The travel time curve plots the 129Xe signal amplitude in the
detection coil as a function of the flow time. After the magnetization is
inverted in the encoding coil, the xenon signal travels from the encoding coil
to the detection coil, and the resulting signal amplitude in the detection
coil after a given flow time is read out. (A) Both coils are placed
inside a high-field magnet (7 T). It takes 28–60 ms for the encoded
129Xe to travel a distance of ≈4 cm from one coil to the other.
(B) The encoding coil is placed inside a low-field magnet (4–7
mT), and the detection coil is placed inside a high-field magnet (4.2 T).
Here, the encoded 129Xe travels 7–10 s, corresponding to a
distance of ≈5 m from one magnet to the other.