1. Website for intro to radiology modalities:
2. MRI neuroanatomy
3. Gradient Recalled Echo MRI:
-This is the most sensitive test for blood in the brain parenchyma-- it highlights ferromagnetic effects, such as that caused by blood.
-Blood will appear dark on GRE.
-Better than non-contrast CT for detecting intraparenchymal hemorrhage, but worse for detecting SAH.
-DAI will appear as punctate hypodense areas = punctate hemorrhage from axonal injury 
4. Contraindications for MRI: 
-Spine stimulators (some)... I think I remember the medtronic reps saying the new ones are MRI-safe at the last CNS meeting... but lots of patients complain that they can feel the devices heating up during MRI so who knows? VNS are safe though.
-Old aneurysm clips: ones used in the last 15 years are generally not ferromagnetic, but check the op note to be sure.
-Pacemakers/AICD/LVAD etc, any implanted cardiac devices.
-Breast tissue expanders (before implant surgery)
-Any metallic foreign bodies
-When in doubt, check MRIsafety.com for a full list of specific products and MRI safety.
5. Subarachnoid hemorrhage: (info here)
-Non contrast CT best in first 12 hours, sensitivity decreases after
-If the CT is negative but clinical suspicion is high => LP to look for xanthochromia (looks pink), elevated RBCs, elevated opening pressure. 
-Look for blood (hyperdense on non contrast CT) in sulci and cisterns, esp supracellar (aka chiasmatic) and interpeduncular cisterns, as they can show a small amount of blood. (great lecture on cisterns)
From ABC radiology blog:

 

Supracelllar cistern & interpeduncular cistern separated by Liliequist membrane. 

6. Interventricular hemorrhage:
-Usually due to tearing of subependymal veins.
-Often associated with corpus callosum injury
-Best place to look: occipital horns of lateral ventricles.
-Choroid plexus can calcify and look hyperdense on CT
7. Signs that may indicate herniation on CT:
-Midline shift
-Compression of ipsilateral ventricles
-Loss of supracellar cistern (replacement by herniated brain)
-Cephalad shift of brainstem
-Caudal shift of cerebellum
8. Types of herniation: 
-Subfalcine: supratentorial mass forces cingulate gyrus across falx. Shift in septum pellucidum, can compress ACA causing ischemia.
-Descending transtentorial: cerebrum herniates through incisura into posterior fossa. On CT you will see effacement of basal (interpenduncular) and suprasellar cisterns.
-Uncal: uncus of temporal lobe herniates through incisura, effaces suprasellar cistern, may compress PCA.
-Ascending transtentorial: posterior fossa mass/fluid causes anterior displacement of midbrain/brainstem, cerebellar vermis may herniate up as well.
-Cerebellar tonsil: cerebellar tonsils herniate down through foramen magnum, compress brainstem anteriorly.
-Good website on herniation
9. Diffuse Axonal Injury: (good website on DAI)
-Rapid accel/decel forces-- brain decelerates at different rates due to differing densities, leading to shearing force applied to brain parenchyma and axonal injury.
-Most common places to have DAI: grey-white matter junction, basal ganglia, internal capsule, splenium/body of corpus callosum, brainstem.
-Findings on non-contrast CT: punctate hyperintense points, suggestive of microhemorrhage or subtle hypointense regions representing edema
-Findings on gradient echo MRI: punctate hypodense areas corresponding to areas of microhemorrhage where axons were damaged.
-Findings on T2 and T2/FLAIR MRI: oval hyperintense regions = edema
-Findings on Diffusion Weighted MRI: oval hyperintense regions, corresponding to cytotoxic edema
10. Subdurals & CT
-Acute subdural (<3 days): hyperdense on non-contrast CT
-Subacute subdural (3 days to 3 weeks): isodense on non-contrast CT, hard to see-- look for midline shift, increased thickness of grey matter (subdural will look like grey matter), loss of sulci.
-Chronic subdural: hypodense on non-contrast CT
-Acute on chronic subdural: will look heterogenous on CT (mixing of hypodense and hyperdense) or will demonstrate a hematocrit line, where there is a horizontal separation between hyperdense and hypodense.