Beam Restriction (collimator)

Question 1

Collimation ____________ image quality

Answer 1

Increases

Question 2

Collimation ____________ patient dose

Answer 2

Reduces

Question 3

Collimation decreases __________, ___________, ____________,and _______ creating more black and white increasing ____________

Answer 3

Density, scatter, fog, and noise

Contrast

Question 4

When collimating never exceed the _______ of the image receptor.

Answer 4

Size

Question 5

Collimation

Answer 5

Controls the size and shape of the primary beam, minimizes amount of scatter radiation reaching the film and patient, absorbs off focus radiation

Question 6

As kVp increases scatter __________

Answer 6

Increases

Question 7

As kVp increases patient dose _________, because….

Answer 7

Decreases ; the photons pass through the patient

Question 8

Scatter is produced in the __________ by the ___________ __________.

Answer 8

Patient ; Compton effect

Question 9

Irradiated material

Answer 9

The volume and atomic number of the material being irradiated

Question 10

As volume increases scatter ___________

Answer 10

Increases

Question 11

If you decrease the tissue exposed you will __________ scatter produced

Answer 11

Decrease

Question 12

As the field size increases, scatter ___________ therefore: you should ___________

Answer 12

Increases ; collimate

Question 13

Increase collimation equals __________ scatter

Answer 13

Decreased

Question 14

Increased collimation equals a ____________ in contrast

Answer 14

Increase

Question 15

Increased collimation equals a ____________ in Compton

Answer 15

Decrease

Question 16

Increased collimation equals a ____________ in density film/screen

Answer 16

Decrease

Question 17

Increased collimation equals a ____________ in quantum mottle with digital

Answer 17

Increase

Question 18

Increased collimation equals a ___________ in technical factors

Answer 18

Increase

Question 19

Increased collimation does not effect:

Answer 19

Detail, distortion, or magnification

Question 20

What are the three types of beam restrictors?

Answer 20

Aperture diaphragm, cones/cylinders, collimators

Question 21

Aperture diaphragm

Answer 21

Flat sheet of metal, usually lead, with opening in the center
Simple and inexpensive
Use different diaphragms for different film size

Question 22

What are three disadvantages of the aperature diaphragm?

Answer 22

Increased penumbra, increase in off-focus radiation, and a Fixed field size

Question 23

In the aperature diaphragm, the closer the diaphragm is to the patient the less ___________

Answer 23

Penumbra

Question 24

What is an aperature diaphragm used in?

Answer 24

Chest units, head units, dental, and mammo

Question 25

For an aperature diaphragm, how do you calculate the size of the circle it will produce on the IR?

Answer 25

SID X Diameter of the diaphragm / Distance from focal spot to diaphragm Example: 40" X 2" = 80 80/ 5" = 16" circle

Question 26

Cones/ Cylinders

Answer 26

Circular aperature diaphragm with metal extension attached to housing Simple inexpensive

Question 27

Disadvantages of cone/cylinders

Answer 27

Can be heavy and fixed field size

Question 28

Cylinders can be good in reducing ___________ and ________ _________.

Answer 28

Penumbra ; off-focus radiation

Question 29

Cones/ cylinders have greater beam limitation when the cone is ___________ and the diameter is ____________.

Answer 29

Longer ; Smaller

Question 30

For a cone/cylinder, how do you calculate the size of the circle it will produce on the IR?

Answer 30

SID X lower Diameter of the cone / Distance from focal spot to cone bottom Example: 40" X 3" = 120" 120" / 16" = 7.5" circle

Question 31

When you make the cone longer you will have a ___________ coverage.

Answer 31

Smaller

Question 32

Collimator

Answer 32

``` 2 sets of lead shutters at right angles to one another ( 1 is for off focus radiation and 1 if for beam restriction) Most common used Expensive Field sixes vary Light source ```

Question 33

Collimation must be accurate within ______% of the SID

Answer 33

2%

Question 34

Between 1974-1993 the federal law required fixed machines to be equipped with __________ ___________ _________ that works on sensors.

Answer 34

Positive Beam Limitation (PBL)

Question 35

The bottom shutters of the collimators reduce __________.

Answer 35

Penumbra

Question 36

Accuracy of the collimators are check regularly. True or False?

Answer 36

True

Question 37

Collimators provide up to _____mm of added filtration.

Answer 37

1

Question 38

Disadvantages of collimators

Answer 38

Cost, maintenance, and over collimation

Question 39

Always allow _____" of light beyond each edge of anatomy.

Answer 39

1/2"

Question 40

For collimators, as distance increases the size of the field _________.

Answer 40

Increases

Question 41

2 ancillary devices

Answer 41

Lead blockers and lead masks

Question 42

Lead blockers

Answer 42

Sheat of lead rubber

Question 43

Lead masks

Answer 43

Cut to correspond to field size

Question 44

What do ancillary devices do?

Answer 44

Absorb scatter

Question 45

Increased field size = _________ scatter

Answer 45

Increased

Question 46

Increased kVp = _________ scatter

Answer 46

Increased

Question 47

We should collimate to ________ scatter and patient dose

Answer 47

Reduce

Question 48

Increased collimation = ________ patient dose, _________ scatter, and ________ quantum noise.

Answer 48

Decreased patient dose Decreased scatter Increased quantum noise

Question 49

Flat panel detectors are _______ size. Therefore it is very critical for a radiographer to __________.

Answer 49

One ; collimate