Which are the limitations of CT scanning of the head?

Head ct. On year ct the contrast between structures is not that great. Ct is good to see bleeding in the brain or skull, a shift due to a mass can see a stroke a couple if hours old. Also good to see boney structure. Mri has better contrast differentiation but has other trade offs.
Low resolution. A ct has advantages and disadvantages: a ct is cheap, fast done and gives a great information about blood, bone and calfifications. However, it is done with x- ray, and has low resolution of tissue such as the brain. An MRI might be at time better, depending on the goal of the exam.
Head CT. CT of the brain is quick and provides an excellent screen for large pathology. Early strokes or subtle tumors are not as well seen. For better characterization of the tissue itself, MRI is far superior. In an emergency setting or screen for pathology, CT is usually the 1st choice. CT also uses radiation which also a consideration.