Brain Imaging Lecture Flashcards
Order from most white to most black on a CT image…
haematoma, fat, brain, bone, gas
Most white to most black Bone Haematoma Brain Fat Gas
What artificial contrast is used in CT to produce a “CT angiogram?” and what colour is it?
Iodine - dense in electrons, white on scan
Does contrast usually pass into the brain?
Iodinated contrast does not normally pass into the brain because of the ‘blood brain barrier’ however this can be disrupted by tumours or inflammation and a CT scan 5mins after contrast injection will show ‘enhancement’ ( whiteness) where BBB is disrupted
What is MRI contrast determined by? (3)
Proton density
T1
T2
What are T1 and T2 concerning MRIs?
Measurements of the chemical and molecular environments of protons
What contrast makes T1 weighted images whiter? Demonstrating and enhancing disruption of BBB
Paramagnetic substances such as Gadolinium eg magnevist, dotarem
What does a “BOLD” functional MRI mean?
Brain ‘activity’ – actually venous oxygen saturation- is demonstrated using the BOLD Blood Oxygen Level Dependant technique. Haemoglobin has altered magnetism when unsaturated and this can be demonstrated on MRI—-still largely a research tool.
Some pros and cons of using CT (10)
Fast Good bone detail Acute haematoma easily seen Easy to monitor Well tolerated Poor post fossae Poor multiplane views Pathology contrast variable Moderately expensive Ionising
Some pros and cons of using MRI (10)
Slower Less good bone detail Less easily seen Difficult to monitor Few claustrophobic patients Good post fossae Excellent multi plane views Pathology contrast usually very good Very expensive Non ionising
Indications for brain angiography
Ix of spontaneous sub arachnoid haemorrhage
- suspected anuerysm/AVM
- carotid stenosis
In brain angiography a femoral puncture shaped catheter is introduced to which arteries?
Vertebral and carotid arteries
Hyperintense (bright) on T1
Fat and the 4M’s
Fat (unless deliberately suppressed) Methemoglobin (subacute hematoma) Mineral deposition (Ca, Mg, Mn, etc.)
Melanin (melanoma)
“Mush” (highly proteinaceous fluid)
Contrast material (gadolinium)
Hypointense (dark) on T1
Water, paucity of mobile protons (air, cortical bone) High flow (e.g. arterial “flow voids”)
Hyperintense on T2
Water T2 bright = more water and/or less tissue (“T2 = H20”) e.g. fluid collections, edema, demyelination, gliosis, some tumors, et al… (non-specific!!) Fat (but usually suppressed by design)
Hypointense on T2
Some blood products (subacute hematoma) Mineral deposition (Ca, Mg, Mn, etc.) Paucity of water or mobile protons (air, cortical bone) High flow (e.g. arterial “flow voids”)
