Why can't a Neurorad/msk(or dual certified in them) do a neurophys/electrodiagnosis/EMG NCS fellowship and why can't INR do gamma knife procedures?

Was just wondering why a neuro and msk certified rad(in either both or neurorad) cannot do a electrodiagnostics fellowship and why an INR cannot do gamma knife procedures when it is minimally invasive and he/she clearly knows the neuroanatomy/radioanatomy as well as or better than a neurosurgeon or radiation oncologist? Has it just never been considered as something a radiologist could do?
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Tags: Radiology Source Type: forums