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MRI is a non-invasive way for doctors to create a 3D image of internal structures without radiation. T-1 and T-2 MRI protocols use electromagnetic waves to align atoms and produce images. T-2 MRI is more sensitive to changes in tissue effects caused by cancer, inflammation, and blood flow disorders. FLAIR imaging is critical in identifying plaques in the brain for multiple sclerosis diagnosis. MRI machines allow for different orientations and contrast mediums can distinguish abnormal tissue.
Magnetic resonance imaging (MRI) is a non-invasive procedure by which doctors formulate a three-dimensional image of the body’s internal structures without ionizing radiation. Doctors gather various information using different MRI protocols, the two most common of which are T-1 MRI and T-2 MRI. Both use electromagnetic waves to align positively charged atoms, such as hydrogen, in a head-to-toe orientation for a T-1 MRI, or a left-to-right orientation for a T-2 MRI. A radio frequency pulse then shifts the direction of rotation of the atoms, and when the pulse is broken, the atoms return to their normal alignment, emitting a signal from which the system constructs an echo or image. T-2 MRI produces lower resolution images than its counterpart, T-1-weighted MRI, but accentuates differences in fluid and cell content, making T-2 MRI images the most sensitive to changes in tissue effects caused by cancer, inflammation and blood flow disorders.
T-2-weighted MRIs selectively use a long interval between pulses (TR), typically between 1500 and 300 milliseconds, and a long interval between each pulse and analysis (TE), typically between 75 and 250 milliseconds. The T-1 scan, unlike the T-2 scan, has a short TR of only 200-700 milliseconds and a short TE time of 20-35 milliseconds. In the head, T-1 scans produce a noticeable contrast between the gray matter and white matter of the brain and fat accent areas. A T-2 MRI shows blood, tissue swelling, and areas of liquefaction.
The extraordinarily strong signals on a T-2 MRI from the fluid can hide tissue abnormalities in a surrounding area. For example, T-2 MRI produces a hyperintense signal from the cerebrospinal cord in the brain’s fluid channels, the ventricles. Fluid-attenuated inversion recovery (FLAIR) dampens the fluid signal on a T-2 MRI, making this variety of MRI suitable for examining the periventricular white matter of the brain. In multiple sclerosis, plaques develop in the white matter surrounding the ventricles. Identifying plaques in the brain through the use of FLAIR imaging is critical to making the diagnosis.
Modern MRI machines acquire data in a way that allows the doctor to view tissue “slices” in a front-to-back (sagittal), side-to-side (axial), or top-to-bottom ( coronal) with no patient needing to change position in the scanner. With these alternatives in orientation, the ordering physician can obtain the best views to visualize the anatomical region of interest. Additionally, radiologists may give the patient an injectable contrast medium, called gadolinium, which changes the local magnetic field of the tissues. Abnormal tissue reacts to gadolinium differently than normal tissue, providing a way to clearly distinguish any disease processes.
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