The 3D images derived from non-contrast Computed Tomography (NCCT) scans provide a glimpse into the intra- and extracranial structures, based on the ability of electromagnetic X-rays to penetrate through various tissue densities. The gray matter, for example, possesses a higher density than the white matter, absorbs more X-rays, allows less penetration (attenuation), and thus has larger Hounsfield units (HU), the mathematical value of attenuation coefficient. The CT scanner’s wide availability and ease of use allow for quick assessment of acute neurosurgical abnormalities, such as hemorrhages, mass effect, hydrocephalus, and traumatic injuries. An attenuation value of +60 to +90 HU generally indicates blood, and a HU of +100 signifies calcification. Less common causes of hyperattenuation on a head CT include tumors, contrast agent artifacts, and metabolic conditions like hyperglycemia, depending on the location (extra- or intra-axial, subarachnoid or intraparenchymal, etc.), morphology (linear or oblong, circumscribed or diffuse, etc.), and Hounsfield Unit (HU) value of the lesion. CT yields high sensitivity and specificity within six hours of symptom onset in detecting acute hemorrhage in the brain. Understanding the principles of CT may guide the practicing clinician in distinguishing blood from high-density non-blood products.
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