Hogwash Resolution Enhancement Program

Hogwash is a resolution enhancement program running on the Bruker X32 workstation. The program is based on the one introduced by Shaka and Keeler and Freeman [J. Magn. Reson. 56, 294 (1984)]. A more recent article by Davies et al. describes many of the practical aspects [J. Magn. Reson. 76, 476 (1988)].
The version for the X32 was written by Kirk Marat from the University of Manitoba, Canada.

I adapted to program to run under SunOS as well on Aug 30, 96

I adapted to program to run under Linux n Septermber 9, 96, and under IRIX6,2 on December 13, 96.

This program has the advantage of operating on the Fourier transformed spectrum rather than the fid. Resolution enhancement using various multiplication schemes (Gaussian, sine bell etc.) of the fid invariably results in a severe loss of signal to noise ratio. Hogwash largely circumvents this problem. The program basically uses subtraction of an ideal Lorentzian line (referred to as synthetic mask) or a single line in the spectrum (observed mask) from the peaks in the spectrum. Depending on the nature of the problem, one might be preferred over the other.
Using a synthetic mask provides some more control over the enhancement factor.
Using an observed mask takes into account non-ideal line shape due to on-perfect field homogeneity. In addition, since the peak used for the observed mask has a finite S/N, there will be additional noise in the reconstructed spectrum.

General Information

On the X32: The program resides in /u/prog and is named hogwash. To run it, use the hw shell script. hw takes arguments in the form:

• u - use last spectrum selected in uxnmr.
• p - specify regions in ppm rather than Hz.
• s - use synthetic mask
• b - provided debug output (display progress of calculations and other information)

The typical use therefor could be 'hw u p s' to use last spectrum with range input in ppm and a synthetic peak mask. Note that if the program is run from within uxnmr (not recommended), you need to type '!hw u p s'. Whenever possible, run hw from the second terminal, otherwise you will not be able to use or quit uxnmr at all while a calculation is in progress.

On bloch.cchem the program resides in /usr/local/bin. You can also use 'hw' instead of 'hogwash'. The 'u' argument cannot be used, Xpsec does not support that feature.
The typical use therefor could be 'hw p s'

Calculation times vary with the number of data points used. For a large data set (128 k data points, full proton spectrum of rotenone) the calculation on the X32 required about 75 minutes!. If only a small area is used, the calculation finishes in a few seconds. Bloch is much faster!

If, after a calculation, you decide that a change of parameters is needed, you must re-transform the spectrum first! Otherwise, a calculation is done in addition to the previous one! This results in very interesting but generally useless spectra.

'man hw' displays the instructions supplied with the program. 'nmrhelp hog' provides some additional hints by Kirk Marat.

Setting Up and Running Hogwash

X32:

Hogwash requires high digital resolution relative to the natural line width. The fid should thus be zero-filled (uxnmr SI processing parameters) before FT. A small exponential multiplication is recommended if the S/N is marginal. Select a small trial region, note the limits (in ppm, or Hz)and the mask peak position and width if s is not used.

• After the program has started, the low and high field limits are requested.
• If the synthetic mask is used (e.g., 'hw u p s'), the mask line width is prompted for. The mask line width is the amount of broadening to subtracted. Entering too small a value results in only a small enhancement, too large a value may produce negative wings and/or spurious peaks.
  With an observed mask (hw u p), the shift will be prompted for as well as the "mask range". The range specifies the width of the mask region. It must be wide enough so that the entire peak is included (and the sides of the peak are at the base line level) but not contain any other peaks. Note that the width may need to be entered in ppm!
• The loop gain constant g needs to be experimentally determined. Reasonable values range from 0.02 to 0.05.
• The next parameter, the threshold, must be set low enough to include small peaks yet, at the same time, must be high enough to exclude noise. The value is entered as a ratio, e.g. 0.01 means the threshold is set to 1% of the tallest peak in the selected region of the spectrum. Changing regions may thus require a change in this parameter as well.
• The last parameter, the reconstruction line width, specifies the width (at half-height) of the resulting lines. The ratio of mask-width/reconstruction-width is equivalent to the resolution enhancement factor. Note that the reconstructed width should be several times wider than the digital resolution.
• After the calculation is complete, the spectrum must be read by uxnmr (re # # or [TASKS] -> [last data sets] ) before the result can be seen. (You might need to read a different dataset (orProcNo) to force re-reading of the spectrum!) Plotting etc. can now be done as with any other data set.

Bloch.cchem:

• Process a data set, i.g., test 1 1.
• Read another one, e.g., test 1 2
• Run hogwash on test 1 1
• after hogwash has finished, read test 1 1 again.

Quench.cchem and Purcell.cchem:

Hogwash Example

The proton spectrum of Rotenone was used for comparison of results between Hogwash and Sine Bell Multiplication.

Felicia Etzkorn (at the time a student in Prof. P.A.Bartlett's group) has subsequently applied this technique to a small peptide with impressive results. While resolution enhancement of the fid failed due to S/N limitations, Hogwash worked very well. Rather unfortunately, I do not have a copy of her work...

Expansions of Protons 4'b at 2.97 ppm.

Below are expansions of protons 4'b at 2.97 ppm.

The coupling patterns are ddd with coupling constants of 15.8 (4'b), 8.1 (5') and 0.7 (11) for the a proton and 15.8 (4'a), 9.8 (5') and 0.7 Hz (11) for the b proton. Further couplings are indicated but not resolved.

A regular spectrum with exponential multiplication, lb of 0.1 Hz.

Using unshifted sine bell multiplication

Hogwash of the upfield region.

Hogwash Parameters:

• LB of 0.3 Hz applied before FT.
• Synthetic mask width of 0.9 Hz.
• Loop gain of 0.02.
• Threshold of 0.05.
• Reconstruction line width of 0.2 Hz.

An expansion of protons 4'b at 2.97 ppm.

Hogwashed

Sine Bell Multiplied.

Felicia's results will go here, if I can find them....