Figure 3.

Analog results as shown in Figure 2, but for spatially encoded 2D HSQC acquisitions involving a lower ν₁-resolution, and hence a higher SNR. (A) Schematic pulse sequence used. (B) 2D purely absorptive spectrum obtained using a conventional G_a = ±23 G/cm square-wave modulation (same as in Fig. 2A but with a 40% smaller gradient). The reduced gradient allowed us to use a narrower receiver bandwidth, and hence acquire a spectrum in only two scans. Processing was as for Fig. 2B, and the spectrum is displayed at a 20% contour level. (C) Purely-absorptive HSQC spectrum obtained using a non-periodic sampling and a iterative reconstruction approach, enabling acquisitions with |G_a| ≤ 4.5 G/cm and leading to a x3 SNR improvement. These two-scan data are shown at a 20% contour level, and their processing involved similar characteristics as for Fig. 2D. (D) Non-periodic gradient waveform used in the latter acquisition, and corresponding k/ν₁-t₂ trajectory.