MRI, or magnetic resonance imaging, is a medical imaging technique that provides detailed pictures of the structure of your brain. Unlike methods that use radiation, such as X-rays, MRI applies strong magnets. The reasons for abnormal MRI results are numerous--from migraines to brain tumors--and it is not uncommon to see abnormal MRI results before the patient experiences any symptoms.
Why is MRI Scan Being Done?
MRI can be used to diagnose many diseases and disorders, such as infections, bleeding, tumors, multiple sclerosis and Alzheimer's disease. MRI results are not automatic and the reliability of MRI scans depends strongly on the expertise of the doctor. There are also huge differences between different MRI scanners in the quality of the image that they can render. Moreover, because MRI is a method that tests brain structure and not brain functions, the scan results could be normal even though the patient has some abnormal brain functions, according to a study published in the May 15, 2000 "Neuroreport."
Normal and Abnormal MRI Findings
In normal MRI scans, the left and right sides of the brains are nearly identical in size. If there is a large difference in size between some parts of the brain, it is usually a sign of an abnormal finding. Most illnesses or disorders affect only a fairly small part of the brain, so it is common to have normal images in most areas and abnormal findings in only a small area.
Diagnosing Multiple Sclerosis (MS) with MRI
One of the diseases that has benefited from the discovery of MRI is multiple sclerosis (MS). MRI is considered among the best tools to diagnose MS; however, about 5 percent of MS patients do not have abnormal MRI findings. According to a study published in a 1999 issue of "Neurology," some other diseases show abnormal MRI findings that closely resemble those seen in MS patients. Thus, abnormal findings on MRI scans alone are not enough to diagnose MS. A 2003 issue of "Neurology" reported that a third of the patients who had no MS symptoms but whose MRI scans showed MS-like results developed MS within an average of about five years.
Alzheimer's disease and MRI
Just as with MS, MRI might be able to detect Alzheimer's disease before the first cognitive symptoms appear, according to an article in the November 2003 issue of "Radiology." One key finding is that the hippocampus, an area of the brain responsible for memory, is much smaller in Alzheimer's patients than in healthy controls. This difference in size is clearly observable in MRI as shown by Dr. Olivier Colliot and his colleagues in a study published in the July 2008 issue of "Radiology."
Detecting Bleeding with MRI
A study published in "JAMA" in 2004 reported that MRI is equal to computed tomography (CT) at detecting acute bleeding and is more accurate than CT in revealing chronic bleeding in the brain. The authors concluded that MRI can outline the presence, size, location and extent of blocked blood vessel and bleeding.
References
- "Neuroreport"; Increased distractibility in closed head injury as revealed by event-related potentials; M.L. Kaipio, et al; May 15, 2000
- "Neurology"; The contribution of magnetic resonance imaging to the diagnosis of multiple sclerosis; F. Fazekas, et al; 1999
- "Radiology"; Discrimination between Alzheimer Disease, Mild Cognitive Impairment, and Normal Aging by Using Automated Segmentation of the Hippocampus; Olivier Colliot, et al; July 2008
- "Radiology"; Regional brain atrophy rate predicts decline; H. Rusinek, et al; December 2003
- "JAMA"; Comparison of MRI and CT for Detection of Acute Intracerebral Hemorrhage; Chelsea S. Kidwell, et al; Oct. 20, 2004
