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Dear Rebecca,
The output produced on the scanner corresponds to the magnitude images at the two echo times and their phase difference. This can be used as input to the Field
Map toolbox using the “Presubtracted Phase and Magnitude Data” option via the batch. Using this option, the toolbox will scale the data to the [-pi pi] range.
The phase difference is saved like this on the scanner to exploit the full dynamic range of the integer data type that gets stored in the scanner’s database.
Hope that helps,
Martina
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]
On Behalf Of Rebecca Kerestes
Sent: 05 November 2014 14:47
To: [log in to unmask]
Subject: [SPM] Trouble using gradient field map toolbox GUI in SPM
SPM experts,
I need some assistance with using gradient field maps in the SPM field map toolbox GUI.
We acquired field maps on a Siemens 3T and by default, Siemens saves 2 magnitude maps (one for short TE, one for long TE) but wont save the phase map. Instead it produces a precalculated field map in scanner
units that needs to be converted to Hz.
I ran a matlab script that converts the field map to Hz for use in SPM, however when I go to load the precalculated field map (in Hz) in the GUI it wont recognize the file.
Any pointers would be great!
Rebecca