Diagnostic Imaging

Question 1

anterior projection vs posterior projection

Answer 1

anterior projection: aka posterior to anterior (PA) projection - patient’s anterior side faces film/posterior side faces x-ray source

posterior projection: aka anterior to posterior (AP) projection - patient’s posterior side faces film/anterior side faces x-ray source

Question 2

do you want the object of your x-ray to be closer to the light source or the film?

Answer 2

closer to the film = greater resolution

projections chose to maximize resolution - for example, if you want a heart image you’re going to do an anterior projection (PA), in which anterior side faces film

Question 3

T/F: frontal images are always viewed as if you are looking at the patient face to face, regardless of wether it is an AP or PA projection

Answer 3

TRUE - patient’s right is always on your left

Question 4

in an x-ray, are higher radio-densities lighter or darker?

Answer 4

in x-ray, higher radio-density structures appear whiter (bone) vs lower radio-density areas (fat, air)

note this is usually the convention applied to CT scans, but these can also be programmed to show the image in reverse grey-scale

*also note this does not apply to MRI!! it’s usually opposite (fat would be white) - not based on radio-density

Question 5

what is the convention of viewing a CT scan?

Answer 5

remember a CT scan is a “slice”

anterior is on top, left is on the RIGHT - like you are looking up at the slice while the patient faces the opposite way as you

Question 6

how is the greyscale of ultrasonography determined?

Answer 6

based on echogenicity - measure of the ability of a tissue to reflect an ultrasound wave (liquids vs solids)

hyperechoic are brighter (white), hypoechoic/anechoic are darker