Tissue Border Enhancement by inversion recovery MRI at 7.0 Tesla (original) (raw)
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Application of Quantitative MRI for Brain Tissue Segmentation at 1.5 T and 3.0 T Field Strengths
PLoS ONE, 2013
Background: Brain tissue segmentation of white matter (WM), grey matter (GM), and cerebrospinal fluid (CSF) are important in neuroradiological applications. Quantitative Mri (qMRI) allows segmentation based on physical tissue properties, and the dependencies on MR scanner settings are removed. Brain tissue groups into clusters in the three dimensional space formed by the qMRI parameters R 1 , R 2 and PD, and partial volume voxels are intermediate in this space. The qMRI parameters, however, depend on the main magnetic field strength. Therefore, longitudinal studies can be seriously limited by system upgrades. The aim of this work was to apply one recently described brain tissue segmentation method, based on qMRI, at both 1.5 T and 3.0 T field strengths, and to investigate similarities and differences.
Academic Radiology, 2000
Rationale and Objectives. This study was undertaken to clarify the difference in signal pattern on contrast material-enhanced Tl-weighted magnetic resonance (MR) magnetization transfer (MT) images between enhancing and nonenhancing lesions in various intracranial diseases and to determine the necessity of nonenhanced MT images for evaluating lesional contrast enhancement. Materials and Methods. MR images of 116 patients who underwent nonenhanced Tl-weighted imaging, nonenhanced MT imaging, and contrast-enhanced MT imaging were reviewed. The increase in signal intensity of lesions relative to normal brain was compared between nonenhanced Tl-weighted images and contrast-enhanced MT images. Signal intensity of lesions was compared with that of the striate nucleus and white matter on contrast-enhanced MT images. True enhancement was determined by comparison with nonenhanced MT images. Results. In all, 143 lesions, including 86 enhancing and 57 nonenhancing lesions, were identified among 63 patients. Almost all (99%) of the enhancing lesions were hyperintense to striate nucleus on contrast-enhanced MT images, and most (>87%) showed moderate to marked signal intensity increase from nonenhanced Tl-weighted images to contrast-enhanced MT images. Most (>95%) of the nonenhancing lesions showed mild or no increase in relative signal intensity, and most (75%) were iso-or hypointense to striate nucleus on contrast-enhanced MT images. A few nonenhancing lesions (4%-6%), however, showed increase in signal intensity that was indistinguishable from true enhancement without comparison to nonenhanced MT images. Conclusion. Nonenhanced MT images should be obtained to assess pathologic enhancement accurately.
Investigative Magnetic Resonance Imaging, 2016
Advances of magnetic resonance imaging (MRI), especially that of the Ultra-High Field (UHF) MRI will be reviewed. Materials and Methods: Diffusion MRI data was obtained from a healthy adult young male of age 30 using a 7.0T research MRI scanner (Magnetom, Siemens) with 40 mT/m maximum gradient field. The specific imaging parameters used for the data acquisition were a single shot DW echo planar imaging. Results: Three areas of the imaging experiments are focused on for the study, namely the anatomy, angiography, and tractography. Conclusion: It is envisioned that, in near future, there will be more 7.0T MRIs for brain research and explosive clinical application research will also be developed, for example in the area of connectomics in neuroscience and clinical neurology and neurosurgery.
PLoS ONE, 2014
Simultaneous, hybrid MR-PET is expected to improve PET image resolution in the plane perpendicular to the static magnetic field of the scanner. Previous papers have reported this either by simulation or experiment with simple sources and detector arrangements. Here, we extend those studies using a realistic brain phantom in a recently installed MR-PET system comprising a 9.4 T MRI-scanner and an APD-based BrainPET insert in the magnet bore. Point and line sources and a 3D brain phantom were filled with 18 F (low-energy positron emitter), 68 Ga (medium energy positron emitter) or 120 I, a non-standard positron emitter (high positron energies of up to 4.6 MeV). Using the BrainPET insert, emission scans of the phantoms were recorded at different positions inside and outside the magnet bore such that the magnetic field was 0 T, 3 T, 7 T or 9.4 T. Brain phantom images, with the 'grey matter' compartment filled with 18 F, showed no obvious resolution improvement with increasing field. This is confirmed by practically unchanged transaxial FWHM and 'grey/white matter' ratio values between at 0T and 9.4T. Field-dependent improvements in the resolution and contrast of transaxial PET images were clearly evident when the brain phantom was filled with 68 Ga or 120 I. The grey/white matter ratio increased by 7.3% and 16.3%, respectively. The greater reduction of the FWTM compared to FWHM in 68 Ga or 120 I line-spread images was in agreement with the improved contrast of 68 Ga or 120 I images. Notwithstanding elongations seen in the z-direction of 68 Ga or 120 I point source images acquired in foam, brain phantom images show no comparable extension. Our experimental study confirms that integrated MR-PET delivers improved PET image resolution and contrast for medium-and high-energy positron emitters even though the positron range is reduced only in directions perpendicular to the magnetic field.
2010 7th IEEE International Symposium on Biomedical Imaging: From Nano to Macro, ISBI 2010 - Proceedings, 2010
Magnetic resonance imaging of the brain at high fields (e.g. 3T) provides high resolution and high signal to noise ratio images suitable for a wide range of clinical applications. However, radiofrequency (or B 1) inhomogeneity increases with the magnetic field and produces undesired intensity variations responsible for inaccuracies in quantitative analyses. A method to perform brain segmentation using T 1 maps whose inhomogeneity was corrected using previously acquired B 1 maps is described. A library of B 1 maps was created and a method to compensate the T 1 inhomogeneity using a B 1 map from another subject (template) was developed. The performance of the template-based method was evaluated in 19 healthy volunteers. Our method produced significantly better segmentations than the retrospective N3 method and the one without B 1 inhomogeneity correction.
NeuroImage, 2010
Most current automated segmentation methods are performed on T 1 -or T 2 -weighted MR images, relying on relative image intensity that is dependent on other MR parameters and sensitive to B 1 magnetic field inhomogeneity. Here, we propose an image segmentation method based on quantitative longitudinal magnetization relaxation time (T 1 ) of brain tissues. Considering the partial volume effect, fractional volume maps of brain tissues (white matter, gray matter, and cerebrospinal fluid) were obtained by fitting the observed signal in an inversion recovery procedure to a linear combination of three exponential functions, which represents the relaxations of each of the tissue types. A Look-Locker acquisition was employed to accelerate the acquisition process. The feasibility and efficacy of this proposed method were evaluated using simulations and experiments. The potential applications of this method in the study of neurological disease as well as normal brain development and aging are discussed.
High-Resolution MR Imaging of the Human Brainstem In vivo at 7 Tesla
Frontiers in Human Neuroscience, 2013
The human brainstem, which comprises a multitude of axonal nerve fibers and nuclei, plays an important functional role in the human brain. Depicting its anatomy non-invasively with high spatial resolution may thus in turn help to better relate normal and pathological anatomical variations to medical conditions as well as neurological and peripheral functions. We explored the potential of high-resolution magnetic resonance imaging (MRI) at 7 T for depicting the intricate anatomy of the human brainstem in vivo by acquiring and generating images with multiple contrasts: T 2-weighted images, quantitative maps of longitudinal relaxation rate (R 1 maps) and effective transverse relaxation rate (R 2 * maps), magnetic susceptibility maps, and direction-encoded track-density images. Images and quantitative maps were compared with histological stains and anatomical atlases to identify nerve nuclei and nerve fibers. Among the investigated contrasts, susceptibility maps displayed the largest number of brainstem structures. Contrary to R 1 maps andT 2-weighted images, which showed rather homogeneous contrast, R 2 * maps, magnetic susceptibility maps, and track-density images clearly displayed a multitude of smaller and larger fiber bundles. Several brainstem nuclei were identifiable in sections covering the pons and medulla oblongata, including the spinal trigeminal nucleus and the reticulotegmental nucleus on magnetic susceptibility maps as well as the inferior olive on R 1 , R 2 * , and susceptibility maps. The substantia nigra and red nuclei were visible in all contrasts. In conclusion, high-resolution, multi-contrast MR imaging at 7T is a versatile tool to non-invasively assess the individual anatomy and tissue composition of the human brainstem.
Magnetic resonance separation imaging using a divided inversion recovery technique (DIRT)
Magnetic Resonance in Medicine, 2010
The divided inversion recovery technique is an MRI separation method based on tissue T 1 relaxation differences. When tissue T 1 relaxation times are longer than the time between inversion pulses in a segmented inversion recovery pulse sequence, longitudinal magnetization does not pass through the null point. Prior to additional inversion pulses, longitudinal magnetization may have an opposite polarity. Spatial displacement of tissues in inversion recovery balanced steadystate free-precession imaging has been shown to be due to this magnetization phase change resulting from incomplete magnetization recovery. In this paper, it is shown how this phase change can be used to provide image separation. A pulse sequence parameter, the time between inversion pulses (T180), can be adjusted to provide water-fat or fluid separation. Example water-fat and fluid separation images of the head, heart, and abdomen are presented. The water-fat separation performance was investigated by comparing image intensities in short-axis divided inversion recovery technique images of the heart. Fat, blood, and fluid signal was suppressed to the background noise level. Additionally, the separation performance was not affected by main magnetic field inhomogeneities.
High-field magnetic resonance imaging of the human temporal lobe
NeuroImage: Clinical, 2015
Background: Emerging high-field diffusion weighted MR imaging protocols, along with tractography, can elucidate microstructural changes associated with brain disease at the sub-millimeter image resolution. Epilepsy and other neurological disorders are accompanied by structural changes in the hippocampal formation and associated regions; however, these changes can be subtle and on a much smaller scale than the spatial resolution commonly obtained by current clinical magnetic resonance (MR) protocols in vivo. Methods: We explored the possibility of studying the organization of fresh tissue with a 17.6 Tesla magnet using diffusion MR imaging and tractography. The mesoscale organization of the temporal lobe was estimated using a fresh unfixed specimen obtained from a subject who underwent anterior temporal lobectomy for medically refractory temporal lobe epilepsy (TLE). Following ex vivo imaging, the tissue was fixed, serial-sectioned, and stained for correlation with imaging. Findings: We resolved tissue microstructural organizational features in the temporal lobe from diffusion MR imaging and tractography in fresh tissue. Conclusions: Fresh ex vivo MR imaging, along with tractography, revealed complex intra-temporal structural variation corresponding to neuronal cell body layers, dendritic fields, and axonal projection systems evident histologically. This is the first study to describe in detail the human temporal lobe structural organization using high-field MR imaging and tractography. By preserving the 3-dimensional structures of the hippocampus and surrounding structures, specific changes in anatomy may inform us about the changes that occur in TLE in relation to the disease process and structural underpinnings in epilepsy-related memory dysfunction.