Preprocessing

jMRUI provides several preprocessing methods that operate in the time domain:

  • Mathematical functions to sum, subtract, average, conjugate, multiply by scalar, divide by scalar, and normalise nmr signals.
  • Apodisation
  • Cadzow
  • Convolution
  • DC correction
  • Conversion of echo signals to fid
  • ER-filter
  • Group delay correction
  • OS-filter
  • Phase correction
  • Frequency/time shift
  • Spectral reliability testing
  • Peak remover (HLSVD and HLSVDPro)
  • Quality
  • Truncation
  • Zero filling

HLSVD and HLSVDPro

With HLSVD and HLSVDPro filters it is possible to suppress certain components in the time domain signal.  The filters are interactive and enable the user to choose the peak that should be suppressed (e.g. water peak).

svd1
HLSVD filter for water peak suppression. Select the peak.
svd2
Results of water peak suppression.

References

  • HLSVD water filtering – van den Boogaart, A., van Ormondt, D., Pijnappel, W.W.F., de Beer, R., and Ala-Korpela, M. (1994). In Mathematics in Signal Processing III, (J.G. McWhirter, Ed.), pp. 175-195, Clarendon Press, Oxford.

ER filter

With this band-pass filter function you can select a region of interest in the spectrum to be used in further preprocessing and quantitation. This is a frequency domain operation. The selected region is then cut out from the spectrum (spectra) and inverse Fourier transformed to a time domain signal that represents the spectrum in the region that has just been selected. The number of time-domain samples and the sampling rate get reduced, as corresponds to the Nyquist conditions for the truncated spectrum, while the time-domain extent of the signal remains intact.

 

User can choose the region of interest and perform filtration
The user can choose the region of interest and perform the filtration.

erfilter2

References

  •  Cavassila, S., Fenet, B., van den Boogaart, A., Rémy, C., Briguet, C., Graveron-Demilly, D. ER-Filter: a preprocessing technique to improve the performance of SVD-based quantitation methods. Journal of Magnetic Resonance Analysis 3: 87-92, 1997.
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