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1.
NMR Biomed ; 28(11): 1589-97, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26449628

RESUMO

Diffusion tensor imaging (DTI) is a popular method to assess differences in fiber organization in diseased and healthy muscle tissue. Previous work has shown that muscle DTI measurements depend on signal-to-noise ratio (SNR), %fat, and tissue T2. The goal of this study was to evaluate the potential biasing effects of these factors on skeletal muscle DTI data in patients with Duchenne Muscular Dystrophy (DMD). MR images were obtained of the right lower leg of 21 DMD patients and 12 healthy controls on a Philips 3T system. DTI measurements were combined with quantitative in-vivo measures of mean water T2, %fat and SNR to evaluate their effect on DTI parameter estimation. All outcome measures were determined within ROIs drawn for six lower leg muscles. Between group analysis, using all ROIs, revealed a significantly elevated FA in the GCL, SOL and PER muscles (p<0.05) and an increased mean diffusivity (p<0.05) and λ3 (p<0.05) in the TA muscle of DMD patients. In-vivo evaluation of the individual confounders showed behaviour in line with predictions from previous simulation work. To account for these confounders, subsequent analysis used only ROIs with SNR greater than 20. With this criterion we found significantly greater MD in the TA muscle of DMD patient (p<0.009) and λ3 in the TA and GCL muscles (p<0.001) of DMD patients, but no differences in FA. As both increased %fat and lower SNR are expected to reduce the apparent MD and λ3, these between-group differences are likely due to pathophysiology. However, the increased FA, observed when using all ROIs, likely reflects the effect of low SNR and %fat on the DTI parameter estimation. These findings suggest that measuring mean water T2, %fat and SNR is essential to ascribe changes in DTI measures to intrinsic diffusion changes or to confounding influences.


Assuntos
Imagem de Tensor de Difusão/métodos , Músculo Esquelético/patologia , Distrofia Muscular de Duchenne/patologia , Adolescente , Criança , Pré-Escolar , Feminino , Humanos , Perna (Membro)/patologia , Masculino , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Razão Sinal-Ruído
2.
Magn Reson Med ; 68(6): 1836-45, 2012 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-22362637

RESUMO

Spatio-temporal magnetic field changes in the brain caused by breathing or body movements can lead to image artifacts. This is especially a problem in T(2)(*)-weighted sequences. With the acquisition of an extra echo (navigator), it is possible to measure the magnetic field change induced frequency offset for a given slice during image acquisition. However, substantial local variation across a slice can occur. This work describes an extension of the conventional navigator technique that improves the estimation of the magnetic field distribution in the brain during strong field fluctuations. This is done using the combination of signals from multiple coil elements, the coil sensitivity profiles, and frequency encoding: termed sensitivity-encoded navigator echoes. In vivo validation was performed in subjects who performed normal breathing, nose touching, and deep breathing during scanning. The sensitivity-encoded navigator technique leads to an error reduction in estimating the field distribution in the brain of 73% ± 16% compared with 56% ± 14% for conventional estimation. Image quality can be improved via incorporating this navigator information appropriately into the image reconstruction. When the sensitivity-encoded navigator technique was applied to a T(2)(*)-weighted sequence at 7 T, a ghosting reduction of 47% ± 13% was measured during nose touching experiments compared with no correction.


Assuntos
Algoritmos , Artefatos , Encéfalo/anatomia & histologia , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Imageamento por Ressonância Magnética/métodos , Humanos , Campos Magnéticos , Dinâmica não Linear , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
3.
NMR Biomed ; 24(7): 873-9, 2011 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-21834010

RESUMO

The intrinsic nonuniformities in the transmit radiofrequency field from standard quadrature volume resonators at high field are particularly problematic for localized MRS in areas such as the temporal lobe, where a low signal-to-noise ratio and poor metabolite quantification result from destructive B1⁺ field interference, in addition to line broadening and signal loss from strong susceptibility gradients. MRS of the temporal lobe has been performed in a number of neurodegenerative diseases at clinical fields, but a relatively low signal-to-noise ratio has prevented the reliable quantification of, for example, glutamate and glutamine, which are thought to play a key role in disease progression. Using a recently developed high-dielectric-constant material placed around the head, localized MRS of the medial temporal lobe using the stimulated echo acquisition mode sequence was acquired at 7 T. The presence of the material increased the signal-to-noise ratio of MRS by a factor of two without significantly reducing the sensitivity in other areas of the brain, as shown by the measured B1⁺ maps. An increase in the receive sensitivity B1⁻ was also measured close to the pads. The spectral linewidth of the unsuppressed water peak within the voxel of interest was reduced slightly by the introduction of the dielectric pads (although not to a statistically significant degree), a result confirmed by using a pad composed of lipid. Using LCmodel for quantitative analysis of metabolite concentrations, the increase in signal-to-noise ratio and the slight decrease in spectral linewidth contributed to statistically significant reductions in the Cramer-Rao lower bounds (CRLBs), also allowing the levels of glutamate and glutamine to be quantified with CRLBs below 20%.


Assuntos
Espectroscopia de Ressonância Magnética/instrumentação , Espectroscopia de Ressonância Magnética/métodos , Lobo Temporal/anatomia & histologia , Lobo Temporal/metabolismo , Adulto , Humanos , Pessoa de Meia-Idade , Adulto Jovem
4.
Neuroimage ; 51(3): 1082-8, 2010 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-20338252

RESUMO

The altered iron concentration in many neurodegenerative diseases such as Alzheimer's disease (AD) has led to the development of MRI sequences that are sensitive to the accompanying changes in the transverse relaxation rate. Heavily T(2)*-weighted imaging sequences at high magnetic field strength (7T and above), in particular, show potential for detecting small changes in iron concentration. However, these sequences require a long echo time in combination with a long scanning time for high resolution and are therefore prone to image artifacts caused by physiological fluctuations, patient motion or system instabilities. Many groups have found that the high image quality that was obtained using high resolution T(2)*-weighted sequences at 7T in healthy volunteers, could not be obtained in AD patients. In this study the source of the image artifacts was investigated in phantom and in healthy volunteer experiments by incorporating movement parameters and resonance frequency (f0) variations which were measured in AD patients. It was found that image degradation caused by typical f0 variations was a factor-of-four times larger than artifacts caused by movement characteristic of AD patients in the scanner. In addition to respiratory induced f0 variations, large jumps in the f0 were observed in AD patients. By implementing a navigator echo technique to correct for f0 variations, the image quality of high resolution T(2)*-weighted images increased considerably. This technique was successfully applied in five AD patients and in five subjective memory complainers. Visual scoring showed improvements in image quality in 9 out of 10 subjects. Ghosting levels were reduced by 24+/-13%.


Assuntos
Algoritmos , Doença de Alzheimer/patologia , Artefatos , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Imageamento por Ressonância Magnética/métodos , Feminino , Humanos , Pessoa de Meia-Idade , Movimento (Física) , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
5.
AJNR Am J Neuroradiol ; 36(2): 378-83, 2015 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-25147195

RESUMO

BACKGROUND AND PURPOSE: In many centers, MR imaging of the inner ear and auditory pathway performed on 1.5T or 3T systems is part of the preoperative work-up of cochlear implants. We investigated the applicability of clinical inner ear MR imaging at 7T and compared the visibility of inner ear structures and nerves within the internal auditory canal with images acquired at 3T. MATERIALS AND METHODS: Thirteen patients with sensorineural hearing loss eligible for cochlear implantation underwent examinations on 3T and 7T scanners. Two experienced head and neck radiologists evaluated the 52 inner ear datasets. Twenty-four anatomic structures of the inner ear and 1 overall score for image quality were assessed by using a 4-point grading scale for the degree of visibility. RESULTS: The visibility of 11 of the 24 anatomic structures was rated higher on the 7T images. There was no significant difference in the visibility of 13 anatomic structures and the overall quality rating. A higher incidence of artifacts was observed in the 7T images. CONCLUSIONS: The gain in SNR at 7T yielded a more detailed visualization of many anatomic structures, especially delicate ones, despite the challenges accompanying MR imaging at a high magnetic field.


Assuntos
Orelha Interna/anatomia & histologia , Perda Auditiva Neurossensorial/patologia , Adulto , Idoso , Artefatos , Implantes Cocleares , Orelha Interna/inervação , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Imageamento por Ressonância Magnética/métodos , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos
6.
Neuromuscul Disord ; 24(5): 409-16, 2014 May.
Artigo em Inglês | MEDLINE | ID: mdl-24613733

RESUMO

The purpose of this study was to assess leg muscle quality and give a detailed description of leg muscle involvement in a series of Duchenne muscular dystrophy patients using quantitative MRI and strength measurements. Fatty infiltration, as well as total and contractile (not fatty infiltrated) cross sectional areas of various leg muscles were determined in 16 Duchenne patients and 11 controls (aged 8-15). To determine specific muscle strength, four leg muscle groups (quadriceps femoris, hamstrings, anterior tibialis and triceps surae) were measured and related to the amount of contractile tissue. In patients, the quadriceps femoris showed decreased total and contractile cross sectional area, attributable to muscle atrophy. The total, but not the contractile, cross sectional area of the triceps surae was increased in patients, corresponding to hypertrophy. Specific strength decreased in all four muscle groups of Duchenne patients, indicating reduced muscle quality. This suggests that muscle hypertrophy and fatty infiltration are two distinct pathological processes, differing between muscle groups. Additionally, the quality of remaining muscle fibers is severely reduced in the legs of Duchenne patients. The combination of quantitative MRI and quantitative muscle testing could be a valuable outcome parameter in longitudinal studies and in the follow-up of therapeutic effects.


Assuntos
Perna (Membro) , Músculo Esquelético/patologia , Músculo Esquelético/fisiopatologia , Distrofia Muscular de Duchenne/patologia , Distrofia Muscular de Duchenne/fisiopatologia , Tecido Adiposo/patologia , Adolescente , Corticosteroides/uso terapêutico , Criança , Humanos , Hipertrofia/patologia , Hipertrofia/fisiopatologia , Processamento de Imagem Assistida por Computador , Imageamento por Ressonância Magnética/métodos , Masculino , Força Muscular , Distrofia Muscular de Duchenne/tratamento farmacológico , Tamanho do Órgão , Músculo Quadríceps/patologia , Músculo Quadríceps/fisiopatologia
7.
Neuroimaging Clin N Am ; 22(2): 159-71, ix, 2012 May.
Artigo em Inglês | MEDLINE | ID: mdl-22548926

RESUMO

High-field magnetic resonance (MR) imaging is showing potential for imaging of neurodegenerative diseases. 7 T MR imaging is beginning to be used in a clinical research setting and the theoretical benefits of higher signal-to-noise ratio, sensitivity to iron, improved MR angiography, and increased spectral resolution in spectroscopy are being confirmed. Despite the limited number of studies to date, initial results in patients with multiple sclerosis, Alzheimer disease, and Huntington disease show promising additional features in contrast that may help the diagnosis of these disorders.


Assuntos
Encéfalo/patologia , Aumento da Imagem/métodos , Imageamento por Ressonância Magnética/métodos , Doenças Neurodegenerativas/patologia , Humanos
8.
J Magn Reson ; 200(1): 161-6, 2009 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-19595618

RESUMO

Morphological and functional cardiac MRI can potentially benefit greatly from the recent advent of commercial high-field (7tesla and above) MRI systems. However, conventional hardware configurations at lower field using a body-coil for homogeneous transmission are not available at these field strengths. Sophisticated multiple-transmit-channel systems have been shown to be able to image the human heart at 7tesla but such systems are currently not widely available. In this paper, we empirically optimize the design of a simple quadrature coil for cardiac imaging at 7tesla. The size, geometry, and position have been chosen to produce a B(1) field with no tissue-induced signal voids within the heart. Standard navigator echoes for gating were adapted for operation at the heart/lung interface, directly along the head-foot direction. Using this setup, conventional and high-resolution cine functional imaging have been successfully performed, as has morphological imaging of the right coronary artery.


Assuntos
Coração/anatomia & histologia , Imageamento por Ressonância Magnética/métodos , Vasos Coronários/anatomia & histologia , Imagem Ecoplanar , Eletrocardiografia , Campos Eletromagnéticos , Desenho de Equipamento , Humanos , Processamento de Imagem Assistida por Computador , Músculos Papilares/anatomia & histologia
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