Digital Subtraction Angiography

Question 1

what is the aim of DSA?

Answer 1

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

Question 2

when are images taken

Answer 2

images are taken before and after the injection of contrast

Question 3

how many images are taken before contrast-injection and why?

Answer 3

two images; first to adjust exposure factors, second as the mask image which is then stored in the system

Question 4

the ____ image is subtracted from the ____ image _____ by _____. this produces the ____ image.

Answer 4

the mask image is subtracted from the contrast image pixel by pixel. this produces the final image

Question 5

what does image subtraction increase, and what effect does this have on the Signal-Noise Ratio?

Answer 5

image subtraction increases noise, therefore reducing the SNR

Question 6

what does rotational angiography involve?

Answer 6

this involves taking images at various angles between 0 and 90 degrees

Question 7

what is roadmapping?

Answer 7

the frame with the maximum vessel opacification is selected, this is the mask frame. the mask frame is then subtracted from the live fluoroscopic images.

Question 8

what is pixel shift?

Answer 8

moving the mask image up or down a few pixels

Question 9

what does pixel shift correct?

Answer 9

pixel shift corrects patient movement