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PubMed2004

Comprehensive approach for correction of motion and distortion in diffusion-weighted MRI.

Patient motion and image distortion induced by eddy currents cause artifacts in maps of diffusion parameters computed from diffusion-weighted (DW) images. A novel and comprehensive approach to correct for spatial misalignment of DW imaging (DWI) volumes acquired with different strengths and orientations of the diffusion sensitizing gradients is presented. This approach uses a mutual information-based registration technique and a spatial transformation model containing parameters that correct for eddy current-induced image distortion and rigid body motion in three dimensions. All parameters are optimized simultaneously for an accurate and fast solution to the registration problem. The images can also be registered to a normalized template with a single interpolation step without additional computational cost. Following registration, the signal amplitude of each DWI volume is corrected to account for size variations of the object produced by the distortion correction, and the b-matrices are properly recalculated to account for any rotation applied during registration. Both qualitative and quantitative results show that this approach produces a significant improvement of diffusion tensor imaging (DTI) data acquired in the human brain.

Algorithms↗
PubMed1994

Transient cell depolarization after permanent middle cerebral artery occlusion: an observation by diffusion-weighted MRI and localized 1H-MRS.

Focal cerebral ischemia causes rapid intensity changes in diffusion-weighted images (DWI) and elevated lactate as detected by localized proton spectroscopy (1H-MRS). To investigate whether such changes can also be evoked by perischemic depolarizations, we combined DWI and 1H-MRS measurements with DC potential recordings. About 40 min after occlusion of the middle cerebral artery in a rat, a negative DC deflection was observed indicating transient cell depolarization. Coincidentally with the depolarization a transient increase of the DWI signal intensity and a partially reversible increase of lactate occurred in the periphery of the ischemic territory. These results show that peri-ischemic depolarization, known to contribute to the evolution of cerebral infarction, evokes disturbances that can be detected by DWI and 1H-MRS.

Animals↗
PubMed2003

Diffusion-weighted MRI findings in patients with capsular warning syndrome.

BACKGROUND AND PURPOSE: The 'capsular warning syndrome' (CWS) of recurrent stereotyped episodes of motor or sensory dysfunction is clinically well recognized, and is associated with a high risk of imminent lacunar infarction with permanent deficits resembling those of CWS. However, the pathophysiology of CWS has not been well characterized. We report a clinicoanatomic correlation with MR imaging studies in the acute and chronic phases in patients with CWS. MATERIAL AND METHODS: Between April 1997 and March 2001, we prospectively studied 8 patients, mean age 73.3 years, presenting with 4-17 motor or sensorimotor transient ischemic attacks (TIAs; duration 2-90 min) up to 3 days after onset of the first episode. Four patients were free of symptoms between the attacks and had no residua, whereas 4 patients developed a pure motor or sensorimotor stroke within 1-3 days after symptom onset. Diffusion-weighted echoplanar MRI (DWI) and T(2)-weighted MRI studies were performed within 1 week after symptom onset and were repeated 1-2 months later. RESULTS: Seven of the 8 patients had an appropriate lesion on DWI in the acute phase. DWI abnormalities in the 3 patients with TIAs were 4-10 mm in diameter and confined to the lateral thalamus or medial globus pallidus without involving the internal capsule, whereas 4 patients who developed a stroke had abnormalities localized to the putamen extending to corona radiata (3 patients), or the pontomesencephalic junction (1 patient). All 6 patients who underwent follow-up MRI had an infarct on T(2)-weighted images corresponding to, but usually smaller than, the acute phase DWI abnormality. CONCLUSIONS: Small infarcts in the basal ganglia or the pons, close to central motor pathways, appear to be the primary lesion in CWS. The pathophysiology of CWS is complex, and may involve hemodynamic mechanisms in penetrating arterial territories, as well as molecular mechanisms, such as peri-infarct depolarizations affecting adjacent motor pathways.

Aged↗
PubMed2000

Diffusion-weighted MRI diagnosis of pure motor stroke limited to primarily distal leg weakness.

Pure motor stroke (PMS) manifesting as distal weakness of a single extremity has rarely been described. The authors report a 59-year-old man with PMS who had primarily distal weakness of a single lower extremity, which to the authors' knowledge has not been previously described. Four days after onset, positive diffusion-weighted imaging confirmed that the small subcortical T2-weighted hyper-enhancing and nonenhancing T1-weighted hypo-intensity noted on magnetic resonance imaging (MRI) represented an acute PMS that was the cause of the patient's weakness. Increased awareness of this rare clinical presentation of PMS coupled with the promise of imaging the PMS with diffusion-weighted MRI should lead to earlier stroke intervention in these patients.

Brain↗
PubMed1999

Clinical severity in CADASIL related to ultrastructural damage in white matter: in vivo study with diffusion tensor MRI.

BACKGROUND AND PURPOSE: CADASIL is a newly recognized cause of subcortical ischemic strokes that progressively leads to dementia associated with pseudobulbar palsy and severe motor disability. This deleterious progression and the severity of clinical presentation are widely variable among affected subjects. The exact role played by MRI white-matter abnormalities, a hallmark of the disease, in the severity of the clinical phenotype remains poorly understood. METHODS: To address this issue, we used diffusion tensor imaging (DTI), a new MRI technique highly sensitive to white-matter microstructural changes, in 16 symptomatic patients and 10 age-matched controls. Mean diffusivity and anisotropy of diffusion were measured within hyperintensities identified on T2-weighted images (T2WI) and outside these lesions on 4 slices at the level of centrum semiovale. RESULTS: We found a 60% increase of water mean diffusivity and a parallel loss of diffusion anisotropy in hyperintensities identified on T2WI. The same pattern of diffusion changes, but of lesser intensity, was found in the normal-appearing white matter on T2WI. Mean diffusivity in regions with increased signal on T2WI was higher in patients with severe clinical disability compared with those with no or mild deficit (1.33+/-0.11 versus 1.13+/-0.11 10(-3) mm(2)/s, P<0.01). Furthermore, diffusion measured within T2 hyperintensities correlated with both the Mini-Mental State Examination and Rankin scale scores. In patients with a severe clinical status, the increase of water diffusion in these regions exceeded 70% in comparison with values obtained in the normal white matter in control subjects. CONCLUSIONS: These results indicate that DTI is able to detect important ultrastructural changes in regions with increased signal on T2WI and within the normal-appearing white matter in CADASIL. The diffusion changes might be related to both neuronal loss and demyelination. The degree of the underlying ultrastructural alterations is related to the severity of the clinical status with a possible threshold level of white-matter damage above which severe neurological impairment may occur in this disease. DTI appears to be a promising technique for monitoring disease progression in CADASIL.

Adult↗
PubMed2005

Foundations of advanced magnetic resonance imaging.

During the past decade, major breakthroughs in magnetic resonance imaging (MRI) quality were made by means of quantum leaps in scanner hardware and pulse sequences. Some advanced MRI techniques have truly revolutionized the detection of disease states and MRI can now-within a few minutes-acquire important quantitative information noninvasively from an individual in any plane or volume at comparatively high resolution. This article provides an overview of the most common advanced MRI methods including diffusion MRI, perfusion MRI, functional MRI, and the strengths and weaknesses of MRI at high magnetic field strengths.

Animals↗
PubMed2005

In vivo diffusion weighted 19F MRI using SF6.

Diffusion weighted 19F images of rat lung in vivo using SF6 are presented. Projection-reconstruction images were acquired by filling the rat lung with a mixture of SF6 and air, during 64 successive apneas. Each apnea lasted for 6 s, the time required to perform 100 accumulations of each k-space radial phase step for the five values of the diffusion gradient (TR = 10 ms). After diffusion images were acquired, an apparent diffusion coefficient (ADC) map was generated, yielding an average value for the ADC of 2.22 x 10(-6) m2/s and SD for ADC values of 1.27 x 10(-6) m2/s. To the best of our knowledge, this is the first in vivo diffusion weighting imaging application and the first ADC map obtained using 19F MRI.

Administration, Inhalation↗
PubMed2005

Transient encephalopathy after intrathekal methotrexate chemotherapy: diffusion-weighted MRI.

Methotrexate (MTX) is an indispensable antimetabolite for the treatment of oncological and immunological disorders in all age groups. Chronic leukoencephalopathy is a well know side effect of MTX, especially in conjunction with intrathecal administration and whole brain radio therapy. However, acute neurotoxicity with confusion, disorientation, seizures and focal deficits has also been reported. Because acute neurological symptoms in patients under chemotherapy for neoplastic disorders may have many reasons, MR-imaging is usually necessary to identify the underlying pathology. Apart from conventional sequences, diffusion-weighted imaging (DW-MRI) is frequently performed. We report on clinical and imaging findings of reversibly restricted diffusion in a patient with transient encephalopathy after intrathecal administration of MTX for recurrent acute lymphatic leukaemia.

Adolescent↗
PubMed2005

Cognitive functions correlate with white matter architecture in a normal pediatric population: a diffusion tensor MRI study.

A possible relationship between cognitive abilities and white matter structure as assessed by magnetic resonance diffusion tensor imaging (DTI) was investigated in the pediatric population. DTI was performed on 47 normal children ages 5-18. Using a voxelwise analysis technique, the fractional anisotropy (FA) and mean diffusivity (MD) were tested for significant correlations with Wechsler full-scale IQ scores, with subject age and gender used as covariates. Regions displaying significant positive correlations of IQ scores with FA were found bilaterally in white matter association areas, including frontal and occipito-parietal areas. No regions were found exhibiting correlations of IQ with MD except for one frontal area significantly overlapping a region containing a significant correlation with FA. The positive direction of the correlation with FA is the same as that found previously with age, and indicates a positive relationship between fiber organization and/or density with cognitive function. The results are consistent with the hypothesis that regionally specific increased fiber organization is a mechanism responsible for the normal development of white matter tracts.

Adolescent↗
PubMed1998

[Diffusion-weighted MRI detectability of acute cerebral ischemia: comparison with eventual infarction].

To clarify the clinical significance of diffusion-weighted magnetic resonance imaging (DWI) hyperintensity in acute cerebral ischemia, 34 patients were investigated with cerebral ischemia that had lasted no more than 8 hours. Either a spin echo sequence with navigator echo (n = 21) or an echo planar sequence (n = 13) was used for DWI using 1.5 tesla magnet. The eventual infarction was judged from T2-weighted image (T2 WI) or CT performed 2-12 days after the onset and was classified into cortical (n = 24) or perforating artery (n = 10) area. The eventual infarction was compared in size with the acute DWI finding and expressed as larger, same or smaller. Thirty patients showed ischemic hyperintensity lesions on acute DWI (6 patients on T2 WI). In cortical artery areas, the eventual infarction was same as hyperintensity area of acute DWI in 15 cases, larger in 8 cases, smaller in 2 cases. In perforating artery areas, the eventual infarction was same as hyperintensity area of acute DWI in 8 cases, and larger in 2 cases. These results suggest that in the perforating artery areas, the acute DWI hyperintensity is a good predictor of the eventual infarction and that in cortical artery areas, dynamic ischemic process may continue for hours before resulting in the eventual infarction.

Acute Disease↗
PubMed1999

[What to expect from MRi in the investigation of the central nervous system?].

Functional Magnetic Resonance Imaging (fMRI) has appeared as a new tool which is very powerful for cognitive neuroscience, offering the potential to look at the dynamics of cerebral processes underlying cognition, noninvasively and on an individual basis. Work remains to be done to optimize the technique and to better understand its basic mechanisms, but one may expect to build in a few years a functional list of the brain cortical networks of regions implicated in sensory-motor or cognitive processes. Still, the real understanding of brain function requires direct access to the functional unit made of the neuron, so that one may look at the transient temporal relationships that exist between largely distributed groups of hundreds or thousands of neurons. Furthermore, communication pathways between networks must be identified to establish connectivity maps at the individual scale, taking into account individual variability resulting from genetic factors and cerebral plasticity. In this respect, MRI of molecular diffusion is very sensitive to water molecular motion and, thus, to tissue dynamic microstructure, such as cell geometry. Preliminary data suggest that diffusion MRI visualizes dynamic tissue changes associated with large neuronal activation and space orientation of large bundles of myelinated axons in the white matter.

Brain Ischemia↗
PubMed2000

What to expect from MRI in the investigation of the central nervous system?

Functional magnetic resonance imaging (fMRI) has appeared as a new tool that is very powerful for cognitive neuroscience, offering the potential to look at the dynamics of cerebral processes underlying cognition, non-invasively and on an individual basis. Work remains to be done to optimize the technique and to better understand its basic mechanisms, but one may expect to build in a foreseeable future a functional list of the main brain cortical networks implicated in sensory-motor or cognitive processes. Still, the real understanding of brain function requires direct access to the functional unit consisting of the neuron, so that one may look at the transient temporal relationships that exist between largely distributed groups of hundreds or thousands of neurons. Furthermore, communication pathways between networks, which are carried by brain white matter, must be identified to establish connectivity maps at the individual scale, taking into account individual variability resulting from genetic factors and cerebral plasticity. In this respect, MRI of molecular diffusion is very sensitive to water molecular motion and, thus, to tissue dynamic microstructure, such as cell size and geometry. Preliminary data suggest that diffusion MRI visualizes dynamic tissue changes associated with large neuronal activation and space orientation of large bundles of myelinated axons in the white matter.

Animals↗
PubMed2003

The effect of unilateral ureteral obstruction on renal function in pigs measured by diffusion-weighted MRI.

The objective of this study was to examine the effect of unilateral ureteral obstruction on the apparent diffusion coefficient (ADC) in pig kidney. Changes in ADC is suggested to reflect changes in the ratio of extracellular to intracellular volume. Thirteen pigs were allocated into three groups: 1) pigs subjected to acute unilateral ureteral obstruction (AUO) (n = 3), 2) pigs subjected to chronic partial unilateral obstruction (CPUO) (n = 3), and 3) control pigs (n = 7). The extra- to intracellular volume ratio was indirectly measured in both the ipsilateral obstructed kidney and contralateral non-obstructed kidney by the ADC of the renal tissue using diffusion-weighted echo-planar magnetic resonance imaging. ADC was 2.07 +/- 0.27 x 10(-3) mm2/s in the cortex and 2.10 +/- 0.24 x 10(-3) mm2/s in the medulla of normal control kidneys. In the obstructed kidney from the AUO group the ADC of the medulla was significantly reduced 24 hours after occlusion of the ureter (1.65 +/- 0.05 x 10(-3) mm2/s vs 2.10 +/- 0.24 x 10(-3) mm2/s; p < 0.05). Similarly ADC decreased slightly in the cortex of the ipsilateral kidney. In contrast, ADC of the ipsilateral kidney of CPUO pigs was increased both in the renal medulla (3.13 +/- 0.21 x 10(-3) mm2/s vs. 2.10 +/- 0.24 x 10(-3) mm2/s; p < 0.05) and cortex (3.09 +/- 0.14 x 10(-3) mm2/s vs. 2.07 x 10(-3) mm2/s, p < 0.05). In conclusion, the results of the present study suggest that diffusion weighted imaging (ADC) may be a useful parameter to incorporate when identifying whether a ureteric obstruction is acute or chronic.

Animals↗
PubMedDate not supplied

Value of echo-planar diffusion-weighted MRI in the detection of secondary and postoperative relapsing/residual cholesteatoma.

PURPOSE: To assess the utility of echo-planar diffusion-weighted magnetic resonance imaging (EPI-DWI) in the diagnosis of secondary cholesteatoma of the middle ear and in the differential diagnosis between residual/relapsing cholesteatoma and non-cholesteatomatous tissues (scar, granulation and inflammatory tissue) after conservative mastoidectomy. MATERIALS AND METHODS: Twenty-four patients, who had previously undergone clinical and CT investigation, were prospectively examined by standard and EPI-DWI magnetic resonance imaging (MRI) after conservative mastoidectomy. Secondary cholesteatoma was suspected in 5 patients and residual/relapsing cholesteatoma in 19 patients. Two radiologists, blinded to patient's identity, clinical data and CT findings, reached consensus on the presence of tissue consistent with cholesteatoma in conventional CT and areas of altered signal in EPI-DWI in the petrous bone. All patients underwent mastoidectomy, second time of tympanoplasty or review surgery within 15 days from MR investigation. Sensitivity, specificity and negative and positive predictive values were evaluated separately for standard and EPI-DWI MRI. RESULTS: In EPI-DWI sequences, 11/12 patients with cholesteatoma showed an area of hyperintense signal, whereas patients with non-cholesteatomatous tissue showed no pathologic signal in the petrous bone. In the single case of cholesteatoma undetected on EPI-DWI a cholesteatomatous pearl approx. 2 mm in diameter was visible in the surgical cavity. Sensitivity, specificity, positive and negative predictive values were 92%, 100%, 100%, 92% for EPI-DWI MRI and 92%, 25%, 55%,75% for standard MRI, respectively. CONCLUSIONS: EPI-DWI sequences are useful in the diagnosis of secondary cholesteatoma and in the differential diagnosis between residual/relapsing cholesteatoma and non-cholesteatomatous tissues after conservative mastoidectomy. However, the usefulness of EPI-DWI sequences as a screening test after conservative mastoidectomy requires further assessment.

Adolescent↗
PubMed2000

Changes in diffusion-weighted MRI after status epilepticus.

A 3-year-old male developed hemiplegia and aphasia after convulsive status epilepticus. Diffusion-weighted magnetic resonance images demonstrated cytotoxic edema in the white matter 6 days after the seizure episode and subsequently in the gray matter after an additional 7 days. Diffusion-weighted magnetic resonance images demonstrated a subacute evolution of the pathologic process after the status epilepticus.

Brain Edema↗
PubMedDate not supplied

MRI-guided diffuse optical spectroscopy of malignant and benign breast lesions.

We present the clinical implementation of a novel hybrid system that combines magnetic resonance imaging (MRI) and near-infrared (NIR) optical measurements for the noninvasive study of breast cancer in vivo. Fourteen patients were studied with a MR-NIR prototype imager and spectrometer. A diffuse optical tomographic scheme employed the MR images as a priori information to implement an image-guided NIR localized spectroscopic scheme. All patients who entered the study also underwent gadolinium-enhanced MRI and biopsy so that the optical findings were cross-validated with MR readings and histopathology. The technique quantified the oxy- and deoxyhemoglobin of five malignant and nine benign breast lesions in vivo. Breast cancers were found with decreased oxygen saturation and higher blood concentration than most benign lesions. The average hemoglobin concentration ([H]) of cancers was 0.130+/-0.100 mM, and the average hemoglobin saturation (Y) was 60+/-9% compared to [H]=0.018+/-0.005 mM and Y=69+/-6% of background tissue. Fibroadenomas exhibited high hemoglobin concentration [H]=0.060+/-0.010 mM and mild decrease in oxygen saturation Y=67+/-2%. Cysts and other normal lesions were easily differentiated based on intrinsic contrast information. This novel optical technology can be a significant add-on in MR examinations and can be used to characterize functional parameters of cancers with diagnostic and treatment prognosis potential. It is foreseen that the technique can play a major role in functional activation studies of brain and muscle as well.

Biopsy↗