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" " MRI [ magnetic resonance imaging ] scans show us that , during sleep , brain regions shift dramatically , " notes Matthew Walker , director of the Sleep and Neuroimaging Lab at Beth Israel Deaconess Medical Center . The team compared results of the tests with images of the patients ' brains taken through MR perfusion imaging , a type of MRI ( magnetic resonance imaging ) that highlights tissue " distressed " because of low oxygen and nutrients . Radiology is concerned with the interpretation of imaging modalities including x-rays , ultrasound , radioisotopes , and MRI ( Magnetic Resonance Imaging ) . MRI ( magnetic resonance imagery ) , and CT ( computed tomography ) may be useful in confirming the diagnosis . Other tests include an MRI ( magnetic resonance imaging ) , EEG ( electroencephalogram ) , lumbar puncture , ultrasound testing , and cerebral angiography , which are only performed if there is reason to suspect an underlying disease . The doctor may also order an MRI ( magnetic resonance imaging ) scan , which uses magnetic waves to make a picture of the inside of the brain .