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Weighted MRI (weighted + mri)
Selected AbstractsDynamics of Dot-Like Hemosiderin Spots on T2*-Weighted MRIs Associated with Stroke RecurrenceJOURNAL OF NEUROIMAGING, Issue 3 2007Toshio Imaizumi MD ABSTRACT Background and Purpose. Dot-like low-intensity spots (dot-like hemosiderin spots: dotHSs) on gradient echo T2*-weighted (-w) brain magnetic resonance imaging (MRIs) are frequently associated with cerebral small vessel disease (SVD), including deep intracerebral hemorrhages and lacunar infarctions. This study investigated how numbers of newly appeared dotHSs contribute to recurrent SVD. Methods. We prospectively analyzed numbers of newly appeared dotHSs in 12 patients with prior SVD (8 males, 4 females; mean 67.6 ± 10.7 years old) readmitted with recurring SVD between October 2001 and March 2003. Numbers of appeared dotHSs per year were counted on T2*-w MRI scans after SVD recurrence and compared to previous MRIs. Seventy-one outpatients (35 males, 36 females; mean 64.3 ± 9.6 years old) with histories of intracerebral hemorrhages (ICH) that came to the hospital during the study period served as controls. The hazard ratio (HR) for recurrence was estimated from a multivariate logistic regression model, using the number of appeared dotHSs (per year) and other risk factors. Results. Multivariate analyses revealed that an elevated rate of recurrence was found in patients with substantial numbers of appeared dotHSs (,5/year) (HR, 7.34; P= 0.0008). We also analyzed factors associated with the numbers of appeared dotHSs. A number of appeared dotHSs (,5/year) was significantly and independently associated with the initial number of dotHSs (,10) on T2*-w MRIs following the first SVD (HR, 18.6; P= 0.0001). Conclusions. Though a small sample size limited the power of our analyses, our findings suggest that a number of newly appeared dotHSs may be associated with SVD recurrence. [source] Bifunctional Eu3+ -doped Gd2O3 nanoparticles as a luminescent and T1 contrast agent for stem cell labelingCONTRAST MEDIA & MOLECULAR IMAGING, Issue 2 2010Zhilong Shi Abstract Magnetic resonance tracking of stem cells has recently become an emerging application for investigating cell,tissue interactions and guiding the development of effective stem cell therapies for regeneration of damaged tissues and organs. In this work, anionic Eu3+ -doped Gd2O3 hybrid nanoparticles were applied as a contrast agent both for fluorescence microscopy and T1 -weighted MRI. The nanoparticles were synthesized through the polyol method and further modified with citric acid to obtain anionic nanoparticles. These nanoparticles were internalized into human mesenchymal stem cells (hMSCs) as confirmed by confocal laser scanning microscopy and quantified by inductively coupled plasma,mass spectrometry. MTT assay of the labeled cells showed that the nanoparticles did not possess significant cytotoxicity. In addition, the osteogenic, adipogenic and chondrogenic differentiation of the hMSCs was not influenced by the labeling process. With MRI, the in vitro detection threshold of cells after incubation with nanoparticles at a Gd concentration of 0.5,mMfor 2,h was estimated to be about 10 000 cells. The results from this study indicate that the biocompatible anionic Gd2O3 nanoparticles doped with Eu3+ show promise both as a luminescent and T1 contrast agent for use in visualizing hMSCs. Copyright © 2010 John Wiley & Sons, Ltd. [source] Plasma total homocysteine levels are associated with advanced leukoaraiosis but not with asymptomatic microbleeds on T2*-weighted MRI in patients with strokeEUROPEAN JOURNAL OF NEUROLOGY, Issue 3 2006H. Naka Both leukoaraiosis and asymptomatic microbleeds are associated with small-artery diseases. Although an association between hyperhomocysteinemia and leukoaraiosis has been reported, no studies have evaluated the association between total homocysteine (tHcy) level and presence of microbleeds in stroke patients. We evaluated the association between tHcy level and leukoaraiosis or microbleeds in stroke patients. In 102 patients with stroke (69.5 ± 10.3 years old, 54 men and 48 women), microbleeds on T2*-weighted MR images were counted, leukoaraiosis on T2-weighted images was graded and fasting plasma tHcy concentrations were measured. Plasma tHcy level was significantly higher in patients with advanced leukoaraiosis than in those without advanced leukoaraiosis (13.9 ± 4.6 ,mol/l vs. 10.2 ± 3.4 ,mol/l, P < 0.0001). Plasma tHcy level was not significantly different in patients with microbleeds and those without microbleeds (11.3 ± 4.1 ,mol/l vs. 11.4 ± 4.3 ,mol/l, P = 0.9441). Elevated tHcy level is significantly and independently associated with advanced leukoaraiosis [odds ratio (OR), 1.330; 95% CI, 1.130,1.565] but not with the presence of microbleeds. Elevated tHcy level appears to be associated with ischemic small-artery disease rather than with bleeding-prone small-artery disease. [source] Nonblinking and Nonbleaching Upconverting Nanoparticles as an Optical Imaging Nanoprobe and T1 Magnetic Resonance Imaging Contrast AgentADVANCED MATERIALS, Issue 44 2009Yong Il Park Core/shell upconverting nanoparticles (UCNPs) of NaGdF4:Er3+,Yb3+/NaGdF4 (see figure) are shown to serve as a multimodal imaging probe that works for both background-free optical imaging and magnetic resonance imaging (MRI). The nonblinking and nonbleaching properties of UCNPs can contribute to minimization of possible artifacts in long-term imaging experiments. Owing to Gd3+ ions in the host matrix, contrast is enhanced in T1 -weighted MRI. [source] A pulse sequence for rapid in vivo spin-locked MRIJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2006Arijitt Borthakur PhD Abstract Purpose To develop a novel pulse sequence called spin-locked echo planar imaging (EPI), or (SLEPI), to perform rapid T1, -weighted MRI. Materials and Methods SLEPI images were used to calculate T1, maps in two healthy volunteers imaged on a 1.5-T Sonata Siemens MRI scanner. The head and extremity coils were used for imaging the brain and blood in the popliteal artery, respectively. Results SLEPI-measured T1, was 83 msec and 103 msec in white (WM) and gray matter (GM), respectively, 584 msec in cerebrospinal fluid (CSF), and was similar to values obtained with the less time-efficient sequence based on a turbo spin-echo readout. T1, was 183 msec in arterial blood at a spin-lock (SL) amplitude of 500 Hz. Conclusion We demonstrate the feasibility of the SLEPI pulse sequence to perform rapid T1, MRI. The sequence produced images of higher quality than a gradient-echo EPI sequence for the same contrast evolution times. We also discuss applications and limitations of the pulse sequence. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Detection of changes in articular cartilage proteoglycan by T1, magnetic resonance imagingJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2005Andrew J. Wheaton Abstract The purpose of this work is to demonstrate the feasibility of T1, -weighted magnetic resonance imaging (MRI) to quantitatively measure changes in proteoglycan content in cartilage. The T1, MRI technique was implemented in an in vivo porcine animal model with rapidly induced cytokine-mediated cartilage degeneration. Six pigs were given an intra-articular injection of recombinant porcine interleukin-1, (IL-1,) into the knee joint before imaging to induce changes in cartilage via matrix metalloproteinase (MMP) induction. The induction of MMPs by IL-1 was used since it has been extensively studied in many systems and is known to create conditions that mimic in part characteristics similar to those of osteoarthritis. The contralateral knee joint was given a saline injection to serve as an internal control. T1, -weighted MRI was performed on a 4 T whole-body clinical scanner employing a 2D fast spin-echo-based T1, imaging sequence. T1, relaxation parameter maps were computed from the T1, -weighted image series. The average T1, relaxation rate, R1, (1/T1,) of the IL-1,-treated patellae was measured to be on average 25% lower than that of saline-injected patellae indicating a loss of proteoglycan. There was an average reduction of 49% in fixed charge density, measured via sodium MRI, of the IL-1,-treated patellae relative to control corroborating the loss of proteoglycan. The effects of IL-1,, primarily loss of PG, were confirmed by histological and immunochemical findings. The results from this study demonstrate that R1, is able to track proteoglycan content in vivo. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] Four-dimensional spectral-spatial RF pulses for simultaneous correction of B1+ inhomogeneity and susceptibility artifacts in T2*-weighted MRIMAGNETIC RESONANCE IN MEDICINE, Issue 1 2010Cungeng Yang Abstract Susceptibility artifacts and excitation radiofrequency field B1+ inhomogeneity are major limitations in high-field MRI. Parallel transmission methods are promising for reducing artifacts in high-field applications. In particular, three-dimensional RF pulses have been shown to be useful for reducing B1+ inhomogeneity using multiple transmitters due to their ability to spatially shape the slice profile. Recently, two-dimensional spectral-spatial pulses have been demonstrated to be effective for reducing the signal loss susceptibility artifact by incorporating a frequency-dependent through-plane phase correction. We present the use of four-dimensional spectral-spatial RF pulses for simultaneous B1+ and through-plane signal loss susceptibility artifact compensation. The method is demonstrated with simulations and in T2*-weighted human brain images at 3 T, using a four-channel parallel transmission system. Parallel transmission was used to reduce the in-plane excitation resolution to improve the slice-selection resolution between two different pulse designs. Both pulses were observed to improve B1+ homogeneity and reduce the signal loss artifact in multiple slice locations and several human volunteers. Magn Reson Med 64:1,8, 2010. © 2010 Wiley-Liss, Inc. [source] T1 -weighted magnetic resonance imaging shows fatty deposition after myocardial infarctionMAGNETIC RESONANCE IN MEDICINE, Issue 5 2007James W. Goldfarb Abstract Pathologic studies have shown an increased lipid content in areas of myocardial infarction (MI). We sought to show the ability of precontrast T1 -weighted MRI to noninvasively detect fat deposition in MI and show its association with infarct age. Thirty-two patients with MI were studied. Precontrast inversion-recovery (IR) cine steady-state free precession (SSFP) imaging was used to generate both fat- and muscle-nulled images to locate areas of fat deposition in the left ventricular (LV) myocardium. Postcontrast delayed hyperenhanced (DHE) imaging was also performed. Image contrast in regions of MI on precontrast images and postcontrast DHE images was measured. The association of image contrast with infarct age was determined by means of correlations and Student's t -test. We found a significant association between infarct age and image contrast in both fat- and muscle-nulled images. Precontrast T1 -weighted MRI is a promising method for detecting myocardial fat deposition in chronic MI, and can be used to assess myocardial infarct age. Magn Reson Med 57:828,834, 2007. © 2007 Wiley-Liss, Inc. [source] Method for reduced SAR T1, -weighted MRIMAGNETIC RESONANCE IN MEDICINE, Issue 6 2004Andrew J. Wheaton Abstract A reduced specific absorption rate (SAR) version of the T1, -weighted MR pulse sequence was designed and implemented. The reduced SAR method employs a partial k -space acquisition approach in which a full power spin-lock pulse is applied to only the central phase-encode lines of k -space, while the remainder of k -space receives a low-power spin-lock pulse. Acquisition of high- and low-power phase-encode lines are interspersed chronologically to minimize average power deposition. In this way, the majority of signal energy in the central portion of k -space receives full T1, -weighting, while the average SAR of the overall acquisition can be reduced, thereby lowering the minimum safely allowable TR. The pulse sequence was used to create T1, maps of a phantom, an in vivo mouse brain, and the brain of a human volunteer. In the images of the human brain, SAR was reduced by 40% while the measurements of T1, differed by only 2%. The reduced SAR sequence enables T1, -weighted MRI in a clinical setting, even at high field strengths. Magn Reson Med 51:1096,1102, 2004. © 2004 Wiley-Liss, Inc. [source] Magnetic resonance imaging and biological properties of pancreatic islets labeled with iron oxide nanoparticlesNMR IN BIOMEDICINE, Issue 8 2009Hoe Suk Kim Abstract This study was undertaken to investigate the in vitro effect of islet labeling with iron oxide nanoparticles for MRI on islet viability, insulin secretion, and gene expression. Isolated rat islets were labeled with Resovist (25,200,µg Fe/mL, a clinically approved MRI contrast agent) in the presence or absence of poly- l -Lysine (PLL, 1.5,µg/mL) for 48,h. The iron content of labeled islets was found to increase in a dose-dependent manner. More than 90% of the islets were labeled with 100,µg Fe/mL. We confirmed the localizations of iron oxide nanoparticles within islet , -cells by insulin immunostaining. As the concentration of Resovist increased, T2 values as determined by T2 -weighted MRI on a 1.5,Tesla MR scanner decreased. Labeling of 100 islets in a medium containing 100,µg Fe/mL of Resovist in the absence of PLL provided sufficient contrast for islet visualization on T2 -weighted MRI. MTT assays showed that the viability of labeled islets was not different from that of unlabeled islets. No statistical difference was observed between labeled (2.91,±,0.36) and unlabeled islets (2.83,±,0.61) in terms of the ability to secrete insulin, as determined by the glucose stimulation index. We also evaluated the effect of iron oxide incorporation on the gene expressions in islet cells using RT-PCR (reverse transcriptase PCR). Insulin expression in labeled islets was significantly elevated (1.83,±,0.25 fold vs. unlabeled; p,=,0.005), but not the expression of somatostatin (1.39,±,0.18 fold vs. unlabeled; p,=,0.085) or glucagons (1.28,±,0.13 fold vs. unlabeled; p,=,0.09). Expression of an important transcription factor for insulin gene transcription, BETA2 (beta-cell E-box trans-activator), was increased in labeled islets (1.67,±,0.15 fold vs. unlabeled; p,=,0.029). The findings of this study indicate that Resovist provides a satisfactory means to image islets and has no deleterious effect on islet function or gene expression. Copyright © 2009 John Wiley & Sons, Ltd. [source] Quantitative characterization of hemodynamic properties and vasculature dysfunction of high-grade gliomasNMR IN BIOMEDICINE, Issue 6 2007Vijaya Nagesh Abstract Aberrations in tumor and peritumoral vasculature may not be distinguishable by cerebral blood flow (CBF) or cerebral blood volume (CBV) alone. The relationships between CBF and CBV were examined to estimate vasculature-specific hemodynamic characteristics. Twenty glioma patients were studied with dynamic susceptibility T2*-weighted MRI [(dynamic contrast-enhanced magnetic resonance imaging (DSC-MRI)] before and during week 1 and 3 of radiotherapy (RT). CBF and CBV were calculated from DSC-MRI, and relationships between the two were evaluated: the physiological measure of mean transit time (MTT),=,CBV/CBF; empirical fitting using the power law CBV,=,constant,×,(CBF),. Three different tissue types were assessed: the Gd-enhancing tumor volume (GEV); non-enhanced abnormal tissue located beyond GEV but within the abnormal hyperintense region on FLAIR images (NEV); normal tissue in the hemisphere contralateral to the tumor (CNT). The effects of tissue types, CBV magnitudes (low, medium and high), before and during RT, on MTT and , were analyzed by analysis of variance (ANOVA). The MTT and , for the three tissue types were significantly different (p,<,0.009). MTT increased from CNT (1.60,s) to NEV (1.93,s) to GEV (2.28,s) (p,<,0.0005). , was significantly greater in GEV (1.079) and NEV (1.070) than in CNT (1.025). , increased with increasing CBV magnitude while MTT was independent of CBV magnitude. There was a significant decrease in MTT of NEV and GEV during week 3 of RT compared with pre-RT values for all CBV magnitudes. There was a significant increase in , during RT in the tumor and peritumor. Progressive abnormalities in vasculature and hemodynamic characteristics of the vascular bed were delineated, with significant disorder in the tumor but mild abnormality in peritumoral tissue. Copyright © 2007 John Wiley & Sons, Ltd. [source] MRI monitoring of focal cerebral ischemia in peroxisome proliferator-activated receptor (PPAR)-deficient miceNMR IN BIOMEDICINE, Issue 3 2007Jean-Baptiste Pialat Abstract Peroxisome proliferator-activated receptors (PPARs) are a potential target for neuroprotection in focal ischemic stroke. These nuclear receptors have major effects in lipid metabolism, but they are also involved in inflammatory processes. Three PPAR isotypes have been identified: ,, , (or ,) and ,. The development of PPAR transgenic mice offers a promising tool for prospective therapeutic studies. This study used MRI to assess the role of PPAR, and PPAR, in the development of stroke. Permanent middle cerebral artery occlusion induced focal ischemia in wild-type, PPAR, -null mice and PPAR, -null mice. T2 -weighted MRI was performed with a 7 T MRI scan on day 0, 1, 3, 7 and 14 to monitor lesion growth in the various genotypes. General Linear Model statistical analysis found a significant difference in lesion volume between wild-type and PPAR-null mice for both , and , isotypes. These data validate high-resolution MRI for monitoring cerebral ischemic lesions, and confirm the neuroprotective role of PPAR, and PPAR, in the brain. Copyright © 2007 John Wiley & Sons, Ltd. [source] T2*-weighted magnetic resonance imaging with hyperoxia in acute ischemic strokeANNALS OF NEUROLOGY, Issue 1 2010Krishna A. Dani MBChB Objective We describe the first clinical application of transient hyperoxia ("oxygen challenge") during T2*-weighted magnetic resonance imaging (MRI), to detect differences in vascular deoxyhemoglobin between tissue compartments following stroke. Methods Subjects with acute ischemic stroke were scanned with T2*-weighted MRI and oxygen challenge. For regions defined as infarct core (diffusion-weighted imaging lesion) and presumed penumbra (perfusion-diffusion mismatch [threshold = Tmax ,4 seconds], or regions exhibiting diffusion lesion expansion at day 3), T2*-weighted signal intensity,time curves corresponding to the duration of oxygen challenge were generated. From these, the area under the curve, gradient of incline of the signal increase, time to maximum signal, and percentage signal change after oxygen challenge were measured. Results We identified 25 subjects with stroke lesions >1ml. Eighteen subjects with good quality T2*-weighted signal intensity,time curves in the contralateral hemisphere were analyzed. Curves from the diffusion lesion had a smaller area under the curve, percentage signal change, and gradient of incline, and longer time to maximum signal (p < 0.05, n = 17) compared to normal tissue, which consistently showed signal increase during oxygen challenge. Curves in the presumed penumbral regions (n = 8) showed varied morphology, but at hyperacute time points (<8 hours) showed a tendency to greater percentage signal change. Interpretation Differences in T2*-weighted signal intensity,time curves during oxygen challenge in brain regions with different pathophysiological states after stroke are likely to reflect differences in deoxyhemoglobin concentration, and therefore differences in metabolic activity. Despite its underlying complexities, this technique offers a possible novel mode of metabolic imaging in acute stroke. ANN NEUROL 2010;68:37,47 [source] A Short-echo-time Proton Magnetic Resonance Spectroscopic Imaging Study of Temporal Lobe EpilepsyEPILEPSIA, Issue 9 2002Robert J. Simister Summary: ,Purpose: We used short-echo-time proton magnetic resonance spectroscopy imaging (MRSI) to study metabolite concentration variation through the temporal lobe in patients with temporal lobe epilepsy (TLE) with and without abnormal MRI. Methods: MRSI was performed at TE = 30 ms to study 10 control subjects, 10 patients with TLE and unilateral hippocampal sclerosis, and 10 patients with TLE and unremarkable MRI (MRI negative). We measured the concentrations of N -acetyl aspartate +N -acetyl aspartyl-glutamate (NAAt), creatine (Cr), choline (Cho), glutamate + glutamine (Glx), and myoinositol, in the anterior, middle, and posterior medial temporal lobe (MTL), and in the posterior lateral temporal lobe. Segmented volumetric T1 -weighted MRIs gave the tissue composition of each MRSI voxel. Normal ranges were defined as the control mean ± 3 SD. Results: In the hippocampal sclerosis group, seven of 10 had abnormally low NAAt in the ipsilateral anterior MTL. In the MRI-negative group, four of 10 had low NAAt in the middle MTL voxel ipsilateral to seizure onset. Metabolite ratios were less sensitive to abnormality than was the NAAt concentration. Group analysis showed low NAAt, Cr, and Cho in the anterior MTL in hippocampal sclerosis. Glx was elevated in the anterior voxel contralateral to seizure onset in the MRI-negative group. Metabolite concentrations were influenced by voxel position and tissue composition. Conclusions: (a) Low NAAt, Cr, and Cho were features of the anterior sclerotic hippocampus, whereas low NAAt was observed in the MRI-negative group in the middle MTL region. The posterior temporal lobe regions were not associated with significant metabolite abnormality; (b) The two patient groups demonstrated different metabolite profiles across the temporal lobe, with elevated Glx a feature of the MRI-negative group; and (c) Voxel tissue composition and position influenced obtained metabolite concentrations. [source] | ||||||||||||||||||||||