CT scans generally **cannot reliably show cerebral microbleeds (CMBs)**, which are tiny brain hemorrhages associated with cognitive decline. Microbleeds are very small, often just a few millimeters or less, and are best detected using specialized MRI techniques rather than CT imaging.
CMBs are deposits of blood breakdown products like hemosiderin around small blood vessels in the brain. They are important markers of cerebral small vessel disease (CSVD), a condition linked to cognitive impairment and dementia, including Alzheimer’s disease. These microbleeds are typically visualized as small, dark spots on MRI sequences that are sensitive to iron, such as susceptibility-weighted imaging (SWI) or T2*-weighted gradient echo MRI. These MRI methods exploit the magnetic properties of iron in blood breakdown products to highlight microbleeds with high sensitivity.
In contrast, **CT scans use X-rays and are less sensitive to small amounts of blood or iron deposits**. CT is excellent for detecting larger hemorrhages, strokes, or structural abnormalities but lacks the resolution and contrast mechanisms to detect microbleeds reliably. Microbleeds are often too small and have too subtle a difference in density compared to surrounding brain tissue to be distinguished on CT images.
The clinical significance of detecting microbleeds lies in their association with cognitive decline. Studies have shown that the **number and location of microbleeds correlate with specific cognitive deficits**. For example, microbleeds in the lobar regions of the brain, often linked to cerebral amyloid angiopathy, are associated with memory and visuospatial impairments. Microbleeds in deeper brain structures, related to hypertensive arteriopathy, tend to affect executive function and processing speed. The presence of multiple microbleeds increases the risk of accelerated cognitive decline over time.
Because of this, MRI is the preferred imaging modality when investigating patients with suspected microbleeds and cognitive impairment. MRI can also detect other features of small vessel disease, such as white matter lesions, lacunar infarcts, and brain atrophy, which together provide a more comprehensive picture of vascular contributions to cognitive decline.
In summary, while CT scans are widely available and useful for many brain imaging purposes, they **do not have the sensitivity or specificity to detect cerebral microbleeds associated with cognitive decline**. MRI with specialized sequences remains the gold standard for identifying these small hemorrhagic lesions and understanding their impact on cognition.
