I'm not super familiar with ABI, but MRI/CT is pretty standard for diagnosing brain injuries. I would say talk to your doc, but it is probably worth it.

You might not even need an MRI, ask about an Electroencephalogram (EEG). They put some sticky probes on your head and just read the motion of brainwaves.

I had one and it showed a big 'blot' that the doc said was abnormal delta waves floating around my brain. Much less expensive than an MRI, and might reveal what you need to know or at least drop a few possibilities.

FWIW, I have thought perhaps it’s an abi for years, but it would have been easier to get an adhd dx rather than an abi. With the no for the adhd, it’s become more likely that it’s an abi or something. So I am investigating that.