Physics

Question 1

Focal spot sizes

• mammo
• general X ray
• CT

Answer 1

• Mammo: 0.1 mm and 0.3 mm
• general X ray: 0.6 and 1.2 mm
• CT: 0.6 and 1.2 cm

Question 2

Things that improve (decrease) heel effect

Answer 2

• focus to film distance: larger FFD = less heel effect
• film size: smaller film = less heel effect
• larger anode angle = less heel effect

Question 3

Beam intensity

• what is it?
• what is it measured in?

Answer 3

Beam intensity = number of X rays x energy

• Roentgens per minute (R/min)
• increases in proportion to kvP ^ 2

Question 4

five factors that change the x ray spectrum

Answer 4

• mAs: quantity
• kVp: quantity and quality
• voltage generator: quantity and quality
• filtration: decreases quantity, increases quality
• target material: changes characteristic peaks; higher atomic number increases X-ray quality and quality

Question 5

Effect of mA and kVp on focal spot

Answer 5

• high mA, low kVp = wider focal spot (blooming)

- higher kVp = smaller spot (thinning)

Question 6

Probability of PE

Answer 6

directly proportional to Z ^3

inversely proportional to incident photon energy ^ 3

Question 7

Attenuation of X ray in tissue depends on what 3 things?

Answer 7

• Z
• tissue density
• X ray beam Quality

Question 8

3 things that increase scatter

Answer 8

• higher KVP
• larger field of view
• thicker part (person)

Question 9

limiting factor for spatial resolution

• for film
• for CR
• for DR

Answer 9

• flim: size of grain of photographic chemical
• CR: size of laser used to read the phosphor palte
• DR: size of individual thermoluminescent transistor

Question 10

factors causing geometric unsharpness

Answer 10

• larger focal spot
• increased object to detector distance
• decreased source to object distance
• more magnification

Question 11

Magnification factor

Answer 11

source to image distance / source to object distance

SID/SOD

Question 12

modulation transfer function (image)

Answer 12

= information recorded/ information available

Question 13

Susceptibility artifact

Answer 13

• worse with longer TE

- worse with GRE sequences

Question 14

Adjusting mAs

• for fat people?
• for children 6-12
• for children 0-25

Answer 14

double mAs for every 4 cm of patient tissue

• 50% for age 6-12
• 25% for age 0-5

Question 15

ways to reduce scatter

Answer 15

• collimate
• compression
• lower kVp
• grid or air gap

Question 16

spatial resolution for

• film screen mammo?
• digital mammo?
• digital radiograph?
• CT
• MRI

Answer 16

• 15 lp/mm
• 7 lp/mm
• 3 lp/mm
• 0.7 lp/mm
• 0.3 lp/mm

Question 17

Flat field test

Answer 17

Imaging large piece of acrylic; done to improve image quality and calibrate digital detectors in mammo

Question 18

Target rate for MQSA audit

• recall rate
• cancers/1000 screened

Answer 18

5-7%

3-8 per 1000

Question 19

MQSA processor QC

Answer 19

Daily

Question 20

MQSA darkroom cleanliness

Answer 20

Daily

Question 21

MQSA viewbox conditions

Answer 21

Weekly

Question 22

MQSA phantom evaluation

Answer 22

Weekly

Question 23

MQSA repeat analysis

Answer 23

Quarterly

Question 24

MQSA compression test

Answer 24

Semi annually

Question 25

MQSA darkroom fog

Answer 25

Semi annually

Question 26

MQSA screen film contrast

Answer 26

Semi annually

Question 27

MQSA line pair phantom

Answer 27

13 Lp/mm in anode cathode direction

11 lp/mm right to left

Question 28

Limit on AERC exposure rate

Answer 28

87 mGy/ min or

10 R/min

Question 29

How does electronic mag affect air Kerma and kerma area product?

Answer 29

Increases KERMA

Does not Change KAP

Question 30

Air Kerma limit?

For fat people?

Answer 30

87 mGy/min (10 R/min)

High level control : 176 mGy/min (20 R/min)

Question 31

Fill factor

Answer 31

Fill factor = sensitive area / pitch ^2