What color does cortical bone appear on MRI?

What color does cortical bone appear on MRI?

• A. White
• B. Light gray
• C. It is not visible on MRI
• D. Black

Answer: (D)

Cortical bone appears black on MRI because it has very few mobile hydrogen protons and an extremely short T2 relaxation time, so it generates almost no MR signal. On standard MRI sequences this lack of signal shows up as a signal void, a dark outline surrounding the bone marrow and soft tissues. While bone may be a visible boundary as a dark line, it isn’t bright or gray; it’s the absence of signal that makes it look black. (Very short TE sequences can sometimes show bone more, but with routine imaging the cortex is dark.)

Cortical bone appears black on MRI because it has very few mobile hydrogen protons and an extremely short T2 relaxation time, so it generates almost no MR signal. On standard MRI sequences this lack of signal shows up as a signal void, a dark outline surrounding the bone marrow and soft tissues. While bone may be a visible boundary as a dark line, it isn’t bright or gray; it’s the absence of signal that makes it look black. (Very short TE sequences can sometimes show bone more, but with routine imaging the cortex is dark.)