Figure 2.

Pulse sequences used for direct comparison of polarization transfer by CRIPT (a), INEPT (b), and CRINEPT (c). In each scheme, the coherence flow is indicated by a gray curved arrow. The narrow and wide bars indicate nonselective 90 and 180° pulses, which are applied with phase x unless indicated otherwise above the pulses; ψ₁ = (x, −x), φ₁ = (x, −x). Sine-bell shapes represent selective 90° pulses on the water resonance, which keep the water magnetization along +z during the whole sequence (17). On the line marked PFG, rectangles indicate pulsed magnetic field gradients applied along the z axis. The steady state magnetization of the S spins was suppressed by a 90° pulse on S followed by a pulsed field gradient before the first proton pulse. In c, two experiments are recorded, one with phase x and the second one with phase −y on the second proton pulse, as indicated. The phase of the associated water flip back pulse also is changed.