CSPAMM tagging. (a) CSPAMM pulse sequence. The sequence runs two SPAMM sequences, with the polarity of the second tagging RF pulse changed in the second SPAMM acquisition. Notice also the ramped flip angles of the imaging RF pulses to compensate for fading tagging. (b) Example of a CSPAMM grid-tagged image. Notice that non-tagged tissues appear black due to the elimination of the offset DC signal. (c) The concept of magnetization subtraction in CSPAMM. Two scans are acquired as shown in the pulse sequence, which results in positive and negative sinusoidal tagging patterns from the first and second scans, respectively. With time, the tagging patterns experience longitudinal relaxation, trying to reach equilibrium (M0). The relaxation has two effects on the tagging pattern: the peak-to-peak (AC) magnitude is decreased; and the tagging pattern now has non-zero average (DC) value. However, the DC component is the same in both scans. Thus, at any time point, when the two acquired images are subtracted, the DC component cancels out and the peak-to peak magnitude doubles as shown.