General radiology Flashcards
What is CT?
Computed tomography- produces cross-sectional images by scanning a slice of tissue from multiple directions using a fan X-ray beam
How do we described white and dark on CT? What does it mean in terms of x-ray absorption?
increased attenuation/hyperdensity= white (more X rays absorbed)Decreased attenuation/hypodensity= dark (less X rays absorbed)
Axial scan orientations for CT?
imagine you are looking up from the feet. So the right hand side of the image is often the left of the patient
What are the Houston units for bone, haemorrhage, water and air?
Bone >500Haemorrhage +50-80Water= 0Air= -1000
What is windowing in CT?
We can select certain tissues/fluids etc on the image by selecting the housten units. for example, if you wanted to see just soft tissue, then you would set the HU to +40
What contrast agents are used for CT?
positive agents that include iodine and barium
What are some advantages of CT?
good resolution and quick to perform
What are some disadvantages of CT?
high radiation dose and adverse SE to contrast
How do we know that contrast has been delivered?
when blood vessels appear more dense (whiter) than muscle or brain
If we wanted to see an arterial phase or venous phase- after contrast has been delivered, how would we see this on CT scan?
After contrast is injected, it would go through the arteries first–> use early scans, then go to the veins next–> see later scans.
What does anechoic mean on U/s? what substances lead to this?
dark- fluids like blood, bile, urine
What does echogenic mean on U/s? what substances are echogenic?
bright. fat, connective tissue etc.
What are U/s usually used for?
gallbladder (looking for stones), liver, obstretrics etc
What is a doppler u/s used for?
looking at blood flow
What is a hot spot?
focal area of increased isotope uptake–> darker
What are radioisotope imaging used for?
bone scans (reflects OB activity), thyroid scans and lung scans (V/q)
What do we use PET for?
PET used for detecting tumours and staging cancer. It is capable of demonstrating metabolic activity and function to a much greater extent than the modalities.
What are the most common applications of MRI?
CNS, spine, musculoskeletal
Difference between T1 T2 weight?
T2= fluid is bright (CSF, bile, urine)
what is flair MRI?
T2 image but CSF is nullified
How do we describe increased whiteness or blackness on a MRI?
hyper intensity and hypointensity respectively
What contrast is used in MRI contrast?
Gadolinium
What do we use DWI MRI for?
looking at ischaemic stroke and abscesses
What is MRA?
looking at angiography and flow of blood
MRCP?
MRI imaging of biliary system and pancreatic ducts. Less risky than ERCP
What is a danger of contrast administration in MRi?
Nephogenic systemic fibrosis in renal impaired individuals
Advantages of MRI?
no radiation, high resolution, superior soft tissue contrast than CT, does not need contrast for angiography/cholangiography.
