In Inversion Recovery, where does the first slice excitation pulse place LMz?

In Inversion Recovery, the first slice excitation pulse plays a crucial role in manipulating the longitudinal magnetization (LMz) of the spins within the imaging volume. Initially, when spins are relaxed in thermal equilibrium, their magnetization exists along the +Z axis, representing the equilibrium state.

Upon application of a 180-degree inversion pulse, the longitudinal magnetization is inverted, and its orientation is flipped to the -Z axis. This inversion is pivotal because it allows for the recovery of the longitudinal magnetization over time, leading to the unique contrast that Inversion Recovery sequences provide.

Subsequent to the inversion pulse, the spins will begin to relax back towards equilibrium along the +Z axis, which is what the technique is designed to optimize for imaging. Hence, when asking about the placement of LMz immediately after the first slice excitation pulse in Inversion Recovery, the correct understanding is that it becomes oriented along the -Z axis.