Ch13 Imaging and Angiography Flashcards
(45 cards)
What is the orbito-meatal line?
A line from the lateral canthus of the eye to the EAM (aka Towne’s view)
What are the Hounsfield units of air, water and dense bone?
-1000, 0 and +1000 respectively. Remember that Hounsfield units are a measure of attenuation so no attenuation (air) has negative valves.
What are the Hounsfield units of disc and theca on spinal CT?
Disc is 2x that of the theca The theca is 30 and disc is 60.
What are the Hounsfield units of acute blood?
60-80
How is a CT perfusion acquired?
Areas of interest in the 3 different vascular territories (ACA, MCA, PCA) are selected from a non-enhanced CT. Contrast is then given and scans are repeated at intervals through that slab (2 cm thick). The CBV, CBF, MTT and TTP can be calculated. In stroke the MTT is increased and the CBF is decreased.
What is a Diamox challenge?
After an initial CT-perfusion a Diamox (acetazolamide) challenge is performed (1 g) and a scan is repeated after 10 minutes. This acts as a vasodilator and the change in the parameters indicates the extent to which the stenosis resulting in ischaemia is compensated already by vasodilation.
What are the 3 responses to a Diamox challenge?
1 - Normal CBF that increases after Diamox 2 - Decreased CBF that increases after Diamox (i.e. retained reserve) 3 - Decreased CBF that does not increase or falls further after Diamox (i.e. no reserve) as a result of a steal phenomenon. **These patients are the ones that will benefit from cerebral revascularisation.
What is the action of carbonic anhydrase?
Converts Co2 + H20 to HCO3- and H+ and vice versa. The action of acetazolamide inhibits this. There is a build-up of H+ (acid) which cause vasodilation.
What is bright on T1?
Fat, contrast, melanin and subacute blood. Hence WM is brighter as the myelin contains fat.
What is the best sequence for detecting SAH on MRI?
FLAIR
How long must breastfeeding be interrupted after gadolinium administration?
48 hours
When did aneurysm clips become non-ferrous (MRI safe)?
1990
What is the risk of analphylaxis with gadolinium?
1 in 1000
What is a potential complication of using Gad in patients with renal failure?
Nephrogenic systemic fibrosis - fibrosis of skin, joints and other organs.,
What is a DWI : PWI mismatch?
Where is there is a difference between the diffusion weighted (infarcted) and perfusion weighted (ischaemic penumbra) images. This identifies salvageable brain.
What are the peaks on MR Spectroscopy?
- 5 Myoinostitol
- 2 Choline
- 0 Creatinine
- 0 NAA
- 3 Lactate
- 0 Lipid
What MR Spectroscopy changes are seen in gliomas?
High Cho:Cr ratio (note the higher the Cho the higher the grade)
Low NAA
Higher lactate and lipid peaks
What is suggested by Low NAA with normal Cho:Cr ratio?
MS plaque
What does a large inositol MR Spectroscopy peak suggest?
Haemangiopericytoma > Meningioma
What is the distinction between the centrum semiovale, corona radiata and internal capsule?
WM above the lateral ventricles - centrum semiovale
Below ventricles above the putamen - corona radiata
Level of the putamen and GP - internal capsule
How is a bone scan performed (SPECT)?
Tc-99 label attached to phosphorous which accumulates in areas of increased osteoblastic activity. Used to identify occult sources of infection, bone tumours, Paget’s disease, fractures and pain generators.
What are the MR imaging features of an early infarction?
Low ADC, Bright on DWI, Low CBF, Low MTT and Low CBV
Note: the ischaemic penumbra will have a low CBF and high CBV. This mismatch suggests mechanical thrombectomy will be beneficial.
What is NAA?
N-acetyl aspartate
Synthesised in the mitochondria of neurones with unknown function.
What is Creatinine a marker of in MR spectroscopy?
Metabolic activity
