The Double Pulsed-Field-Gradient Echo (DPFGE) scheme is a double echo experiment (based on the  so-called Excitation Sculpting) in which each selective 180º pulse is flanked by two gradients. It is used for efficient selective and band-selective excitation purposes.
 

Easy implementation on any AVANCE spectrometer equipped with pulsed field gradients and selective excitation using shaped pulses.

The DPFGE scheme consists of two selective 180 pulses (S), each one flanked by two gradients (G1-S-G1-G2-S-G2). Using different values for G1 and G2, only the selected resonances will be refocused at the end of the echo whereas all other signals are efficiently defocused. An alternative scheme based in a single echo (SPFGE scheme) can minimise relaxation losses when long selective pulses are needed.

The phase properties of the DPFGE scheme depends only on the inversion profile of the refocusing pulse, while the amplitude is scaled both by the inversion profile of the refocusing pulse and by unavoidable losses due to relaxation during the spin echo. Some advantages of the SPFGE and DPFGE schemes compared with other methods are:

Ultra-clean pure-absorption phase 1D spectra are simply obtained without frequency-dependent phase variations of the excited signal throughout the selected region.

No presence of sidelobes and/or sidebands outside the effective bandwith.

The full refocusing of all J-evolution at the end of the echo.

The sequence is very tolerant to miscalibrated pulses and rf inhomogeneities.

Requires no phase cycling, thus avoiding the need for difference spectroscopy.

Excellent results are always obtained with a very simple performance.

The DPFGE scheme has been succesfully incorporated in:
 
• Selective excitation in 1D experiments:
• Single selective proton excitation in selective ge-1D NOESY ( 95JACS4199 , 97JMR302-125 , and 96JMRA295-119 ), COSY ( 96JMRB183-111 ), RELAY ( 96JMRB183-111 ),  ROESY ( 97JMR267-124 ), TOCSY ( 96JMRB183-111 and 97JMR267-124 ), TOCSY-ROESY ( 97JMR267-124 ) and ROESY-TOCSY ( 97JMR267-124 ) experiments.
• Single selective carbon excitation in the HETGOESY experiment ( 96MRC554 )
• Multisite selective proton excitation ( 98JMR50-135 ): Application to selective ge-1D TOCSY ( 98JMR162-130 ), 2D selective-TOCSY-COSY experiment ( 98JMR173-133 ),  2D selective-TOCSY-TOCSY experiment ( 98JMR162-130 ), and EXSIDE ( 96JMRA33-121 ) experiments. In-phase double selective excitation has also been reported ( 98JMR173-133 )
• Band-selective excitation in 2D experiments:
•  Semi-selective proton excitation in band-selective ge-2D NOESY ( 98JMR154-132 ), ROESY ( 98JMR154-132 ), TOCSY  ( 96JMRB46-113 and 97MRC9 ) and INEPT-type ( 96JMRB75-112 ) experiments.
•  Semi-selective carbon excitation in band-selective ge-2D HSQC experiment ( 99JMR454-139 )
 
Related DPFGE schemes using Radiofrequency gradients (RF-gradients) have been also proposed in selective 1D experiments and non-selective 2D experiments ( 98JMR183-133 ).

Effective in-phase excitation of overlapping multiplets using modified DPFGE schemes ( 00JMR389-142 )

The DPFGE experiment can be run with minor changes from a predefined parameter set. The only parameter to consider is the selectivity of the selective inversion pulse: The user must define the shape, the duration and the power level needed for a defined excitation profile.

The DPFGE scheme affords pure in-phase selective excitation without phase distortions in its whole excitation bandwith.

The DPFGE scheme can be included as a starting building block in any selective 1D experiment using the following pulse sequence:

SPFGE scheme