Diagnostic Imaging: Radiographic Quality (C4)

85 terms by candiceclarke 

Create a new folder

Advertisement Upgrade to remove ads

Radiographic quality depends on what three factors?

1. Radiogrphic Density 2. Radiographic Contrast 3. Radiographic Geometric Detail

To produce a certain number of x-rays (mAs) you can either increase __ and decrease ___, or decrease __ and increase ___. Which way is better?

-mA -seconds -since we always want the shortest exposure time possible when we want to increase mAs we do it by increasing mA rather than seconds, if possible

What is radiographic density?

the degree of the blackness of the radiograph

What does a radiograph with the proper amount of density look like?

-it provides visualization of all the structures of interest and not be too dark or too light

The more x-rays that strike the film the ____ the radiograph, therefore _____ is dependent on the number of x-rays reaching the film

-blacker -density

What are the factors that affect radiographic density? (5)

Exposure Settings: 1. mAs 2. kVp Developing: 3. Time and Temperature 4. Subject thickness and density 5. SID (source image distance)

How does mAs factor into radiographic density?

-As mAs is increased, intensity of the primary beam increases and more x-rays reach the subjectwhich means more will emerge from the subject and strike the film making it blacker and therefore increasing the density

How does kVp factor into radiographic density?

-As the kVp is increased the penetrating power of the x-rays increases so more go through the subfect and strike the film making it blacker and therefore increasing the density

How does time and temperature of development factor into radiographic density?

-As either/both of these is increased, unexposed silver halide crystals are turned into metallic silver (when they shouldn't be) which results in a darker radiograph = more density

How does subject thickness and density factor into radiographic density

The thicker and denser the subject (e.g bone v.s. soft tissue), the more x-rays it will absorb/ block from reaching the film resulting in a whiter/greyer radiograph or decreased density

How does SID factor into radiographic density?

-As the distance of the x-ray machine to the film increases, the number of x-rays striking the film decreases, resulting in decreased density

What is radiographc contrast?

-the visible difference in density between two adjacent areas on a radiograph

What does it mean for a radiograph to have high contrast? Low contrast?

-High contrast means big differences in density within the radiograph (lots of black and white) -Low contrast means little difference in density within the radiograph (lots of shades of grey)

What kind of contrast (range of densities) does a good quality radiograph have? Why?

-a range of densities (black, white and shades of grey) -so that all the anatomical details are easily distinguished

What is the most common cause of poor contrast?

-inappropriate exposure factors (mAs and kVp)

How does mAs factor into radiographic contrast?

-Only affect contrast if its significatnly too high or low -Significantly too low mAs means a big decrease in density resulting in the entire radiograph being too pale which lowers contrast -Significantly too high mAs means a big increase in density resulting in the radiograph being too dark although the contrast isn't altered much

What affects contrast more way too high mAs or way too low?

Way too high mAs, too low mAs doesn't alter contrast much

How does kVp factor into radiographic contrast?

-too little kVp results in low energy x-rays with little penetrating power making the exposed parts of the film dark and the patient structures all white -too much kVp results in high energy x-rays with lots of penetrating power resulting in a radiograph thats dark with all the patients structures being dark with low contrast

T or F kVp affects both contrast and density

T

What is the most important exposure factor controlling contrast? WHy?

-kVp -because it affects x-ray penetration of the structures which should be varied to give a detailed image -it also controls scatter radiation production which exposes inappropriate areas of the film

What is the primary function of mAs?

to produce the desired film density (blackness)

What is the primary function of kVp?

to produce the desired scale of contrast within the recorded image (detailed structures)

Scatter radiation is also known as ..

secondary radiation

What is the effect of scatter radiation on contrast? How does this happen?

-It decreases contrast by exposing inappropriate areas of the film -Too high kVp increases scatter radiation

The larger the subject being x-rayed the ____ the kVp that must be used and the ____ amount of scatter radiation which makes it dificult to do what?

-higher -greater -to obtain a radiograph with the desired scale of contrast

In order to radiograph thick body parts without producing excessive scatter we do what five things?

1. Use aluminum filters in the tube window and lead backed cassettes 2. Collimate 3. Compress the subject 4. Use the lowest kVp possible 5. Use grids

What colors would predominate in a radiograph with low contrast?

shades of grey

What is a grid?

a device placed between the patient and film designed to absorb scatter radiation

When should grids be used?

On any body part that measures greater then 10 cm (that will require a higher kVp setting)

What is a grid made of?

-alternating strips o f lead (0.5 mm thick) and spacer material in a protective case

Why are the lead strips in a grid aligned a certain way?

so that the majority of the primary beam can pass through while x-rays not travelling in the beam direction (scatter) are absorbed

Grids have been designed to be used in certain locations (3)

1.On top of the cassette 2. Built into the cassette 3. Built into the x-ray table (Bucky)

In what six ways do grids vary?

1. Size 2. Number of lead strips per cm 3. Grid ratio 4. Grid focus 5. Pattern 6. Stationary vs. moving (bucky)

What is grid ratio? How does it affect the grids absorption of scatter?

-the relationship of the height of the lead strips to te distance between them -the higher the ratio the more scatter radiation absorbed

In order to be used effectively grids must be _______ correctly

-positioned

What two positioning factors affect grid effectiveness?

1. Focal point: the center point where the beam must be centered 2. Grid Focus: the distance of the grid from the x-ray tube

What is grid cutoff due to?

A misalignment of the grid lines and the primary beam, resulting in too much of the primary beam being absorbed by the grid

What does a radiograph with grid cutoff look like?

it appears as a light underexposed film with distinct white lines

What are four common causes of grid cutoff?

1. Improper centering of the primary beam and grid (Improper Focal Point) 2. Decreased distance between the anode and the grid (Improper Grid Focus) 3. Tilting the tube or grid laterally 4. Focused grid upside down

How do grids factor into the exposure settings (mAs and kVp)? What changes are made?

-Because some of the primary beam is absorbed by the grid, the exposure factors need to be increased. -Usually mAs is increased by doubling the exposure time - kVp is also increased by an amount that depends on the grid ratio

What are the four types of grid patterns?

1. Linear 2. Crossed 3. Parallel unfocused 4. Focused

What type of grid pattern do most table-type x-ray machines have? What is the advantage to this pattern?

-Linear -can angle tube along length of the grid for oblique views

Which grid pattern has the maximum scatter absorption? What is the disadvantage to this pattern?

-Crossed -Cannot use for oblique views

Which kind of grid pattern allows for diverging x-rays to pass through, has a very specific focus and is expensive?

-Focused (progressively angled lead strips)

Which grid pattern can only be used with small fields or cutoff occurs?

unfocused/parallel

What are stationary grids?

Grids which doesn't move during exposure

T or F with stationary grids even with proper use, grid lines will be visible

T

What are moving grids? How do they produce no grid lines? Another name?

-a linear grid placed so the lead strips run parallel to the legnth of the table -the grid moves back and forth during exposure so grid lines are blurred and cannot be seen on the radiograph -aka Bucky (refers to the tray where the grid is held under the table)

What are the disadvantages to bucky grids? (2)

1. can break down 2. cannot be used with portable equipment

How do you change the mA settings when you need to use a grid? the kVp?

-double the exposure time -increase by about 10

What is radiographic detail?

-image sharpness and clarity, how clear the edge of anatomical structures appear

What two things can poor radiographic details?

1. Geometric Unsharpness 2. Geometric Distortion

What six factors cause geometric unsharpness?

1.Motion 2. Poor screen-film contact 3. Increased subject-film distance 4. Improper SID 5. Primary beam not centered at film/subject 6. Double exposure

What is geometric distortion?

When the angle the x-ray beam strikes the subject affects the size, shape, and clarity of the resulting radiographic image

In order to minimize geometric distortion the subject should be: (3)

1. Parallel to the film 2. Close to the film 3. In the centre of the primary beam

What six factors to consider when assessing a radiograph for quality?

1. Positioning 2. Labels and Markers 3. Density and Contrast 4. Detail 5. Film Fog 6. Artifacts

What should you consider when assessing a radiograph for regarding positioning? (4)

Is the correct part of the anatomy: 1. included? 2. In the correct position? 3. In the centre of the film? 4. Not obscured (by markers, collars or shoes)?

What two questions should be asked when assessing a radiograph regarding density and contrast?

1. Is the film too dark or too light? 2. Have the x-rays penetrated the patient and reached the film?

If the film is too dark what two things could have gone wrong?

-overdeveloped(processing) or overexposed (too high mAs or kVp)

If the film is too light what two things could have gone wrong?

-underdeveloped (processing) or underexposed (too low mAs or kVp)

How can a processing problem be confirmed?

If all the films developed at the same time have the same problem

If overdeveloped what two things could have gone wrong?

1. temperature too high 2. left in developer too long

If underdeveloped what three things could have gone wrong?

1. temperature too low 2. not left in the developer long enough 3. chemicals are exhausted

Assessing the penetration is means of determining whether or not the ____ should be changed. If penetration is appropriate then you and processing was ruled out then you know ___ is the problem

-kVp -mAs

Penetration is assessed by looking at the ____ ____ within the patient silhouette. (e.g. ___, ____, _____, ____)

-anatomic structures (-the liver, spleen, intestines, bone)

With underpenetration, the outlines of the ____ are not ______ and the silhouette appears all _____. What should be changed?

-structures -visible -white -the kVp should be raised 10-15%

When the film is too light but there is still adequate penetration what can still be seen? What should be changed?

-The outlines of the structures can still be seen even though they are all too light -the mAs should be raised by 30-50%

When the film is too dark but still has adequate penetration the ____ ____ still looks white. What should be changed?

-bone tissue -lower the mAs 30-50%

When the film is too dark but is overpenetrated the ____ tissue looks _____. What should be changed?

-bone tissue -grey -lower kVp 10-15%

What should you consider when assessing a radiograph for regarding detail? (2)

1. Check for image clarity (is it blurred?) 2. Check for geometric distortion

What is the most important source of film fog? How is it identified?

-Scatter -grey areas on the unexposed area of a processed radiograph

What are five sources of film fog other than scatter?

1. Exposure to x-rays (other than scatter) 2. Chemical Fog (fumes) 3. Exposure to light 4. Storage Fog (too hot or humid) 5. Age Fog (expired)

What are artifacts on a radiograph? Why are they undesirable?

-anything that should not be on the radiograph -they can make diagnosis impossible or lead to a misdiagnosis

When artifacts occur consistently what needs to be checked?

-cassettes and screens need to be checked for cleanliness and damage

What are nine commonly occurring artifacts? What does each look like?

1. Static electricity: a black tree 2. Pressure on the film: black areas 3. Splashed drops of liquid: a white area 4. Contrast media: white blotches 5. Scratches: white lines 6. Portion of the Film is unexposed: white area 7. Stain: any discolouration 8. Failure to prep subject: e.g. collars 9. Crinkle marks: curved black or white lines

How can stains on a radiograph be avoided?

-using fresh chemicals and developing according to a standardized time-temperature table

What causes a portion of the film to be unexposed (artifact)?

the beam not being perpendicular to the subject or the cassette not being centred under the subject/beam

What is the rule of thumb for getting better tisue differentiation?

-decreasing the kV by 5 and doubling the mAs

Why is tight collimation important?(2)

1. reduces secondary radiation (scatter) 2. results in better radiographs

T or F An increase in the temperature of the processing solutions will result in a darker radiograph.

T

The source image distance (SID) is the distance from the x-ray machine to...

film

Grids should be used when any body part measures greater than:

10 cm

Radiographic _______is how clear the edge of the anatomical structures appear.

detail

T or F You note that your radiograph once developed is too dark due to over penetration, you would compensate by decreasing the kVp by 10 - 15%.

T

If the cassette is not centered under the subject or the primary beam, how will the film look?

the image will appear distorted

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again

Example:

Reload the page to try again!

Reload

Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording

Create Set