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PubMed1990

Unusual MRI appearance of diffuse subcortical heterotopia or "double cortex" in two children.

Two children with mild epilepsy and learning and behaviour problems had magnetic resonance imaging (MRI) scans showing an almost identical generalised disorders of neuronal migration. Their computer tomography (CT) scans showed abnormal hypodense white matter. The MRI showed a four layered appearance of the cerebral parenchyma extending from the frontal to the occipital region. There was a normal appearance to the white matter in the periventricular region which had an abnormally smooth junction with a thick diffuse layer of heterotopic grey matter. This was surrounded by a thin layer of white matter which had normal digitations with the overlying cortex. The appearance of the overlying cortex was normal. These and other recently described cases broaden the concept of generalised disorders of neuronal migration and illustrate that it is possible to have a generalised cerebral malformation with few clinical consequences.

Brain↗

PubMed2003

Renal diffusion and BOLD MRI in experimental diabetic nephropathy. Blood oxygen level-dependent.

PURPOSE: To investigate the possibility of using combined blood oxygen level-dependent (BOLD) imaging and diffusion-weighted imaging (DWI) to detect pathological and physiological changes in renal tissue damage of the kidney induced by chronic renal hyperfiltration. MATERIALS AND METHODS: The apparent diffusion coefficient (ADC) and the T(2)* value within the inner compartments of the kidneys of 17 rats with diabetes mellitus were compared with the results obtained from a control group (N = 16). The influence of dynamic changes of the renal function on the blood-oxygen saturation was evaluated by comparing the T(2)* values before and after the active reduction of tubular transport by furosemide injection. RESULTS: All compartments of the diabetic kidney showed significantly (P < 0.05) lower T(2)*-values compared to the control group. In particular, the very low values in the outer stripe (OS) of the outer medulla (OM) (T(2)*-normal: 69.4 +/- 10.9 msec; T(2)*-diabetic: 51.4 +/- 13.9 msec) indicated either hypoxia due to hyperfiltration, or renal blood volume changes. Diffusion imaging of the same area showed significantly lower ADC values (ADC-normal: 1.45 +/- 0.26; ADC-edema: 1.19 +/- 0.25 [10(-9)m(2)/s]) that correlated with pathological findings on histopathology. The injection of furosemide significantly (P < 0.05) increased T(2)* in all compartments of both populations while the ADC remained unchanged. CONCLUSION: BOLD-contrast imaging appears to be able to depict tissue at risk from ischemia by revealing information about the balance between tubular workload and delivery of oxygen, and thus may reflect a measure of the reserve capacity. The diffusion measurements apparently reveal complementary information. Although ADC imaging is not sensitive to the current energy metabolism, it appears toreflect the pathological changes within the issue. Therefore, ADC measurements may be a sensitive indicator of the severity of ischemic lesions.

Animals↗

PubMed2003

Childhood and current cognitive function in healthy 80-year-olds: a DT-MRI study.

Diffusion tensor MR imaging (DT-MRI) yields information on early pathological changes in white matter of the ageing brain which may correlate with cognitive function. However, because individuals vary in their cognitive ability, a measurement of prior cognition from youth is required to understand fully the significance of MR imaging changes associated with ageing. Here, diffusion tensor parameters and cognitive function were measured in a cohort of 30 older subjects whose cognitive ability was measured at age 11 and 80. There was a significant correlation between diffusion anisotropy measured in the centrum semiovale at age 80 and mental ability determined at age 11 and 80. These novel results suggest, that MR imaging studies of white matter structure and its relationship to mental ability in ageing should control for early life cognition.

Aged↗

PubMedDate not supplied

High b-value q-space analyzed diffusion-weighted MRS and MRI in neuronal tissues - a technical review.

This review deals with high b-value q-space diffusion-weighted MRI (DW-MRI) of neuronal tissues. It is well documented that at sufficiently high b-values (and high q-values) neuronal water signal decay in diffusion experiments is not mono-exponential. This implies the existence of more than one apparent diffusing component or evidence for restriction. The assignment of the different apparent diffusing components to real physical entities is not straightforward. However, the apparent slow diffusing component that was found to be restricted to a compartment of a few microns, if originating mainly from a specific pool and if assigned correctly, may potentially be used to obtain more specific MR images with regard to specific pathologies of the CNS. This review examines the utility of analyzing high b-value diffusion MRS and MRI data using the q-space approach introduced by Callaghan and by Cory and Garroway. This approach provides displacement probability maps that emphasize, at long diffusion times, the characteristics of the apparent slow diffusing component. Examples from excised spinal cord, where the experimental conditions for which the q-space analysis of MR diffusion data was developed can be met or approached will be presented. Then examples from human MS patients, where q-space requirement for the short gradient pulse is clearly violated, are presented. In the excised spinal cord studies, this approach was used to study spinal cord maturation and trauma, and was found to be more sensitive than other conventional methods in following spinal cord degeneration in an experimental model of vascular dementia (VaD). High b-value q-space DWI was also recently used to study healthy and MS diseased human brains. This approach was found to be very sensitive to the disease load in MS, compared with other conventional MRI methods, especially in the normal appearing white matter (NAWM) of MS brains. Finally, the potential diagnostic capacity embedded in high b-value q-space analyzed diffusion MR images is discussed. The potentials and caveats of this approach are outlined and experimental data are presented that show the effect of violating the short gradient pulse (SGP) approximation on the extracted parameters from the q-space analysis.

Algorithms↗

PubMed2007

Cerebral and cerebellar ADC values during a migraine attack.

INTRODUCTION: We investigated the diffusion-weighted MRI changes, apparent diffusion coefficient (ADC) values, and conventional MRI findings in specific brain areas during migraine attacks in patients with and without aura. METHODS: Included in the study were 22 patients (2 male, 20 female) aged between 17 and 49 years who were diagnosed as having migraine according to the diagnostic criteria of the International Headache Society. Also included in the study were 18 age- and sex-matched healthy volunteers. Hyperintense lesions were evaluated in conventional MR images. Heavily diffusion-weighted images, ADC maps, and segmented ADC maps generated for regional ADC (rADC) measurements, were also studied. ADC values from specific brain areas were used with appropriate region of interests (ROI). RESULTS: Migraine with aura was diagnosed in 13 patients and migraine without aura was diagnosed in 9 patients. A total of 23 hyperintense lesions within the periventricular white matter and deep white matter were detected in five patients (21.8%). All of these hyperintense lesions were seen in migraine patients with aura. In only one patient did a hyperintense lesion show an increased diffusion pattern on diffusion-weighted images and ADC maps. One hyperintense lesion was detected in the control group (5.5%). There was no significant difference in ADC values between the migraine and control groups. CONCLUSION: T2-weighted hyperintense lesions were significantly more frequent in migraine patients especially in those with aura than in the control group. No diffusion alterations in diffusion-weighted images were detected in the infra- and supratentorial brain areas during migraine attacks in patients with and without aura.

Adolescent↗

PubMed1999

An echo-shifted gradient-echo MRI method for efficient diffusion weighting.

A segmented magnetic resonance imaging (MRI) method is introduced with time-efficient diffusion weighting resulting in total imaging times similar to those of single-shot methods. The approach is based on the principles of echo shifting with a train of observations (PRESTO) MRI sequence. The time efficiency of the sequence is based on the use of diffusion gradient pulses that also serve to shift the echo train to the next TR period, resulting in TE > TR. Each diffusion gradient is therefore used twice, for dephasing one set of spins as well as rephasing a second set of spins. Diffusion weighting and acquisition are thus achieved simultaneously. The sequence is validated in vitro and in vivo on rat kidney.

Animals↗

PubMed2005

Diffusion and perfusion MRI in patients with ruptured and unruptured intracranial aneurysms treated by endovascular coiling: complications, procedural results, MR findings and clinical outcome.

Our purpose was to evaluate treatment safety as well as complications frequency and management in endovascular coiling of intracerebral aneurysms using MR diffusion and perfusion imaging. In this prospective study, 77 MR examinations were performed in conjunction with 43 procedures in 40 patients, 14 patients presented with ruptured and 26 with unruptured aneurysms. Mean time interval between treatment and post-procedure MRI was 29 and 25 h for the ruptured and unruptured aneurysm group, respectively. Peri-procedural complications, including five major events and five minor transient events, occurred in 10/43 procedures (23%), necessitating thrombolytic therapy in two patients and angioplasty in one, all three within the unruptured aneurysm group. Fifty-one new lesions were found on post-treatment DWI and 47 of them were regarded as of ischemic origin. Most lesions were small (<3 mm), ipsilateral to the treated aneurysm and asymptomatic (37/40 patients). Sixty-seven percent of the lesions were found in the ruptured and 33% in the unruptured aneurysm group. The ischemic lesions did occur more frequently in patients treated for aneurysm of large neck size and according to the remodelling technique. The overall morbidity and mortality rates were 14.6 and 7.3% whereas morbidity and mortality rates related to the technique were only 2.6 and 0%, respectively. Silent embolism seems to be more common than clinically evident and partially related to patient presentation, heparinazation and treatment strategy. The capability to depict early complications and analyse their potential causes by using MR with DWI has been of great importance in our modification and improvement of therapeutic protocols, evaluations and strategies.

Adult↗

PubMed1996

[A case of diffuse fasciitis and its MRI findings].

A 36-year-old woman with diffuse fasciitis and her MRI findings are reported. The patient developed pain and swelling in the calves, right forearm, and left arm, predominantly in the right calf muscle. Her body temperature was 38.4 degrees C, the ESR 104 mm/2 hours and white blood cell count 8,000/microliter without eosinophilia. The fascia and muscle were biopsied from her right calf. The light microscopy showed that the fascia was thickened and infiltrated with mononuclear cells with no eosinophils, mostly in perivascular areas. The muscle fibers were spared. MRI of legs revealed marked hyperintensities on T2 and mild hyperintensities on T1-weighted images in the fascia, superficial flexor muscles, especially soleus muscle, and Achilles tendons. Moderate dose of prednisolone was very effective and the abnormal signals on MRI almost disappeared within a month. T2 weighted MRI was very useful to detect the lesions and to evaluate the course of diffuse fasciitis.

Adult↗

PubMed2004

The contribution of MRI to the diagnosis of diffuse meningeal lesions.

We analysed MRI findings in patients in whom a diffuse abnormality of the meninges was revealed by MRI. We looked at T1 and T2-weighted spin-echo or fast spin-echo images and contrast-enhanced T1-weighted images. There were 15 patients with abnormalities on MRI, clinically suspected in ten. Four had meningoencephalitis, one meningeal and subcortical sarcoidosis nodules, four meningeal malignancies--one disseminated oligodendroglioma, one with meningeal infiltration around an adenocarcinoma, three meningeal infiltration by a haematological malignancy, and one a chronic subdural haematoma without a history of injury. We excluded patients with primary meningeal tumours and typical injury-related meningeal bleeding. The relatively small number of patients is due to both the infrequency of diffuse meningeal disease and to the low frequency of suspected meningeal pathology as an indication for MRI. The latter's diagnostic contribution is greatest in infectious disease and neoplastic infiltration, and less obvious in haematological malignancies. Contrast-enhanced T1-weighted images are most useful.

Adenocarcinoma↗

PubMed2005

Diffusion-weighted 19F-MRI of lung periphery: Influence of pressure and air-SF6 composition on apparent diffusion coefficients.

Lung functional magnetic resonance imaging (MRI) has become a reality using different inert hyperpolarized gases, such as 3He and 129Xe, which have provided an extraordinary boost in lung imaging and has also attracted interest to other chemically inert gaseous contrast agents. In this context, we have recently demonstrated the first diffusion-weighted images using thermally polarized inhaled sulfur hexafluoride (SF6) in small animals. The aim of this study was to evaluate whether or not the diffusion coefficient of this fluorinated gas is sensitive to pulmonary structure, gas concentration and air pressure in the airways. Diffusion coefficients of SF6 (both pure and in air mixtures) measured in vitro at different pressures and 20 degrees C showed an excellent agreement with theoretical values. Measurements of diffusion coefficients were also performed in vivo and post-mortem on healthy rats, achieving satisfactory signal-to-noise ratios (SNRs), and SF6 gas was found to be in an almost completely restricted diffusion regime in the lung, i.e., the transport by molecular diffusion is delayed by collisions with barriers such as the alveolar septa. This observed low diffusivity means that this gas will be less sensitive to structural changes in the lungs than other magnetic resonance sensitive gas such as 3He, particularly at human scale. However, it is still possible that SF6 plays a role since it opens a new structural window. Thus, the interest of researchers in delimiting the important limiting technical factors that makes this process very challenging is obvious. Among them, T2 relaxation is very fast, so gradient systems with very fast switching rate and probably large radiofrequency (RF) power and high field systems will be needed for hexafluoride to be used in human studies.

Animals↗

PubMed1990

Early detection of regional cerebral ischemia in cats: comparison of diffusion- and T2-weighted MRI and spectroscopy.

Diffusion-weighted MR images were compared with T2-weighted MR images and correlated with 1H spin-echo and 31P MR spectroscopy for 6-8 h following a unilateral middle cerebral and bilateral carotid artery occlusion in eight cats. Diffusion-weighted images using strong gradient strengths (b values of 1413 s/mm2) displayed a significant relative hyperintensity in ischemic regions as early as 45 min after onset of ischemia whereas T2-weighted spin-echo images failed to clearly demonstrate brain injury up to 2-3 h postocclusion. Signal intensity ratios (SIR) of ischemic to normal tissues were greater in the diffusion-weighted images at all times than in either TE 80 or TE 160 ms T2-weighted MR images. Diffusion- and T2-weighted SIR did not correlate for the first 1-2 h postocclusion. Good correlation was found between diffusion-weighted SIR and ischemic disturbances of energy metabolism as detected by 31P and 1H MR spectroscopy. Diffusion-weighted hyperintensity in ischemic tissues may be temperature-related, due to rapid accumulation of diffusion-restricted water in the intracellular space (cytotoxic edema) resulting from the breakdown of the transmembrane pump and/or to microscopic brain pulsations.

Animals↗

PubMed2000

Pathologic damage in MS assessed by diffusion-weighted and magnetization transfer MRI.

OBJECTIVE: To compare diffusion characteristics of MS lesions, normal-appearing white matter (NAWM) from patients, and normal white matter from control subjects, and to investigate the correlations between the magnetization transfer ratio (MTR) and a directionally averaged tissue water diffusion coefficient (D) in patients. BACKGROUND: MS and other pathologic processes that modify tissue integrity can result in abnormal diffusion of water molecules detectable by diffusion-weighted imaging (DWI). METHODS: Conventional dual-echo and DWI scans were obtained from 35 patients with relapsing-remitting MS and 24 healthy control subjects. MT scans were also obtained from the patients. After coregistration of all scans, MTR and D values from MS lesions and NAWM in different regions were marked using the dual-echo scans as a reference. D values from the same brain regions in control subjects were acquired. Histograms of MTR and D were also produced. RESULTS: Patients with MS had significantly higher D values in all the areas studied. Moreover, histogram metrics (peak height, peak site, and average D) from patients were substantially different from those of control subjects. In patients, average lesion D and MTR were markedly different from those in the NAWM. There was an inverse correlation between average lesion MTR and D inside lesions, whereas no correlation was found for average MTR and D taken from the histograms. CONCLUSIONS: DWI detects severe tissue disruption inside lesions and subtle widespread abnormalities in NAWM in patients with relapsing-remitting MS. MT and DWI may provide information about different aspects of brain pathology in MS.

Adult↗

PubMed1985

The adoption and diffusion of CT and MRI in the United States. A comparative analysis.

This study examines and compares the rates and patterns of diffusion of computerized tomography (CT) and magnetic resonance imaging (MRI) over the first 4 years of their availability. Although early diffusion of CT was more rapid than that of MRI, adoption of MRI in nonhospital settings equaled that of CT. Analysis of attributes of the technologies and attributes of the regulatory, reimbursement, and market environments surrounding the early diffusion of these technologies provides insight into their different diffusion patterns. In particular, the technical and financial uncertainties surrounding MRI have inhibited its diffusion compared with that of CT. Medicare's DRG-based prospective reimbursement system and certificate-of-need (CON) regulation by states have reduced overall MRI diffusion and stimulated purchases of MRI by nonhospital organizations. The FDA's premarket approval (PMA) program has changed marketing strategies and influenced the diffusion of MRI to a lesser degree. This analysis identifies problems in how the present health care system evaluates and adopts new, expensive, diagnostic technologies and suggests changes to make the system more responsive to present needs.

Certificate of Need↗

PubMed2002

Diffusion and perfusion MRI for the assessment of carotid atherosclerosis.

Atherosclerotic disease of the extracranial vessels is a frequent cause of cerebral ischemia and stroke. Many natural history studies and prospective treatment trials with large patient samples have focused on optimal patient assessment in regard to medical or interventional measures. Clinical decision making nowadays is largely based on the identification, visualization, and grading of the local stenosis, and the identification of neurologic symptoms related to carotid artery stenosis. MRI already has contributed considerably as many surgeons no longer require preoperative conventional contrast angiography but may use the combination of duplex ultrasound studies and MRA for visualization of the pathology. Besides MRA improvements, DWI and PWI are increasingly used in addition to conventional MR contrasts (PD, T2-, T1-weighted MRI) in attempts to gather information on tissue status and the pathophysiology of hemodynamic compromise and cerebral ischemia in patients with carotid artery stenosis. Obtaining background information using this array of MR data may eventually become a basis for optimal risk-benefit assessment in patients with carotid artery stenosis.

Arteriosclerosis↗

PubMed2006

Evidence of a developmental cerebello-cerebral disorder.

The objective of this study was to examine the cognitive and neuroanatomical features of an adolescent with developmental hypoplastic left cerebellum who presented with executive and visuo-spatial deficits, nonverbal learning disabilities and interpersonal difficulties. He underwent a neuropsychological assessment, MRI and diffusion tensor imaging MRI. The neuropsychological impairments were primarily in executive functions, spatial and visual perception, graphomotor skills, arithmetic, social perception and comprehension. Fractional anisotropy, which is measured by diffusion tensor imaging and enables assessment of axonal integrity, was reduced in the right cerebral peduncle and right hemisphere white matter (p < 0.001). Based on the results, we hypothesize that disruption of neural circuits linking the hypoplastic left cerebellum to the right hemisphere may contribute to the evolution of a neurocognitive syndrome with characteristics of the developmental right hemisphere syndrome and suggestive of the cerebellar cognitive-affective syndrome.

Adolescent↗

PubMed1987

Effects of selective pulses on the measurement of T2 and apparent diffusion in multiecho MRI.

The effects of using spatially selective and nonuniform radiofrequency pulses on the apparent T2 of a train of multiple echoes have been calculated by computer simulation. It is demonstrated that the use of selective pulses produces errors in estimates of T2 in imaging experiments because regions of the slice are effectively off resonance and therefore receive spin rotations less than in an ideal case. Components of the transverse magnetization that are incompletely rotated by 180 degrees refocusing pulses produce longitudinal components that are later returned to the transverse plane and add to subsequent echoes. These so-called ghost components influence the precise value of T2 estimated, but even when completely removed the resultant estimate is too short. The apparent T2 is influenced by the magnitude of the nutation angle inhomogeneity across the slice and paradoxically is not always more accurate with larger numbers of echoes. The reduction of apparent T2 caused by increasing the slice-selection gradient across a thin slab of material replicates the effects previously ascribed to diffusion and affords an alternative explanation for these without recourse to motion of the spins.

Computer Simulation↗

PubMed2002

The stroke patient who woke up: clinical and radiological features, including diffusion and perfusion MRI.

BACKGROUND AND PURPOSE: Time of stroke onset is uncertain for patients who wake from sleep with stroke. Functional imaging techniques may allow estimation of benefit and risk of acute stroke therapy. We compared the clinical and multimodal MRI findings of patients with uncertain stroke onset with those with known onset time. METHODS: Patients imaged within 24 hours of ischemic stroke onset between January 1997 and June 2000 were identified from a prospective stroke registry. Clinical and imaging data from patients with known stroke onset (group I) were compared with those who woke with stroke (group II). RESULTS: A total of 364 patients were identified, of whom 100 (27%) woke from sleep with stroke. Group I and group II did not differ in age, gender, National Institutes of Health Stroke Scale, or TOAST (Trial of Org 10172 in Acute Stroke Treatment) diagnoses. Time from stroke onset was shorter in group I (mean 6.0 versus 13.3 hours, P<0.001); time from detection did not differ between groups (6.0 versus 5.9 hours). Within 3 hours, diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) lesion volumes were similar in both groups; DWI-PWI mismatch was present in 82% of group I and 73% of group II patients. Mean apparent diffusion coefficient of water (ADC) of group I patients was negatively associated with DWI volume (beta=-0.324, P=0.004) and time from stroke onset (beta=-0.238, P=0.031) in multivariate analysis. The mean ADC of group II patients was lower than that of group I patients within 3 hours of stroke detection (mean 556 versus 665 microm2/s, P<0.01), but individual group II patients had ADC values as high as 742 microm2/s, in addition to a DWI-PWI mismatch pattern. CONCLUSIONS: Onset time is uncertain in over one quarter of acute ischemic stroke patients. Clinical features of these patients do not differ significantly from those with known onset time. Some patients who wake with stroke seem to have favorable imaging characteristics for acute stroke therapy. Further study is needed to determine whether criteria for therapy based on imaging parameters can safely be applied to these patients.

Aged↗

PubMed2001

In-vivo tissue characterization of multiple sclerosis and other white matter diseases using magnetic resonance based techniques.

In several white matter diseases of the central nervous system (CNS), and in particular in multiple sclerosis (MS), conventional magnetic resonance imaging (MRI) has proved to be sensitive for detecting lesions and their changes over time. However, conventional MRI is not able to characterize and quantify the tissue damage within and outside such lesions. Other quantitative MR techniques, including proton MR spectroscopy (1H-MRS), magnetization transfer MRI (MT-MRI) and diffusion-weighted MRI (DW-MRI) have the potential to overcome this limitation and, as a consequence, to provide additional information about the nature and the extent of tissue damage, which would be inevitably lost when only conventional MRI is obtained. Metrics derived from MT- and DW-MRI can quantify the structural changes occurring within and outside lesions visible on conventional MRI scans. 1H-MRS could add information on the biochemical nature of such changes. The application of these MR techniques to the study of MS is increasing dramatically our understanding of how MS causes irreversible disability and it is likely to provide useful insights into the pathophysiology of other diseases of the CNS in the near future.

Brain Chemistry↗