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Forum: Geometry
Re: None Overlap of parameterized volumes (Niklas)
Date: 20 Mar, 2008
From: Joseph Perl <Joseph Perl>

Niklas and I have engaged in some discussion about this offline. Summarizing here for the record.

This is a very interesting problem which will have relevance to many users in imaging, and which seems rather unique to this field (not much in common with needs from HENP or Space communities, which is why it has not yet been solved, rather than because it is in any way not solvable). We should work to come up with an elegant solution.

An inelegant workaround that I have so far suggested to Niklas would involve approximating the elliptical cylinder shape of the patient with a set of several boxes (e.g., approximate a cylinder by a large box with four smaller boxes along the four long sides of the large box). How well this might work, how many boxes one would need, depends on how closely the patient fits into the scanner (a non-trivial issue in medicine).

Makoto Asai suggested a more elegant solution that would take some expertise in navigation and geometry, more or less as follows: Have two parallel geometries: One approximates the patient as a G4Tubs. This is the "mass geometry". A second one, the parallel geometry, is the actual DICOM, a G4Box. Then have the objects in the mass geometry interrogate the parallel geometry to answer such questions as DistanceToOut and Material. I think it would be fairly complicated, but might be worth working out eventually.

Anyway, I leave these comments here as a stub that we can hope to develop further eventually. I'm afraid it's not my particular area of expertise.

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