Tufts Anatomy Yr-1

CT (computed tomography) displays different types of tissues in the body on a scale of shades of gray, from pure black (air) to pure white (metal). This image shows some of the different tissues that CT can discriminate, both on the CT image and on the scale of density at the top.

Note that the density of muscle and blood is about the same--they are similar shades of gray on CT unless you inject something into the blood to make it denser (contrast material). No contrast material was given to this patient.

CT has several advantages over x-rays, including removing overlap of structures and better ability to discriminate tissues of different densities. The main disadvantage is much higher radiation dose than x-rays.