From the Guidelines
When evaluating memory loss, a 3T MRI with specific sequences is the recommended imaging study, including 3D T1 volumetric sequence, fluid-attenuated inversion recovery (FLAIR), T2 (or susceptibility-weighted imaging [SWI]), and diffusion-weighted imaging (DWI). This recommendation is based on the highest quality and most recent evidence available, as outlined in the 5th Canadian Consensus Conference on the diagnosis and treatment of dementia 1. The use of MRI over computed tomography (CT) is preferred due to its higher sensitivity to vascular lesions and certain subtypes of dementia, with 3T MRI being favored over 1.5T if available and without contraindications 1.
Key Sequences for MRI
The following sequences are recommended for MRI when evaluating memory loss:
- 3D T1 volumetric sequence, which includes coronal reformations for hippocampal volume assessment
- Fluid-attenuated inversion recovery (FLAIR)
- T2 (or susceptibility-weighted imaging [SWI] if available)
- Diffusion-weighted imaging (DWI)
These sequences provide comprehensive visualization of brain structures, focusing on areas critical for memory function such as the hippocampus and temporal lobes. The inclusion of DWI sequences helps in identifying potential ischemic changes or small vessel disease, which can contribute to cognitive decline 1.
Importance of Semi-quantitative Scales
For the routine interpretation of MRI scans, the use of semi-quantitative scales is recommended, including:
- Medial temporal lobe atrophy (MTA) scale for medial temporal involvement
- Fazekas scale for white matter changes
- Global cortical atrophy (GCA) to qualify global atrophy These scales aid in the standardized assessment of atrophy and white matter changes, which are crucial in the diagnosis and monitoring of dementia 1.
Avoiding Advanced Sequences
Advanced MR sequences such as rs-FMRI, MR spectroscopy, diffusion tensor imaging (DTI), and arterial spin labeling (ASL) are not recommended for routine clinical use but are considered promising research tools that can be utilized in a research setting or with access to advanced expertise 1. Similarly, quantification software is not recommended for routine use pending larger studies that demonstrate its added diagnostic value 1.
From the Research
Evaluating Memory Loss with MRI
When evaluating memory loss, the type of MRI to order depends on the underlying cause of the memory loss.
- In cases of vitamin B12 deficiency, which can cause memory loss and other neurological symptoms, MRI changes may include T2 hyperintensity in the cervicodorsal region and cord atrophy 2.
- A study of a patient with B12 deficiency found that brain MRI showed multiple focal and confluent T2-weighted white matter hyperintensities, which improved with treatment 3.
- Diffusion-weighted MRI may also be useful in evaluating patients with vitamin B12 deficiency, as it can show microstructural changes in the brain 4.
- In cases of Alzheimer's disease and mild cognitive impairment, MRI modalities such as structural MRI, diffusion tensor imaging (DTI), arterial spin labelling (ASL), magnetic resonance spectroscopy (MRS), and functional MRI (fMRI) may be useful in showing patterns of brain damage and identifying risk of conversion to Alzheimer's disease 5.
- A study of patients with vitamin B12 deficiency found that MRI morphometrics, including frontal horn ratio and bicaudate ratio, were correlated with cognitive performance, particularly in areas such as language, orientation, and mental manipulation 6.
MRI Modalities for Memory Loss Evaluation
The following MRI modalities may be useful in evaluating memory loss:
- Structural MRI: to show patterns of brain damage and identify risk of conversion to Alzheimer's disease 5
- Diffusion tensor imaging (DTI): to show microstructural changes in the brain 5
- Arterial spin labelling (ASL): to show patterns of brain damage and identify risk of conversion to Alzheimer's disease 5
- Magnetic resonance spectroscopy (MRS): to show patterns of brain damage and identify risk of conversion to Alzheimer's disease 5
- Functional MRI (fMRI): to show patterns of brain damage and identify risk of conversion to Alzheimer's disease 5
- Diffusion-weighted MRI: to show microstructural changes in the brain in patients with vitamin B12 deficiency 4