Digital subtraction angiography

Question 1

what is DSA

Answer 1

digital subtraction angiography

• fluoroscopic technique extensively used in IR for visualising blood vessels

Question 2

what is DSA good for

Answer 2

navigation of wires and catheters through vasculature to various areas of the boduy

Question 3

radiopaque structures such as bones are eliminated digitally from image allowing for accurate depiction of blood vessels

Question 4

why cant normal fluoroscopic imaging be used to view vessels

Answer 4

• small vasculature will be obscured by patients bones and soft tissue

Question 5

what is the procedure to acquiring a DSA sequence

Answer 5

1. patient positioned normally with vasculature in view
2. acquisition run, first few images taken should not have contrast
3. that first image is used to select appropriate kV and mA
4. second image is ‘mask’ image
5. now contrast is injected and images are taken. these are ‘fill’ images. (these images record the passage of contrast through vessels)
6. real time subtracted images are created by subtracting the ‘mask’ image from subsequent ‘fill’ image
7. assuming no movement from patient, images in run should show contrast filled vessels only with no other overlying anatomy

Question 6

what is DSA roadmap?

Answer 6

• 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

Question 7

why is DSA roadmapping done

Answer 7

• this alone with contrast acts as a guide to navigate through the vessels

Question 8

if DSA roadmapping cannot be done, what is done alternatively

Answer 8

• ‘blind’ navigation
  or
• constant flow of contrast running through patient vessels

Question 9

why is using constant flow of contrast through vessels to aid navigation bad

Answer 9

• procedure would take hours and you would damage patient kidneys with the amount of contrast used

Question 10

what is the movement artefact found in DSA

Answer 10

• 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

Question 11

how can you reduce motion artefact in DSA

Answer 11

• 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

Question 12

what is another method of dealing with movement artefact and what is this

Answer 12

• pixel shifting
• radiographer manually shifts mask image in small increments in order to minimise the mis-registration of pixels

Question 13

DSA is great for viewing vessels, but why is this not used in the catheter lab?

Answer 13

• 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

Question 14

what is rotational angiography

Answer 14

• 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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Question 15

what is 3D overlay and what does this help with

Answer 15

• superimposition of 3D volume data (ct reconstructions) on live fluro display
• provides more info on patient anatomy and helps with navigation through complex anatomy

Question 16

why is 3D overlay efficient

Answer 16

• 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

Question 17

what is a hybrid theatre

Answer 17

• combined operating theatre and IR suite
• used when IR is needed in surgery
• provides optimal efficient patient care

Question 18

give an example of a case that would require the hybrid theatre

Answer 18

endovascular aortic repair (EVAR)

-need xrays to guide graft into aneurysm through incisions

Question 19

what technique is used for vascular navigation during angiopgrpahy

Answer 19

seldinger technique

Question 20

explain the procedure of using seldinger technique for vascular guide/insertion

Answer 20

1. seldinger needle inserted into vessel under US guidance
2. guidewire inserted through center of hollow needle, into vessel
3. needle withdrawn and guide wire left in vessel
4. 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

Question 21

how can you tell that you have correctly inserted the needle into a vessel

Answer 21

• there will be flashback of blood

Question 22

what compartment of the sheath prevents leakage of blood

Answer 22

end of sheath has a valve which prevents blood leakage

Question 23

what is the most commonly used artery for access for angiography

Answer 23

• common femoral artery in the groin

Question 24

the kit :
- xray
- US
- catheter
- wires
- stents
- coils

Question 25

what are the 3 ways to close a puncture site

Answer 25

1. manual pressure (10 mins) 2. pro glide (internal suture) 3. angioseal (collagen plug)

Question 26

what is angioplasty

Answer 26

surgery using wires, catheters, gallons and stents to reduce the narrowing and restore blood flow in vessels

Question 27

how is a balloon catheter used to remove blockage in artery

Answer 27

- wire is passed through blockage - radiologist then passes balloon catheter over wire - balloon inflates inside blocked vessel to stretch and decrease narrowing

Question 28

what is AAA

Answer 28

- abdominal aortic aneurysm - due to atherosclerosis buildup causing walls of abdominal aorta to be weak and bulge outward like a ballon

Question 29

what equipment would be used for an AAA and how

Answer 29

- graft that has been pre packed into catheter is introduced into artery in groin - under xray guidance, advances into aneurysm and deployed where it expands to fit within aorta - blood will now flow through stent and reduce affect on weak wall of aorta/aneuryms

Question 30

what equipment would be used for a brain aneurysm and how

Answer 30

- small metal coil inserted into aneurysm through arteries running from groin to brain (prevent opening skull) - stop blood flowing into aneurysm so weak wall won't burts

Question 31

what software is used to analyse how much brain function is left after a thrombosis in brain

Answer 31

brainomix

Question 32

what is a thrombectomy

Answer 32

- use specially designed clot removal device inserted through catheter to pull or such out clot to restore blood flow - aspiration may be used along side, as stand reciever surrounds and traps within cloth, suction can be applied simultaneously to ensure the clot doesnt travel anywhere else