Which statement best describes the difference between CT and MRI for evaluating bone?

Which statement best describes the difference between CT and MRI for evaluating bone?

• A. MRI provides superior cortical bone detail.
• B. CT provides superior cortical bone detail; MRI better assesses bone marrow and occult fractures.
• C. MRI provides superior bone marrow detail.
• D. CT provides superior bone marrow detail.

Answer: (B)

The main idea is that CT and MRI excel at different aspects of bone evaluation. CT uses X-ray density and has very high spatial resolution for dense cortical bone, so it shows the outer shell of bone and small cortical disruptions with great clarity. MRI, by contrast, is sensitive to the composition and state of bone marrow, so it highlights marrow signal changes and edema, which can reveal fractures even when the cortical surface appears intact—these are often called occult fractures. That’s why the statement describing CT as giving superior cortical bone detail and MRI as better at assessing bone marrow and occult fractures is the best fit. The other options misstate which modality provides the strongest cortical detail or marrow information (MRI does not provide superior cortical detail, and CT does not show marrow as well as MRI).

The main idea is that CT and MRI excel at different aspects of bone evaluation. CT uses X-ray density and has very high spatial resolution for dense cortical bone, so it shows the outer shell of bone and small cortical disruptions with great clarity. MRI, by contrast, is sensitive to the composition and state of bone marrow, so it highlights marrow signal changes and edema, which can reveal fractures even when the cortical surface appears intact—these are often called occult fractures.

That’s why the statement describing CT as giving superior cortical bone detail and MRI as better at assessing bone marrow and occult fractures is the best fit. The other options misstate which modality provides the strongest cortical detail or marrow information (MRI does not provide superior cortical detail, and CT does not show marrow as well as MRI).