In-vivo short echo-time 1H MRS spectra of the brain have a contain information relating to large macromolecule and lipid resonances in addition to the usual metabolites of interest. The implementation of the LASER sequence in combination with metabolite suppression pulses can be used to null the metabolite signals and acquire a macromolecule spectrum. To reduce the effects of patient motion during scanning, single averages of the Full spectrum and metabolite suppressed Macromolecule spectrum are interleaved. An additional benefit of saving each average is that if a patient can not tolerate the entire length of the scan, the acquisition can be halted and data can be reconstructed up to the point of termination. Following acquisition, these the single averages must be summed for each spectrum prior to post-processing.

Ensure that spec_sum and spec_sum_incomplete are in the system maclib or your own vnmrsys/maclib.

In vnmrJ, there are two macros that are used to sum individual FIDs.

• spec_sum
• spec_sum_incomplete

spec_sum:

1. Load data into an experiment other than Experiment 5
2. Ensure that there is nothing in Experiment 5 that can not be erased as all information in Experiment 5 will be deleted during summation
3. Join to Experiment that has spectroscopy data
4. Type: wft
5. Type: spec_sum

• Enter which spectrum to reconstruct (1 = Full, 2 = Macromolecule)
• Enter 1 for shift adjustment or 0 for none: specify 0 only as shift adjustment is not implemented.
  
  Spectra are now summed and the result is saved in Experiment 5

6. Join to Experiment 5.
7. Save resultant spectrum with a new file name.

spec_sum_incomplete:

This macro should be used when data acquisition is halted prior to full completion

1. Repeat steps 1-4 from above – following wft, note the number of spectra acquired.
2. Type: spec_sum_incomplete

• Enter which spectrum to reconstruct (1 = Full, 2 = Macromolecule)
• Enter 1 for shift adjustment or 0 for none: specify 0 only as shift adjustment is not implemented.
• Enter the total number of elements actually acquired from step 1

3. Repeat steps 6 and 7 from above