Criteria for image evaluation

45 terms by JenFrankland

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Resolution

describes how closely fine details may be associated and still be recognized as separate details before seeming to blend into each other and appear "as one."

The degree of resolution transferred to the IR is a function of:

the resolving power of each of the system components and can be expressed in line pairs per millimeter (lp/mm), line-spread function (LSP), or modulation transfer function (MTF).

Line pairs per millimeter can be measured using:

a resolution test pattern; a number of resolution test tools are available

LSP is measured using a

10-m x-ray beam

MTF measures

the amount of information lost between the object and the IR

line-focus principle

The effective focal spot is the foreshortened size of the actual focal spot as it is projected down toward the IR, that is, as it would be seen looking up into the emerging x-ray beam

Small crescent-shaped artifacts on processed x-ray film are usually the result of

acute bending of the film before or after exposure.

A radiograph made with a parallel grid demonstrates decreased density on its lateral edges. This is most likely due to

decreased SID.

If there was a centering or tube angle problem

there would more likely be a noticeable density loss on one side or the other.

focused grid had been placed upside down

only the central portion of the image (along the long axis of the image receptor) would have been imaged

crescent-shaped kink, or crinkle, marks

caused by acutely bending the x-ray film.

an artifact will usually appear as a plus-density (dark) artifact if it is produced:

before exposure

an artifact will usually appear as a minus-density (light) artifact if it is produced:

after exposure.

X-ray film emulsion is very sensitive to mishandling, particularly after

exposure

Which of the following terms is used to describe unsharp edges of tiny radiographic details?

Blur

geometric blur

the area of blurriness that may be associated with small image details

blurriness can be produced by

using a large focal spot, or by diffused fluorescent light from intensifying screens

umbra

The image proper (ie, without blur)

Mottle

a grainy appearance caused by fast imaging systems

If the grid failed to move during the exposure

there would be grid lines throughout

If the central ray was off-center

there would be uniform loss of density.

When a slow screen-film system is used with a fast screen-film automatic exposure control system, the resulting images

are too light

When an AEC (phototimer or ionization chamber) is used

the system is programmed for the use of a particular screen-film speed (eg, 400 speed).

If a slower-speed screen image receptor is placed in the bucky tray:

the AEC has no way of recognizing it as different, and will time the exposure for the system that it is programmed for

if the AEC is programmed for a 400 screen-film combination, and if a 200-speed screen image receptor is placed in the bucky tray, the resulting radiograph:

will have half the required radiographic density

Foreshortening can be caused by

the radiographic object being placed at an angle to the IR

to reduce shape distortion

Aligning the x-ray tube, anatomic part, and image recorder so that they are parallel

elongation

Tube angulation causes elongation of the part

Size distortion (magnification)

is inversely proportional to SID and directly proportional to OID

Decreasing the SID and increasing the OID serve to

increase size distortion

What are the effects of scattered radiation on the radiographic image?

It produces fog

Scattered radiation

produced as x-ray photons travel through matter, interact with atoms, and are scattered (change direction).

If these scattered rays are energetic enough to exit the body:

they will strike the IR from all different angles

scattered rays

do not carry useful information and merely produce a flat, gray (low-contrast) fog over the image.

Grid cutoff

increases contrast and is caused by an improper relationship between the x-ray tube and the grid, resulting in absorption of some of the useful/primary beam

Treelike, branching black marks on a radiograph are usually the result of

static electrical discharge.

Problems with static electricity are especially prevalent during

cold, dry weather and can be produced by simply removing a sweater in the darkroom.

Grid cutoff due to off-centering would result in

overall loss of density

Over- or underexposure under the anode is usually the result of

exceeding the focusing distance limits in addition to being off-center

Foreshortening of an anatomic structure means that

it is projected on the IR smaller than its actual size

What effect will a stained intensifying screen have on the finished radiograph?

Decreased density

If an intensifying screen becomes stained, either partly or wholly, the stained area:

will not react to x-ray photons as completely and will emit less light.

the film emulsion adjacent to the stained area(s) will exhibit:

decreased density on the finished radiograph.

how would changing exposure factors affect film

The original mAs (regulating radiographic density) was 200. The original kVp (regulating radiographic contrast) was 90. The mAs was cut in half, to 100, causing a decrease in density. The kVp was increased (by 15%) to compensate for the density loss and thereby increase the scale of contrast.

developer temperature

1. The development process slows at the lower temperature, and a much lighter radiograph results.
2. at too high temperature, the development process is accelerated and the radiograph is too dark

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