Question

In a transverse section of the CT of the brain, a ring of the cranium is seen which is absent or not so prominent in MRI. What is this reason?

(a) The cranium is negated out while imaging

(b) Cranial ring is made of bones which do not have water, so it cannot give an MRI

(c) The EM waves received by MRI does not have sufficient magnetic strength to view the bones

(d) MRI images soft tissues so it does not image the cranium properly. Thus, the cranial ring is more prominent in CT than in MRI

I have been asked this question by my college professor while I was bunking the class.

The origin of the question is FMRI topic in division Diagnostic Investigation via Imaging Techniques of Clinical Science

Answer 1

The correct choice is (d) MRI images soft tissues so it does not image the cranium properly. Thus, the cranial ring is more prominent in CT than in MRI

Easiest explanation: The cranium is made of flat bones with spongy bones in between was shock absorbers. They are flat and thin and thus do not have bone marrow. Thus, the hydrogen content in these bones is less than those in long bones. Also, MRI mostly targets Hydrogen in water to get magnetized while the hydrogen in bones is arranged on another structure which restricts its mobility as well. Thus, bones normally don’t show up in an MRI but the bones with bone marrow can be imaged.