Digital subtraction angiography Flashcards
what is DSA
digital subtraction angiography
- fluoroscopic technique extensively used in IR for visualising blood vessels
what is DSA good for
navigation of wires and catheters through vasculature to various areas of the boduy
radiopaque structures such as bones are eliminated digitally from image allowing for accurate depiction of blood vessels
why cant normal fluoroscopic imaging be used to view vessels
- small vasculature will be obscured by patients bones and soft tissue
what is the procedure to acquiring a DSA sequence
- patient positioned normally with vasculature in view
- acquisition run, first few images taken should not have contrast
- that first image is used to select appropriate kV and mA
- second image is ‘mask’ image
- now contrast is injected and images are taken. these are ‘fill’ images. (these images record the passage of contrast through vessels)
- real time subtracted images are created by subtracting the ‘mask’ image from subsequent ‘fill’ image
- assuming no movement from patient, images in run should show contrast filled vessels only with no other overlying anatomy
what is DSA roadmap?
- once you have a series of subtracted images, you pick an image that shows the best view of the vessel of interest
- image selected is overlaid onto of live image of patient when you next start screening
why is DSA roadmapping done
- this alone with contrast acts as a guide to navigate through the vessels
if DSA roadmapping cannot be done, what is done alternatively
- ‘blind’ navigation
or - constant flow of contrast running through patient vessels
why is using constant flow of contrast through vessels to aid navigation bad
- procedure would take hours and you would damage patient kidneys with the amount of contrast used
what is the movement artefact found in DSA
- when patient moves between the acquisition of the mask and fill images
- creates a misregistration between pixels in mask and pixels in fill
- as the pixels are in different positions/misaligned in the mask and fill image, correct subtraction will not occur
- anatomical background will not be competed removed
how can you reduce motion artefact in DSA
- remasking
- new frame is closed from beginning of sequence
- new frame must be further into sequence than original mask image but before the vessels are filled with contrast
- with appropriate frame, this is the new mask image to be used in subtraction
what is another method of dealing with movement artefact and what is this
- pixel shifting
- radiographer manually shifts mask image in small increments in order to minimise the mis-registration of pixels
DSA is great for viewing vessels, but why is this not used in the catheter lab?
- pixel shifting cannot be done for movements such as peristalsis of bowel
- as there will always be a degree of movement and pixel shifting cannot correct the issue
- inability of pixel shift movement is why DSA is pointless in Cath lab due to constant cardiac movement
what is rotational angiography
- 3D rotational angiogrpahy
- c-arm rotates around patient acquiring multiple xray images
- images from different angles are reconstructed to form 3D image
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what is 3D overlay and what does this help with
- superimposition of 3D volume data (ct reconstructions) on live fluro display
- provides more info on patient anatomy and helps with navigation through complex anatomy
why is 3D overlay efficient
- brings advantage of other imaging modalities e.g MRI/CT
- make most out of available pre-procedural info and avoid radiation dose and contrast injections for repeating scans
what is a hybrid theatre
- combined operating theatre and IR suite
- used when IR is needed in surgery
- provides optimal efficient patient care
give an example of a case that would require the hybrid theatre
endovascular aortic repair (EVAR)
-need xrays to guide graft into aneurysm through incisions
what technique is used for vascular navigation during angiopgrpahy
seldinger technique
explain the procedure of using seldinger technique for vascular guide/insertion
- seldinger needle inserted into vessel under US guidance
- guidewire inserted through center of hollow needle, into vessel
- needle withdrawn and guide wire left in vessel
- sheath is slid over guide wire. Sheath stays in place throughout procedure maintaining access to vessel and allowing to slide larger items e.g catheter and stents over guide wire
how can you tell that you have correctly inserted the needle into a vessel
- there will be flashback of blood
what compartment of the sheath prevents leakage of blood
end of sheath has a valve which prevents blood leakage
what is the most commonly used artery for access for angiography
- common femoral artery in the groin
the kit :
- xray
- US
- catheter
- wires
- stents
- coils
