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PubMed2006

Diffusion-weighted magnetic resonance imaging in carotid angioplasty and stenting with balloon embolic protection devices.

We compared the results of two procedures to protect against distal embolism caused by embolic debris from carotid angioplasty with stent deployment (CAS) using diffusion-weighted magnetic resonance imaging (MRI). The study group comprised 39 men and 3 women (42 and 3 CAS procedures, respectively) with severe carotid stenosis (average age 70.0 +/- 6.6 years). During 20 CAS procedures the internal carotid artery was protected with a single balloon. A PercuSurge GuardWire was used for temporary occlusion. During 25 CAS procedures the internal and external carotid arteries were simultaneously temporarily occluded with a PercuSurge GuardWire and a Sentry balloon catheter, respectively. Diffusion-weighted MRI was performed 1 to 3 days after CAS. Data from 26 patients undergoing conventional angiography for diagnosis of cerebral ischemic disease, cerebral aneurysm or brain tumors were included as controls. Diffusion-weighted MRI after conventional diagnostic angiography showed ischemic spots in 3 of the 26 controls (11.5%). Ischemic spots were observed during 11 of 20 CAS procedures with the internal carotid artery protected with a single balloon (55.0%), and were observed during 9 of 25 CAS procedures with both the internal and external carotid arteries protected (36.0%). This difference was significant (P = 0.0068). Ischemic lesions appeared not only ipsilateral to the carotid stenosis but also in the contralateral carotid artery (31.9%) and vertebrobasilar territory (25.3%). Better protection was obtained with simultaneous double occlusion of both the internal and external carotid artery than with single protection of the internal carotid artery during CAS.

Aged↗
PubMed2006

Surgical treatment of paraventricular cavernous angioma: fibre tracking for visualizing the corticospinal tract and determining surgical approach.

Surgical treatment of deep-seated lesions involving the corticospinal tract is one of the most challenging areas of contemporary neurosurgery, even given the recent development of radiological methods including three-dimensional anisotropy contrast magnetic resonance imaging (MRI) axonography. Fibre tracking using diffusion tensor imaging is another MRI technique that can be used to visualize anisotropy and the orientation of white matter tracts in the brain. We report herein a patient with a paraventricular cavernous angioma manifesting as hemiparesis caused by haemorrhage. Preoperative conventional MRI failed to determine the anatomical relationship between the paraventricular lesion and the corticospinal tract, whereas fibre tracking using free software (dTV for MR-DTI analysis) indicated that the corticospinal tract was displaced anterolaterally from the medial side. The paraventricular lesion was completely removed without damaging the corticospinal tract using a transcortical transventricular approach. Preoperative fibre tracking is useful in surgical planning for procedures involving deep-seated lesions adjacent to the corticospinal tract, and may avoid postoperative morbidity due to corticospinal tract injury.

Adult↗
PubMed2003

[Useful MRI findings for diagnosis of postspinal headache: a case report].

A 49-year-old man developed severe headache after spinal anesthesia. We found diffuse meningeal enhancement on gadolinium enhanced MRI and diffuse meningeal thickening on plain MRI. These MRI findings and postural headache suggest intracranial hypotension. Injection of autologous blood 10 ml into his epidural space was effective to ameliorate the headache. MRI findings were useful for the diagnosis of postspinal headache.

Anesthesia, Spinal↗
PubMed1997

Blood-brain barrier disturbances after rt-PA treatment of thromboembolic stroke in the rat.

We studied the effects of rt-PA (recombinant tissue type-plasminogen activator) treatment on the blood-brain barrier (BBB) after thromboembolic stroke in rat. New MRI methods of diffusion and perfusion imaging to observe the hemodynamic and biophysical effects of thrombolysis were combined with methods for assessment of BBB disturbances. In untreated animals clot embolism produced a rapid drop in MRI perfusion values and the ADC (apparent diffusion coefficient), with subsequent infarction. BBB disturbances, visualised as extravasation of serum proteins on cryostat sections, were manifest in nearly all animals in the borderzone of infarcts. In animals treated with rt-PA 15 min after clot embolism thrombolysis resulted in reperfusion of affected brain regions with subsequent improvement of ADC values. Final lesion size on ADC maps was reduced by 36% relative to untreated animals. However, BBB disturbances were not improved after treatment. To the contrary, rt-PA treated animals showed further regions with serum protein extravasation in the infarcted territories and in distant non-ischemic brain regions. MR imaging with the BBB tracer GdDTPA showed more pronounced and widespread contrast enhancement in the rt-PA treated than in the untreated group. Increased blood-brain barrier disturbances have to be taken into account even when thrombolytic therapy is started very early after the onset of stroke.

Animals↗
PubMed1993

Neuroradiologic evaluation of pediatric craniocerebral trauma.

Although cranial computed tomography (CT) remains the initial diagnostic test in the evaluation and triage of the pediatric head-injury patient, magnetic resonance imagining (MRI) has become the next step in the diagnostic evaluation of those with focal or diffuse neurologic deficits. MRI is better able to demonstrate the extent and location of both hemorrhagic and nonhemorrhagic injury, thereby providing prognostic information. In nonaccidental head injury, MRI has proved valuable in detecting subtle subacute contusions and even not so subtle chronic subdural hematomas that may be difficult to see on CT or that can mimic enlargement of the subarachnoid space on CT.

Brain Injuries↗
PubMed2005

Fast detection of diffuse axonal damage in severe traumatic brain injury: comparison of gradient-recalled echo and turbo proton echo-planar spectroscopic imaging MRI sequences.

BACKGROUND AND PURPOSE: Diffuse axonal injury (DAI) is a common type of primary neuronal injury in patients with severe traumatic brain injury (TBI), and is frequently accompanied by tissue tear hemorrhage. T2-weighted gradient-recalled echo (GRE) sequences are more sensitive than T2-weighted spin-echo images for detection of hemorrhage. The purpose of this study is to compare turbo Proton Echo Planar Spectroscopic Imaging (t-PEPSI), an extremely fast sequence, with GRE sequence in the detection of DAI. METHODS: Twenty-one patients (mean age 26.8 years) with severe TBI occurred at least 3 months earlier, underwent a brain MR Imaging study on a 1.5-T scanner. A qualitative evaluation of the t-PEPSI sequences was performed by identifying the optimal echo time and in-plane resolution. The number and size of DAI lesions, as well as the signal intensity contrast ratio (SI CR), were computed for each set of GRE and t-PEPSI images, and divided according to their anatomic location as lobar and/or deep brain. RESULTS: There was no significant difference between GRE and t-PEPSI sequences in the detection of the total number of DAI lesions (291 vs. 230, respectively). GRE sequence delineated a higher number of DAI in the temporal lobe compared to the t-PEPSI sequence (74 vs. 37, P < .004), while no differences were found for the other regions. The SI CR was significantly lower with the t-PEPSI than the GRE sequence (P < .00001). CONCLUSION: Owing to its very short scan time and high sensitivity to the hemorrhage foci, the t-PEPSI sequence may be used as an alternative to the GRE to assess brain DAI in severe TBI patients, especially if uncooperative and medically unstable.

Adolescent↗
PubMed2006

Controlling diffusion of 3He by buffer gases: a structural contrast agent in lung MRI.

PURPOSE: To study the influence of admixing inert buffer gases to laser-polarized (3)He in terms of resulting diffusion coefficients and the consequences for image contrast and resolution. MATERIALS AND METHODS: The diffusion coefficient of (3)He was altered by admixing buffer gases of various molecular weights ((4)He, N(2), and SF(6)). The influence of the pulse sequence and the diffusion coefficient on the appearance of MRI of (laser-polarized) gases was analyzed by comparison of basic theoretical concepts with demonstrative experiments. RESULTS: Excellent agreement between theoretical description and observed signal in simple gradient echoes was observed. A maximum signal gain can be predicted and was experimentally validated. Images acquired under such conditions revealed improved resolution. The nature and concentration of the admixed gas defines a structural threshold for the observed apparent diffusion coefficient (ADC) as demonstrated with diffusion-weighted MRI on a pig's lung flooded with suitable gas mixtures. CONCLUSION: A novel procedure is proposed to control the diffusion coefficient of gases in MRI by admixture of inert buffer gases. Their molecular mass and concentration enter as additional parameters into the equations that describe structural contrast. This allows for setting a structural threshold up to which structures contribute to the image. For MRI of the lung this enables images of very small structural elements (alveoli) only, or in the other extreme, all airways can be displayed with minimal signal loss due to diffusion.

Contrast Media↗
PubMed2002

Monitoring disease progression in CADASIL with diffusion magnetic resonance imaging: a study with whole brain histogram analysis.

BACKGROUND AND PURPOSE: In cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a large increase in water diffusion has been found both inside and outside the cerebral lesions as detected on conventional MRI. The aim of the present study was to assess the sensitivity of diffusion tensor imaging for monitoring the progression of cerebral tissue damage during the course of CADASIL. METHODS: With the use of diffusion tensor imaging, whole brain trace of the diffusion tensor [Trace(D)] histograms were obtained in 22 CADASIL patients and 12 age-matched controls at baseline, in 14 patients after a mean delay of 21 months, and in 5 controls after a mean delay of 29 months. Parameters derived from these histograms (mean value, peak height, and peak location) were analyzed at baseline and during the follow-up. RESULTS: At baseline, all the histogram parameters differed between patients and controls and were found to be significantly correlated with both the Mini-Mental State Examination score and Rankin Scale score in the patient group. The follow-up study showed a decrease in the peak height associated with an increase in the mean value of whole brain Trace(D) histograms in the 14 CADASIL patients scanned twice. The diffusion changes appeared larger in the patients whose Rankin score increased during the study period. CONCLUSIONS: These results suggest that the measurement of water diffusion over time is a sensitive marker for the progression of tissue damage in the brain. Thus, quantitative diffusion MRI can be used to monitor disease progression in CADASIL and possibly in other types of small-vessel brain disorders.

Adult↗
PubMed2003

Definition of displacement probability and diffusion time in q-space magnetic resonance measurements that use finite-duration diffusion-encoding gradients.

In q-space diffusion NMR, the probability P(r,td) of a molecule having a displacement r in a diffusion time td is obtained under the assumption that the diffusion-encoding gradient g has an infinitesimal duration. However, this assumption may not always hold, particularly in human MRI where the diffusion-encoding gradient duration delta is typically of the same order of magnitude as the time offset Delta between encoding gradients. In this case, finite-delta effects complicate the interpretation of displacement probabilities measured in q-space MRI, and the form by which the signal intensity relates to them. By considering the displacement-specific dephasing, , of a set of spins accumulating a constant displacement vector r in the total time Delta+delta during which diffusion is encoded, the probability recovered by a finite-delta q-space experiment can be interpreted. It is shown theoretically that a data analysis using a modified q-space index q=gammadeltaetag, with gamma the gyromagnetic ratio and eta=square root (Delta-delta/3)/(Delta+delta), recovers the correct displacement probability distribution if diffusion is multi-Gaussian free diffusion. With this analysis, we show that the displacement distribution P(r,texp) is measured at the experimental diffusion-encoding time texp=Delta+delta, and not at the reduced diffusion time tr=Delta-delta/3 as is generally assumed in the NMR and MRI literature. It is also shown that, by defining a probability P(y,Delta) that a time t deltac then eta is not equal to square root (Delta-delta/3)/(Delta+delta) which implies that we can no longer obtain the correct displacement probability from the displacement distribution. In the case that /g/=18 mT/m and Delta-delta=5 ms, the parameter deltac in ms is given by "deltac=0.49a2+0.24" where a is the sphere's radius expressed in microm. Simulation of q-space restricted diffusion MRI experiments indicate that if eta=square root (Delta-delta/3)/(Delta+delta), the recovered displacement probability is always better than the Gaussian approximation, and the measured diffusion coefficient matches the diffusion coefficient at time texp=Delta+delta better than it matches the diffusion coefficient at time tr=Delta-delta/3. These results indicate that q-space MRI measurements of displacement probability distributions are theoretically possible in biological tissues using finite-duration diffusion-encoding gradients provided certain compartment size and diffusion encoding gradient duration constraints are met.

Journal Article↗
PubMed2006

Elevated mean diffusivity in widespread brain regions in congenital central hypoventilation syndrome.

PURPOSE: To investigate whether mean diffusivity (MD) values are altered in brain areas underlying cardiovascular and respiratory control in congenital central hypoventilation syndrome (CCHS). MATERIALS AND METHODS: Conventional and diffusion tensor imaging were performed in 15 CCHS and 30 control subjects, using a 3.0-Tesla MRI unit. Mean diffusivity maps were calculated from diffusion-weighted images, spatially normalized, smoothed, and compared between groups using analysis of covariance at each voxel with age as covariate. Global mean MD values of gray and white matter were determined in individual subjects and compared between groups and with age. RESULTS: Increased MD values appeared in CCHS over control subjects within multiple areas influencing breathing and cardiovascular control, including the midbrain, pons, and dorsal and ventral medulla. Other altered sites included cerebellar cortex and deep nuclei, basal ganglia, basal forebrain, and temporal and frontal cortices. Global mean MD values for gray and white matter did not differ between groups; however, gray matter MD values significantly increased with age (P < 0.02) in CCHS patients only. CONCLUSION: Increased MD values suggest regional alterations or injury; affected areas include brainstem sites classically associated with autonomic and respiratory control. Other altered regions mediate additional physiological characteristics impaired in CCHS.

Adolescent↗
PubMed1992

[A comparison of the value of magnetic resonance tomography and computed tomography in Nelson syndrome patients].

The hypophyses of 13 patients with Nelson syndrome following bilateral adrenalectomy were examined by MRI and CT. Diffuse enlargement of the hypophysis was demonstrated in 8 patients by CT and in 9 by MRI. Compared with CT, MRI provides better demonstration of tumour development, such as abnormal convexity of the cranial margin of the hypophysis (MRI 4/13, CT 1/13), displacement of the infundibulum (MRI 4/13, CT 0/13) or optic chiasm (MRI 2/13, CT 0/13). MRI also provides diagnostically important differentiation between scar tissue and recurrence of tumour following hypophysectomy (MRI 1/3, CT 0/3) and more accurate demonstration of infiltration of the cavernous sinus (MRI 4/13, CT 2/13). CT is superior only in showing the floor of the sella. MRI is the method of choice for imaging in cases of Nelson syndrome.

Adrenalectomy↗
PubMed2003

Diffusion magnetic resonance imaging study of a rat hippocampal slice model for acute brain injury.

Diffusion magnetic resonance imaging (MRI) provides a surrogate marker of acute brain pathology, yet few studies have resolved the evolution of water diffusion changes during the first 8 hours after acute injury, a critical period for therapeutic intervention. To characterize this early period, this study used a 17.6-T wide-bore magnet to measure multicomponent water diffusion at high b-values (7 to 8,080 s/mm(2)) for rat hippocampal slices at baseline and serially for 8 hours after treatment with the calcium ionophore A23187. The mean fast diffusing water fraction (Ffast) progressively decreased for slices treated with 10-microM/L A23187 (-20.9 +/- 6.3% at 8 hours). Slices treated with 50-micromol/L A23187 had significantly reduced Ffast 80 minutes earlier than slices treated with 10-microM/L A23187 (P < 0.05), but otherwise, the two doses had equivalent effects on the diffusion properties of tissue water. Correlative histologic analysis showed dose-related selective vulnerability of hippocampal pyramidal neurons (CA1 > CA3) to pathologic swelling induced by A23187, confirming that particular intravoxel cell populations may contribute disproportionately to water diffusion changes observed by MRI after acute brain injury. These data suggest diffusion-weighted images at high b-values and the diffusion parameter Ffast may be highly sensitive correlates of cell swelling in nervous issue after acute injury.

Acute Disease↗
PubMedDate not supplied

Primary angiitis of the central nervous system: an ante-mortem diagnosis.

A rare case of primary angiitis of the central nervous system (PACNS) is reported with its clinical and magnetic resonance imaging (MRI) features. A 20-year-old girl presented with headache, projectile vomiting, unsteadiness of gait and urgency of micturition. She had left seventh nerve upper motor neuron type paresis, increased tone in all four limbs, exaggerated deep tendon reflexes, cerebellar signs, and papilloedema. Cerebrospinal fluid showed lymphocytosis with elevated protein and normal glucose level. Cerebral computerised tomographic scan and MRI showed bilateral diffuse asymmetric supra- and infra-tentorial lesions (predominantly in the supratentorial and left cerebrum). On MRI, the lesions were hyperintense on T2, and proton density-weighted images and hypointense on T1-weighted images. Based on the clinical findings of raised intracranial tension and MRI features, initial diagnoses of gliomatosis cerebrii, tuberculous meningitis, primary central nervous system lymphoma and chronic viral encephalitis were considered. PACNS was not included in the initial differentials and, an open brain biopsy was advised which established the definitive diagnosis.

Adult↗
PubMed1996

[MRI aspect and course of supra-tentorial sarcoidosic lesions].

Central nervous system lesions resulting from sarcoidosis occur in 5% of cases, but supratentorial mass lesions are uncommon. We report 3 cases of intracranial pseudo-tumoral lesions, due to sarcoidosis: 1 woman and 2 men. Clinical features included left facial myoclonus, headache and vertigo, right hemiparesis and unique general seizure. Sarcoidosis was diagnosed upon conjonctival biopsy in the first case, infiltrative lesions of the lungs and mediastinal lymph nodes in the second case, and intracerebral lesion plus lymph nodes biopsies in the last case. In the first case, CT scan and MRI images showed diffuse subcortical high signal, suggesting pachymeningitis with vasogenic oedema. In the second case, GT scan and MRI revealed numerous small granuloma in the left rolandic area, and one in the striatum. In the third case, CT scan showed an enlargement of the left temporal horn, due to an enhanced left periventricular lesion. MRI with gadolinium showed that the lesion encircled the ventricle horn. In all cases, clinical and radiological improvement was obtained after corticoid therapy.

Adult↗
PubMed2005

Magnetic resonance imaging and diffusion-weighted imaging in methylmalonic acidemia.

Methylmalonic acidemia (MMA) is an inborn disorder of amino acid metabolism, often presenting with neurological symptoms. We present the results of magnetic resonance imaging (MRI) and diffusion-weighted imaging (DWI) of the brain in a 16-month-old male patient with classic neurological and laboratory findings for MMA. MRI demonstrated the hyperintensity within globi pallidi both on T2-weighted image and DWI during the acute episode of metabolic acidosis.

Acidosis↗
PubMed2000

Differences in water diffusion and lactate production in two different types of postinfectious encephalopathy.

We compared two different types of postinfectious encephalopathy using magnetic resonance imaging (MRI), including diffusion-weighted images and MR spectroscopy. Acute disseminated encephalomyelitis (ADEM) and acute necrotizing encephalopathy (ANE) showed different distribution of abnormal intensity areas and different diffusion of water measured by diffusion-weighted imaging (DWI). Proton MR spectroscopy (MRS) showed lactate production in both cases, which returned to a normal range; the rate of increased lactate production was much lower in the ANE case. Water diffusion showed a difference in pathophysiological background between the two encephalopathies, but the lactate elevation observed by proton MRS did not correlate with clinical severity.

Body Water↗
PubMed2005

MRI evidence for multiple sclerosis as a diffuse disease of the central nervous system.

The classical view of MS as a chronic inflammatory demyelinating disease leading to the formation of focal central nervous system (CNS) white matter (WM) lesions has been recently challenged by pathological studies and by the extensive application of modern MRI-based techniques. There is now overwhelming evidence supporting the following statements: MS causes widespread tissue damage in the normal-appearing white matter (NAWM) of the brain and spinal cord, whose extent and severity is more strictly associated to the clinical manifestations of the disease than the extent of focal pathology. Discrete, macroscopic lesions are just the tip of the iceberg of MS pathology. Grey matter (GM) damage is a consistent feature of all MS phenotypes, which is progressive from the start of the relapsing-remitting phase of the disease. As is the case for WM, GM damage is also a mixture of focal lesions and diffuse pathology. High-field strength MR scanners are improving our ability to image focal GM lesions and modern MR-based techniques are enabling us to quantify in vivo the extent and severity of GM pathology, which have been shown to correlate only moderately with the amount of WM changes. At least part of GM pathology in MS is not secondary to retrograde degeneration of fibers traversing WM lesions. The neurodegenerative component of the disease is not a late phenomenon and it is not completely driven by inflammatory demyelination. In fact, neurodegeneration occurs very early in the course of MS and the correlation between MRI measures of inflammation and neurodegeneration is weak in all disease phases. The interplay of inflammation and neurodegeneration is a complex and still poorly understood phenomenon. At least part of MS-related neurodegeneration is not directly driven by Wallerian degeneration. Functional cortical changes can be seen in virtually all MS patients and are likely to play a central role in the ability of the MS brain to respond to tissue injury and, hence, limit the functional consequences of structural damage. MS disability is not just the result of tissue destruction but rather a balance between tissue destruction, tissue repair and adaptive cortical reorganization. All of this calls for the concept of MS as a focal, inflammatory demyelinating, WM disease to be reexamined and to start viewing MS as a diffuse CNS disease with an important neurodegenerative component. This is central for identifying novel and effective treatment strategies.

Central Nervous System Diseases↗
PubMed2004

B factor dependence of the temporal characteristics of brain activation using dynamic apparent diffusion coefficient contrast.

Functional MRI studies to date have been generally performed using the blood oxygenation level dependent (BOLD) contrast mechanism. Recently, it has been proposed that dynamic change in the apparent diffusion coefficient (ADC), measured using intravoxel incoherent motion (IVIM) weighting, can be used as a robust functional contrast mechanism. Based on the differences in the timing characteristics compared to the BOLD activation, the ADC contrast can be selectively sensitized to upstream vascular pools (e.g., arterial networks). In this study we further investigated the timing characteristics of the functional ADC contrast using multiple degrees of IVIM weighting. It was found that the time course in the high b factor range lagged behind that of the low b factor range, indicating that the low b factor ADC contrast included contributions from the larger and faster moving arteries, and the smaller arterioles and capillaries downstream were reflected in the high b factor changes. These changes help confirm the arterial origin of the ADC contrast and offer a direction to improve the localization of activity to small vessel networks.

Brain Mapping↗