Final answer:
Gradient Echo pulse sequences in MRI use flip angles to control image contrast, which involves adjusting the rotation of magnetization to enhance the visibility of different tissues and pathologies.
Step-by-step explanation:
Gradient Echo pulse sequences utilize flip angles to control the contrast of the image in Magnetic Resonance Imaging (MRI). By adjusting the flip angle, which is the amount by which the magnetization is rotated away from its equilibrium position, different tissues can be made to appear with varying degrees of brightness on the MRI image. A large flip angle, closer to 90 degrees, may increase signal from certain tissues, while a smaller flip angle can be used to shorten the scanning time or alter the contrast between different tissues.
It's important to select the appropriate flip angle to obtain the optimal contrast required for the diagnostic purpose. A specific flip angle, known as the Ernst angle, can maximize signal intensity for a given repetition time (TR) and tissue relaxation properties (T1). Adjusting the flip angle allows radiologists and MRI technicians to enhance the diagnostic quality of images by emphasizing the particular tissues or pathology of interest.