I has a CT why do I need an MRI

I’ve been suffering headaches and my doctor ordered a CT. Now I need to have an MRI. If the CT wasn’t good enough, why didn’t I just have the MRI in the first place?

Headaches are common.  If your doctor ordered a CT it was out of concern for something unusual in your specific symptoms.  One of the most frequent concerns along these lines is that bleeding in the head may be the cause for the headache.  CT is the best non-invasive way to look for bleeding in the head.  If the CT happens to find something else that may be worrisome, an MRI might be ordered to evaluate it further.   MRI is not often used as the first study to evaluate headaches mainly because it takes longer than a CT, is very sensitive to patient movement, is less available, more expensive, and may miss small amounts of bleeding on the surface of the brain that CT excels at finding.