Ch. 18 Carlton

What is the primary function of a grid in X-ray imaging?

To remove scatter radiation before it reaches the film, thereby improving image contrast.

Describe the sequence of components in a typical grid setup.

X-ray beam > Patient > Grid > Image Receptor (photoelectric stimulated plate).

What are the criteria for using a grid based on body part thickness?

more than 10cm.

What kVp level generally necessitates the use of a grid?

kVp above 60, but in practice, typically above 70.

What kVp is used when an air gap is present?

90 kV or higher

What kVp is typically used for chest x-rays, necessitating the use of a grid?

90 kV or higher

What materials compose a grid?

Radiopaque strips (lead) alternate with radiolucent interspace strips (aluminum or plastic fiber).

What is the function of radiopaque strips in a grid, and what material are they made of?

They absorb scatter radiation and are typically made of lead.

What is the function of radiolucent interspaces in a grid, and what materials are they made of?

They allow radiation to pass through and are typically made of aluminum or plastic fiber.

Define grid ratio.

height of the grid strips divided by the distance between them (H/D).

What does a higher grid ratio indicate in terms of scatter removal?

more scatter is removed, improving image contrast.

Describe an 8:1 grid ratio and its use.

Thinner grid used for low to moderate scatter situations, making it suitable for general radiographic imaging.

Describe a 16:1 grid ratio and its use.

Thicker grid used in high scatter environments, such as in fluoroscopy or when imaging thicker body parts.

How does lead content affect a grid's performance?

The higher lead content, removal of scatter and improval of contrast increases

Name the two primary grid patterns.

Linear (parallel & focused) and Criss-Cross.

What is significant about focused grids?

Match the divergence of the X-ray beam.

When are parallel grids best used?

long SIDs (Source-to-Image Distance).

Describe the 'Off-Level' grid error and its effect.

Grid is not aligned to the bucky

Describe the 'Off-Center' grid error.

Grid is not centered, leading to uneven exposure across the IR

Describe the 'Off-Focus' grid error and its effect.

Grid lines are blurred or distorted because the SID (Source to Image Distance) is not within the grid's focal range causing grid cutoff.

Describe the 'Upside-Down' grid error and its appearance.

Grid appears rotated 180 degrees from the intended orientation, causing severe grid cutoff.

Describe the 'Moire Effect' grid error, when it occurs, and its effect.

Grid lines are captured at the same angle as the scanning lines in the image reader. This misalignment causes a distorted, wavy appearance, making it difficult to interpret the intended details of the image. Often seen with stationary grids that aren't perfectly aligned with the imaging system. 

What is the key to preventing grid cutoff?

Proper alignment between the X-ray tube and the grid.

What is vital for using focused grids correctly?

The tube must be centered, at the correct distance, and the correct side.

What are the consequences of improper tube/grid alignment?

Results in lighter, fogged films with lessened detail.

Describe the air gap technique as an alternative to using a grid.

increasing the OID (Object-to-Image Distance) to reduce scatter reaching the IR