Dear Jesper,
>I *think* it is quadratic for the released version.
yes, it is! 16 coulumns;)
Thanks a lot.
Best wishes,
Andreas
Am 12.12.14 14:08 schrieb "Jesper Andersson" unter
<[log in to unmask]>:
>Hi Andreas,
>
>> what is the default for --flm ?
>
>I *think* it is quadratic for the released version. You can easily work
>that out by looking at how many columns there are in your eddy_parameters
>output. linear->10 columns, quadratic->16 columns.
>
>It is definitely the case that for our scanners and for the HCP scanners
>quadratic does better. Old scanners with a bore the length of the channel
>tunnel were very different creatures.
>
>Jesper
>
>> I am wondering if I better adjust to quadratic for our new Skyra64.
>> Cheers,
>> Andreas
>>
>> Am 12.12.14 11:50 schrieb "Jesper Andersson" unter
>> <[log in to unmask]>:
>>
>>> Dear Mark,
>>>
>>>> I should have searched before posting: I now know the parameters are 3
>>>> rigid body, 3 rotation angles followed by terms describing the
>>>> eddy-induced field. My real aim is to turn this set of parameters
>>>>into a
>>>> transformation. How can I relate these eddy field terms to the skews,
>>>> scalings and transforms they describe?
>>>
>>> the first three are translations in mm. The meaning of the remaining
>>> parameters depend on what model you have specified for the EC fields.
>>>If
>>> it is a linear model (which doesn©öt really work for short bore
>>>scanners)
>>> it is just the weights of linear gradients in the x-, y- and
>>> z-directions, followed by a fourth parameter that is the DC offset of
>>>the
>>> field (non-zero if the centre of the FOV is different from the scanner
>>> iso-centre).
>>>
>>> If you use the quadratic model it is x, y, z, x^2, xy etc fields, and
>>> again lastly followed by the DC component.
>>>
>>> It isn©öt straightforward to build the total resulting fields though
>>>since
>>> you need to combine them with the susceptibility field, remembering
>>>that
>>> the susceptibility field is (as a first approximation) stationary
>>>w.r.t.
>>> the subject and the EC field is stationary w.r.t. the FOV. I might one
>>> day get around to writing all the combined fields out, but there are
>>> other things with higher priority.
>>>
>>> I am not sure what you want to do, but I think I would just let eddy
>>> worry about applying the transforms.
>>>
>>> Good luck Jesper
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