beam geometry

Question 1

what is magnification caused by

Answer 1

the diverging beam (form isotropic emission)

Question 2

what is magnification affected by

Answer 2

SID, SOD/OID

Question 3

what is the magnification factor

Answer 3

how much larger the object appears in the image

Question 4

what is the formula for magnification factor

Answer 4

MF = SID/SOD

Question 5

how can you reduce magnification

Answer 5

increase SID
decrease OID (better)

Question 6

when is magnification helpful

Answer 6

sometimes can be used to increase object size

Question 7

what is distortion

Answer 7

unequal magnification of an object

Question 8

what are the 2 types of distortion

Answer 8

elongation
foreshortening

Question 9

what affects distortion

Answer 9

SID OID, object position, object thickness

Question 10

how does foreshortening happen

Answer 10

IR is flat, but the object is angled

Question 11

how does elongation happen

Answer 11

object is parallel to IR, CR is angled
CR is perpendicular, but the IR is angled

Question 12

how is distortion used to our advantage

Answer 12

bisecting angle method and superimposition reduction

Question 13

what is the bisecting angle method

Answer 13

reduces the distortion on naturally angled bones

Question 14

what angle is used for the bisecting angle method

Answer 14

angle of CR to IR = 1/2 angle of object to IR

Question 15

what causes focal spot blur

Answer 15

diverging beam and multiple point sources

Question 16

what does focal spot blur create

Answer 16

penumbra (geometric unsharpness)

Question 17

how can we prevent blur

Answer 17

longer SID
shorter OID
smaller focal spot size

Question 18

what is the inverse square law

Answer 18

(I1/I2) = (d2/d1)^2

Question 19

what is the line focus principle

Answer 19

uses the angle to achieve large actual focal spot but small effective focal spot (high ratings, less blur)

Question 20

what is the effective focal spot

Answer 20

focal spot as seen from the POV of the IR

Question 21

what are the pros and cons of a large focal spot

Answer 21

more areas for beam
less pitting
higher ratings

more point sources
more blur

Question 22

what are the pros and cons of a small focal spot

Answer 22

sharper image
less blur

lower ratings allowed
more easily damaged

Question 23

what is the common anode angle

Answer 23

12-17 degrees

Question 24

is anode angle is 45 then effective size = ?

Answer 24

incident electron beam size

Question 25

is anode angle is <45 then effective size = ?

Answer 25

effective is smaller than incident

Question 26

is anode angle is >45 then effective size = ?

Answer 26

effective is larger than incident

Question 27

what is the anode heel effect

Answer 27

lowered intensity (around 75%) on the anode side

Question 28

what causes the anode heel effect

Answer 28

angled target (some photons are travelling through the target itself

Question 29

when can the anode heel effect be useful

Answer 29

it can act as a filter, such as in a T-spine or abdomen exposure

Question 30

how to reduce anode heel effect

Answer 30

longer SID smaller field size