mrs_tools info interprets dwelltime and spectral width wrongly when time unit is not second

[Microdeep-ZL]

Hi,

I'm working on developing a tool to convert Bruker ParaVision 6.0.1 specoscopy data into NIfTI-MRS format (because spec2nii crashes with our data). When I tested the generated .nii.gz file, I found that mrs_tools info doesn't interpret dwell time and spectral width correctly when time unit is not second.

FSL-MRS version: 2.3.1
python version: 3.12

Below is a minimal example to reproduce the error.

import nibabel as nib
import numpy as np
import json

N=128
dwelltime=125

fid = np.linspace(1,10,N,dtype=np.complex64).reshape(1,1,1,N)
hdrext = json.loads('''
{
        "ResonantNucleus": [
            "13C"
        ],
        "SpectrometerFrequency": [
            100.679124582065
        ]
}
''')

header=nib.nifti2.Nifti2Header()
header.set_data_dtype(fid.dtype)
header.set_xyzt_units('mm','usec')
header["intent_name"]=np.array([b'mrs_v0_9'],dtype='S16')
header["dim"]=np.array([4,1,1,1,N,1,1,1])
header["pixdim"]=np.array([1,10000,10000,10000,dwelltime,1,1,1])

vox_offset=np.ceil((header["sizeof_hdr"] + 4 + header.extensions.get_sizeondisk())/16)*16
header["vox_offset"]=vox_offset
header.single_vox_offset=vox_offset


headerext=nib.nifti1.Nifti1Extension(44,json.dumps(hdrext).encode())
header.extensions.append(headerext)
spec=nib.nifti2.Nifti2Image(fid,None,header)
nib.nifti2.save(spec,'demo.nii.gz')

$ mrs_tools info ./demo.nii.gz
File demo.nii.gz (/home/nmr/Projects/NIfTI_MRS_converter)
NIfTI-MRS version 0.9
Data shape (1, 1, 1, 128)
Dimension tags: [None, None, None]
Spectrometer Frequency: 100.679124582065 MHz
Dwelltime (Spectral bandwidth): 1.250E+02 s (0 Hz)
Nucleus: 13C
Field Strength: 9.40 T

As you can see, dwell time is interpreted as 125s instead of 125 us.

I found the problem is due to from fsl.data.image import Image, where Image doesn't interpret dwell time correctly. However, I attempted to fix this problem but failed.
For now, the workaround is always using second as the time unit. Don't use "usec" or "msec".

[Microdeep-ZL]

Hi,

I found the way to correct it.
I'll close this issue and then submit a pull request.