I was not expecting the CT scan to be able to identify the cores within the die.
But now I think about it, the metal layers (especially traces carrying power) are probably think enough, and different enough to show up. And even just power distribution is enough for the shape of the cores to be visible.
You don't even need a CT to identify the cores; they are already quite obvious in regular die photos as repeated areas.
https://commons.wikimedia.org/wiki/File:Intel_Core_i9-13900K...
You can typically see the L1/L2 SRAM cache regions just by looking for continuous patterns, then try to divide it into the number of cores or core groups you're looking for.
LTT Labs are writing up a lot of nice content of late.
Sadly posts from one of their employees, Lucas, are auto-dead and don't get seen which is sad given their effort and quality.