RAD121 Ch8 Scatter Control

Although increased fog negatively impacts the quality of the image, image contrast can be computer manipulated by changing the

Window width

What are 2 tools that the radiographer can use to limit the amount of scatter radiation reaching the IR

Beam-restricting devices

Grids

What device decreases the xray beam field size and the amount of tissue irradiated

Beam restricting devices

What device is used to improve radiographic image quality by absorbing scatter radiation exiting the patient

Grids

Scatter radiation is primarily the result of ______ interactions

Compton

Incoming x-ray photon loses energy and changes direction. This is called....

Compton interaction

What 2 major factors affect the amount and energy of scatter radiation exiting the patient

kVp

Volume of irradiated tissue

Volume of irradiated tissue depends on the (2)

Thickness of the part

And

X-ray beam field size

Using a higher kVp increases x-ray ______ and reduces its overall ______ (photoelectric interactions)

Transmission; absorption

Higher kVp will ______(increase or decrease) the percentage of Compton interactions and the energy of scatter radiation exiting the patient

Increase

Using higher kVp or increasing the volume of irradiated tissue result in ______(increased or decreased) scatter radiation exiting the patient

Increased

What are the 2 purposes of beam restriction

limiting patient exposure

and

reducing the amount of scatter radiation produced within the patient

The unrestricted primary beam is ____ shaped

Cone

Limiting the x-ray beam field size is accomplices with a __________ device

Beam-restricting device

What is located below the xray tube housing and changes the shape and size of the primary beam

Beam-restricting device

Most popular type of beam restricting device

collimator

If you increase collimation, you _____ the field size (increase or decrease?)

Decrease

If you decrease collimation, you _____ the field size (increase or decrease?)

Increase

In addition to decreasing the patient dose, beam restricting devices reduce the amount of (2)

Amount of scatter radiation produced within the patient and amount of scatter to which the IR is exposures

When less scatter radiation reaches the IR, radiographic contrast ______

Increases

As collimation increases, scatter radiation decreases and radiographic contrast will

Increase

As collimation decreases, scatter radiation increases and radiographic contrast will

Decrease

If you increase collimation, _____ photons strike the patient and reach the IR

Less

When you increase collimation, what do you have to do to your technique factors

Increase to maintain exposure to the IR

Significant collimation requires the ____ to be increased by 30% to 50% to compensate for the decrease in IR exposure

mAs

Significant collimation requires the mAs to be increased by __% to ___% to compensate for the decrease in IR exposure

30 to 50%

Increase in collimation = ____ patient dose

Decrease

Increase in collimation = ______ scatter radiation production

Decrease

Increase in collimation = _____ radiographic contrast

Increase

Increase in collimation = ____ exposure to the IR

Decrease

Increase x-ray filed size = _____ patient dose

Increase

Increase x-ray field size = ____ scatter radiation production

Increase

Increase X-ray field size = _____ radiographic contrast

Decrease

Increase xray field size = ______ exposure to IR

Increases

Most beam restricting devices are made of

Metal

The simplest type of beam restricting device

aperture diaphragm

A flat piece of lead that contains an opening (for beam-restricting)

Aperture diaphragm

Where are aperture diaphragms lcoated

Below the xray tube window

How do you make an aperture diaphragm

Cut a rubberized lead into the size needed to create the diaphragm and curing a hole of the appropriate shape and size into the center to create the aperture

When using an aperture diaphragm, what is not adustable

X-ray field size because the aperture cannot be adjusted from the designed size

Because of the apertures close proximity to the radiation source (focal spot) a large area of _________ suuounds the radiographic image

Unsharpness

An aperture diaphragm that has an extended flange attached to it

Cone or cylinder

The flange of a cone or cylinder can vary in

Length

The flange of a cone or cylinder can be made to _____, increasing its total length

Telescope

Cones and cylinders limit the _____ surrounding radiographic images more than aperture diaphragms do

Unsharpness

Do cones or cylinders do a slightly better job at limiting unshaprness of the radiographic iamge

Cylinders do a better job

Cones and cylinders are limited in terms of

Available sizes and are not interchangeable among tube housings

Do cones or cylinders have a disadvantages compared with the other

Cones

If the angle of the flange of the ____ is greater than the angle of divergence of the primary beam, the base plate or aperture diaphragm of the ___ is the only metal restricting the primary beam

Cone

Are cones or cylinders more useful than the other

Cylinders are more useful

Adjustable cylinders are sometimes used for _____ images as the collimation is closer to the patients skin surface. This helps reduce exposure and improve image quality since the beam restriction is closer to the PTs anatomy

Sinus

The most sophisticated, useful, and accepted type of beam restricting device for radiography today is the

Colliamtor

Another name for the collimator

Variable aperture

A collimator has 2 or 3 sets of

Lead shutters

In the collimator, 1 or more sets of adjustable lead shutters are located __ to ___ cm below the tube

8 to 18cm

The shutters of the collimator consist of lingutidal and lateral _____/_____, each with its own control

Leaves/blades

The xray field shape procured by a collimator is always _______, unless an aperture diaphragm, cone, or cylinder is slide below the collimator

Rectangle or square

Collimators are equipped with a _____ source and a ______ to project a light field onto the patient

White light source and a mirror

What is the purpose of the light in the collimator

To accurately indicate where the primary xray beam will be projected during exposure

In case of failure of the collimator light, what is present on the front of the collimator

An xray field measurement guide

The xray field measurement guide of the collimator indicates the projected field size on the basis of the adjusted size of the collimator opening at

Source to image receptor distances (SIDS)

What could cause inaccuracy of the light field of a collimator

The mirror or the light bulb could be out of position

QC: What can be easily imaged and evaluated for proper alignment for the collimator field light or CR

A collimator and beam alignment test tool template and cylinder

QC: collimator misalignment should be less than ___% of the SID used

+-2%

QC: perpendicualrity of the xray Central ray must be misaligned no more than ___% of the SID used

+-1%

An automatic collimator is also called a

positive beam limiting device (PBL)

What type of collimator limits the size and shape of the primary beam to the size and shape of the IR

Automatic collimator/PBL

For a few years, what agency required automatic collimators

US Federal Law

Where is the Bucky tray located

Just below tabletop and behind the front of the upright unit

Automatic collimation makes it difficult for the radiographer to increase the size of the primary beam to a field larger than that of the ____

IR

The radiographic grid was invented in

1913

Who invented the radiographic grid

Gustavo Bucky

The most effective means for limiting the amount of scatter that reaches the IR

Grids

Grids are about ____cm or ___in thick

0.625cm or 0.25 inches

Grids range from what sizes

20 x 25 cm (8 x 10in)

To

43 x 43cm (17 x 17in)

A device consisting of very thin lead strips with radiolucent interpsaces intended to absorb scatter radiation emitted from the patient

Grid

Where are grids placed

Between the PT and the IR

Grids work well to improve radiographic ______

Contrast

What is a drawback of using a grid

It requires increase in mAs, increasing PT dose

Grids are used when an anatomic part is __cm (___in) or greater in thickness

10cm or 4 inches

Grids are used when more than ___kVp is needed for the exam

60 kVp

Grids contain thin ____ strips or lines that have precise height, thickness, and space between them

Lead

What separates the lead lines in grids

Radiolucent interspace materials

Interspace material typically is made of

Aluminum or carbon fiber composite

Which type of grid is considered "low-dose" grids because the interspace absorbs less primary radiation

Carbon fiber-type grids

An ______ front and back panel pavers the lead lines and interspace material of the grid. What type of grid is this

Aluminum

Grid construction can be described by

grid frequency and grid ratio

The number of lead lines per unit length, in inches, centimeters, or both

grid frequency

Grid frequencies can range in value from

25 to 80 lines/cm (63 to 200 lines/inch)

A typical value for grid frequency might be

40 lines/cm or 100 lines/inch

The ratio of height of the lead strips to the distance between them

grid ratio

Grid ratio formula

Grid ratio = h/D

Grid ratios can range from

5:1 to 16:1

Which type of ratio grid removes or cleans up more scatter radiation than the other grid, having the same grid frequency

A. Low-ratio grids

B. High-ratio grids

High ratio grids

Increasing the grid ratio for the same grid frequency _____ the amount of of lead content and therefore ____ scatter absorption

increases, increases

As grid ratio decreases for the same grid frequency, scatter cleanup becomes ____ effective and radiographic contrast _____

Less; decreases

Where can you find information about a grids construction

on a label placed on the tube side of the grid

What does the label of a grid state (5)

The type of interspace material used

Grid frequency

Grid ratio

Grid size

And information about the range of SIDs that can be used with the grid

The linear pattern of the lead lines of a grid

grid pattern

What 2 types of grid patterns exist

Linear and crossed/crosshatched