Hi,
I've used sigloss, and find it to be quite useful. One thing, try
experimenting with the TE value, and comparing it with your echo planar
images. I find I have to give sigloss a higher TE than the acquired value to
get an equivalent image to our EPIs.
Dave
On 12/7/07 12:15, "wolf zinke" <[log in to unmask]> wrote:
> Hi Mark,
>
> Thanks for the detailed reply, it was very helpful.
>
> cheers,
> wolf
>
>
> Mark Jenkinson wrote:
>> Hi,
>>
>> This program calculates signal loss as a dimensionless fraction such
>> that if you multiply
>> the image without loss by this image then you would get the equivalent
>> image with
>> signal loss. Hence the output is actually more like signal retained.
>> That is, a value of
>> 1 in the output means no signal loss, while a value of 0 means all the
>> signal was lost.
>>
>> The default value of TE is set to a ridiculous value so that you can't
>> run it sensibly
>> with the default, as you really must specify a correct TE value and
>> there is no
>> typical value that would work for any sizable number of people.
>>
>> This program is very simple in concept, and just works out the signal
>> loss factor
>> for the through slice dephasing, based on an ideal slice selection -
>> which is a sinc
>> function. Any number of papers/books will probably contain this,
>> although the
>> formula here is derived from scratch given that I do several slightly
>> tricky things
>> with estimating field-gradients separately in different sub-components
>> of the voxel.
>>
>> Hope this helps.
>>
>> All the best,
>> Mark
>>
>>
>> wolf zinke wrote:
>>
>>> Hi all,
>>>
>>> I came across the sigloss tool, which might do exactly what I want.
>>> So, instead of reinventing wheels I would like to understand this
>>> program a bit better.
>>>
>>> The output is in the range of 0 to 1 if I got everything right. What
>>> is the dimension and how do I interpret the values.
>>> There is the --te option. Do I understand it right that this results
>>> in an estimate of signal loss for a given TE? Why is it than set per
>>> default to 1s, which is far beyond normally used values? Is there any
>>> reference this program is based on?
>>>
>>> Thanks in advance for your help,
>>> wolf
>>
>>
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