Fig. 2.
Examples of x gradient waveforms that can be used to sample both a FISP and a PSIF echo. Data-sampling windows are shown as thick gray lines along the Gx(t) waveform. a) Both the so-called ‘FISP’ and ‘PSIF’ echoes are sensitive to temperature, and this sensitivity is proportional to the length of the horizontal gray arrows, TE-τ/4 and TR-TE-τ/4. τ is the readout duration, and A is the gradient area corresponding to a k-space offset of ΔK (Fig. 1). b) While the FISP was sampled first in (a), here the PSIF is sampled first for improved temperature sensitivity, as seen from the longer horizontal gray arrows. c) A gradient waveform with non-zero total area is associated with flow sensitivity. For example, such sensitivity could be a problem if oriented in the S/I direction, as most organs move mostly along S/I during breathing. In contrast, it can be useful if oriented along the R/L direction, to help detect vessels oriented along R/L. Unlike for the sequence in (b), the sequence in (c) has a gradient imbalance along z (rather than x), showing that the flow-sensitized direction can be rotated.