MRI Protocol for Dementia Evaluation

Standard Protocol Recommendation

The American College of Radiology recommends brain MRI without contrast as the appropriate initial imaging study for all dementia evaluations, including suspected Alzheimer disease, frontotemporal dementia, dementia with Lewy bodies, vascular dementia, and idiopathic normal-pressure hydrocephalus 1, 2
The Alzheimer's Association guidelines state that brain MRI without contrast is appropriate for evaluation of Alzheimer's disease and related dementias when available and not contraindicated 3, 4

MRI excludes potentially reversible causes of dementia, including tumors, inflammatory conditions, infectious processes, subdural hematomas, and normal-pressure hydrocephalus 3, 4
MRI identifies atrophy patterns that probabilistically suggest specific neurodegenerative diagnoses with high accuracy, though not as high as molecular biomarkers 3, 4
MRI detects microhemorrhages critical for patient selection and monitoring for amyloid-related imaging abnormalities (ARIA) in patients receiving disease-modifying antiamyloid therapies 3, 4

For Alzheimer disease, MRI shows atrophy in medial temporal lobes, lateral temporal and parietal cortices, with ventricular enlargement 3, 4
For idiopathic normal-pressure hydrocephalus, MRI identifies ventricular enlargement with Evans index >0.3, enlargement of temporal horns, callosal angle <90 degrees, and aqueductal flow void 1, 2
For vascular dementia, MRI assesses white matter hyperintensities using the Fazekas scale and identifies strategic infarcts 5

The American College of Radiology considers MRI without contrast and CT without contrast as "usually appropriate" and equivalent alternatives, but MRI is strongly preferred when available due to higher sensitivity for detecting vascular lesions and specific dementia subtypes 1, 2
MRI has superior ability to identify rare conditions causing dementia and better visualization of atrophy patterns and microhemorrhages 5

Most patients over age 80 with cognitive impairment harbor more than one type of brain pathological change, making mixed etiology dementia common 3, 4
Specific molecular biomarkers remain necessary to confirm Alzheimer disease diagnosis and for treatment with disease-modifying therapy, despite supportive MRI findings 3, 4

The American College of Radiology recommends MRI brain without IV contrast as the preferred initial imaging study for all dementia evaluations, with CT head without contrast as an acceptable alternative when MRI is unavailable or contraindicated 6
MRI brain without IV contrast is the recommended first-line study to exclude treatable structural abnormalities and demonstrate atrophy patterns in medial temporal lobes, lateral temporal and parietal cortices 6, 7
CT head without contrast is an acceptable alternative when MRI is unavailable, though less sensitive for detecting hippocampal atrophy and vascular lesions 8, 9

For Alzheimer disease, brain FDG-PET/CT and brain amyloid PET/CT are appropriate advanced imaging studies that support clinical diagnosis when combined with clinical history and other biomarkers 6, 7
For frontotemporal dementia, MRI brain without IV contrast is recommended to assess for frontal and temporal lobe atrophy patterns, and brain FDG-PET/CT is highly recommended to demonstrate characteristic frontal and temporal hypometabolism 7, 10
For dementia with Lewy bodies, MRI brain without IV contrast or CT head without contrast is recommended to exclude structural mimics, and brain striatal SPECT/CT is recommended to demonstrate dopaminergic loss in basal ganglia 10

MRI brain without IV contrast is mandatory to identify imaging findings that may preclude treatment, particularly pre-existing microhemorrhages and superficial siderosis, before initiating antiamyloid therapy 7, 10
Brain amyloid PET/CT is recommended to confirm presence of amyloid in brain parenchyma before initiating therapy, and to demonstrate clearance of amyloid from brain parenchyma after treatment 7, 10

MRI is superior to CT for detecting vascular lesions, microhemorrhages, hippocampal atrophy, and rare dementia causes 6
Amyloid PET can be positive in cognitively normal individuals who never develop dementia, and a negative scan does not exclude non-AD neurodegenerative conditions 8, 9
MR spectroscopy, fMRI, and routine use of IV contrast are not recommended for initial dementia evaluation in most scenarios 6, 7, 10