How does a T1 weighted sequence create a higher signal from fat compared to fluid?

A T1 weighted sequence is designed to emphasize differences in tissue characteristics based on their T1 relaxation times. In these sequences, fat has a significantly shorter T1 relaxation time compared to water or fluid. This rapid relaxation allows fat to recover its longitudinal magnetization much quicker after the application of the radio frequency (RF) pulse.

This quick return to the longitudinal magnetization results in fat appearing much brighter on T1 weighted images than fluids. Thus, in a T1 weighted image, fat will create a higher signal intensity because it can reclaim its magnetization sooner and reach a stronger signal during imaging. In contrast, fluids, such as water, take longer to recover their longitudinal magnetization, resulting in a lower signal intensity on T1 weighted images.

The emphasis on fat's quicker relaxation and subsequent higher signal output is what defines the contrast seen in T1 weighted images, making option A the correct choice.