[Rtk-users] Insufficient Data For Proper Parker Weighting

[Brani Rusanov]

Hi Simon,

Sorry for the late reply, I have been quite busy recently.
My projections are 1024x768. I cropped the largest dimension and noticed that "half the beam angle" value decreases slightly, gets close to the value 9.951, but with further reduction in dimension size the beam angle suddenly jumps to ~20 degrees (observed value during reconstruction). So cropping the projection does not seem to solve the problem. Do you have any ideas how to fix this?

If you require any geometry or projection files, I would be happy to send them over.

Kind regards,
Brani
________________________________
From: Simon Rit <simon.rit at creatis.insa-lyon.fr>
Sent: Monday, June 15, 2020 8:59:19 PM
To: Brani Rusanov <Brani_Rusanov at hotmail.com>
Cc: rtk-users at public.kitware.com <rtk-users at public.kitware.com>
Subject: Re: [Rtk-users] Insufficient Data For Proper Parker Weighting

Hi,
You are getting this because RTK detects that the scan is too short. Parker weighting requires pi + the fan-angle to be able to reconstruct exactly the central slice of your scan. Check here<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FSimonRit%2FRTK%2Fblob%2Fmaster%2Finclude%2FrtkParkerShortScanImageFilter.hxx%23L139&data=02%7C01%7C%7C6a5c9d4d141144d23ea908d8112ba92a%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637278226503872156&sdata=rhmqcGwHfDKDsJy62xyMD2jhf6KMyJ04OwwWwiF8bkM%3D&reserved=0> how this is calculated in RTK.
Possible solutions are cropping the projections to reduce the fan angle. I'm not sure what are the consequences but they'll probably be small since not much is missing in your case. It's even likely that RTK could be improved by discretizing differently the integral in parker weighting, in which case you'd get enough projections.
Simon


On Mon, Jun 15, 2020 at 10:56 AM Brani Rusanov <Brani_Rusanov at hotmail.com<mailto:Brani_Rusanov at hotmail.com>> wrote:

Hi,

I am attempting to reconstruct Varian raw cone-beam data. The specific type of scan is a short scan, 200 degrees generating 501 projections. During reconstruction I get the message: “you do not have enough data for proper Parker weighting (short scan) Delta is 9.951 degrees and should be more than half the beam angle I.e. 11.2359 degrees.”

Since I have not generated the geometry myself, rather, used a pre-set Varian protocol, I am unsure why I get this error.

How could I rectify this issue? Furthermore, what consequences are there to not applying a Parker weighting?

The geometry header is attached.

Your response is greatly appreciated,
Brani
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