Spectroscopy: Converted file contains 2080 data points instead of 2048

[darrencl]

Hi all,

Thanks for creating this tool.

We are trying to use this tool to convert our spectroscopy TWIX data to ISMRMRD. Upon further inspection, the number of channels seems to be correct, but the number of data points is not.

We would expect to have 2048 array in each channel and acquisition, but it has 2080 for some reason when loading via ismrmrd-python.
When comparing against the data loaded using suspect, we also found that the actual complex numbers are rounded – this might not be an issue, but it's worth noting for future reader.

In [207]: twix[0,0,0] # suspect's
Out[207]: np.complex128(-5.602138116955757e-06-1.1758645996451378e-05j)

In [208]: f.read_acquisition(4).data[0, 0]
Out[208]: np.complex64(-5.602138e-06+1.1758646e-05j)

In [209]: twix[0,0,-1]
Out[209]: np.complex128(2.2049061954021454e-07+5.906913429498672e-07j)

In [210]: f.read_acquisition(4).data[0, 2047]
Out[210]: np.complex64(2.2049062e-07-5.9069134e-07j)

Now from that taking the first-2048 seems to be okay, but we have tested this in another dataset and the 2048 data are in the index 12:2060 (example below).

I have a couple of questions in regards to this:

1. Is there any explanation as to why it contains 2080 data points instead of 2048?
2. Is there any way we can get that 'offset'? e.g., in our second dataset the 2048 data started from index 12, so that seems random to me.

In [21]: f.read_acquisition(1).data[0, 12:2060]
Out[21]:
array([-7.6105352e-06+1.2077391e-05j, -1.1375640e-05+1.3110228e-05j,
       -1.4022691e-05+1.6696751e-05j, ...,  1.2526289e-07+5.0617382e-07j,
       -3.6135316e-07-8.4377825e-07j, -7.7532604e-08-5.6857243e-07j],
      dtype=complex64)

In [22]: twix[0,0] # suspect's
Out[22]:
MRSData([-7.61053525e-06-1.20773911e-05j, -1.13756396e-05-1.31102279e-05j,
         -1.40226912e-05-1.66967511e-05j, ...,
          1.25262886e-07-5.06173819e-07j, -3.61353159e-07+8.43778253e-07j,
         -7.75326043e-08+5.68572432e-07j])

In [23]: f.read_acquisition(2).data[0, 12:2060]
Out[23]:
array([-7.2314870e-06+1.2506265e-05j, -1.2170756e-05+1.3003359e-05j,
       -1.2640376e-05+1.5741447e-05j, ...,  2.6891939e-07-1.1231750e-06j,
        8.9406967e-08-7.8557059e-07j,  1.9115396e-07+1.5669502e-07j],
      dtype=complex64)

In [24]: twix[1,0] # suspect's
Out[24]:
MRSData([-7.23148696e-06-1.25062652e-05j, -1.21707562e-05-1.30033586e-05j,
         -1.26403756e-05-1.57414470e-05j, ...,
          3.68919393e-07+1.12317502e-06j,  8.94069672e-08+7.85570592e-07j,
          1.91153958e-07-1.56695023e-07j])

Cc @budij