Chapter 5: Scatter Control (Important Relationships)

*Off-Level Error and Grid Cutoff*

Angling the x-ray tube across the grid lines or angling the grid itself during exposure produces an overall decrease in exposure on the radiograph.

*Focused Versus Parallel Grids*

Focused grids have lead lines that are angled to match approximately to the divergence of the primary beam. Thus, focused grids allow more transmitted photons to reach the IR than parallel grids.

*Off-Focus Error and Grid Cutoff*

Using an SID outside of the focal range creates a loss of exposure at the periphery of the radiograph.

*Beam Restriction and Patient Dose*

As beam restriction or collimation increases, field size decreases, and patient dose decreases. As beam restriction or collimation decreases, field size increases, and patient dose increases.

*Collimation and Exposure to the Image Receptor*

As collimation increases, exposure to the IR decreases; as collimation decreases, exposure to the IR increases

*Collimation and Scatter Radiation*

As collimation increases, the field size decreases, and the quantity of scatter radiation decreases; as collimation decreases, the field size increases, and the quantity of scatter radiation increases.

*Collimation and Radiographic Contrast*

As collimation increases, the quantity of scatter radiation decreases, and radiographic contrast increases;as collimation decreases, the quantity of scatter radiation increases, and radiographic contrast decreases.

*Grid Ration and Radiographic Contrast*

As grid ratio increases for the same grid frequency, scatter cleanup improves, and radiographic contrast increases; as grid ratio decreases for the same grid frequency, scatter cleanup is less effective, and radiographic contrast decreases.

*Grid Ratio and Exposure to Image Receptor*

As grid ratio increases, exposure to the IR decreases as grid ratio decreases, exposure to IR increase.

*Grid Ratio and Patient Dose*

As grid ratio increases, patient dose increases; as grid ratio decreases, patient dose decreases.

*Off- Center Error and Grid Cutoff*

If the center of the x-ray beam is not aligned from sided to side with the center of focused grid, grid cutoff occurs.

*Upside-Down Focused Grids and Grids Cutoff*

Placing a focused grid upside-down on the IR causes the lateral edges of the radiograph to be very underexposed.

*Scatter Radiation and Image Quality*

Scatter radiation adds unwanted exposure to the IR and decreases image quality.

*Air Gap Technique and Scatter Control*

The air gap technique is an alternative to using a grid to control scatter reaching the IR. By moving the IR away from the patient more of the scatter radiation will miss the IR. The greater the gap, the less scatter reaches the IR.

*kVp and Scatter*

The amount and energy of scatter radiation exiting the patient depends, in part, on the kVp selected. Examinations using higher kVp produce a greater proportion of higher- energy scattered scattered x-rays compared with examinations using low kVp.

*X-ray Beam Field Size, Thickness of the Part, and Scatter*

The larger the x-ray beam field size, the greater the amount of scatter radiation produced. The thicker the part being imaged, the greater the amount of scatter radiation produced.

*Volume of Tissue Irradiated and Scatter*

The volume of tissue irradiated is affected by both the part thickness and the x-ray beam field size. Therefore, the greater the volume of tissue irradiated , because of either or both factors, the greater the amount of scatter radiation produced.