Current Protocols in Magnetic Resonance Imaging最新文献

When imaging patients for vasculitis, the goals are: (1) to determine if there is evidence of acute or subacute cerebral injury and (2) to assess the contour of the major intracranial arteries. An additional but still experimental goal is (3) to determine if there are areas of altered perfusion that suggest active small vessel disease. Standard MR images and diffusion-weighted imaging are used to detect and determine the age of parenchymal lesions. The 3-D TOF MRA helps evaluate the large and medium vessels. Perfusion-weighted imaging may detect regions of altered relative blood flow and blood volume. This unit contains a basic protocol for the evaluation of stable patients as well as an alternative protocol for unstable patients.

MRI provides comprehensive information on gastrointestinal diseases, including infectious, inflammatory, and malignant processes. We employ a set protocol incorporating breath-hold SS RARE imaging combined with gadolinium-enhanced, fat-suppressed SPGR imaging in the transverse and coronal planes. Bowel distension is accomplished with inexpensive water-soluble intraluminal contrast agents.

This unit reviews the physical principles and methodologies involved in diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) for clinical applications. Diffusion-sensitive MRI noninvasively provides insight into processes and microscopic cellular structures that alter molecular water mobility. Formalism to extend the Bloch equation to include effects of random translational motion through field gradients is reviewed. Definition of key acquisition parameters is also reviewed along with common methods to calculate and display tissue diffusion properties in a variety of image formats. Characterization of potential directional-dependence of diffusion (i.e., anisotropy), such as that which exists in white matter, requires DTI. Diffusion tensor formalism and measurement techniques then reduce the diffusion tensor into standard anisotropy quantities that are summarized along with commonly used methods to depict directional information in an image format.

The rapid growth of magnetic resonance imaging systems with enhanced gradient systems together with improved pulse sequences has improved the ability to image blood vessels with a spatial and temporal resolution similar to conventional X-ray angiography. With patients who cannot undergo X-ray angiography because they are contraindicated for iodinated contrast agents (having a creatinine level > 2.0), MRA (magnetic resonance angiography) has proven to be the modality of choice. Since the first demonstration of such contrast-enhanced studies in the abdominal aorta, there have been continual improvements in methods due to improved hardware/software capabilities. This unit presents the MR protocols to image vascular morphology using contrast-enhanced 3-D-MRA techniques. The pulse sequences described herein are based on the authors' experience with a Siemens 1.5 T Vision and 1.5 T Sonata scanners, but are expected to be equally applicable to machines from other manufacturers.

Carotid atherosclerosis is an important medical condition associated with a high potential risk of stroke. In addition to the degree of artery stenosis, the size and tissue composition of the atherosclerotic plaque are thought to be important factors for disease management and prognosis. This unit presents a protocol for high-resolution multi-contrast MRI of the carotid artery wall. The protocol employs a combination of bright-blood magnetic resonance angiography and black-blood imaging with different contrast weightings (T1, T2, and proton-density contrasts) in order to provide comprehensive characterization of the atherosclerotic lesion. The images obtained with the protocol presented here can be used to identify basic tissue components of the atherosclerotic plaque (fibrous matrix, lipid core, calcificates, and hemorrhage) and to conduct morphological measurements of plaque size and distribution.

This appendix presents the screening forms that are to be filled by the patient prior to being scanned. Completion of these screening forms is also required for any person accompanying the patient into the magnet room. There are certain answers that will absolutely contraindicate the patient being scanned (e.g., if the patient has a cardiac pacemaker or ferromagnetic implant) while other questions are more designed to evaluate the patient's tolerance (such as whether they are claustrophobic). Other questions (such as those relating to renal disease) will determine if it is safe to use a contrast agent and make the physician aware of the medical status of the patient.

This unit provides step-by-step instructions on how to perform diffusion tensor imaging (DTI) in a clinical setting. A brief introduction on DTI techniques and current clinical applications is also presented. Additional technical details, practical considerations, and anticipated results are discussed in a commentary section.