[Rtk-users] Angular weighting in gated FDK

[Simon Rit]

Ok I get it. My conclusion on this exact same matter was that using
one or two projections per cycle was probably the best option with
FDK:
http://www.creatis.insa-lyon.fr/site/en/publications/RIT-07c
I know that others came up to the same conclusion. The idea is that
what you lack is not projections in general but well sampled
projections to fill this integral over the angle I was referring to.
Simon

On Wed, Sep 4, 2013 at 11:14 AM, MORY, CYRIL <Cyril.Mory at philips.com> wrote:
> Hi Simon,
>
> I have those gaps because ECG-gating on a single-sweep acquisition gives you clusters of consecutive projections separated by large gaps.
> It is also unclear to me whether I should perform Parker weighting or not (prior to gating).
>
> Thanks for your answers. I'll investigate this matter further when I have time.
>
> Cyril
>
> -----Message d'origine-----
> De : simon.rit at gmail.com [mailto:simon.rit at gmail.com] De la part de Simon Rit
> Envoyé : mardi 3 septembre 2013 18:39
> À : MORY, CYRIL
> Cc : rtk-users at openrtk.org
> Objet : Re: [Rtk-users] Angular weighting in gated FDK
>
> Hi Cyril,
> I am a bit lost by what you say. FDK comes from a continous formula and the angular weighting is the discretization of the integral on gantry angle. I don't see how it could be smarter than the gap with the neighbors and this is precisely why we obtain the attenuation.
> How come you have a factor 10 between projections? Isn't it regular since heart beating is rather regular?
> The only improvement I know off is to use a gating function which takes other values than 0 and 1 but I can't remember it is accounted for in the reconstruction.
> Simon
>
> On Tue, Sep 3, 2013 at 6:26 PM, MORY, CYRIL <Cyril.Mory at philips.com> wrote:
>> Hi RTK users,
>>
>>
>>
>> I'm working on ECG-gated FDK reconstruction, and I'd like to obtain
>> realistic absorption coefficients, because my gated FDK images have to
>> compared to other reconstruction results which do have realistic
>> values. In FDK, projections are weighted by their angular gaps. I have
>> replaced that by a weighting by 1, because some angular gaps are huge
>> in ECG-gated projection data, and there is no reason why a single
>> projection should be weighed ten times as much as the others. But 1
>> obviously isn't the right value (with a 20%-wide gating window, I'm
>> getting values about ten times too high). I'm experimenting with
>> smarter choices, like the minimum of the angular gaps (this time it's
>> 10 times too low), and I'll keep experimenting until I find something satisfying.
>>
>>
>>
>> Does anyone know if there is a standard way of weighting the
>> projections in ECG-gated FDK ? I've made a quick search (maybe too
>> quick), but couldn't find anything on this topic.
>>
>>
>>
>> Regards,
>>
>> ==========================================
>>
>> Cyril Mory
>>
>> PhD student at Philips Medisys and CREATIS
>>
>>
>>
>> Groupement Hospitalier Est
>>
>> Hôpital Cardiologique Louis Pradel
>>
>> Laboratoire CREATIS - Bât. B13
>>
>> CNRS UMR5220, INSERM U1044, INSA-Lyon, Univ. Lyon 1
>>
>> 28, Avenue du Doyen LEPINE
>>
>> 69677 Bron cedex FRANCE
>>
>>
>>
>> Office : +33 4 72 35 74 12
>>
>> Cell : +33 6 69 46 73 79
>>
>>
>>
>>
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