Journal of magnetic resonance imaging : JMRI
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J Magn Reson Imaging · Oct 2004
ReviewFunctional MRI of the lung using hyperpolarized 3-helium gas.
Lung imaging has traditionally relied on x-ray methods, since proton MRI is limited to some extent by low proton density in the lung parenchyma and static field inhomogeneities in the chest. The relatively recent introduction of MRI of hyperpolarized noble gases has led to a rapidly evolving field of pulmonary MRI, revealing functional information of the lungs, which were hitherto unattainable. This review article briefly describes the physical background of the technology, and subsequently focuses on its clinical applications. Four different techniques that have been used in various human investigations are discussed: ventilation distribution, ventilation dynamics, and small airway evaluation using diffusion imaging and oxygen uptake assessment.
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Pulmonary embolism (PE) is one of the most frequently encountered clinical emergencies. The diagnosis often involves multiple diagnostic tests, which need to be carried out rapidly to assist in the safe management of the patient. ⋯ Techniques include MR angiography (MRA) and thrombus imaging for direct clot visualization, perfusion MR, and combined perfusion-ventilation MR. As will be demonstrated, some of these techniques are now entering the clinical arena, and it is anticipated that MR imaging (MRI) will have an increasing role in the initial diagnosis and follow-up of patients with acute PE.
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In vivo magnetic resonance spectroscopy (MRS) addresses metabolic pathways and their steady states in different tissue types. The brain has by tradition, and due to technical limitations in other organs, been one of the tissues most studied by MRS, and both 1H- and 31P-MRS have been used. ⋯ Furthermore, MR sensitivity is much greater for protons than it is for phosphorus and 1H-MRS, therefore allowing better spatial resolution. This review focuses on neurospectroscopy and diagnostic insights into diverse neurological problems provided by 1H-MRS applied as a clinical tool.
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J Magn Reson Imaging · Jan 1997
ReviewEffects of contrast dose, delayed imaging, and magnetization transfer saturation on gadolinium-enhanced MR imaging of brain lesions.
This paper discusses the types of paramagnetic agents available for clinical brain imaging and reviews investigations that have sought to optimize the use of these agents by varying the administered dose, delaying the imaging time after contrast administration, and altering image contrast by using magnetization transfer saturation pulses.
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Contrast agents have greatly expanded the role of MR imaging (MRI) to allow assessment of physiologic, or "functional," parameters. Although activation mapping generally does not require contrast agents, other forms of functional MRI, including mapping of cerebral hemodynamics (eg, perfusion imaging), are best done with the use of contrast agents. Serial echo planar images are obtained after bolus injection of lanthanide chelates. ⋯ Functional MRI perfusion imaging of intraaxial tumors is analogous to positron emission tomography for delineation of metabolic activity, yet may be even more sensitive to neovascularity and possesses improved image quality. Clinical applications include biopsy site selection and postirradiation follow-up. Further improvements in data analysis and map generation techniques may improve diagnostic accuracy and utility.