Hi,
Here is the setup for my question: I have lung CT scans from multiple time points for multiple patients. Our team’s radiologist is using Slicer
to perform semi-automated contouring of lung nodules. In addition, he is saving/recording the [xyz]
coordinates of the nodule centroid in anatomical space. Each nodule identified in the CT scans has an ID number. Unfortunately, the nodule IDs are not consistent across scans. The IDs are assigned in order the nodule was observed, and so lesion #1
on one scan might be lesion #2
on another scan, even if they are the same lesion.
So, of course we can have the radiologist manually review scans to determine which lesions IDs are actually the same lesions across scans. But this is prohibitively slow to do. I thought I should be able to use the nodule centroid anatomical coordinates to link lesions across scans. So we looked at the data for two scans for two lesions we know are the same, and yet the anatomical [xyz]
differed substantially. We realized the origins differ, and these numbers are relative to the origin.
So I extracted the image origin coordinates from DICOM header using Slicer
, and then calculated the nodules “distance from origin” using the origin and centroid coordinates. For example:
First scan: centroid [126.3, -38.5, -166.7]
; image origin [185.2, 180.0, -347.7]
Second scan: centroid [121.4, 103.2, -215.9]
; image origin [180.6, 316.6, -382.2]
Subtracting the nodule coordinate from the origin coordinate, we get the “distance from origin”:
First scan: [58.9, 218.5, -181.0]
Second scan: [59.2, 213.5, -166.3]
These numbers are fairly close, which suggested to me I was on the right track. I would expect these numbers to be identical ONLY if the fiducial for the centroid was placed in the EXACT same physical location across scans, right? Does anyone have any thoughts on whether this approach could be used to “link” nodules from different scans?