Midterm Flashcards
An image-processing technique commonly used to identify the edges of an image and assess the raw data prior to image display
Histogram Analysis
Includes all the pixel values that represent the image before edge detection and rescaling
Data set
Scatter radiation is primarily the result of (1) in which an incoming xr photon (2) and (3)
- compton interactions
- loses energy
- changes direction
Two major factors affect the amount and energy of the scatter radiation exiting the patient
- Kilovoltage peak (kVp)
- Volume of irradiated tissue
Beam restriction serves 2 purposes:
- Limiting pt exposure
- Reducing amount of scatter radiation produced within the pt
Limiting the xr beam field size is accomplished with a beam-restricting device. Located (1), the beam-restricting changes the size and shape of the (2)
- just below the XRT housing
- primary beam
Beam restriction and pt dose relationship
Indirect
Collimation and scatter radiation relationship
Indirect
Most sophisticated, useful, and accepted type of beam-restricting device for radiography
Collimators
Automatically limits the size and shape of the primary beam to the size and shape of the IR
Automatic collimators
Automatic collimators aka
Positive beam-limiting device
Makes it difficult for the radiographer to increase the size of primary beam to a field size larger than that of the IR, which would result in increasing pt’s radiation exposure
Automatic collimation
Device consisting of very thin lead strips with radiolucent interspaces intended to absorb scatter radiation emitted from the pt
Radiographic grid
Radiographic grids are approx. (1) thick and ranging from (2) to (3)
- 1/4 in
- 8x10 inches (20x25 cm)
- 17x17 in (43x43 cm)
Grid vs filter
Grid
- b/n pt and IR
- absorbs scatter rad’n = improved image quality
Filter
- b/n xrt and pt
- absorbs low energy xrs and allows high-energy to pass through = improved image contrast
Grids contain thin lead strips or lines that have a precise (1), (2), (3)
- height
- thickness
- space between them
Grid construction
- (1) materials separates the lead lines
- Interspace material is typically made of (2)
- Lead lines and interspace material of the grid are covered by a/n (3) front and back
- Radiolucent interspace
- aluminum
- aluminum
Determines the efficiency of absorption mechanism of grids
Grid ratio
Grid ratio formula
height/ distance
Linear pattern of the lead lines of a grid
Grid pattern
Two types of grid pattern
- Linear
- Cross or cross-hatched
Orientation of the lead lines relative to one another
Grid Focus
2 types of grid focus
- Parallel
- Focused
Decrease in the number of transmitted photons that reach the IR because of some misalignment of the grid
Grid Cut-off
Grid Cut-off Errors
- Upside-Down Focused
- Off-Level
- Off-Center
- Off-Focus
Placing a focused grid upside down on the IR
Significant underexposure to the lateral edges of the IR
Upside-Down Focused
Angling the x-ray tube across the grid lines or angling the grid itself during exposure
Decrease in radiation exposure to the IR
Off-Level
