Hi,
So, my experience with coding, especially in C, is extremely limited. I mostly
work in MATLAB, and as such I've been primarily using the built-in console
applications to perform reconstruction on CBCT datasets. The rtksart
application works great and provides a beautiful reconstruction. My goal is to
effectively do the same reconstruction, but tack on motion compensation to each
iteration.
After delving into the algorithm implementation in rtksart as much as I am
able, I wrote a MATLAB workflow that boils down to:
*
Start with image of zeros
*
Randomize gantry angle order
*
Iterate over gantry angles:
*
Load current projection forward and backward motion compensation DVFs
*
Deform current image iteration to current gantry angle breathing state
*
Forward project deformed image
*
Subtract deformed projections from raw CBCT image data
*
Back project the subtraction image
*
NORMALIZE BACK PROJECTION (this is where I think my issue is)
*
Deform normalized back projection back to the original image space
*
Update current image: img = img + lambda * (normalized_back_projection /
number_of_gantry_angles)
*
Note: This step, as it also contains normalization, may also be a source of my
issue...
*
Set negatives to 0
*
Repeat
I get an image that is much as I expect - a much sharper diaphragm and
generally higher definition in soft tissue structures. So I must be generally
on the right track. The issue is that the normalization is clearly off in some
way. I have a bright circle artifact in the middle of the image and some
striping throughout. Try as I might to understand it, I couldn't discern how
normalization was done in the rtksart application. So, this is the method I
used:
*
Create an image of 1s of the size of the final (SART reconstructed) image.
*
Forward project through this image of 1s
*
Back project through the resulting forward projection
*
In the normalization step in the MCSART process detailed above, I simply divide
by this resulting back projection.
Knowing all of that, any idea what my issue might be leading to my artifacts?
Ultimately, I know it would be more ideal if I just altered the rtksart
application itself to include motion compensation, and then I'd just be using
the built-in normalization that clearly works, but I find my abilities lacking
when I attempt to do this... So instead I am just seeking to understand how
that application implements normalization, so that I can use a similar
normalization in my algorithm!
I greatly appreciate any help provided!
Best,
R. Andosca
GSR
UCLA Health
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