Lecture 5: image detail and quality control

What is a radiograph?

A 2D image of a 3D object

Radiograph images will var in respect to what?

The orientation of the x-ray beam.

What are 3 reasons to reject a radiograph?

1) geometric unsharpness

2) motion unsharpness

3) quantum mottle (noise)

What is penumbra?

When the object is far from the detector, causing unsharpness.

Is it better to have an object far from or close to the imaging plate?

Close to the imaging plate. When it is too far, that causes magnification and unsharpness.

T/F: when possible, keep area of interest far from film to reduce magnification.

False — keep close.

What is quantum mottle (noise)?

The effect of a limited number of x-ray photons on the appearance of the radiograph.

More x-ray photons = better image.

What is distortion?

- when the image misrepresents the true shape or position of the object.

- results from unequal magnification of different parts of the same film (aka when parts are not parallel to the film).

Where should you center the x-ray beam to avoid distortion?

On the area of interest.

How can you best deal with the loss of depth perception with a radiograph?

By taking at least 2 views (orthogonal projections) at a 90 degree angle to each other.

What are the 5 radiographic opacities from most radiolucent to most radiopaque?

- gas

- fat

- soft tissue / water

- mineral / bone

- metal

Describe summation.

When 2 structures of the same density that do not touch each other are superimposed.

It results in added opacities (making the superimposition more radiopaque).

What is another term for border effacement?

Silhouetting

Describe border effacement.

Occurs when 2 structures of the same radio parity are in contact.

Causes the loss of individual margins (aka looks like 1 structure).

What are the 3 main things to look at for film quality?

- detail

- contrast

- density