Reducing the flip angle yields images with what change in image contrast?

When the flip angle is reduced in a magnetic resonance imaging (MRI) sequence, there is an increase in T1 weighting of the images. This is primarily because the flip angle, which is the angle by which the net magnetization vector is tilted away from the longitudinal axis, directly influences the longitudinal relaxation time (T1).

A smaller flip angle leads to less excitation of the protons and, as a consequence, longer relaxation times remain in effect, which enhances the differences in signal intensity based on T1 relaxation properties of different tissues. This results in images that demonstrate more pronounced T1 contrast, making tissues with shorter T1 times appear brighter compared to those with longer T1 times.

Conversely, a larger flip angle tends to produce images that contain more T2 contrast as the contributions from the longitudinal relaxation are diminished while T2 decay is prominent. Therefore, reducing the flip angle yields a greater emphasis on T1 characteristics within the resulting images.