Imagine firing a beam of x-rays through a slice of brain tissue. As the x-rays travel, they encounter gray matter, white matter, possibly brain tumors, blood clots, and so on. These tissues absorb the x-rays’ energy to a greater or lesser degree, depending on the type of tissue it is. The goal of CT is to map the absorption pattern in the whole slice. From that information, CT can reveal where tumors or clots may be. CT doesn’t see the brain directly; it sees the x-ray–absorption pattern in the brain.
