Magnetic Resonance Imaging (MRI)

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Magnetic Resonance Imaging (MRI)

In the world of diagnostic medicine, a major scientific breakthrough is the MRI. Magnetic resonance imaging revolutionized medical imaging.
Basically, to start the study, the patient is placed in a tube where various magnetic fields are applied to the body. The way the body responds to those fields and how it relaxes when the magnetic field is removed is noted and sent to a computer along with information about where the interactions occurred. Myriads of these points are sampled and fed into a computer that processes the information and creates an image.
An interesting feature of magnetic resonance imaging is that flowing things have a distinctive appearance on MRI scans (similar to Doppler ultrasound). Flowing structures cause “flow voids,” which appear as black holes on the scans. There are computers powerful enough to extract information about a given flow void, such as in the carotid arteries in the neck. The computer does this for each and every slice and puts together images of the vessel causing the flow void. The images look just like someone had had dye injected, as in an angiogram. This type of magnetic resonance angiography (MRA), offers another way of looking at vascular structures in the body. For example, in cases where the aorta is injured by arteriosclerosis, aging, or trauma, MRA can provide exquisite images. Resolution can be somewhat of a problem, however, for small structures, such as the carotid arteries. In those cases, angiograms remain the method of choice to delineate the specific pathology.

MRI creates precise images of the body based on the varying proportions of magnetic elements in different tissues. Very minor fluctuations in chemical composition can be determined. MRI images have greater natural contrast than standard x rays, computed tomography scan (CT scan), or ultrasound, all of which depend on the differing physical properties of tissues. This sensitivity allows the MRI to distinguish fine variations in tissues deep within the body. It is also particularly useful for spotting and distinguishing diseased tissues (tumors and other lesions) early in their development. Often, doctors require an MRI scan to investigate more fully earlier findings of other imaging techniques.

The entire body can be scanned, from head to toe and from the skin to the deepest recesses of the brain. MRI scans are not obstructed by bone, gas, or body waste, which can hinder other imaging techniques. (Although the scans can be degraded by motion such as breathing, heartbeat, and bowel activity.) The MRI process produces cross-sectional images of the body that are as sharp in the middle as on the edges, even of the brain through the skull. A close series of these two dimensional images can provide a three-dimensional view of the targeted area. Along with images from the cross-sectional plane, the MRI can also provide images sagitally (from one side of the body to the other, from left to right for example), allowing for a better three-dimensional interpretation, which is sometimes very important for planning a surgical approach.

What MRI can do that other imaging techniques don’t do as well:

  • Brain: One of the few imaging tools that can see through bone (the skull) and deliver high-quality pictures of the brain’s delicate soft tissue structures.
  • Spine: Identifying and evaluating degenerated or herniated spinal discs. It can also be used to determine the condition of nerve tissue within the spinal cord.
  • Joints: Diagnose and assess joint problems providing clear images of the bone, cartilage, ligament, and tendon that comprise a joint.
  • Skeleton: The properties of MRI that allow it to see through the skull also allow it to view the inside of bones. Accordingly, it can be used to detect bone cancer, inspect the marrow for leukemia and other diseases, assess bone loss (osteoporosis), and examine complex fractures.
  • Heart and circulatory system: MRI evaluates the heart and blood flow and provides a good natural contrast medium that allows structures of the heart to be clearly distinguished.