For either one, you need to know neuro-anatomy pretty well. Make sure you understand the ventricular system and the subarachnoid cisterns.
If you wanted to devote yourself to learning the basics of head CT, this book is quite good: Emergency CT Scans of the Head: A Practical Atlas
. It's not cheap, but you might be able to borrow a copy from somewhere. You can definitely learn the basics from that. The key things to be able to recognize are hydrocephalus, extra-axial collections (subdural hematoma, epidural hematoma, subarachnoid hemorrhage), and acute/chronic infarction. The book can teach you to recognize them by showing you good examples, which is helpful.
Reading a brain MRI is extremely complicated and takes a long time to learn. It's unlikely to be a good return on your investment unless you're going to be a neuroradiologist or a neurologist. Here's a super-basic approach to looking at one:
- First, look at the diffusion-weighted images (DWI). These are the best way to detect acute ischemia; it will be bright on DWI. It's not 100% specific, though; other things can cause restricted diffusion (i.e., brightness). And it's usually not subtle; radiologists call it "the lightbulb sign"
- Second, look at the FLAIR images. These are T2-weighted images on which water appears bright except the water in the CSF. You can see all kinds of edema, inflammation, and masses reasonably easily. Figuring out what they are can be more complicated, but at least you'll have a decent chance at identifying an abnormality.
- Third, look at the enhanced and unenhanced T1 images side-by-side. When there's a gadolinium enhanced scan, try to look at the pre-contrast and post-contrast images side-by-side. Especially in the brain, if something gets bright on the post-contrast T1 images, it's likely to be abnormal (e.g., primary brain cancer, metastatic lesions, weird inflammatory things).
Being able to read these scans takes a lot
of training. It's not really the kind of thing you can teach yourself, but you can learn about it, and try to talk to radiologists (especially neuroradiologists) whenever they interpret a scan on one of your patients.