a) For our Siemens 7T data, the command mrinfo DWI_raw.mif shows a value
TotalReadoutTime = 0.329 is that the value required for dwifslpreproc? Is there a reason one is called readout the other total readout?
This is simply brevity of the command-line option. I considered calling it ā-trt
ā for Total Readout Time, but decided it was too abstract, so went for -readout_time
. But theyāre not intended to refer to different things.
Googling finds several sources telling Total Readout Time (again not readout time, which seems to generic to googleā¦) is calculated as number of echoes * echo_spacing, which would suggest itās the dwell-time..
Thereās various definitions around, but what eddy
& topup
expect is documented here , and refers to the total readout time - the duration of the full echo train.
There is a slight nuance here: FSLās convention (and what is calculated by MRtrix3 when reading from DICOM) is the time between the centre of the first echo and the centre of the last echo, which is not āthe total time taken to perform the EPI readoutā.
If dwell-time = TotalReadOutTime = readout-time I could share the information how to extract it from a Philips dicom header. Might be useful? Even potentially automatically importing it?
b) for our Philips 3T mrconvert does not seem to find a value called TotalReadoutTime, but I have found a way to compute the dwell time and this boils down to echo_spacing * EPFactor
If there are DICOM fields that can be used to calculate this parameter that MRtrix3 is not currently reading, then yes, this is something that would be useful to add to the code. Though Iām constantly concerned around this code that calculations need to be correct in the presence of factors such as parallel imaging / segmented EPIā¦
O.K. that is not quite what a Philips document I got is saying.
Assuming echo spacing = inter echo time this is still the total readout time, just with a name thatās in disagreement with your terminology.
I reckon a large proportion of people in the know would disagree with Philipsā definition of ādwell timeā here.
One must also be wary here of parallel imaging; e.g. if only every second line is acquired, then either ES needs to correspond to the time between acquired *k-space lines and ETL needs to correspond to the number of acquired lines, or ES needs to correspond to the effective time in between k-space lines and ETL needs to correspond to the number of k-space lines in the phase encoding direction.
Their calculation also doesnāt include the minus-one effect of wanting the time between the centres of the first and last echoes, which is ultimately the parameter against which the magnitude of geometric distortions scales.