POI 1

1. Technique

2. kVp

3. Milliamperes

4. Time

5. Distance

What are the technical factors that control exposure?

Technical factors

What controls and affects image exposure?

Technique

The systematic procedure when creating a radiographic image

kVp, mA, time, and distance

Proper technique is the adequate use of ___, ___, ____, and _____ to produce images with adequate contrast and density

shortest

optimum

sufficient

Good technique uses _____ exposure time, _____ kVp, and _____ mAs.

kVp

The force that accelerates electrons from cathode to anode

energy/quality, as well as the penetrability and production of scatter radiation, and contrast

What does kVp directly control?

crest

photon energy

kVp is the _____ of the waveform that represents _____ _____.

density (15%)

kVp has direct impact on _____ (__%)

mA

Represents the current flow through the cathode filament

quantity of x-ray photons, as well as the quantum mottle and image noise

What does mA control?

focal spot blooming

mAs is a factor to consider in _____ ____ _____.

Time

Sets the length of exposure

Distance: SID/FFD

Length of space from focal spot to recording medium

reduced to ¼

If SID is increased 2x, the intensity of the beam is _____ to __.

Sharp image with adequate density and contrast

What is a high quality image

The exactness of representation of px anatomy on radiographic image

What is radiographic image quality?

density and contrast

What are the components of the photographic aspect?

Density

The overall blackening of the film

Contrast

Variation or differences in density level that makes detail visible

definition and distortion

What are the components of the geometric aspect?

Definition

Clarity and sharpness of structural lines

Distortion

Undesired change in size and shape

Resolution

The ability to image two separate objects and visually distinguish one from the other

Spatial resolution

The ability to image small objects that have high subject contrast

Contrast resolution

Ability to image anatomic structures of similar subject contrast

Detail and recorded detail

Degree of sharpness of structural lines of a radiograph

Visibility of detail

The ability to visualize the record detail when the image contrast and optical density (OD) are optimized

Radiographic noise

What are the random fluctuations in the optical density of the radiograph, or the speckled background on the image?

Caused by ⬆ screen speed and ⬆ kV techniques

What causes radiographic noise?

1. Film graininess

2. Structure mottle

3. Quantum mottle

4. Speed

What re the four components of radiographic noise?

Film graininess

Affected Toby the distribution and size of the silver halide crystals in the emulsion, and is inherent to the film

Structure mottle

Affected by the speed of the intensifying screens, determined by the phosphor size and DQE/CE and is inherent to the intensifying screen. This is uncontrolled by the RT

Quantum mottle

An image produced with just a few x-ray photons will have this

Speed

Interconnects the resolution and noise; each of the three factors influence each other

Radiographic density

The opacity of the radiograph, or the overall blackening/darkening of the film

They lose significance

What will happen to all the other factors if there is no density?

Radiographic density

The amount of blackness on a given area of a radiograph

Brightness

How is radiographic density described as in digital imaging?

kVp, distance, grids, film screen speed, collimation, anatomic part, anode heel effect, reciprocity law, generator output, filtration, and film processing

What influences radiographic density?

Radiographic contrast

What is the variation, changes, or differentiation of adjacent densities on the radiograph?

Photoelectric effect

What produces radiographic contrast?

To make detail visible

What is the primary function of radiographic contrast?

kVp

What controls contrast?

differential absorption

energy

kVp controls _____ _____ of the x-ray beam by the body because of its control of the x-ray beam _____

Grids, collimation, OID, CM, processing, and air-gap technique

What influences radiographic contrast?

window width and bit depth

Radiographic contrast is ultimately controlled by _____ _____ and ___ _____

1. Film contrast

2. Subject contrast

3. Latitude

4. Scale of contrast

Kinds of radiographic contrast

Recorded detail

The sharpness with which the anatomical structures re displayed on an image receptor

Definition, image resolution, spatial resolution (in digital imaging)

What are the components of recorded detail?

Visibility of detail

How well the recorded detail can be seen

recorded detail

visibility of detail

Density has no effect on _____ ______ density but has effect on _____ of _____ because it obscures detail

Contrast resolution

In digital imaging, definition is termed as _____ _____

Umbra

True image

Penumbra

Geometric unsharpness, or the blurred areas around the umbra

SID, OID, and focal-spot size

What primarily controls definition?

Recorded detail

The technical sharpness

Visibility of detail

The perception of details depending on the exposure and contrast

Umbra - true shadow

Penumbra - shadow of the shadow

In simple terms, define umbra and penumbra

Geometric unsharpness

Blurred area around the umbra

Magnification

What is inversely related to recorded detail?

⬇

⬆ magnification = __ recorded detail

SID and OID

What regulates magnification and image blur

Focal spot size

What controls image blur?

Image blur

What does tube/patient motion cause?

Image blur

What does tube/patient motion cause?

Distortion

Any geometric misrepresentation of an anatomical structure on an image receptor that alters its true size and shape

1. Size distortion (magnification)

2. Shape distortion (elongation and foreshortening)

What are the two types of distortion?

Contrast

Difference in adjacent densities that makes detail visible

⬆ kVp = ⬇ wavelength rays = ⬆ penetrabillity = ⬇ absorption/photoelectric interaction = ⬆ gray tones = longer contrast scale

⬆ kVp = ___ wavelength rays = ___ penetrabillity = ___ absorption/photoelectric interaction = ___ gray tones = longer contrast scale

⬇ kVp = ⬆ wavelength rays = ⬇ penetrabillity = ⬆ absorption/photoelectric interaction = ⬇ gray tones = shorter contrast scale

⬇ kVp = ___ wavelength rays = ___ penetrabillity = ___ absorption/photoelectric interaction = ___ gray tones = shorter contrast scale

⬆ OID (15 - 25 cm) = air gap technique = ⬆ scatter cleanup (equivalent to 8:1 grid ratio) = ⬆ contrast

⬆ OID (15 - 25 cm) = air gap technique = ___ scatter cleanup (equivalent to ___ grid ratio) = ___ contrast

⬆ magnification, ⬆ SID, and ⬆ mAs to maintain density

Air gap technique disadvantage

= ___ magnification, ___ SID, and ___ mAs to maintain density

Grids: ⬇ scatter reaching the IR = ⬇ scatter fog = ⬇ gray tones = ⬆ contrast

Grids: ___ scatter reaching the IR = ___ scatter fog = ___ gray tones = ___ contrast

Beam restriction

Limits the area being irradiated

Beam restriction: ⬇ field size = ⬇ number of Compton interactions = ⬇ scatter = ⬇ px dose = ⬇ gray tones = ⬆ contrast

Beam restriction: ⬇ field size = ___ number of Compton interactions = ___ scatter =___ px dose = ___ gray tones = ___ contrast

harder

shorter

As filtration increases, the beam becomes _____, meaning the average photon striking the patient has _____ wavelength

⬆ filtration = harder photons = ⬆ Compton scattering = ⬇ contrast air gap technique = ⬇ contrast

⬆ filtration = harder photons = ___ Compton scattering = ___ contrast air gap technique = ___ contrast

Anatomy and pathology

What is also known as the subject contrast, which causes differential absorption of x-ray photons which result in contrast?

⬆ contrast, photoelectric effect

⬇ contrast, Compton scattering

⬆ contrast, photoelectric effect

Anatomy and Pathology controls contrast with variations in the following:

= ⬆ atomic number = ___ contrast (owning to _____ _____)

= ⬆ tissue density = ___ contrast (owning to _____ _____)

= use of contrast agent = ___ contrast (owning to _____ ______)

⬆ processing time = ⬆ chemical fog = ⬇ contrast

Processing

⬆ processing time = ___ chemical fog = ___ contrast

⬆ chemical temperature = ⬆ chemical fog = ⬇ contrast

Processing

⬆ chemical temperature = ___ chemical fog = ___ contrast

⬆

Processing

Extended processing (3 minutes) for rad obtained from very low kVp = ___ contrast

No change in exposure factor

Casts and splints

Fiber =

mAs +50% or +8% kVp

Fiberglass + plaster =

Fiberglass + solid plastic =

¾ inch wood =

⬆ mAs 2x or +15% kVp

Casts

Dry plaster

⬆ mAs 3x or +22% kVp

Casts

Large dry plaster or

Medium wet plaster

⬆ mAs 4x or +30% kVp

Casts

Large wet plaster

When fiberglass or inflatable (air) is used

When will there be no increase in factors in the presence of splints?

When using wood, aluminum, or plastic, and only if they are in the path of the primary beam

When using splints, when will there be exposure of factor?

IR contrast x subject contrast

Radiographic contrast = ______ x ______

Image receptor contrast, influenced somewhat by the processing of film

What contrast is inherent in the screen-film combination, and what somewhat influences it?

Affected by film (IR), film type, and direct/IS exposure

What affects IR contrast?

higher

Film-screen images have _____ contrasts than direct film exposure images

Controlled by anatomy and pathology

What controls subject contrast?

Through variations of Z, tissue thickness, and tissue density

How does anatomy and pathology affect subject contrast?

more

Tissue thickness ➡ thick body sections attenuate ____ x-rays than thin body sections

tissue mass density

Variations in _____ _____ _____ contribute to subject contrast.

cube of Z

Effective atomic number ➡ photoelectric effect varies in proportion to the ____ of _