Beam Restriction

Question 1

Compton scatter is dependent on:

Answer 1

the thickness and density of the part
(more matter, more scatter)
(more available electrons)

Question 2

Increasing kVp increases the amount of…

Answer 2

scatter relative to the photoelctric effect

Question 3

What does the use of grids do?
(2)

Answer 3

-absorb scatter radiation within the patient
-improves image contrast at the expense of patient dose

Question 4

Technique must be increased to compensate for the use of a grid because grids remove part of the primary beam

Answer 4

Note

Question 5

What’s something we can do to reduce patient dose and reduce scatter radiation?

Answer 5

restrict the beam or collimate

Question 6

What is collimation?
(2)

Answer 6

-decreases the amount of radiation that interacts with the patient
-reduces the patient dose

Question 7

By properly collimating we..
(2)

Answer 7

-reduce the amount of scatter produced
- reduced the amount of matter that the photons can interact with

Question 8

Collimation should be limited to

Answer 8

-1” beyond the anatomy of interest on all 4 sides on tabletop exams

Question 9

Collimation should not exceed…

Answer 9

the recommended field size for a particular part

Question 10

When we collmate properly we are…
(4)

Answer 10

-reducing scatter radiation
-reducing unnecessary exposure by the primary beam
-increasing contrast
-reducing patient dose

Question 11

According to Bushong, the atomic number of material has…

Answer 11

no effect on likehood of scattering

Question 12

Atomic number does not directly…

Answer 12

affect scatter

Question 13

What is the device collimator?

Answer 13

the foremost method of restricting the primary beam field size

Question 14

What is the most commonly employed beam restrictor in radiography?

Answer 14

Collimator

Question 15

Most collimators now equipped with an accessory known as a…

Answer 15

Positive beam limitation (PBL) device

Question 16

What does the PBL do?

Answer 16

it automatically collimates the beam to the size of the image receptor

Question 17

What is the collimator function?
(3)

Answer 17

-Permits an infinite number of field sizes
-Provides a light source for the radiographers to properly placing the tube and central ray
-Reduces penumbra

Question 18

What do entrance shutters do?

Answer 18

help remove off-focus radiation

Question 19

Off focus radiation?

Answer 19

Xrays created in other parts of the tube not the anode

Question 20

How many sets do the collimator shutters have?

Answer 20

2 sets of shutters
(sometimes 3)

Question 21

The second set collimator shutter?

Answer 21

is the one the technologist adjusts

Question 22

Length and width of field are independently…

Answer 22

controlled by technologist

Question 23

The light field?

Answer 23

uses a light reflected off mirror to project the area of the x-ray beam

Question 24

Proper adjustment of mirror is necessary because…

Answer 24

to accurately display location of exposure field

Question 25

The light field/xray beam coincidence testing should be part of the...

Answer 25

QC program -Needs to be accurate within +/- 2% of the SID

Question 26

The use of a collimator results in some filtration of the xray beam because...

Answer 26

the primary beam is passing through the mirror in the collimator -About 1mm Al/Eq

Question 27

Features of collimator housing?

Answer 27

-Central ray must be marked -Some units project location of photo timer sensors in light field -An alignment light helps to center beam with the image receptor

Question 28

What is penumbra?

Answer 28

a geometric unsharpness around the periphery of the image also known as edge unsharpness

Question 29

X-rays photons are being created in all areas of the focal spot rather than at just a single point

Answer 29

note

Question 30

Xrays originating from slightly different spots on the anode take slightly different angles to hit the same point on the detector

Answer 30

note

Question 31

Primary photons diverge from the tube at varying angles and intersects with...

Answer 31

structures of interest at varying angles when creating image

Question 32

What does the shutter reduce?

Answer 32

the penumbra along the periphery of the beam because of their greater distance from the focal spot

Question 33

Closer to the light source it looks blurry and the father away from the light source...

Answer 33

you have sharper edges

Question 34

What are other beam restriction devices?

Answer 34

Aperture diaphragms and cones/cylinders

Question 35

The cones/cylinders are devices that are historically...

Answer 35

used to restrict the beam but are not in common use today

Question 36

What is the aperture diaphragm? (Simplest of all beam-restricting devices)

Answer 36

is a flat sheet of metal, usually lead with an opening cut in the center and attached to the x-ray tube head

Question 37

Disadvantages of aperture diaphragm?

Answer 37

Greater amount of penumbra and off focus radiation due to the proximity to the tube port

Question 38

Aperture diaphragm allows...

Answer 38

-field to cover area just smaller than image receptor -can be supplemented with cones and cylinders

Question 39

Cones and cylinders are essentially...

Answer 39

circular aperture diaphragms with metal extensions

Question 40

A cone has an...

Answer 40

extension that flares or diverges with the upper diameter smaller than the bottom flared end

Question 41

A cylinder does not..

Answer 41

flare

Question 42

What are cones and cylinders used for?

Answer 42

-for greater detail visibility in small area -reduction in scatter which make images appear more sharper

Question 43

Some applications of cones and cylinders are?

Answer 43

-Head work: sinus or skull -Spine work: spot films -Cross: table hip -Dental

Question 44

Cylinders reduce the amount of irradiated material and therefore...

Answer 44

-reduce patient dose -reduce scatter -increase contrast

Question 45

Ideally the beam restrictors decrease field size to anatomy of interest and also?

Answer 45

-unnecessary tissue exposure decreases -Scatter decreases -Contrast increases (Scale of contrast shortens) -Visibility of detail increases

Question 46

What is ancillary devices?

Answer 46

-Devices tailored for a specific use during given procedure -designed to restrict the beam to a specific shape for particular examination

Question 47

Examples of ancillary of devices

Answer 47

Lead blockers and lead masks

Question 48

What is a lead blocker? Will help absorb scatter that is produce in the soft tissue of the patient's back

Answer 48

its placement of it on a radiography table during radiography of a lower spine in lateral position

Question 49

Lead mask is usually cut to correspond...

Answer 49

to the field size desired and is then secured to the end of the collimator.

Question 50

Lead mask were sometimes used during cerebral angiography to help improve...

Answer 50

image quality by reducing scatter