Virginia Thornley, M.D.
Neurologist, Epilptologist
June 8, 2020
As part of a neurological work-up, diagnostic tests are ordered as an extension to confirm a diagnosis.
At the end of an interview and neurological examination, neuroimaging is often ordered to determine the anatomy of the brain.
An MRI or magnetic resonance imaging has finer resolution compared to a CT scan which translates into greater detail. This means you get a better quality of the image. It uses a magnet and not radiation so the risk of radiation is less. Frequent exposure to radiation is concerning for those at risk for cancer. With the MRI, a magnetic field is induced through a large magnet. This allows the positive protons of hydrogen present in the tissue to spin. The amount of hydrogen protons varies per type of tissue and this translates into an image. There are different specific sequences that are specific to certain diagnoses. For instance, DWI or diffusion-weighted imaging will be positive for strokes. In the first 24 hours, the signal will be evident when the stroke becomes subacute meaning less than 6 months the signal fades. For the gradient echo sequence, microhemorrhage will be seen which is old. There are other patterns of sequences that can determine how old or new the bleeding is.
A CT scan uses radiation to form the images of the brain. The pros include being quick to detect intracranial hemorrhage or head bleeds. It only takes 5 minutes which is crucial in the setting of an emergency. AN MRI of the brain will detect microhemorrhage or small amounts of bleeding on the gradient echo sequence but it takes at least 40 minutes from start to finish. In addition, one has to stay very still for an MRI in an enclosed space in order to get the fine details otherwise there will be a motion artifact that distorts the images.
Disclaimer: This is medical information only not advice please talk to your doctor.
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