Mammo

Question 1

Why does mammo use lower energy xrs?

Answer 1

The photoelectric effect dominates at lower kVp. Small differences really amplify the chance of PE because of the cubed mathematical relationship

(Z/E)³

When E increases, photoelectric effect exponentially decreases!

Question 2

Optimal kVp in mammo?

Answer 2

25-30kVp

(16-23 keV)

Question 3

Target anodes in mammo

Answer 3

molybdenum or rhodium anodes (low Z targets –> lower E characteristic xrays)

(general rads uses tungsten)

Question 4

characteristic k-shell E of molybdenum

Answer 4

18 keV

Question 5

Which has a slightly stronger binding energy, Rh or Mo?

Answer 5

Rh (20.2 keV)

Mo is 18 keV

Question 6

Purpose of a Mo or Rh filter

Answer 6

block both HIGH and LOW photons –> more monoenergic beam

benefit: removes low E photons (only gives dose) and high E photons (which decrease contrast)

Question 8

What possible combos can you have for target and filter regarding Mo and Rh?

Answer 8

Mo/Mo

Rh/Rh

Mo/Rh *

You can have a Mo anode with Rhodium filter to produce an intermediate E spectra (Take Molly before your Road trip, it’s more fun)

**Can NEVEr have Rh/Mo

Question 9

mammo focal spot

Answer 9

0.1 - 0.3 mm

Question 10

What is the issue with a tiny focal spot?

Answer 10

smaller focal spot = more concentrated beam of E –> anode can’t tolerate all that heat so there is a limit to mA

mA 50 for focal spot of 0.1 mm

mA 100 for focal spot of 0.3mm

Question 11

lower mA in mammo results in what?

Answer 11

longer exposure time (still try and keep it under 2s

Question 12

what is the effect anode angle?

Answer 12

anode angle + tube angle

Question 13

cathode side of the beam is oriented:

Answer 13

toward the chest wall

Cathode; Chest wall

Question 14

what material is the exit window made of in mammo vs general?

Answer 14

mammo window = Beryllium (less xray attenuation)

General = pyrex glass

Question 15

What is a major advantage of compression in mammo?

Answer 15

dose and scatter reduction

reduced thickness = less scatter = lower kVp can be chosen

lower kVp and less scatter = improved contrast

Reduced thickness = Less mAs as needed = Less dose

Breast doesn’t move = less motion artifact –> improved spatial res

breast smashed closer to bucky = less geometric mag –> improved spatial res

Question 16

grid ratio in mammo

Answer 16

4-5

general xr uses a grid ratio of 6-16

Question 17

is dose increased or reduced with a grid?

Answer 17

increased.

more photons required to get adequate exposure

Question 18

do mag views increase dose?

Answer 18

yes.

brining the boob closer to the source increases the dose (inverse square law)

Question 19

what is the point of an air gap

Answer 19

reduces scatter

essentialy like an anti scatter grid. off-axis scatter coming out of the patient will miss the target

Question 20

what technique is used to reduce scatter in mag views?

Answer 20

air gap.

no grid is used in mag views

Question 21

what are some parameters changed to improve spatial resolution in mag views?

Answer 21

decrease the focal spot (smaller focal spot)

less mA (so you don’t melt your smaller focal spot)

longer exposure time

Question 22

tube current in mammo vs general

Answer 22

mammo 100mA

general 500mA

**mammo has a much lower tube current!

Question 23

receptor air kerma in mammo vs general

Answer 23

mammo 100uGy **

General 5 uGy

mammo much high receptor air kerma

Question 24

MQSA line pair requirement for digital mammo:

Answer 24

None! Trick question

Question 25

dose on digital vs film mammo

Answer 25

digital machines have 15% less dose compared to analog because the beam quality is better. Digital has fewer repeat exams