Detector intersection area

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Vytautas Gradauskas

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Nov 4, 2025, 5:42:43 AMNov 4

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Hello prof. Fang,

Is there a function in MCX that calculates the "active" intersection (between zero and non-zero label media) area of a detector?

Thank you

Vytas

Qianqian Fang

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Nov 7, 2025, 11:28:16 PMNov 7

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hi Vytas,

no, mcx does not have such function. it is actually not easy to do - tessellating 3D points in to an open surface is surprisingly difficult problem.

over the past two days, I tried a few approaches, including modifying a CRUST algorithm, or using alphaShape() provided by matlab, the results were unsatisfactory. also, neither of them work for co-planar (2D) point cloud.

for example, running the colin27 built-in example

https://github.com/fangq/mcx/blob/master/mcxlab/examples/demo_colin27_atlas.m

you can see the point cloud detected at the 4 detectors

by calling a modified crust function, I can get something following the shape, but there are a lot of holes - with some places missing big patches. alphaShape() failed in different ways.

in the attached figure, top shows the detected photon positions for the 4 detectors in the colin27 example; the bottom panels showed the crust-recovered surface mesh for det#1 and det#2. both of them showed partial recovery, thus calculating area is not accurate

Qianqian

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