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Diffusion-weighted Imaging (diffusion-weighted + imaging)

Distribution by Scientific Domains

Medical Sciences	96%

Distribution within Medical Sciences

Radiology & Imaging	64%
Neurology	29%
2 Other Subdomains	7%

Selected Abstracts

Diffusion-weighted imaging and magnetic resonance spectroscopy findings in a case of neonatal hypoglycaemia

DEVELOPMENTAL MEDICINE & CHILD NEUROLOGY, Issue 8 2009
Rachel E Musson MBCHB MRCP
No abstract is available for this article. [source]

Diffusion-weighted imaging of the liver: Comparison of navigator triggered and breathhold acquisitions

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2009
Bachir Taouli MD
Abstract Purpose To compare a free breathing navigator triggered single shot echoplanar imaging (SS EPI) diffusion-weighted imaging (DWI) sequence with prospective acquisition correction (PACE) with a breathhold (BH) DWI sequence for liver imaging. Materials and Methods Thirty-four patients were evaluated with PACE-DWI and BH DWI of the liver using b-values of 0, 50, and 500 s/mm2. There were 29 focal liver lesions in 18 patients. Qualitative evaluation was performed on a 3-point scale (1,3) by two independent observers (maximum score 9). Quantitative evaluation included estimated SNR (signal to noise ratio), lesion-to-liver contrast ratio, liver and lesion apparent diffusion coefficients (ADCs), and coefficient of variation (CV) of ADC in liver parenchyma and focal liver lesions (estimate of noise contamination in ADC). Results PACE-DWI showed significantly better image quality, higher SNR and lesion-to-liver contrast ratio when compared with BH DWI. ADCs of liver and focal lesions with both sequences were significantly correlated (r = 0.838 for liver parenchyma, and 0.904 for lesions, P < 0.0001), but lower with the BH sequence (P < 0.02). There was higher noise contamination in ADC measurement obtained with BH DWI (with a significantly higher SD and CV of ADC). Conclusion The use of a navigator echo to trigger SS EPI DWI improves image quality and liver to lesion contrast, and enables a more precise ADC quantification compared with BH DWI acquisition. J. Magn. Reson. Imaging 2009;30:561,568. © 2009 Wiley-Liss, Inc. [source]

Feasibility of diffusion-weighted MRI for defining placental invasion

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2009
Satoru Morita MD
Abstract The purpose of this clinical note is to describe the feasibility of using diffusion-weighted imaging for diagnosing placental invasion with a case of placenta increta and six cases without it. Diffusion-weighted imaging (DWI) at a b-value of 1000 sec/mm2 can clearly define the border between the placenta and myometrium because only the placenta shows very high signal intensity. The corresponding image at a b-value of 0 sec/mm2 shows the myometrium with high signal intensity compared with the surrounding fat. Therefore, fusion of the two images can be used additionally to visualize thickness of the myometrium. As a result, DWI can be used to visualize the focal thinning of the myometrium caused by placenta increta, which has been difficult to diagnose on conventional magnetic resonance imaging sequences without contrast enhancement. However, the use of DWI for placental invasion should be determined following careful consideration of its risks and benefits, as fetus safety has not been established. J. Magn. Reson. Imaging 2009;30:666,671. © 2009 Wiley-Liss, Inc. [source]

Methods and applications of diffusion imaging of vertebral bone marrow

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2006
José G. Raya MSc
Abstract Diffusion-weighted imaging (DWI) is an MRI technique that is sensitive to random water movements at spatial scales far below typical MRI voxel dimensions. DWI is a valuable tool for the diagnoses of diseases that involve alterations in water mobility. In the spine, DWI has proven to be a highly useful method for the differential diagnosis of benign and malignant compression fractures. In these pathologies, the microscopic structure of bone marrow is altered in a very different ways, leading to different water mobility, which can be depicted by DWI. Most of the pulse sequences developed for MRI can be adapted for DWI. However, these DWI-adapted sequences are frequently affected by artifacts, mostly caused by physiological motion. Therefore, the introduction of additional correction techniques, or even the development of new sequences is necessary. The first part of this article describes the principles of DWI and the sequences used for DWI of the spine: spin echo (SE), turbo spin echo (TSE), single-shot echo planar imaging (EPI), and steady-state free precession (SSFP) sequences. In the second part, clinical applications of DWI of the spinal bone marrow are extensively discussed. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source]

Diffusion-weighted imaging of the spinal cord: Interleaved echo-planar imaging is superior to fast spin-echo

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2002
Roland Bammer PhD
Abstract Purpose To compare and evaluate two novel diffusion-weighted sequences, based either on fast spin-echo (FSE) or interleaved echo-planar imaging (EPI) methods, as potential tools for investing spinal cord abnormalities. Materials and Methods Following recent improvements, both interleaved EPI (IEPI) and FSE techniques could be alternative approaches for rapid diffusion-weighted imaging (DWI). Therefore, a navigated diffusion-weighted multishot FSE sequence and a fat-suppressed navigated diffusion-weighted IEPI sequence with local shimming capabilities were tested. Both methods were compared in a consecutive series of five healthy volunteers and five patients with suspected intramedullary lesions. The sequences were graded qualitatively as either superior, inferior, or equal in quality, and also quantitatively by measuring the amount of ghosting artifacts in the background. Quantitative measurements of the diffusion coefficients within the spine were included. Results The overall image quality of IEPI was superior to FSE. Two out of five FSE scans were rated with poor image quality, whereas all IEPI scans were of sufficient quality. The ghosting levels ranged from approximately 3.3% to 6.2% for IEPI and from approximately 7.5% to 18.9% for FSE. Diffusion coefficients measured in healthy volunteers were similar for both IEPI and FSE, but showed higher fluctuations with the FSE technique. Conclusion Despite potential advantages of FSE, the IEPI technique is preferable for DWI applications in the spinal cord. J. Magn. Reson. Imaging 2002;15:364,373. © 2002 Wiley-Liss, Inc. [source]

Ipsilateral Hemiplegia in a Lateral Medullary Infarct, Opalski's Syndrome

JOURNAL OF NEUROIMAGING, Issue 1 2003
Yasuyuki Kimura MD
ABSTRACT A 42-year-old man was admitted complaining of the sudden onset of headache, vomiting, vertigo, and gait disturbance. The authors found hemiparesis of his right limbs, right Horner's syndrome, and decreased pain and temperature sensation of his right face and left limbs. Diffusion-weighted imaging (DWI) showed an acute small infarct located on the right side of the lateral lower medulla. This is the first report of Opalski's syndrome with lower medullary infarction detected by DWI. [source]

Diffusion-weighted imaging and magnetization transfer imaging of tardive and edentulous orodyskinesia

MOVEMENT DISORDERS, Issue 9 2008
Abdesslem Khiat PhD
Abstract Oral dyskinesias occur in elderly individuals in relation to drug use (tardive dyskinesia, TD) or edentulousness (edentulous orodyskinesia, EOD) but their characterization remains incomplete. Our aim was to investigate whether magnetic resonance techniques such as diffusion-weighted imaging (DWI) and magnetization transfer imaging (MTI) of the brain could be used to differentiate dyskinetic patients from control subjects. Eight drug-treated patients with TD, 12 EOD patients, 8 drug-treated patients without TD, and 10 control subjects were recruited and examined by DWI and MTI. Measurements in the caudate nucleus, putamen, and globus pallidus yielded globally different apparent diffusion coefficient (ADC) values between drug treated patients with TD and control subjects but the magnetization transfer ratios showed no significant variations. The discrimination between dyskinetic patients and control subjects offered by ADC values was however slightly poorer than the discrimination offered by the previously published choline/creatine ratios measured by MR spectroscopy in the basal ganglia. The results are consistent with the pathophysiological hypothesis of damage to cholinergic interneurons. © 2008 Movement Disorder Society [source]

Characterizing the diffusion/perfusion mismatch in experimental focal cerebral ischemia

ANNALS OF NEUROLOGY, Issue 2 2004
Xiangjun Meng MD
Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) can rapidly detect lesions in acute ischemic stroke patients. The PWI volume is typically substantially larger than the DWI volume shortly after onset, that is, a diffusion/ perfusion mismatch. The aims of this study were to follow the evolution of the diffusion/ perfusion mismatch in permanent and 60- minute temporary focal experimental ischemia models in Sprague-Dawley rats using the intraluminal middle cerebral artery occlusion (MCAO) method. DWI and arterial spin-labeled PWI were performed at 30, 60, 90, 120, and 180 minutes after occlusion and lesion volumes (mm3) calculated At 24 hours after MCAO, and infarct volume was determined using triphenyltetrazolium chloride staining. In the permanent MCAO group, the lesion volume on the ADC maps was significantly smaller than that on the cerebral blood flow maps through the first 60 minutes after MCAO; but not after 90 minutes of occlusion. With 60 minutes of transient ischemia, the diffusion/perfusion mismatch was similar, but after reperfusion, the lesion volumes on ADC and cerebral blood flow maps became much smaller. There was a significant difference in 24- hour infarct volumes between the permanent and temporary occlusion groups. [source]

Diffusion-weighted magnetic resonance imaging of white matter in bipolar disorder: a pilot study

BIPOLAR DISORDERS, Issue 2 2006
William T Regenold
Objective:, Diffusion-weighted magnetic resonance imaging (MRI) has shown increased sensitivity in detecting brain white matter disease compared to traditional T2-weighted MRI. Diffusion-weighted imaging (DWI) can quantitatively assess the microstructural integrity of white matter using the average apparent diffusion coefficient (ADCav), a measure of the extent to which water molecules move freely within tissue. On the basis of numerous studies suggesting white matter disease in bipolar patients, particularly patients with more severe illness, this study aimed to test the utility of DWI in assessing the white matter integrity of bipolar patients with severe illness. Methods:, The existing MRI scans of eight bipolar patients and eight age-matched controls with neurological illness were examined retrospectively. ADCav values for pixels within white matter regions of interest (ROIs) were calculated and used to plot ADCav frequency histograms for each ROI. Mean ADCav values for the two groups were then compared by ANCOVA. Results:, The bipolar mean ADCav (0.855 ± 0.051 × 10,3 mm2/s) for combined white matter ROIs significantly exceeded that of controls (0.799 ± 0.046 × 10,3 mm2/s), while covarying for age (F = 4.47, df = 3, p = 0.025). Conclusions:, This is the first report of an elevated ADCav in the white matter of a group of patients with bipolar disorder. In this group of patients with severe illness, increased white matter ADCav suggests microstructural changes consistent with decreased white matter integrity. DWI may be an additional, useful tool to assess white matter abnormalities in bipolar disorder. [source]

The classic lacunar syndromes: clinical and neuroimaging correlates

EUROPEAN JOURNAL OF NEUROLOGY, Issue 7 2008
J. De Reuck
Background:, Although lacunar syndromes (LSs) are aimed to be linked to lacunar infarcts, the relation between both is still not very well defined. Purpose:, The present retrospective study tries to define more specifically the clinical and the neuroimaging characteristics of the five most classic LSs. Patients and methods:, Out of a series of 1617 consecutive stroke patients, admitted to the Ghent University Hospital, 293 presented a classic LS. Magnetic resonance imaging (MRI) with diffusion-weighted imaging (DWI) was performed within 5 days after stroke onset in 227 patients. An acute territorial infarct was demonstrated in 54 patients. The study population finally consisted of 173 patients with a classic LS in whom the responsible lacune was demonstrated or in the absence of another type of infarct. Results:, The responsible lacune was demonstrated with DWI in 104 patients. Pure motor stroke (MS) correlated significantly with the presence of the responsible lacune in the internal capsule (P = 0.000147) and with the stroke severity (P = 0.00724). No significant correlation was observed between the location of the lacunes and the other LS's. Conclusion:, Pure MS has to be considered as the most specific lacunar syndrome. [source]

Posterior reversible encephalopathy in eclampsia: diffusion-weighted imaging and apparent diffusion coefficient-mapping as prognostic tools?

EUROPEAN JOURNAL OF NEUROLOGY, Issue 3 2006
K. Ulrich
No abstract is available for this article. [source]

Generalized Diffusion Tensor Imaging (GDTI): A Method for Characterizing and Imaging Diffusion Anisotropy Caused by Non-Gaussian Diffusion

ISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2003
Chunlei Liu
For non-Gaussian distributed random displacement, which is common in restricted diffusion, a second-order diffusion tensor is incapable of fully characterizing the diffusion process. The insufficiency of a second-order tensor is evident in the limited capability of diffusion tensor imaging (DTI) in resolving multiple fiber orientations within one voxel of human white matter. A generalized diffusion tensor imaging (GDTI) method was recently proposed to solve this problem by generalizing Fick's law to a higher-order partial differential equation (PDE). The relationship between the higher-order tensor coefficients of the PDE and the higher-order cumulants of the random displacement can be derived. The statistical property of the diffusion process was fully characterized via the higher-order tensor coefficients by reconstructing the probability density function (PDF) of the molecular random displacement. Those higher-order tensor coefficients can be measured using conventional diffusion-weighted imaging or spectroscopy techniques. Simulations demonstrated that this method was capable of quantitatively characterizing non-Gaussian diffusion and accurately resolving multiple fiber orientations. It can be shown that this method is consistent with the q-space approach. The second-order approximation of GDTI was shown to be DTI. [source]

Magnetic resonance imaging in the evaluation of (deep infiltrating) endometriosis: The value of diffusion-weighted imaging

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2010
M.P.H. Busard MD
Abstract Purpose To assess the value of magnetic resonance (MR) diffusion-weighted imaging (DWI) in the evaluation of deep infiltrating endometriosis (DIE). Materials and Methods In a prospective single-center study, DWI was added to the standard MRI protocol in 56 consecutive patients with known or suspected endometriosis. Endometriotic lesions as well as (functional) ovarian cysts were analyzed for location, size, and signal intensity on T1, T2, and DWI. Apparent diffusion coefficient (ADC) values were calculated using b-values of 50, 400, 800, and 1200 s/mm2. Statistical analysis included the Spearman correlation coefficient, Mann,Whitney U, and Kruskal,Wallis tests. Results A total of 112 lesions (62 endometrial cysts and 48 DIE) were detected, 60 of which were large enough to analyze. Mean ADC values of endometrial cysts and functional ovarian cysts were 1.11 × 10,3/mm2/s and 2.14 × 10,3/mm2/s, respectively. Mean ADC values of DIE retrocervical, infiltrating the colon, and bladder were 0.70 × 10,3/mm2/s, 0.79 × 10,3/mm2/s, and 0.76 × 10,3/mm2/s, respectively. ADC values of DIE did not show a significant difference between varying pelvic locations (P = 0.63). Conclusion Results of our study suggest that ADC values of DIE are consistently low, without significant difference between pelvic locations. J. Magn. Reson. Imaging 2010;31:1117,1123. © 2010 Wiley-Liss, Inc. [source]

Diffusion-weighted imaging of the liver: Comparison of navigator triggered and breathhold acquisitions

Prostate cancer detection with multi-parametric MRI: Logistic regression analysis of quantitative T2, diffusion-weighted imaging, and dynamic contrast-enhanced MRI

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2009
Deanna L. Langer MSc
Abstract Purpose To develop a multi-parametric model suitable for prospectively identifying prostate cancer in peripheral zone (PZ) using magnetic resonance imaging (MRI). Materials and Methods Twenty-five radical prostatectomy patients (median age, 63 years; range, 44,72 years) had T2-weighted, diffusion-weighted imaging (DWI), T2-mapping, and dynamic contrast-enhanced (DCE) MRI at 1.5 Tesla (T) with endorectal coil to yield parameters apparent diffusion coefficient (ADC), T2, volume transfer constant (Ktrans) and extravascular extracellular volume fraction (ve). Whole-mount histology was generated from surgical specimens and PZ tumors delineated. Thirty-eight tumor outlines, one per tumor, and pathologically normal PZ regions were transferred to MR images. Receiver operating characteristic (ROC) curves were generated using all identified normal and tumor voxels. Step-wise logistic-regression modeling was performed, testing changes in deviance for significance. Areas under the ROC curves (Az) were used to evaluate and compare performance. Results The best-performing single-parameter was ADC (mean Az [95% confidence interval]: Az,ADC: 0.689 [0.675, 0.702]; Az,T2: 0.673 [0.659, 0.687]; Az,Ktrans: 0.592 [0.578, 0.606]; Az,ve: 0.543 [0.528, 0.557]). The optimal multi-parametric model, LR-3p, consisted of combining ADC, T2 and Ktrans. Mean Az,LR-3p was 0.706 [0.692, 0.719], which was significantly higher than Az,T2, Az,Ktrans, and Az,ve (P < 0.002). Az,LR-3p tended to be greater than Az,ADC, however, this result was not statistically significant (P = 0.090). Conclusion Using logistic regression, an objective model capable of mapping PZ tumor with reasonable performance can be constructed. J. Magn. Reson. Imaging 2009;30:327,334. © 2009 Wiley-Liss, Inc. [source]

Chronic hepatitis: Role of diffusion-weighted imaging and diffusion tensor imaging for the diagnosis of liver fibrosis and inflammation

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2008
Bachir Taouli MD
Abstract Purpose To determine the diagnostic performance of liver apparent diffusion coefficient (ADC) measured with conventional diffusion-weighted imaging (CDI) and diffusion tensor imaging (DTI) for the diagnosis of liver fibrosis and inflammation. Materials and Methods Breathhold single-shot echo-planar imaging CDI and DTI with b-values of 0 and 500 second/mm2 was performed in 31 patients with chronic liver disease and 13 normal volunteers. Liver biopsy was performed in all patients with liver disease with a median delay of two days from MRI. Fibrosis and inflammation were scored on a 5-point scale (0,4). Liver ADCs obtained with CDI and DTI were compared between patients stratified by fibrosis stage and inflammation grade. Receiver operating characteristic (ROC) curve analyses were conducted to evaluate the utility of the ADC measures for prediction of fibrosis and inflammation. Results Patients with liver fibrosis and inflammation had significantly lower liver ADC than subjects without fibrosis or inflammation with CDI and DTI. For prediction of fibrosis stage , 1 and stage , 2, area under the ROC curve (AUC) of 0.848 and 0.783, sensitivity of 88.5% to 73.7%, and specificity of 73.3% to 72.7% were obtained, for ADC ,1.40 × 10,3 mm2/second and ,1.30 × 10,3 mm2/second (using CDI), respectively. For prediction of inflammation grade , 1, AUC of 0.825, sensitivity of 75.0%, and specificity of 78.6% were obtained using ADC , 1.30 × 10,3 mm2/second (using CDI). CDI performed better than DTI for diagnosis of fibrosis and inflammation. Conclusion Liver ADC can be used to predict liver fibrosis and inflammation with acceptable sensitivity and specificity. J. Magn. Reson. Imaging 2008;28:89,95. © 2008 Wiley-Liss, Inc. [source]

Diffusion-weighted MRI of cholesteatomas of the petrous bone

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2002
Clemens Fitzek MD
Abstract Purpose To investigate if primary cholesteatomas of the petrous bone show high signal in diffusion-weighted imaging (DWI). Materials and Methods In this blinded study, we compared 15 patients with clinically certain cases and later surgically proven cholesteatomas vs. 12 patients with clinically acute otitis of the middle ear and 20 volunteers without petrous bone disease. Two blinded readers without knowledge of the clinical data decided in consensus agreement whether there was a pathologic signal increase in the petrous bone in an anisotropic single-shot echo-planar imaging (EPI) DWI sequence, an artifact, or no signal increase. Results Thirteen of 15 patients with cholesteatomas showed bright signal in EPI DWI, whereas 10 of 12 patients with acute otitis media and all volunteers presented the usual low signal of petrous bone. Conclusion EPI DWI is a fast diagnostic method that may be an additional valuable tool in the workup of suspected cholesteatomas. The ability of this technique to differentiate between cholesteatomas and granulomas or chronic otitis is not yet available. J. Magn. Reson. Imaging 2002;15:636,641. © 2002 Wiley-Liss, Inc. [source]

Diffusion-weighted imaging of the spinal cord: Interleaved echo-planar imaging is superior to fast spin-echo

Rheumatoid Leptomeningitis: Magnetic Resonance Imaging and Pathologic Findings,A Case Report

JOURNAL OF NEUROIMAGING, Issue 2 2010
Alessandro Cianfoni MD
ABSTRACT BACKGROUND AND PURPOSE Rheumatoid arthritis (RA) is a chronic inflammatory multisystem disease with articular and extra-articular manifestations. Intracranial manifestations of RA are rare. Purpose of this article is to report on a rarely described leptomeningeal involvement in RA, and on its neuroimaging features, including diffusion-weighted imaging (DWI). METHODS The authors describe the case of a 74-year-old woman with a 5-year history of RA presenting with progressive left-side weakness and hypoesthesia. The patient underwent laboratory investigation and brain contrast-enhanced MRI, also with DWI, before undergoing brain biopsy. RESULTS Neuroimaging revealed abnormal high T2-signal in right frontal and parietal lobes, restricted diffusion in the subarachnoid space, and diffuse thick linear leptomeningeal contrast-enhancement. These findings were interpreted as rheumatoid leptomeningitis, and brain biopsy confirmed this diagnosis. CONCLUSIONS In summary, rheumatoid meningitis is a rare neurological complication of RA, but it should be considered in the proper clinical setting when patient presentation and laboratory results fail to support the other differential diagnostic possibilities proposed by the MR imaging findings. [source]

Statistical evaluation of diffusion-weighted imaging of the human kidney

MAGNETIC RESONANCE IN MEDICINE, Issue 2 2010
Hans-Jörg Wittsack
Abstract The signal of diffusion-weighted imaging of the human kidney differs from the signal in brain examinations due to the different microscopic structure of the tissue. In the kidney, the deviation of the signal behavior of monoexponential characteristics is pronounced. The aim of the study was to analyze whether a mono- or biexponential or a distribution function model fits best to describe diffusion characteristics in the kidney. To determine the best regression, different statistical parameters were utilized: correlation coefficient (R2), Akaike's information criterion, Schwarz criterion, and F-test (Fratio). Additionally, simulations were performed to analyze the relation between the different models and their dependency on signal noise. Statistical tests showed that the biexponential model describes the signal of diffusion-weighted imaging in the kidney better than the distribution function model. The monoexponential model fits the diffusion-weighted imaging data the least but is the most robust against signal noise. From a statistical point of view, diffusion-weighted imaging of the kidney should be modeled biexponentially under the precondition of sufficient signal to noise. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source]

Diffusion imaging in humans at 7T using readout-segmented EPI and GRAPPA

MAGNETIC RESONANCE IN MEDICINE, Issue 1 2010
Robin M. Heidemann
Abstract Anatomical MRI studies at 7T have demonstrated the ability to provide high-quality images of human tissue in vivo. However, diffusion-weighted imaging at 7T is limited by the increased level of artifact associated with standard, single-shot, echo-planar imaging, even when parallel imaging techniques such as generalized autocalibrating partially parallel acquisitions (GRAPPA) are used to reduce the effective echo spacing. Readout-segmented echo-planar imaging in conjunction with parallel imaging has the potential to reduce these artifacts by allowing a further reduction in effective echo spacing during the echo-planar imaging readout. This study demonstrates that this approach does indeed provide a substantial improvement in image quality by reducing image blurring and susceptibility-based distortions, as well as by allowing the acquisition of diffusion-weighted images with a high spatial resolution. A preliminary application of the technique to high-resolution diffusion tensor imaging provided a high level of neuroanatomical detail, which should prove valuable in a wide range of applications. Magn Reson Med 64:9,14, 2010. © 2010 Wiley-Liss, Inc. [source]

Water diffusion heterogeneity index in the human brain is insensitive to the orientation of applied magnetic field gradients,

MAGNETIC RESONANCE IN MEDICINE, Issue 2 2006
Kevin M. Bennett
Abstract The , diffusion-weighted imaging (DWI) method was developed to study heterogeneous water diffusion in the human brain using magnetic resonance imaging (MRI). An advantage of this model is that it does not require an assumption about the shape of the intravoxel distribution of apparent diffusion rates, and it has a calculable relationship to this distribution. The ,- DWI technique is useful for detecting microstructural tissue changes associated with brain tumor invasion, and may be useful for directing therapy to invading tumor cells. In previous work, ,- DWI was performed with magnetic field gradients applied along a single direction in order to avoid artificially introducing a source of heterogeneity to the decay. However, it is known that restricted diffusion is anisotropic in the brain, and the ,- DWI method must take this into account to be complete. In this work the relationship between the applied magnetic field gradients and the fitted stretched-exponential model parameters was studied in the human brain. It was found the distributed diffusion coefficient (DDC) varies with the direction of applied gradients, while the heterogeneity index , is relatively direction-insensitive. It is proposed that in clinical use, maps of , can be created using diffusion-weighting gradients applied in a single direction that reflect the tissue heterogeneity. Magn Reson Med, 2006. Published 2006 Wiley-Liss, Inc. [source]

Multiple spin-echo spectroscopic imaging for rapid quantitative assessment of N-acetylaspartate and lactate in acute stroke

MAGNETIC RESONANCE IN MEDICINE, Issue 2 2004
Astrid Stengel
Abstract Monitoring the signal levels of lactate (Lac) and N-acetylaspartate (NAA) by chemical shift imaging can provide additional knowledge about tissue damage in acute stroke. Despite the need for this metabolic information, spectroscopic imaging (SI) has not been used routinely for acute stroke patients, mainly due to the long acquisition time required. The presented data demonstrate that the application of a fast multiple spin-echo (MSE) SI sequence can reduce the measurement time to 6 min (four spin echoes per echo train, 32 × 32 matrix). Quantification of Lac and NAA in terms of absolute concentrations (i.e., mmol/l) can be achieved by means of the phantom replacement approach, with correction terms for the longitudinal and transversal relaxation adapted to the multiple spin-echo sequence. In this pilot study of 10 stroke patients (symptom onset < 24 hr), metabolite concentrations obtained from MSE-SI add important information regarding tissue viability that is not provided by other sequences (e.g., diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI)). Metabolic changes extended beyond the borders of the apparent diffusion coefficient (ADC) lesion in nine of the 10 patients, showing a rise in Lac concentrations up to 18 mmol/l, while NAA levels sometimes dropped below the detection level. Considerable differences among the patients in terms of the Lac concentrations and the size of the SI-ADC mismatch were observed. Magn Reson Med 52:228,238, 2004. © 2004 Wiley-Liss, Inc. [source]

Neuroprotective effects of an immunosuppressant agent on diffusion/perfusion mismatch in transient focal ischemia

MAGNETIC RESONANCE IN MEDICINE, Issue 6 2004
Toshihiko Ebisu
Abstract The immunosuppressant FK506 (tacrolimus) exerts potent neuroprotection following focal ischemia in animals; however, the separate effects of FK506 on the ischemic core and penumbra have not been reported. The ischemic penumbra is clinically defined as the difference between a large abnormal area on perfusion-weighted imaging (PWI) and a smaller lesion on diffusion-weighted imaging (DWI). The goal of this study was to determine the effect of FK506 on DWI/PWI match and mismatch areas in transient focal ischemia in rats. Twelve rats were subjected to 1 hr of transient middle cerebral artery (MCA) occlusion, and given an intravenous injection of a placebo (N = 6) or 1 mg/kg FK506 (N = 6) immediately before reperfusion. Magnetic resonance imaging (MRI) was performed during MCA occlusion, and 0.5, 1, and 24 hr after reperfusion. FK506 significantly protected the ischemic brain only in the mismatch cortex where the initial apparent diffusion coefficient (ADC) was normal and there was a mild reduction of cerebral blood flow (CBF). This is the first report to describe the protective effects of FK506 on ischemic penumbra, as measured by DWI/PWI mismatch. The findings provide direct evidence for the utility of DWI/PWI mismatch as a guideline for therapeutic intervention with FK506. Magn Reson Med 51:1173,1180, 2004. © 2004 Wiley-Liss, Inc. [source]

Online motion correction for diffusion-weighted imaging using navigator echoes: Application to RARE imaging without sensitivity loss

MAGNETIC RESONANCE IN MEDICINE, Issue 5 2001
David G. Norris
Abstract This article describes the first application of true online motion correction to diffusion-weighted RARE imaging. Two orthogonal navigator echoes were acquired and zeroth and first-order phase corrections applied in less than 8 ms between a diffusion-weighted magnetization preparation and data acquisition using the RARE sequence. The zeroth-order phase correction was realized by pulsing the system's B0 -coil: the first-order error corrected with appropriate magnetic field gradient pulses. Online correction ensured that no irreversible signal loss could occur in the imaging experiment. Diffusion-weighted images of the brain were obtained from healthy volunteers. EGG-triggered acquisition was applied at 400 ms after the R-wave. Data were acquired on a matrix of 256 × 256 with a RARE factor of 16 and a b -value of 804 smm,2. The images obtained with online motion correction showed a remarkably high image quality, while those acquired without motion correction were severely degraded by artifacts. Magn Reson Med 45:729,733, 2001. © 2001 Wiley-Liss, Inc. [source]

Diffusion-weighted imaging and magnetization transfer imaging of tardive and edentulous orodyskinesia

Progress in diffusion-weighted imaging: concepts, techniques and applications to the central nervous system

NMR IN BIOMEDICINE, Issue 7 2010
Jens H. Jensen
No abstract is available for this article. [source]

Coagulopathy and embolic signal in cancer patients with ischemic stroke

ANNALS OF NEUROLOGY, Issue 2 2010
Jin Myoung Seok MD
Objective It has been reported that embolic signal (ES) detected by transcranial Doppler (TCD) has clinical significance, especially in patients with recent stroke attributable to arterial or cardiac embolism. Therefore, we conducted this study to determine whether the prevalence of ES is high in ischemic stroke patients with cancer and related to hypercoagulopathy. Methods We prospectively studied cancer patients with acute ischemic stroke within the middle cerebral artery (MCA) distribution on diffusion-weighted imaging. Conventional stroke mechanisms (CSMs) were determined using cardiologic and vascular studies. Additionally, the coagulation status was assessed based on the serum D-dimer levels, and TCD monitoring was performed on both MCAs for 30 minutes to detect ES. Clinical features including vascular risk factors, characteristics of ischemic stroke, and cancer and laboratory findings associated with the presence of ES were evaluated. Results A total of 74 patients were finally included in this study. ES was more commonly observed in patients without CSMs (22 of 38 patients, 57.9%) than in those with CSMs (12 of 36 patients, 33.3%) (p = 0.034). Moreover, ES was more commonly detected in patients with high D-dimer levels (p < 0.001), and D-dimer levels were significantly correlated with the number of ESs in patients without CSMs (r = 0.732, p < 0.001), but were poorly correlated in patients with CSMs (r = 0.152, p = 0.375). Higher levels of D-dimer (odds ratio [OR], 1.082 per 1,g/ml increase; 95% confidence interval [CI], 1.014,1.154) and adenocarcinoma (OR, 3.829; 95% CI, 1.23,13.052) were independently associated with the presence of ES. The use of anticoagulants dramatically decreased the D-dimer levels. Interpretation A high prevalence of ES was observed in cancer patients with ischemic stroke, especially in those without CSMs. Elevated D-dimer levels were independently associated with ES, and decreased dramatically with the use of anticoagulants. ANN NEUROL 2010;68:213,219 [source]