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(for RadioProcessor and iSpin-NMR)
The CPMG experiment runs much like the Hahn-Echo experiment, however it applies additional 180 degree pulses after the first 180 degree pulse to measure the decaying echo response. The rate of this exponential decay of echo peaks is measured by T2. The CPMG experiment program is available for download at the bottom of this page, as well as in the RadioProcessor section of the SpinAPI Example Downloads.
Figure1. CPMG Continuous Results (32 echoes, a sample of household cooking oil using a 10.8MHz permanent magnet)
Figure 1 shows the resultant FID response when capturing data continuously during a CPMG experiment. The large negative spikes are caused by the 180 degree pulses being applied.
Since a large number of echoes may be required to accurately measure T2, the CPMG program allows for segmented scanning acquisition. This mode reduces memory usage by allowing the RadioProcessor to only acquire a set number of points per echo (as little as a single point per echo). Figure 2 and 3, below, show multiple point and single point segmented scans.
Figure2. CPMG Segmented Results (80 echoes, 16 points per echo, a sample of household cooking oil using a 10.8MHz permanent magnet)
Figure3. CPMG Segmented Results (80 echoes,1 point per echo, a sample of household cooking oil using a 10.8MHz permanent magnet)
Figure 4, below, shows the pulse sequence used by the RadioProcessor to perform this experiment. Each vertical line is a new instruction, and the names of the durations used are shown above each time range.
Figure4. CPMG Pulse Sequence
The CPMG program accepts command line parameters to specify the values for each of the pulse program parameters. It takes the following arguments as inputs:
Table1. CPMG Input Arguments
CPMG Acquisition Tips
Several suggestions for acquiring CPMG data
are listed below:
Here are a few other tips:
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