Bo maps acquired according to the svFieldMap pulse sequence (Bruker, Paravision 6.0) should give as an intensity per pixel the offset of Bo in Hz. However, when converting the 2Dseq files (32 bit signed integers) to the DICOM format with Paravision 6.0 the data format is changed into 16 bit signed integers.
To obtain the actual offset in Hz per pixel. The intensities per pixel should be multiplied with the slope. Is it true that this is the VisuParCoreSlope for the 2Dseq data and the RescaleSlope from the metadata for the DICOM format?
So if I multiply the intensities of each pixel of the Bo map in DICOM format (16 bit) with the RescaleSlope I obtain the absolute values of the offset of B0 map in Hz?
Hi, I'm not very sure about B0 maps, but I worked with flow sequences a few years ago and, as flow true values can be negative, I had to use the .RescaleSlope and .RescaleIntercept from metadata to obtain the true values of flow applying the linear equation. So, it makes sense what you are saying. Cheers.
Dear Juan,
Apparantly for the raw data (2Dseq) the VisuParCoreDataSlope and VisuCoreDataIntercept should me take into account. For the DICOM images the RescaleSlopeescaleIntercept (from DICOM metadata) as well as the VisuCoreDataIntercept and VisuCoreDataSlope from the VisuPar file should be taken into account to obtain true Bo offset values in Hz.
Kind regards,
Hanne
Dear Hanne. It might be late for you, but i just answer this question since it can be a problem for other researchers as well. If you check, you see that the maximum value in DICOM is always 32768. Because -32768 to 32768 which almost equals to 65535 is the maximum which can be saved as a 16-bit integer. So, first you have to divide the matrix with 32768. Then multiply it by VisuCoreDataMax, and finally multiply it by VisuCoreDataSlop. So, you will have the results in Hz.
As a comparison to validate the process, you can use Viewing tab in Palette tab in ParaVision. It shows the results in Hz as well.
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