Rad 1: Radiographic Quality Review

What is radiographic density?

Degree of blackness on a radiograph.

State 3 things that influence radiographic density.

• Total # of x-rays that reach the film

• Penetration power

• Developer time/temperature of developer

State 2 things that we can increase to produce greater radiographic density.

• kVp

• mAs

What does mAs determine?

Density.

What happens to the density if the mAs is increased?

More x-rays are produced, increase in density.

What does increasing kVp do?

• Increases penetrating power

• Increases density

How will your radiograph appear in relation to subject thickness?

It can’t penetrate through the thicker tissue as well.

Thicker the patient, the ______________ the radiograph.

Lighter.

When the difference in density is great, the radiograph has ________ contrast and a _________ scale of contrast.

• High contrast

• Low scale of contrast

List five things that can influence radiographic contrast:

• kVp level

• Scatter

• Using a grid

• Subject contrast

• Film fog

State the most common cause of poor contrast.

• Inappropriate exposure factors— you do not have the correct kVp.

• Patient movement.

• Penumbra.

If your kVp is too low, how will the overall appearance of your radiograph be?

Soot, white washed appearance (gray/white). You can’t distinguish between organs.

Where does scatter radiation come form?

Non-image forming radiation scattered in all directions. Comes from the primary beam.

The most effective way to reduce scatter is to:

Collimate.

What is a grid? What is it composed of?

Lead strips embedded in spacing material that sits between the patient and the film.

3 places the grid can be located:

• Between the patient and the cassette— built into the table.

• On top of the cassette- snap on

• Built into the top of the cassette

Always placed between the patient and the film!

State 2 uses of a grid:

• Decrease scatter

• Increase image detail + quality

List 2 types of grids:

• Parallel

• Focused

What is a potter-bucky diaphragm?

Moveable grid— not used much.

Contrast helps determine the overall detail of our graph. Define contrast.

The measurable difference between two adjacent densities.

List the 2 factors which can cause geometric unsharpness:

• Foreshortening, magnification= distortion.

• Penumbra, focal size, and motion can also be involved.

What is foreshortening?

The image appears shorter than the actual size because the plane of interest is not parallel to the film surface.

Define magnification:

The image appears larger and magnified due to increased object film distance.

The degree of blackness, “darkness” on a radiograph:

Density.

Density in reference to the mA function equates to:

Quantity of the beam.

Density in reference to the kVp function equates to:

Quality of the beam.

Subject contrast from most to least:

• Metal

• Bone

• Water/organs/tissue

• Fat

• Gas/air

Radiographic density from most to least:

• Gas/air

• Fat

• Water/organs/tissues

• Bone

• Metal

This is the distance from the source of the x-ray to the film":

FFD or SID

The ________ the grid ratio, the more efficient.

Higher.

When you increase the object-film distance, you will have:

A fuzzier image that is larger.

When using a grid, you will always position it between the patient and the film.

True or false?

True.

You have a radiograph that is too light on both anatomy and the background of your image. You can see your anatomical structures. Which technical factor would you increase?

mA.

Does contrast equate to quality or quantity?

Quality.

Which exposure factor effects contrast and quality of the radiograph?

kVp knob.

An abdominal film would require this scale (long or short) of contrast?

Long (low) scale.

The most common cause of poor contrast:

Inappropriate exposure factors.

Your radiograph is too light and under-penetrated. You can only see the outline of the animal. This is the exposure factor you would adjust to improve your image.

kVp knob.

Our radiograph has a whitewashed appearance. This is a problem with this exposure factor:

kVp knob— too low.

Which 2 factors will cause geometric unsharpness?

Foreshortening and magnification.

The image looks short because one end of the object is elevated more than the other and not parallel to the film. This is caused by which geometric factor?

Foreshortening.

What is the name of this geometric distortion that is described as:

When an object is moved towards the tube head and away from the cassatte, the image will be larger and blurred.

Magnification.

Define inverse square law.

If you decrease the distance of radiation, you have to change the amount of radiation to have comparable exposure.

(further away we are, less radiation we get).