CT first invented in 1973 by Hounsfield.
Helped us go from 2D to 3D images.
CT quick, reliable, low cost, good for calcium.
MR actually was invented in the 1940s, but computing power inadequate.
MRI involves hydrogen nuclei magnetic moment begin aligned in a magnet, then a radiofrequency pulse causing precession.
MRI provides better resolution and ability to discriminate soft tissues, e.g. brain tumours.
T1 and T2 are properties of the tissues. MRI also removes bone artifacts in the posterior fossa that you get in CT. Also you have a multiplanar capability. But weakness in detection of calcification. Also more claustrophobic. But no radiation.
Principle of cellular density (nucleus/cytoplasmic ratio) to help determine diagnosis. And contrast enhancement helps as a blood-brain barrier marker.
– proteinaceous fluid
- calcium, manganese, copper
- extraaxial VS. intraaxial
- Water diffusion
- bright if restricted diffusion
- MR spectroscopy
- NAA nonspecific but detects neuronal loss.
- Perfusion imaging
- lots of edema
- grey-white interface
-e.g. cyst, intraaxial, blood vessels – hemangioblastoma most common adult primary posterior fossa tumour
Common sella tumours
-Rathke’s cleft cyst
Skull base tumours
- sinonasal carcinoma
- pineal, germ cell origin tumours
- arachnoid cyst
- choroids plexus papilloma
- cenral neurocytoma
- giant cell astrocytoma
- thrombosed aneurysm
- mesial temporal sclerosis
- HSV encephalitis
- Dural AV fistula
- vascular, aneurysm
- toxic/metabolic, e.g., Fahrer’s disease
- epidural – biconvex
- subdural – cresenteric, isodense if chronic
- on FLAIR, you see loss of black CSF spaces
- hypertensive hemorrhages
- vascular – aneurysm, AVM, cavernous malformation
- drug related – cocaine, phenylephedrine, anticoagulants, fibrinolytics
- vasculitis, vasculopathy – amyloid angiopathy
- infection – encephalitis, herpes, fungal
- germinal matrix hemorrhage
T1 - Grey White Black
T2 – Black White Black
If MRI done early, can’t rely on methemoglobin on MRI imaging for detecting thrombosis.