Imaging: MRI, CT, X-ray Flashcards
Difference between T1 and T2 weighted MRI?
In T2, H2O is bright
Technical consideration of CT: View? Age? Angle on imagine plane? Colour range?
View: Caudal (so image is looking from the feet)
Age: As age increases there is loss of brain matter so more dark areas seen around edges and ventricles appear more visible
Angle: Diagonal image plane
Colour: Interpretting greyness. Bone= white, air = black.
How to interpret a CT and MRI?
[A]
- Adequacy
- Alignment
- Artifact
[B]
- Bones
- Blood
- Brain
[C]
- Cisterns and ventricles
[S]
- Subcutaneous and soft tissue
- Surfaces
What is the difference between SDH and EDH?
EDH
- Extradural haemorrhage
- More common in younger
- Lemon shaped due to tight bonding between layers of meninges
SDH:
- Subdural haematoma
- More common in older
- More of a diffuse ring around entire brain
Use of contract agents in CT?
Rim and edges light up e.g. useful for meningioma
Enhances areas of low density
What is more likely to cause a stroke, leakage or blockage?
Blockage of a blood vessel
Order the following in terms of colour appearance in a CT:
Bone, air, blood clot, water, fat, grey mater, CSF, white mater
[White] Bone Blood clot Grey M White M CSF Water Fat Air [black]
Technical considerations of MR scanning: View? Age? Plane? Weighting? Generated by?
View: Caudal
Age effect: Atrophy better shown on MR than CT. Need to establish if level of atrophy is due to age and not hydrocephalus
Plane? Any. Can be used to show pacemaker, cochlear implant, metal around eye/head
Weighting? T1 weighed means the spinal fluid is WHITE. T2 weighted means the spinal fluid is white
Generated by emission
Difference in T1 and T2 weighting in MRI?
T1 weighed means the spinal fluid is BLACK. T2 weighted means the H2O is WHITE (WW2: Water, white 2 )
What are the different MRI variants?
Diffusion weighted ADC (Apparents diffusion coefficient) FLAIR (Fluid attenuated inversion recovery) GRE (Gradient echo imaging) EPI (echo planar imaging, reduces motion artifact) Perfusion Angiography Functional (spectrography)
Best way to scan for spinal lesion?
MRI scanning
What is SPECT?
Single photo emission tomogrpahy
Used radiosotope and gamma rays
What is PET?
Positron emission tomography
Requires cyclotron
MRI variants?
Diffusion weighted (DWI)
ADC (apparent diffusion co-efficient, uses DWI)
FLAIR (fluid attenuated inversion recovery)
Angiography
Perfusion
Systematic approach to interprettig abdominal CT?
“BBC Approach”
Bowel and other organs
Bones
Calcification and artefact
If bowel perforation is being considered, you don’t usually require an abdominal film, instead you need an..
Erect chest x-ray, as this allows free gas under the diaphragm to be identified (the patient needs to have sat upright for at least 15-20 minutes prior to the x-ray to allow time for air to rise).
In abdominal x-ray, what is looked at when assessing the bowels?
Small and large bowel
- SI has full width mucosual folds called Kerckring folds or plicae circulares
- LI has haustra, pouches which protrude into lumen, with plicae semilunaris inbetween
Normal diameters
SI = 3cm
LI= 6cm
Caecum = 9cm
Signs of obstruction in both LI and SI
Features of bowel inflammation
Causes of SI obstruction?
Adhesions due to previous abdominal surgery
Abdominal hernias
Intrinsic/extrinsic compression by neoplastic masses
Sign: Dilated loops of the small bowel = coiler spring appearance
Causes of LI obstruction?
Colorectal carcinoma *
Diverticular strictures *
Hernias
Volvulus (twisting of the bowel on its mesentry, commonly at the sigmoid and caecum)
Features of inflammatory bowel disease on AXR?
Thumb-printing – mucosal thickening of the haustra due to inflammation and oedema causing them to appear like thumb prints projecting into the lumen
Lead-pipe (featureless) colon – loss of normal haustral markings secondary to chronic colitis
Toxic megacolon – colonic dilatation without obstruction associated with colitis
