What parameter is used in Inversion Recovery but not in Spin Echo?

Inversion Recovery is a specific MRI technique that utilizes an additional parameter known as Inversion Time (TI). This parameter is critical because it determines the time elapsed between the application of an inversion pulse and the beginning of data acquisition, which influences the contrast and the amount of signal from tissues in the image based on their T1 relaxation characteristics.

In contrast, Spin Echo sequences do not involve a separate inversion pulse and therefore do not make use of TI. Instead, they rely primarily on Repetition Time (TR) and Echo Time (TE) to manipulate the image contrast and timing. While both sequences have TR and TE as essential parameters, only Inversion Recovery incorporates TI to achieve its unique imaging capabilities, allowing for better suppression of fat or fluid signal, resulting in clearer images of specific tissues or pathologies.

Thus, the use of TI is unique to Inversion Recovery, distinguishing it from the Spin Echo technique.