Image Production & Criteria for Evaluation - 267

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A foreign body in the image receptor

will be sharply imaged on the finished radiograph.

an artifact that has sharply delineated edges indicates that it is located

adjacent to the intensifying screens within the cassette.

An inverted focused grid will result in

an area of exposure down the middle of the image and grid cutoff everywhere else

As kVp is increased, the percentage of scattered radiation relative to primary radiation

increases, hence a grayer appearance

chemical fog usually produces

a very gray image

Examples of processing artifacts are

guide shoe marks, roller marks, and scratches

excessively high contrast caused by

too low kVp, too short a scale of contrast

factors are most likely to be the cause of quantum noise/mottle?

Fast film and screens with low mAs and high kVp

Focal spot blur would cause

a slight blur of anatomic details

Grid cutoff appears

as a gradually decreasing density

Grid cutoff is absorption of the primary beam by the grid and usually results in

loss of density and visibility of grid lines.

Grids are designed to

selectively absorb scattered radiation while absorbing as little of the primary radiation as possible

Images produced with higher ratio grids will possess

: fewer grays than those made with lower ratio grids

light fog generally results in

a very black finished radiograph

Overdevelopment makes a radiograph appear

very dark, and sometimes gray

Poor screen-film contact results in

very blurry areas of the finished radiograph.

Quantum noise, or mottle, is a grainy appearance on a finished radiograph that is seen especially in

fast-imaging systems

Scattered radiation fog gives the radiograph a

flat, gray appearance.

The farther the object is from the image receptor, the more

: blurred its edges will be as a result of magnification distortion.

The film exposed by a large static discharge ("tree static") frequently exhibits

black, branching artifacts

the most effective way to remove scattered photons from those exiting the patient?

a grid

The production of scattered radiation will also be limited if the field size is

as small as possible

too much background density is caused by

too much mAs

Use of optimal kilovoltage for each anatomic part is helpful in keeping scatter

to a minimum

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

A black crescent usually results from bending

after exposure

A characteristic curve compares

the exposure, given the film with the resultant density

A characteristic curve has three portions:

the toe, the straight-line portion (region of correct exposure), and the shoulder

A characteristic curve is used to

predict the speed, contrast, and exposure latitude of a particular film emulsion.

A decrease in source-image distance causes

magnification and blurriness of recorded detail.

a destructive disease such as osteoporosis will decrease

contrast

A grid is usually employed

1. when radiographing a large or dense body part.
2. when using high kilovoltage.

A grid is

a thin wafer placed between the patient and the IR to collect scattered radiation. It is made of alternating strips of lead and a radiolucent material such as plastic or aluminum.

A higher milliamperage with a short exposure time is generally

preferable

A histogram is a

graphic representation showing the distribution of pixel values

A microswitch initiates and terminates replenishment as

it senses the beginning and end of each film.

A radiograph exposed using a 12:1 ratio grid may exhibit a loss of density at its lateral edges because the

SID was too great

A technique chart should include which of the following information?

1. Recommended SID
2. Grid ratio
3. Screen-film combination

According to the line focus principle, an anode with a small angle provides

1. improved recorded detail.
2. improved heat capacity.
The line focus principle illustrates that as the target angle decreases, the effective focal spot decreases (providing improved recorded detail), but the actual area of electron interaction remains much larger (allowing for greater heat capacity). It must be remembered, however, that a steep (small) target angle increases the heel effect, and part coverage may be compromised.

acromegaly

an increase in bone size and density

All of the following are related to recorded detail

A. motion.
B. film-screen contact.
C. SID.

Although SID affects exposure rate (according to the inverse square law of radiation), and therefore affects density (according to the density maintenance formula), it is not used to regulate

radiographic density

An additive pathology such as Paget's disease will increase

contrast

An increase in exposure factors is usually required in which of the following circumstances?

1. Edema
2. Ascites
3. Acromegaly

An increase in kVp with appropriate compensation of mAs will result in

increased exposure latitude

An overall image density arising from factors other than the light or radiation used to expose the image is called

fog

anatomic parts measuring in excess of 10 cm require

a grid.

Anything other than intensifying screen light or primary x-radiation is

undesirable in terms of image exposure

artifact

anything foreign to the image; the term could include fog, but it also covers many physical interferences.

As focal spot size increases, recorded detail

decreases because more penumbra is produced.

As focal-object distance and SID decrease, so does

magnification

As kVp is increased,

x-ray photons begin to interact with atoms of tissue via the Compton scattered interaction

As SID increases, so does

recorded detail, because magnification is decreased

As temperature increases,

contrast decreases.

As the kilovoltage is increased

more penetration will occur and a greater range of densities (grays) will be apparent in the image

Atelectasis

a collapsed or airless lung; it requires an increase in exposure factors.

Beam restrictors function to

limit the x-ray field size, thereby reducing the production of scattered radiation and shortening the scale of contrast.

Because mammographic techniques operate at very low kVp levels, the cassette front material

becomes especially important.

because of the target angle,

penumbral blur varies along the longitudinal tube axis, being greater at the cathode end of the image and less at the anode end of the image.

Because shorter SIDs and larger IR sizes require greater divergence of the x-ray beam to provide coverage,

the anode heel effect will be accentuated.

Bronchiectasis

is a chronic dilatation of the bronchi with accumulation of fluid

Change is affected in

average exposure level and exposure's latitude; these changes will be reflected in the images informational numbers ("S number," "Exposure Index," etc)

changing from single-phase to three-phase, 12-pulse equipment; therefore the new mAs should be

half the original

Comparison of Technical Factors Required

Single-Phase (x mAs)
Three-Phase, 6-Pulse (2/3x mAs)
Three-Phase, 12-Pulse (1/2x mAs)

Compensating filters

can be accommodated by tracks in the tube head.

Compensating filters

can be wedge-shaped (with the thicker part of the wedge paralleling the thinner body part), thus compensating for greater or lesser tissue densities (as in a large decubitus abdomen)

Crescent-shaped black marks on the finished radiograph are usually due to

bending the film acutely

Degree of accuracy in positioning and centering

can have a significant effect on histogram appearance (as well as patient dose)

Differential absorption refers to

the different attenuation, or absorption, properties of adjacent body tissues

Each film passing through the processor solutions

takes with it a certain amount of solution

Emphysema

a chronic pulmonary disease characterized by an increase in the size of the air-containing terminal bronchioles.

exposure factors that would properly expose one part will

severely overexpose or underexpose the neighboring part (as with lungs vs thoracic spine)

Factors that affect screen speed will also affect

radiographic density.

Focal spot size is thus inversely related to

radiographic sharpness or recorded detail.

Focal spot size

one of the geometric factors affecting recorded detail; it has no effect on the scale of contrast.

Focal-object distance and SID are inversely proportional to

magnification

Geometric unsharpness is influenced by which of the following?

1. Distance from object to image
2. Distance from focus to object
3. Distance from focus to image

Geometric unsharpness is most likely to be greater

at the cathode end of the image

Going from three-phase, 12-pulse to single-phase requires

twice the mAs.

Greater latitude is available to the radiographer when using

1. high kVp factors.
2. a slow film-screen combination.

Guide shoes

also called deflector plates, serve to keep the film on its proper course by directing or guiding it around corners.

he type of chemistry used in the automatic processor and especially the temperature of the solution can have a big impact on

the resulting image contrast.

High radiographic contrast also results when

radiographing anatomic parts that have high subject contrast, such as the chest.

High radiographic contrast is, in part, a result of

lower energy photons (lower kVp).

Higher contrast is

shorter scale contrast; it is present in an image that has few shades of gray between white and black.

Histogram analysis and use of the appropriate LUT together function to

produce predictable image quality in CR.

How can the radiographer reduce the amount of scattered radiation generated during a radiographic examination?

1. Use optimum kVp.
2. Collimate closely.

How would the introduction of a 6-inch OID affect image contrast?

Contrast would be increased

ID can affect contrast when it is used as

an air gap.

If 10% of the illuminator's light passes through the image, that image has a density of

1.0

If a 6-inch air gap (OID) is introduced between the part and IR

much of the scattered radiation emitted from the body will not reach the IR

If intensifying-screen phosphors are covered with dust

either they will not fluoresce or their fluorescence will not reach the IR emulsion

If single-emulsion film was loaded into its cassette with the emulsion facing away from the intensifying screen, the resulting image would demonstrate

decreased density

If the central ray was off-center, there would be

uniform loss of density.

If the exposure is then made, scattered radiation from the tabletop (where there is no absorber) will undercut the part, causing

excessive image density.

if the film were loaded with the antihalation side against the light-emitting screen, the film emulsion would

receive very little exposure

If the grid failed to move during the exposure, there would be

grid lines throughout.

if the grid is not used within its recommended SID (focus) range (ie, if the SID is too great or too little), there will be

a decrease in density at the periphery of the image.

If the quantity of black metallic silver on a particular radiograph is such that it allows 1% of the illuminator light to pass through the image, that image has a density of

2.0

if the screen is scratched and phosphors are removed,

there will be no fluorescence to expose the IR.

If the x-ray beam is not centered to the grid, or if the x-ray tube and grid surface are not parallel (level), there will be a fairly uniform decrease in

radiographic density across the entire image.

If the x-ray tube is angled significantly across the lead strips of a focused grid, there is

uniform loss of density (grid cutoff)

If, for example, a blue-sensitive emulsion were matched with green-emitting screens, the resulting radiograph would be

underexposed because the blue-sensitive film emulsion was not responsive to the green-emitting phosphors.

If, however, a lead rubber mat is placed on the overhanging illuminated area, most of this scatter will be

absorbed.

Improper spectral matching between rare earth intensifying screens and film emulsion results in

insufficient density

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