[Rtk-users] Angular gaps

[Andy Shieh]

Hi Simon,

First of all, I regret not being able to going to ICCR, otherwise I could
really thank you for your work in RTK. It has really helped me a lot in my
research! Fortunately a few of my colleagues got a chance to talk to you
(Ricky and John, if you remember). Hopefully I'll see you this year in
AAPM!!

So today I want to ask you about two things.

1. Failed reconstruction (due to maximum angular gap too big?)
I noticed that occasionally RTK gives reconstruction that looks like this.
[image: 內置圖片 1]
In case the picture is not sent through, the image has a big angular region
where the intensity is essentially zero when viewed axially. This happens
when I use displacement binning, and using half-fan data.
I summarized all my reconstructions and realize this only happens when the
"maximum angular gap" of the projections in that bin is greater than 20
degrees. Therefore I assume it's because the half-fan projection on one
side not being able to find its corresponding projection image on the other
side. I just want to check with you if that's what's happening here.

2. There is a paper on direct weighting of uneven angular spaced
projections.
http://link.springer.com/chapter/10.1007%2F978-3-642-33415-3_23
I think the idea is basically lower the weight of closely spaced
projections.
Is this already implemented in RTK?

Thanks Simon !! :)

Cheers,
Andy
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