Attenuation refers to how dense a part of the body appears relative to other body parts on a CT scan or X-ray, according to MedPix; while hypoattenuation means lower density, hyperattenuation refers to higher density. Attenuation is used to compare and contrast the density of the area with that of other body parts, to diagnose such things as tumors, lesions and strokes.
Hypoattenuated, or low-density, areas appear darker on CT scans than hyperattenuated, or high-density, areas. The most dense body parts, such as bone, appear the brightest. As stated on MedPix, blood clots and tumors in the brain appear whiter than brain matter. Areas of the brain affected by strokes appear hypoattenuated, or darker, than the brain around the affected area, and hypoattenuating brain tissue is an early sign of stroke, according to Radiology Assistant. According to the American Heart Association, finding areas of hypoattenuation on a CT scan soon after a stroke can help determine appropriate treatment, but a lack of hypoattenuation does not rule out brain tissue damaged by a stroke. CT scans are readily available in hospitals at all hours, states Radiology Assistant, and these scans are the best tools for diagnosing a stroke within the first 24 hours.