special subjects
Magnetic Resonance Imaging (MRI)
Variations of MRI
Functional MRI detects metabolic changes that occur when the brain is active. Thus, it can show which areas of the brain are active when a person does a specific task, such as reading, writing, remembering, calculating, or moving a limb. Functional MRI can be used in research and clinical settings, for example, to plan brain epilepsy surgeries. With perfusion MRI, doctors can estimate blood flow in a particular area. This information can be useful during a Overview of Stroke to determine whether blood flow to parts of the brain is decreased. It can also be used to identify areas where blood flow is increased—for example, in tumors. Diffusion-weighted MRI detects changes in water movement in cells that are not functioning normally. It is used primarily to identify early Overview of Stroke . It is also used to detect certain brain disorders and to determine whether tumors have spread to the brain, or to differentiate a brain abscess from a tumor. Use of this technique to image areas other than the brain is limited. Diffusion-weighted MRI is often combined with other techniques to evaluate tumors, mostly in the brain. Magnetic resonance spectroscopy uses radio waves that are emitted almost continuously rather than in pulses as in conventional MRI. Magnetic resonance spectroscopy is used to detect brain disorders, such as Seizure Disorders , This technique is also used to evaluate metabolic disorders in muscles and the nervous system. MRA, like Angiography and Magnetic resonance angiography can show blood flow through arteries and veins or blood flow only in one direction and thus show only arteries or only veins. As in CT angiography, a computer is used to remove all tissues except the blood vessels from the image. Often, a gadolinium contrast agent is injected into a vein to outline blood vessels. The examiner carefully times the scanning so that the images are taken when gadolinium is concentrated in the blood vessels being evaluated. MRA is used to evaluate blood vessels of the brain, heart, abdominal organs, arms, and legs. It is used to detect the following: Overview of Aortic Aneurysms and Aortic Dissection None Aortic Dissection None Narrowed arteries in the limbs Blood clots in veins of the limbs and pelvis Blood flow to tumors Tumors that are affecting blood vessels Magnetic resonance venography is an MRA of veins. It is often used to detect a blood clot in a vein that carries blood away from the brain (cerebral venous thrombosis) and to monitor the effect of treatment on this disorder. Echo planar imaging produces sequences of images in only seconds. It can be used to image the brain, heart, and abdomen. Because it is fast, movement by the person being examined does not blur the images as much. Also, the technique can provide information about how tissues are functioning. However, it requires special equipment and is more likely to misrepresent certain structures than conventional MRI because of the nature of the technique. 