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At least 919 records · Page 51Linked to original sources
PubMed1998

Somatostatin receptor scintigraphy in postsurgical follow-up examinations of meningioma.

UNLABELLED: Surgery is the treatment of choice in patients with meningioma. However, the risk of postoperative, local recurrence is well-known since total resection is not always feasible. Moreover, in these patients MRI may fail to differentiate between tumor remnants, recurrent meningioma or nonspecific hyperperfusion. In this study, the value of functional imaging using somatostatin receptor scintigraphy (SRS) was evaluated in postsurgical follow-up. METHODS: Before and 2-3 mo after surgery, 27 patients with meningioma received MRI as well as SRS after intravenous injection of 200 MBq 111In-octreotide. Planar whole-body images were obtained at 10 min, 1, 4 and 24 hr postinjection, and SPECT was performed at 4 and 24 hr postinjection. The final diagnosis was proven histologically in all patients. RESULTS: Before surgery, MRI showed focal contrast enhancement in all patients, and SRS revealed focal accumulation of 111In-octreotide. Thus, MRI and SRS yielded comparable results in all 27 patients. After surgery, MRI showed diffuse contrast enhancement in the area of the primary tumor site in all patients. Thus, MRI did not allow a differentiation between tumor and nonspecific hyperperfusion. In contrast, SRS revealed focal accumulation of 111In-octreotide in 16 of 27 patients indicating remaining tumor tissue or relapse of meningioma. This resulted either in an operative revision or in more frequent postsurgical follow-up examinations. In 11 of 27 patients, SRS was negative. Thus, total resection of meningioma was assumed, and no further interventions were performed. CONCLUSION: Functional imaging using SRS is a highly specific imaging modality and has a significant impact in postsurgical follow-up in patients with meningioma.

Female↗
PubMed2002

Monitoring cytotoxic tumour treatment response by diffusion magnetic resonance imaging and proton spectroscopy.

Exposure of tumours to anti-cancer drugs, gene or radiation therapy consistently leads to an increase in water diffusion in the cases expressing favourable treatment response. The diffusion change coincides cytotoxic cell eradication and precedes volume reduction in drug or gene therapy-treated experimental tumours. Interestingly, the recent studies from human brain tumour patients undergoing chemotherapy show similar behaviour of diffusion, suggesting important application for MRI in patient management. In this review observations from diffusion MRI and MRS in the tumours during cytotoxic treatment are summarized and the cellular mechanisms affecting molecular mobility are discussed in the light of tissue microenvironmental and microdynamic changes.

Animals↗
PubMed1999

Rapid monitoring of diffusion, DC potential, and blood oxygenation changes during global ischemia. Effects of hypoglycemia, hyperglycemia, and TTX.

BACKGROUND AND PURPOSE: The increasing interest in diffusion-weighted MRI (MRI) for diagnosis and monitoring of acute stroke in humans calls for a sound understanding of the underlying mechanisms of this image contrast in acute cerebral ischemia. The present study aimed to show that a rapid decrease in brain-water apparent diffusion coefficient (ADC) occurs coincident with anoxic depolarization and that this change is delayed by hyperglycemia and sodium channel blockade but accelerated by hypoglycemia. METHODS: Rats were divided into groups: normoglycemic, hypoglycemic, and hyperglycemic, and those given local tetrodotoxin (TTX) application. Cardiac arrest was effected by intravenous KCl injection during serial high-speed diffusion and blood oxygenation-sensitive gradient-recalled echo MRI. Brain DC potential was recorded simultaneously. Serial ADC maps were calculated from the diffusion-weighted data and fitted to a model function to measure the delay between cardiac arrest and rapid ADC decrease. RESULTS: The time of anoxic depolarization indicated by DC change agreed well with the rapid drop in ADC in all groups; both were accelerated with hypoglycemia and delayed by hyperglycemia. A more gradual ADC decline occurred before anoxic depolarization, which was more pronounced in hyperglycemic animals and less pronounced in hypoglycemic animals. Rapid drop in ADC was also delayed by local TTX application. Changes in gradient-recalled echo image intensity were not significantly different among groups. CONCLUSIONS: While much of the ADC decrease in ischemia occurs during anoxic depolarization, significant but gradual ADC changes occur earlier that may not be due to a massive loss in ion homeostasis.

Animals↗
PubMed2001

Cerebral abscesses: investigation using apparent diffusion coefficient maps.

The combination of high signal and reduced apparent diffusion coefficients (ADC) within abscesses on diffusion-weighted MRI (DWI) has been reported as characteristic of abscesses, and useful for distinguishing them from cystic or necrotic neoplasms. To assess whether these are consistent findings in abscesses, we used DWI-derived ADC to investigate changes in water diffusibility in cerebral abscesses. We reviewed the MRI studies and clinical records of five patients with brain abscesses, who underwent DWI. Regions of interest were drawn within the abscesses on ADC maps, to obtain the ADC. The center of all five abscesses gave signal higher than that of white matter on DWI. The three largest also appeared bright on ADC maps, i. e., showed ADC substantially lower than those of normal white matter, consistent with restricted diffusion. However, the two smaller abscesses were not visible on ADC maps because their ADC were essentially the same as that of white matter; they did not show restricted diffusion. The absence of restricted diffusion within small abscesses may be related to intrinsic differences in molecular microenvironment between small and large abscesses, or to greater influence of volume averaging with surrounding edema on the ADC in smaller abscesses.

Brain Abscess↗
PubMed2006

ApoE polymorphism and acute stroke: a study with diffusion- and perfusion-weighted MRI and MR angiography.

OBJECTIVES: We examined whether the apolipoprotein E (ApoE) allele epsilon4 influences imaging findings in stroke as assessed by diffusion- (DWI) and perfusion-weighted (PWI) magnetic resonance imaging, and MR angiography (MRA). METHODS: Eight ApoE epsilon4 carriers and 15 non-carriers with acute ischemic stroke in the anterior circulation underwent DWI, PWI, and MRA within 24 h of stroke. DWI and PWI were repeated a week later. The apparent diffusion coefficient, relative cerebral volume (rCBV), relative cerebral blood flow (rCBF) and relative mean transit time were measured in three subregions on day one. RESULTS: In the ischemic core and the area of infarct growth, rCBV values were significantly higher in the epsilon4 carriers compared with the non-carriers. Based on the MRA findings, collateral blood flow was better in the epsilon4 carriers than in the non-carriers. Under the comparable severity of hypoperfusion, the hypoperfused area proceeded to infarction later or did not proceed to infarction at all in the non-carriers. CONCLUSION: These preliminary data suggest that in the ApoE allele epsilon4 carriers the threshold for the brain tissue to survive hypoperfusion versus to proceed to infarction seems to be different from that of the non-carriers.

Acute Disease↗
PubMed2000

Diffusion- and perfusion-weighted MRI patterns in borderzone infarcts.

BACKGROUND AND PURPOSE: The pathophysiology of borderzone infarcts is not well understood. We investigated whether combined diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) could identify pathophysiologically meaningful categories of borderzone infarcts. METHODS: Seventeen patients with borderzone infarcts were identified from the Beth Israel Deaconess Medical Center Stroke Database. All patients had DWI and PWI, the majority of them within the first 24 hours of symptom onset. RESULTS: Three patterns of perfusion abnormalities were associated with the diffusion lesions: 1, normal perfusion (5 patients); 2, localized perfusion deficits matching the area of restricted diffusion (5 patients); and 3, extensive perfusion deficits involving 1 or more vascular territories (7 patients). All but 1 patient with pattern 1 had transient peri-infarct hypotension as the presumed stroke mechanism. Two patients with pattern 2 had cardiac or aortic embolic sources; none had large-artery disease or arterial hypotension. Reperfusion was detected in all patients with this pattern who submitted to a follow-up study. All patients with pattern 3 had severe stenosis or occlusion of a large artery: the internal carotid, anterior cerebral, or middle cerebral. CONCLUSIONS: We postulate that the perfusion abnormality varies according to the mechanism of the borderzone infarction. Transient perfusion deficits occurring with hypotension in the absence of significant large-artery disease may not be revealed by PWI. Embolism may cause some cases of small borderzone perfusion deficits. Critical large-artery disease may cause large territorial perfusion deficits and predispose to borderzone infarction.

Aged↗
PubMed2006

Combined diffuse optical tomography (DOT) and MRI system for cancer imaging in small animals.

Recently, there has been a great amount of interest in developing multi-modality imaging techniques for oncologic research and clinical studies with the aim of obtaining complementary information and, thus, improving the detection and characterization of tumors. In this present work, the details of a combined MR-diffuse optical imaging system for dual-modality imaging of small animals are given. As a part of this effort, a multi-spectral frequency domain diffuse optical tomography system is integrated with an MRI system. Here, a network analyzer provides the rf modulation signal for the laser diodes and measures the amplitude and the phase of the detected signals. Photomultiplier tubes are utilized to measure low-level signals. The integration of this optical imaging system with the 4T MRI system is realized by incorporating a fiber adaptive interface inside the MR magnet. Coregistration is achieved by a special probe design utilizing fiducial markers. A finite element algorithm is used to solve the diffusion equation and an inverse solver based on this forward solver is implemented to calculate the absorption and scattering maps from the acquired data. The MR a priori information is used to guide the optical reconstruction algorithm. Phantom studies show that the absorption coefficient of a 7 mm inclusion in an irregular object located in 64 mm phantom is recovered with 11% error when MR a priori information is used. ENU induced tumor model is used to test the performance of the system in vivo.

Algorithms↗
PubMed2005

How does DWI correlate with white matter structures?

Diffusion-weighted MRI (DWI) is widely used to characterize brain white matter (WM), particularly through the use of diffusion tensor imaging (DTI). In this study the spatial characteristics of DWI in WM of cat visual cortex were investigated at 9.4T at very high resolution. It is shown that the spatial extent of the WM tract as measured from the DWI images depends highly on the b-value. In particular, when the diffusion gradient is applied perpendicular to the main direction of the fiber tract, the estimated thickness of the tract at the commonly used b-value of 1000 s/mm2 exceeds by 50% the thickness as it appears on a T2-weighted image. Only at b-values greater than 6000 s/mm2 does the thickness of the tract approach the thickness characterized by the T2-weighted image and that observed on histological slices of the same area. Further analysis of these results indicates that the choice of b-value of 1000 s/mm2 may not be optimal for the demarcation of anisotropic WM structures. DWI at high b-value may contain spatial information that is more specific to WM tracts.

Animals↗
PubMed2004

Reversal of restricted diffusion in cerebral venous thrombosis: case report.

We report a patient with extensive cerebral venous thrombosis who showed complete reversal of restricted diffusion on MRI, accompanied by excellent clinical recovery. The implications of these findings in relation to interpretation of diffusion changes in cerebral venous thrombosis are discussed, and differences with arterial stroke are highlighted.

Adult↗
PubMed1990

Comparative neuroimaging with pathologic correlates in Alexander's disease.

We describe a case of pathologically confirmed Alexander's disease in which serial cranial ultrasound studies demonstrated unique findings of enlarging subependymal cysts with evolving periventricular hyperechogenicity. Computed tomographic scan of the head showed low attenuation of the periventricular white matter and centrum semiovale. Magnetic resonance imaging (MRI) demonstrated diffuse, confluent high signal predominantly in frontal white matter. These imaging modalities, particularly cranial ultrasound and MRI, may be useful tools in the diagnostic evaluation of children with degenerative neurologic disease, megalencephaly, and suspected Alexander's disease.

Brain↗
PubMed2002

Diffuse magnetic resonance imaging white-matter changes in a 15-year-old boy with mitochondrial encephalomyopathy.

We report a 15-year-old boy who presented with recurrent headaches associated with numbness, confusion, and speech difficulty. Brain magnetic resonance imaging (MRI) revealed diffuse bilateral white-matter hyperintensity on fluid-attenuated inversion-recovery and T2-weighted images in the internal capsule, periventricular and subcortical white matter, base of the pons, and middle cerebellar peduncles. Lesions were isointense on T1-weighted images and nonenhancing. Muscle biopsy showed changes consistent with a mitochondrial myopathy. Mitochondrial respiratory chain enzyme activity analysis revealed a significant reduction in complex II activity. Genetic testing was negative. We conclude that mitochondrial encephalomyopathy may present with unusual diffuse supratentorial and infratentorial white-matter changes on MRI.

Adolescent↗
PubMed1998

Diffusion-weighted magnetic resonance imaging in acute stroke.

BACKGROUND AND PURPOSE: Diffusion-weighted MRI (DWI) is highly sensitive in detecting early cerebral ischemic changes in acute stroke patients. In this study we compared the sensitivity of DWI with that of conventional MRI techniques. Furthermore, we investigated the prognostic value of the volume of ischemic lesions on DWI scans and of the apparent diffusion coefficient (ADC). METHODS: We performed DWI, fluid-attenuated inversion recovery, spin-echo T2-weighted MRI, and spin-echo proton density-weighted MRI in 42 patients with acute stroke and 15 control subjects. The volume of ischemic lesions was measured on early (<60 hours after onset) and follow-up MRI scans. Clinical outcome was measured 4 months after onset of symptoms with the National Institutes of Health Stroke Scale, the Barthel Index, and the Rankin Scale. RESULTS: With DWI, 98% of the ischemic lesions were detected, and with fluid-attenuated inversion recovery, 91% were detected, whereas with early T2-weighted or proton density-weighted scans, only 71% (P=0.002, chi2) and 80% (P=0.02, chi2) of lesions, respectively, were found. Lesion volume on early DWI scans correlated significantly with clinical outcome ratings (P<0.01). In patients with a first-ever stroke, a lesion volume of < or =22 mL on DWI predicted good outcome with a 75% sensitivity and a 100% specificity. The mean ADC of ischemic lesions was 29% lower than the ADC of normal-appearing parts of the brain (P<0.001). The ADC ratio correlated significantly with clinical outcome (P<0.05). CONCLUSIONS: DWI is a better imaging method than conventional MRI in detecting early ischemic lesions in stroke patients. Lesion size as measured on DWI scans and, to a lesser extent, ADC values are potential parameters for predicting clinical outcome in acute stroke patients.

Acute Disease↗
PubMed1999

MRI abnormalities associated with partial status epilepticus.

OBJECTIVE: To report neuroimaging findings in patients with complex partial status epilepticus. BACKGROUND: During status epilepticus, neuroimaging may be used to exclude other neurologic conditions. Therefore, it is important to identify the neuroimaging features that are associated with status epilepticus. In addition, MRI characteristics may provide insight into the pathophysiologic changes during status epilepticus. METHODS: The history and neuroimaging examination results of three patients with complex partial status epilepticus were reviewed. Studies obtained during status epilepticus included diffusion-weighted MRI (DWI), MR angiography (MRA), postcontrast T1-weighted MRI, T2-weighted MRI, and CT. Follow-up MRI was obtained in two patients, and autopsy results were available for the third. RESULTS: Some of the MRI and CT findings during partial status epilepticus mimicked those of acute ischemic stroke: DWI and T2-weighted MRI showed cortical hyperintensity with a corresponding low apparent diffusion coefficient, and CT showed an area of decreased attenuation with effacement of sulci and loss of gray-white differentiation. However, the lesions did not respect vascular territories, there was increased signal of the ipsilateral middle cerebral artery on MRA, and leptomeningeal enhancement appeared on postcontrast MRI. On follow-up imaging, the abnormalities had resolved, but some cerebral atrophy was present. CONCLUSIONS: The radiologic characteristics of status epilepticus resemble those of ischemic stroke but can be differentiated based on lesion location and findings on MRA and postcontrast MRI. The MRI abnormalities indicated the presence of cytotoxic and vasogenic edema, hyperperfusion of the epileptic region, and alteration of the leptomeningeal blood-brain barrier. These changes reversed, but they resulted in some regional brain atrophy.

Adult↗
PubMed2004

ADC mapping of the aging frontal lobes in mild cognitive impairment.

Normal aging, leukoaraiosis (LA) and vascular disease particularly involve the human frontal lobes. We decided to investigate a population of elderly patients referred for neuroimaging because of progressive minor cognitive deficits but no dementia. They underwent conventional Magnetic resonance imaging (MRI) using axial T1 and T2-weighted imaging as well as coronal FLAIR sequences in addition to the axial diffusion-weighted MRI. MRI allowed us to differentiate patients with leukoaraïosis (LA+) from those without it (LA-) and mapping of the apparent diffusion coefficient (ADC) to investigate local tissular water motion. We observed an increase in the ADC in all investigated patients with increasing age (r=0.326, p=0.002). This increase was observed in both patients groups (LA+ and LA-). In addition, the LA+ group had significant higher ADC values than the LA- group after controlling for age (p<0.0001).

Adult↗
PubMed1995

New magnetic resonance techniques for acute ischemic stroke.

Neuroimaging was revolutionized by the development of computed tomography (CT) and standard T1- and T2-weighted magnetic resonance imaging (MRI). Magnetic resonance imaging and CT can adequately distinguish hemorrhage from infarction and depict ischemic stroke 12 to 24 hours after onset. However, during the critical initial hours after the onset of ischemic stroke, these imaging technologies do not adequately demonstrate the location and extent of infarction. Diffusion-weighted MRI and perfusion imaging, as well as advances in magnetic resonance spectroscopy, will enhance our ability to evaluate ischemic stroke shortly after onset. Some of the uses of MRI techniques are as follows: (1) Diffusion-weighted imaging can depict the location and extent of the ischemic lesion as soon as a stroke patient is available for examination. (2) Perfusion imaging evaluates blood flow within the brain's microvasculature and can reveal regions of perfusion deficits corresponding to major vascular territories. (3) Magnetic resonance spectroscopy evaluates metabolic abnormalities associated with focal brain ischemia by specific biochemical measurements. These MRI techniques will rapidly provide important information to clinicians about ischemia, guiding diagnosis and helping in the development of acute stroke interventions to improve outcome.

Brain Ischemia↗
PubMed2003

Cytotoxic edema is independent of NMDA ion channel activation following middle cerebral artery occlusion (MCAO). An in vivo autoradiographic and MRI study.

Massive glutamate release is an important factor leading to ionic imbalance after occlusive stroke, which in turn contributes to cytotoxic edema formation. Currently, measurements of cytotoxic edema using 'diffusion weighted' MRI, is being used in human stroke studies, as a 'surrogate' end point for neuroprotective drug trials, including studies with glutamate antagonists. However, it is not fully understood to what extent glutamate-mediated N-methyl-D-aspartate (NMDA) receptor activation is related to 'cytotoxic' edema formation, and thus, to what degree apparent diffusion coefficient (ADC) changes, assessed by magnetic resonance imaging with 'ACD mapping', represent NMDA receptor activation. To study this relationship, four cats underwent permanent middle cerebral artery occlusion (MCAO). Edema formation was investigated using MRI with 'ACD mapping', while NMDA receptor activation was simultaneously detected in the same animals, using radio labeled 125IodoMK-801, which binds only in activated and open NMDA channels. At 5 h post-occlusion, a large area of edema could be found with significantly lower ADC values in the core and penumbral area of the ischemic lesion when compared to contralateral values. On corresponding sections of the feline brains, increased 125I-MK-801 binding was found in the infarct penumbra. However, there was no significant topographical correlation between ADC values and measured radioactivity. The results indicate that there is not a significant linkage between NMDA receptor activation and 'cytotoxic' edema following permanent MCAO. The detection of a large area of NMDA channel activation within regions of low ADC does however indicate an area of 'penumbral' ischemia susceptible to treatment with NMDA channel blockers.

Animals↗
PubMed2002

[A case suspected of acute gas poisoning by carbon monoxide (CO), presenting with progressive diffuse leukoencephalopathy associated with marked brain edema].

A 51-year-old man was found comatose in a decerebrate posture in a cottage. Brain MRI showed diffuse high-signal-intensity areas in the white matter on T 2-weighted and FLAIR images, and diffusion-weighted images showed marked diffuse high intensity areas in the white matter. Initially inflammatory demyelinating diseases were suspected and methylprednisolone pulse therapy was administered. However, no improvement was noted. On close inspection of the cottage, a gas generator was discovered in the poorly ventilated room. He was therefore suspected to have suffered from gas intoxication, including carbon monoxide (CO). Hyperbaric oxygen therapy was administered, but without any improvement. The diffuse white matter lesions and brain edema progressed with time and the patient died of cerebral herniation. Autopsy revealed no inflammatory processes. Most cases with CO intoxication show hyperintense lesions in the globus pallidus on both sides in T 2-weighted images, and some cases show lesions only in the white matter without any involvement of the globus pallidus. The progressive clinical course, diffuse leukoencephalopathy and brain edema may be due to apoptosis of oligodendrocytes. CO intoxication is thus important in the differential diagnosis of diffuse white matter lesions of the cerebrum.

Brain↗