Scatter Control and Grids Flashcards

Vocabulary flashcards covering scatter radiation control, beam-restricting devices, grid design, grid ratio, grid frequency, GCF calculations, and grid errors.

Scatter Radiation

Unwanted radiation produced primarily by Compton interactions that adds non-diagnostic gray shades to an image, reducing radiographic image quality.

Beam Restricting Devices

Accessories positioned near the X-ray tube window to decrease field size and the volume of tissue irradiated, thereby reducing the scatter produced.

Collimation

The operation of limiting the X-ray field size; increasing collimation decreases field size, scatter, and patient dose while improving image quality.

Aperture Diaphragm

A flat piece of lead containing an opening that slides onto the X-ray tube directly below the window to restrict the field size.

Cones and Cylinders

An aperture diaphragm constructed with an extended flange attached to it that produces a circular projected X-ray field.

Collimator

A beam-restricting device featuring adjustable longitudinal and lateral lead shutters located $3$ to $7\text{ inches}$ below the X-ray tube port.

Positive Beam-Limiting Device (PBL)

An automatic collimator system that restricts the size and shape of the X-ray beam to the dimensions of the image receptor placed in the bucky tray.

Grid

A device invented by Gustave Bucky in 1913, placed between the patient and digital detector, designed to absorb scattered radiation before it reaches the image receptor.

Grid Frequency

An expression of the number of lead strips per unit length in a grid, typically ranging between $25$ and $45\text{ lines/cm}$ ($60$ to $110\text{ lines/inch}$).

Grid Ratio

The ratio of the height of the lead strips ($h$) to the width of the interspace material ($D$), expressed as $\text{Grid ratio} = \frac{h}{D}$.

Grid Conversion Factor (GCF)

A multiplier (Bucky factor) used to adjust $mAs$ when changing grid ratios ($\text{no grid} = 1$, $5:1 = 2$, $6:1 = 3$, $8:1 = 4$, $12:1 = 5$, $16:1 = 6$).

Linear Grid

A grid pattern in which lead strips run parallel in one direction, allowing the X-ray tube to be angled along the length of the strips.

Cross-Hatched Grid

A grid pattern in which lead strips run perpendicular to each other in two directions, providing superior scatter absorption but preventing tube angulation.

Parallel Grid

A non-focused grid construction where lead strips run parallel to each other across the entire surface of the grid.

Focused Grid

A grid designed with lead strips angled to match the divergent path of the primary X-ray beam, allowing greater transmission of primary photons.

Convergent Line and Point

The point or line formed above a focused grid where imaginary extensions of the angled lead strips intersect.

Focal Distance

The distance between the grid surface and the convergent point or line, also referred to as the grid radius.

Focal Range

The recommended range of Source-to-Image Distances (SIDs) that can be used with a focused grid to avoid significant grid cutoff.

Potter-Bucky Diaphragm

A device developed by Hollis Potter and Gustave Bucky that holds a permanently installed grid and moves it slightly during exposure to blur grid lines.

Grid Cutoff

An unwanted reduction in transmitted primary X-ray photons reaching the image receptor due to grid misalignment, causing decreased image exposure.

Upside-Down Focused Grid Error

A grid alignment error occurring when a focused grid is inverted, producing severe exposure loss along the peripheral edges of the radiograph.

Off-Level Grid Error

A grid error caused by angling the primary beam across the lead strips or tilting the grid, resulting in a loss of exposure across the entire detector.

Off-Center Grid Error

A grid alignment error (lateral decentering) that occurs when the central ray is not positioned over the center axis of the grid, producing uniform exposure loss across the image.

Off-Focus Grid Error

A grid cutoff error caused by using an SID that falls outside the specified focal range of a focused grid, leading to exposure loss at the image periphery.

Air Gap Technique

A method to reduce scatter reaching the image receptor without a grid by increasing Object-to-Image Receptor Distance (OID), allowing scattered photons to miss the IR.

Lead Masking

The placement of a lead mat on the table-top to absorb scattered photons exiting the patient before they strike the image receptor and reduce image quality.