Digital Subtraction Angiography

Question 1

What is the focus of DSA?

Answer 1

to produce images of contrast filled vessels in isolation from other tissues

Question 2

What does the technique of DSA improve?

Answer 2

It improves clarity of the image of the vessels, and a reduced amount of contrast medium is required

Question 3

What steps are included in the Temporal subtraction technique?

Answer 3

• Images of the same region are taken before and after injection of contrast medium
• Images are taken in rapid succession to avoid patient movement
• The original image is subtracted from the image using contrast pixel by pixel, producing the final image

Question 4

What is the original image that is taken without contrast known as?

Answer 4

The mask image

Question 5

What is pixel shifting?

Answer 5

The misregistration due to movement can be reduced retrospectively by adjustment or movement of the mask

→ Must be done over full field of view

Question 6

Image noise in DSA

Answer 6

• If images are added together noise is reduced
• However in DSA the images are subtracted, so image noise is increase therefore ↓ SNR
• TO counteract this we need to ↑ mA (increasing dose)

Question 7

What is road mapping?

Answer 7

When a DSA sequence is performed, the frame with the maximum vessel opacification is selected and is used as the road map mask

Question 8

What is road mapping useful for?

Answer 8

Very useful in guiding the guide wire in to a selected blood vessel