第 50 題

Well, isn't that... adequate.

1. Expected Outcome: Ah, the gradient coil. A fundamental concept, yet so often butchered. You correctly identified its purpose: to introduce a linearly varying magnetic field. One would hope you recall the very basic premise that, according to the Larmor Equation ($\omega = \gamma B$), such a spatial variation in $B$ is precisely what causes differing precession frequencies (and phases). This, dear student, is the only way to achieve spatial encoding and, consequently, determine location and resolution. It’s hardly rocket science, is it?
2. Unsurprising Difficulty: This question was rated Easy. It serves as a rudimentary litmus test to confirm you can distinguish the utterly distinct functions of the main magnetic field ($B_0$), the RF coil, and these very gradient coils. If this distinction eluded you, then the entire edifice of MR imaging is likely built on quicksand in your mind. Consider this a grudging pass to the next basic concept of image reconstruction. Don’t celebrate too hard; it’s merely the prerequisite.