparations by a neuropathologist the antemortem diagnosis of GC is still difficult. Discussion of neuropathological and neuroradiological findings in each case in combination with a score system may help to resolve discrepancies.

Adolescent↗
PubMed2005

White matter fiber tractography via anisotropic diffusion simulation in the human brain.

A novel approach to noninvasively tracing brain white matter fiber tracts is presented using diffusion tensor magnetic resonance imaging (DT-MRI). This technique is based on successive anisotropic diffusion simulations over the human brain, which are utilized to construct three dimensional diffusion fronts. The fiber pathways are determined by evaluating the distance and orientation from the fronts to their corresponding diffusion seeds. Synthetic and real DT-MRI data are employed to demonstrate the tracking scheme. It is shown that the synthetic tracts are accurately replicated, and several major white matter fiber pathways can be reproduced noninvasively, with the tract branching being allowed. Since simulating the diffusion process, which is truly a physical phenomenon reflecting the underlying architecture of cerebral tissues, makes full use of the diffusion tensor data, including both the magnitude and orientation information, the proposed approach is expected to enhance robustness and reliability in white matter fiber reconstruction.

Algorithms↗
PubMed1998

[Neuroradiologic diagnosis in acute arterial cerebral infarct. Current status of new methods].

At least three questions has to be answered by imaging methods, when new therapies in acute ischemic stroke should be used: 1. Is there a cerebral ischemia? 2. What is the size of the irreversible damaged tissue and what is the size of the safeable tissue? Is there still a vessel occlusion? New MRI-techniques including MR-angiography, diffusion-weighted imaging and perfusion-MRI, have the potential to describe the status of the brain in detail and to answer these questions. However, the value of these techniques for therapeutical decisions (thrombolysis) is unclear and has to be evaluated in clinical studies. Therefore in clinical routine these decisions should still be based on informations from CT and perhaps CT-angiography.

Brain↗
PubMed2004

Diffusion MR imaging for cerebral abscess.

We report a case of cerebral abscess, which ruptured into the lateral ventricle. The radiological features on conventional MRI, appearance on both diffusion weighted images (DWI) and apparent diffusion coefficient (ADC) maps are described.

Anti-Bacterial Agents↗