Gradient-selected refocused INEPT

The operation of the proton-enhanced sequences is best understood by reference to the original INEPT-INADEQUATE sequence shown in simplified form in Fig. 5.80 in which the individual component parts have been identified and may be followed in a stepwise manner. Thus, initial transfer from proton to carbon is via the INEPT sequence introduced in Chapter 4 followed by the generation of DQC as for the INADEQUATE above. This again evolves to encode c after which gradient selection begins. The DQ then returns to single quantum, and the C- C-coupling is refocused by the spin-echo. The final step is INEPT in reverse to transfer from carbon back onto proton, followed by... 

Figure 9.37. The constant-time-HSQC-IDOSY sequence. The delays T are set to 1/2Jhx as required for the INEPT transfer and the constanttime period 2T remains fixed, its duration being dictated by the desired diffusion time A. The effective ti evolution time is varied by moving the two 180° refocusing pulses within the constant time period (pulses shown with arrows over) and coherence selection is made with the echo/antiecho (E/A) scheme. The diffusion encoding/decoding gradients are applied as bipolar pairs during the INEPT and reverse-INEPT transfer steps.

---