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M1

37問 • 9ヶ月前

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graphic representation of a data set

Histogram

includes all the pixel values represent the image before edge detection and rescaling.

Data set

6 Histogram Analysis Errors IEMULI

- Incorrect Anatomic Menu Selection - EXPOSURE FIELD RECOGNITION ERROR - Multiple fields/plate - UNEXPECTED MATERIAL IN DATA SET - LARGE OVEREXPOSURE ERROR - INAPPROPRIATE RESCALING

should be selected prior to processing the imaging plate; otherwise the image will not process the correct density and contrast.

Correct anatomical menu

If the x-ray exposure field is not properly collimated, sized and positioned, this error would occur.

Exposure field recognition error

•For image histogram to be properly analyzed each collimated field should consist of how many distinct collimated images?

Four

must not overlap and must be parallel to the edges of the plate, otherwise the image may be processed incorrectly and the exposure indicators will be incorrect

Collimated borders

If the exposure pattern does not match one of the segments patterns, the data from the whole plate is included in the?

histogram

Is single plate worse?

Better

If there is unexpected material in data set, image processing and exposure indicators may be?

Incorrect

During large overexposure error, Histogram will try to correct the image but will remove what to do it

Information

Under inappropriate rescaling, If the histogram has excess exposure from poor collimation techniques, this could cause an error in locating the ____

Value of Interest (VOI)

•The imaging plate of the Computed radiography system is sensitive to these two types of radiation

- Background radiation - Scattered radiation

makes scatter control much more important with a digital system (CR) when compared with screen/ film

Low Exposure Response and Dynamic Range

• PSPs respond to exposures as low as

60uR

Background radiation measures

40uR - 80uR/day.

more sensitive to lower-energy levels of radiation such as scatter, which results in increased fog in the image.

Digital IRs

Two major factors that affects the amount and energy of scatter radiation exiting the patient: KV

• 1. kilovoltage peak (kVp) and • 2. volume of tissue irradiated.

this is called the limiting of patient exposure and reducing the amount of scatter radiation produced within the patient.

Beam limitation

- A device that has very thin lead strips with radiolucent interspaces, intended to absorb scatter radiation emitted from the patient. - placed between the patient and the IR, are invaluable in the practice of radiography. - absorb, or clean up, all scattered photons directed toward the IR and would allow all transmitted photons emitted from the patient to pass from the patient to the IR.

Grid

can be described by grid frequency and grid ratio

Grid construction

the # of gridlines per unit distance.

Grid frequency

can range in value from 25 to 80lines/cm (63 to 200 lines/inch).

Grid frequencies

defined as the ratio of the height of the lead strips to the distance between them.

Grid ratio

Grids are typically used only when the anatomic part is __ cm or greater in thickness, and more than __ kVp is needed for the examination

- 10 cm - 60 kVp

The _________ is scanned line by line; IF the SCAN FREQUENCY and the ___ FREQUENCY are similar and oriented in the same direction, a _______ effect will be observed.

- imaging plate - Grid Frequency - Moire Effect

This refers to the linear pattern of the lead lines of a grid.

Grid Pattern

Two Grid Patterns LC

1. Linear 2. Crosshatched/Crossed

has lead strips running parallel to the long axis of the grid.

• •Long Dimension Grids-

has lead strips running perpendicular to the long axis of the grid. may be useful for examinations where it is difficult to center the central ray correctly

Short dimension grid

4 Grid Types PCFM

• Parallel Grid • Crossed Grid • Focused Grid • Moving Grid

Refers to a decrease in the number of transmitted photons that reach the IR because of some misalignment of the grid. Further reduction in the number of photons reaching the IR.

Grid Cut Off

6 TYPES OF GRID CUT OFF ERRORS UFOOO

• Upside-down • Focused • Off level • Off center • Off focus

• grid cut off occurs when a focused grid is placed in this direction on the IR, resulting in the grid lines going opposite the angle of divergence of the x-ray beam. • Significant loss of exposure along the edges of the image • easily avoided because every grid should have a label indicating "Tube Side”

Upside down error

- Results when the x-ray beam is angled across the lead strips. It is the most common type of cutoff and can occur from either the tube or the grid being angled. - seen with mobile radiographic studies or horizontal beam examinations and appears as a loss of exposure across the entire image.

Off level error

Also called lateral decentering, occurs when the central ray of the x-ray beam is not aligned from side to side with the center of a focused grid. - appears as an overall loss of density on radiographic film.

Off center error

- occurs when using an SID outside of the recommended focal range. - occurs if the SID is less than or greater than the focal range. - It appears the same radiographically as a loss of density at the periphery of the film.

Off focus grid cutoff error

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