Digital Imaging Contrast Factors and Radiographic Techniques

The controlling factor of image contrast is

bit depth and LUT

Which combination of technical factors would likely produce the lowest contrast?: 65 kVp, 7x17 field size, 40" SID; 70 kVp, 6x6 field size, 72" SID; 90 kVp, 14x17 field size, 36" SID; 55 kVp, 8x10 field size, 48" SID

90 kVp, 14x17 field size, 36" SID

Increasing window width displays a ________ range of grayscale values, which results in _______ image contrast

wider; lower

Which changes would generally increase image contrast

decreasing kVp, increasing collimation, decreasing scatter reaching the IR

Which factors can influence the final contrast displayed on a digital image

subject contrast, image processing algorithm, window width adjustments, LUT/histogram analysis

In digital imaging, the final displayed image contrast may be affected by

subject contrast and digital image processing

Which statement best defines radiographic contrast?

The visible difference between adjacent densities or grayscale values

Which combination of technical factors would likely produce the highest contrast?: 95 kVp, 16x16 field size, 1.0 mm Al/Eq; 60 kVp, 8x10 field size, 0.5 mm Al/Eq; 80 kVp, 14x17 field size, 3.5 mm Al/Eq; 90 kVp, 10x12 field size, 2.25 mm Al/Eq

60 kVp, 8x10 field size, 0.5 mm Al/Eq

Which sequence best explains how increased field size affects contrast

More tissue is irradiated More scatter is produced More scatter reaches the IR Image contrast decreases

As filtration is added to the x-ray beam, image contrast generally

decreases because the beam becomes more penetrating

True/False: Short-scale contrast is a result of more Compton scatter interactions between x-ray photons and tissue

false

Which are reasons for restricting the x-ray beam

reduce patient dose, reduce scatter production, and improve image contrast

Two abdomen images are taken. Image A uses 70 kVp. Image B uses 90 kVp. All other factors are unchanged. Which image would most likely demonstrate lower subject contrast?

image B

Radiographic contrast is the product of

subject contrast and image contrast

True/False: higher grid ratios require higher exposure factors

true

A higher grid ratio results in

more efficient scatter removal

Which factor primarily controls subject contrast

kVp

Which grid ratio is most commonly used in general radiography

8:1 or 10:1

An abdomen is considered to have

low subject contrast

Grid ratio is defined as

lead strip height divided by interspace

True/False: the air-gap technique increases OID and contrast

true

Which type of matter interaction produces high contrast (black and white)

photoelectric absorption

What are the two materials used in a grid

lead and radiolucent interspace

High kVp creates what type of contrast

low contrast // low scale

A grid should be used when part thickness exceeds

10 cm (4 in)

True/False: the Moiré effect is most common when using a stationary grid with PSP imaging

true

The 15% rule states that increasing kVp by 15% will

double receptor exposure

Positive beam limiting (PBL) devices automatically

adjust collimator shutters to match IR size

When OID is increased (air-gap technique), what happens to contrast

increases

True/False: A 16:1 grid is commonly used in radiography because it offers the best balance between scatter reduction and patient dose

false

The most common beam restricting device in use today is

collimator

What happens with an upside-down focused grid

cutoff occurs at the edges

What is the primary purpose of using a grid

reduce scatter reaching the IR

What is the primary purpose of beam restriction

reduce the production of scatter

Which type of grid error occurs when the tube is angled across grid lines

off-level

Increasing collimation (smaller field size) has what effect on contrast

increases

Filtration primarily

hardens the beam (removes low-energy photons from the beam before they reach the patient)

As filtration is added to the beam, image contrast generally _________ because...

decreases; beam quality increases

The standard filtration material used in diagnostic radiography is

aluminum

Which two factors directly affect beam quality

kVp and filtration

Tissue compression can improve image contrast because it

reduces tissue thickness and therefore reduces scatter production

True/False: collimation reduces scatter production by irradiating less tissue

true

True/False: filtration primarily removes high-energy photons from the useful beam

false

True/False: parallel grids eliminate cutoff along the edges of the image by aligning with beam divergence

false

A Potter-Bucky diaphragm was developed to

move the grid and blur grid lines

Which type of filtration is located in the tube housing

inherent

Which grid type is most common for portable exams

parallel

True/False: digital post-processing tools such as LUT and window width directly influence image contrast

true

The required total filtration when operating above 70 kVp is

2.5 mm Al/Eq

True/False: the HVL is the amount of filtration required to reduce beam intensity to one-half

true

Which pathology increases contrast by adding air to the lungs

emphysema

True/False: increasing filtration will increase contrast

false

Bit depth refers to

the total number of shades of gray assigned to a pixel

True/False: Grids reduce the production of scatter

false

A large window width in post-processing results in

low contrast

Grid frequency refers to

the number of lead strips per cm

True/False: subject contrast is influenced by patient size, tissue density, and atomic number

true

Which grid pattern supports tube angulation

linear

True/False: Grid errors such as off-level, off-center, and off-focus all lead to grid cutoff

true

Radiographic contrast is best described as

the visible differences between adjacent densities/brightness values on an image

In digital imaging, radiographic contrast is produced by the combination of which two of the following

subject contrast and image contrast

Subject contrast refers to

differences in x-ray intensity exiting the patient (absorption/transmission) before image processing

______ is the controlling factor of subject contrast

kVp

Increasing kVp generally causes subject contrast to __________ because...

decrease; more photons penetrate the anatomy and differential absorption decreases

High radiographic contrast is best described as

Many differences between adjacent densities; short scale contrast

Additive pathology generally has what effect on subject contrast

decreases subject contrast due to increased tissue density/absorption

Destructive pathology generally has what effect on subject contrast

Increases subject contrast due to decreased attenuation.

As kVp increases, subject contrast generally

decreases

kVp and subject contrast have a(n) ________ relationship.

inverse

A high-contrast image has

few gray shades and more obvious differences between adjacent structures

A low-contrast image has

many gray shades and a longer scale of contrast

Which prime factor(s) has no direct effect on radiographic contrast in digital imaging

mAs and SID

An additive pathology typically causes the affected tissue to

attenuate more XRs than surrounding tissue

A destructive pathology typically causes the affected tissue to

attenuate fewer x-rays than surrounding tissue

Which of the following primarily influences image contrast after the x-ray beam reaches the detector

image processing algorithm/LUT

In digital imaging, changing window width primarily changes

displayed image contrast

As field size increases, scatter radiation generally __________, which causes radiographic contrast to __________

increases; decreases

As additional filtration is added to the beam, image contrast generally

decreases

Which combination of variables will result in a radiograph with the highest contrast?: 100 kVp, 80 mAs, 14x17 field size; 85 kVp, 40 mAs, 14x17 field size; 75 kVp, 30 mAs, 10x12 field size; 115 kVp, 4 mAs, 10x12 field size

75 kVp, 30 mAs, 10x12 field size

Which of the following factors will affect radiographic contrast?

kVp, filtration, pathology

A radiograph appears very gray with poor separation between soft tissue structures. Identify one possible cause and explain why it affects contrast.

When an image has too many grays, the contrast is too low (long-scale). This could be a result of a too-high kVp, causing more Compton scatter interactions. With more Compton scatter, there is more noise/fog reaching the IR, lowering image contrast.

The primary purpose of a grid is to

absorb scatter radiation before it reaches the image receptor

A grid is placed

between the patient and the image receptor

The two people credited with designing and improving radiographic grids are

bucky and potter

What is grid cutoff

The unwanted absorption of primary radiation due to improper grid alignment or positioning

What is grid conversion factor

The increase in mAs needed when changing from non-grid to grid imaging

A high frequency grid generally has the advantage of

less visible grid lines

A disadvantage of high grid frequency is that it generally

requires higher exposure to maintain receptor exposure

A __________ grid pattern has lead strips running in only one direction

linear

A cross-hatched grid is made from two superimposed linear grids and is more sensitive to

positioning errors

A __________ grid has lead strips that are angled to match beam divergence

focused

A parallel grid has lead strips that are

parallel to one another

Positioning latitude refers to

how much positioning/alignment error can occur before unacceptable grid cutoff appears

The benefit of using a moving grid is that it

blurs grid lines so they are less visible

An ___________ grid error results from using an SID outside the grid's focal range

off-focus

An ___________ grid error occurs when the x-ray tube, grid, or IR is angled improperly

off-level

An ______________ focused grid typically causes severe cutoff along the edges of the image

upside-down

An ______________ grid error results from lateral decentering of the central ray

off-center

Which two grid errors usually cause cutoff across the entire image

off-level and off-center

Which two grid errors usually cause cutoff along only the edges of the image

upside-down and off-focus