Week 14: CT Head Flashcards
1
Q
Indications for CT Head
A
- stroke
- transient ischemic attack (TIA) (stoke that only lasts a few minutes)
- hemorrhage
- trauma
- acute neuro changes
- tumours
- arteriovenous malformation (AVM) (tangle of blood vessels)
- thrombosis
- aneurysm
- headache/seizures
- mass/lesion/hearing loss
- unknown/surprises … parasites
2
Q
CT Head Patient Position
A
- supine, head placed in head holder, head first
- if coronal needed (rare): patient can extend chin and drop head back or patient can be prone instead)
- DFOV 23 cm
- patients OML or better the supraorbital meatal line (SOML) should be parallel with the gantry (tilt gantry or tuck chin down)
- SOML preferred because it reduced dose to the lens of the eye
3
Q
Gantry Tilt
A
- amount of tilt varies form unit to unit
- amount of tilt depends on the patient and how much they can tuck their chin
- how the gantry is tilted and the anatomy is positioned will affect the axial plane
- this plane is seen by the radiologist initially without doing
any reformats/reconstructions
4
Q
Routine Brain
A
- axial scan (because most gantry cannot use helical if angled)
- scan just below base of skull to just above vertex
- slice thickness 1.25 is typical (thinner than in the past) to help reduce beam hardening artifacts from the thick posterior fossa
5
Q
Skull Base (Posterior Fossa)
A
- axial scan
- foramen magnum through petrous ridges
6
Q
Temporal Bones
A
- axial scan
- just below mastoid process o jus above petrous ridges
- DFOV 10 cm
- include entire mastoid, IAC (internal auditory canal) and EAM (external auditory canal)
7
Q
Sella Turcica
A
- 99% performed in MRI
- axial in CT
- below seller floor through dorsum sellae
- DFOV 14cm
8
Q
Contrast for CT Head
A
- non-enhanced: structural imaging of the brain and base of skull
- enhanced: IC contrast used for infection, neoplasms or patient will go to MRI if not contraindicated
- head scans do not need to be power injected, a hand injection can be used (approx. 1.0mL/sec) but power injector with a reduced flow rate is still the most common method
9
Q
Window Settings for the Brain
A
- sort tissue brain, slices in posterior fossa: 160ww/40wl
-soft tissue brain, slices above posterior fossa to vertex : 100ww/30wl - bone: 2500ww/400wl
- blood: 200ww/60wl
- small attenuation differences between grey matter and white matter so narrow widths are used to demonstrate the brains soft tissue
9
Q
Stroke
A
- after a stroke edema progresses ad Brian density decreases proportionally
- sever schema results in a 3% increase in intraparenchymal water within 1 hours
- this corresponds to 7-8 HU decrees in Brian density
- 6% increase in water after 6 hours
10
Q
Intracranial Hemorrhage (ICH) Stroke
A
- CT most frequently used initial exam for imaging ICH
- ICH appearance will change with time
- density loss starts at the periphery of the hematoma, portions become isodense and progresses to become completely hypodense
- important to recognize certain critical pathologic changes to
bring to the attention of the radiologist or ER doc
11
Q
General ICH Density Over Time
A
- hyperdense 1-3 days
- hyperdense centre with concentric hyper/hypodense tissue 4-10 days
- isodense centre surrounded by hypodense tissue 11days-6months
- hypodense to normal brain tissue after 6 months
12
Q
Suspicion of Stroke
A
- tissue plasminogen activator (t-PA) is a pharmacologic treatment for acute ischemic stroke
- to be effective t-PA must be administered within 3 hours of first signs of strokewhicha means the patient must be transported, diagnosed and administered with t-PA within the 3 hour window
- ICH contraindicates t-PA therapy
- non contrast CT brain performed to determine ischemic stoke from hemorrhagic stroke
- CM is used to asses the state of cerebral circulation and tissue and to asses the underlying disease
13
Q
CT Brain Perfusion
A
CT brain perfusion provides additional information by allowing qualitative and quantitative evaluation of cerebral perfusion (obtained by monitoring the passage of iodinated contracts through cerebral vasculature)
