Imaging unit 2

Brightness

Amount of luminance (light emission) on display monitor

Saturation

IR is extremely overexposed, can't be properly exposed & quality is degraded

Exposure indicator

Provides numeric valve indicating level of radiation exposure to digital image receptor

Window level

Adjusts brightness

Contrast resolution

Ability of system to distinguish between small objects that attenuate X-ray beam similarly

Subject contrast

Absorption characteristics of anatomic tissue radiographed & quality of x-ray beam

Radiographic contrast

Affects visibility of structural lines that make up recorded image

Pixel bit depth

Affects # of shades of grey available for image display

Pixel density

# of pixels per unit area

Pixel pitch

Pixel spacing or distance measured from the center of pixel to adjacent pixel

Modulation transfer function

Measure of imaging system's ability to display the contrast of anatomic objects varying in size

Distortion

Radiographic misrepresentation of size or shape

Size distortion

Increase in image size compared with objects actual size

Shape distortion

objects radiographed misrepresented by shape

Artifact

Anything unwanted on radiograph

• Accurately represents the anatomic area of interest
• Information well visualized for diagnosis

What determines the overall quality of a radiographic image

Accuracy of their structural lines that's recorded

How is the visibility of anatomic structures accomplished

Makes it where the image can't be properly processed & the quality is severely degraded

What affect does saturation have on the image

Changes the contrast

What affect does changing the window width have on the image

Changes the brightness

What affect does changing the window level have on the image

Tissue thickness; Density; Atomic #
Different absorption characteristics contribute to X-ray brightness & attenuate the X-ray beam differently

List and explain what contributes to subject contrast

Image will have a foggy look with little differences in densities ; soft tissue visible

Explain the appearance of high scale contrast

Clear image of anatomy on radiograph showing the differences in density

Explain the appearance of short scale contrast

Pixel size & Pixel pitch

How is resolution measured

Determines amount of Sharpness

What is a line pair

Objects appear longer than true object

Describe the image appearance when there is elongation

Objects appear shorter than true objet

Describe the image appearance when there is foreshortening

To determine if image is underexposed or overexposed

Why should the exposure indicator be evaluated

• Image that's too light has excessive brightness to allow visualization of structures
• Image that's too dark has insufficient brightness of anatomic parts can't be well visualized

State the relationship between Image appearance and brightness

• Increasing pixel density & decreasing pixel pitch increases spatial resolution
• Decreasing pixel density & increasing pixel pitch decreases spatial resolution

State the relationship between Spatial resolution/pixel density and pixel pitch

• Increase FOV for same matrix size will increase size of pixel & decrease spatial resolution
• Increase size matrix size for same FOV will decrease pixels Size & increase spatial resolution

State the relationship between Matrix/pixel size & spatial resolution

• Small objects have higher spatial frequency
• Larger objects have lower spatial frequency

Relationship between Object size and spatial frequency

More SID = less magnification & Less SID = More magnification
More OID = More magnification & Less OID = Less magnification

Relationship between OID/SID & magnification

When an image is distorted, spatial resolution is reduced

Relationship between Distortion and spatial resolution

IR with higher D&E requires less x-ray exposure to produce a quality image; This means higher brightness level on image

Relationship between The intensity of radiation and brightness

Increase in CNR increases the visibility of anatomic details

Relationship between Contrast to noise ratio and image quality

Resolution Test pattern

What measures resolution

strength of signal high compared to noise

↑ SNR =

Improved image quality

↑ SNR =

↓ visibility of details

↑ SNR =

Better image

↑ CNR =

Less visibility of details

↓ CNR

Quantum Noise/Quantum Mottle

Not enough photons to IR; Increase mAs

wide window width

many shades of grey =

↓ pixel sized

matrix ↑ =

pixel size ↑

matrie ↓ =

more detail

smaller line pairs =

More detail

# of line pair =

Spatial frequency

# of live pairs per/mm

DQE

Efficiency of IR + ability to convert X-ray exposure

Pixel Density

H of pixels per mm

Pixel Pitch

size of pixel measured from cellter to center

↓ pixel size

FOV ↓ =

pixels become smaller

Fov reduced & no matrix size change =

spatial resolution ↑

↓ Pixel size size =

↓ Spatial resolution

↑ Pixel size =

↑ spatial resuloution

smaller pixel pitch =

↑ spatial resolution

Decrease pixel pitch =

↓ spatial resolution

Increase pixel pitch =

↑ Spatial resolution

Increased Matrix size = small pixels =

↓ spatial resolution

Decreased Matrix size = bigger pixels =

Long - scale Contrast

lower contrast & ↑ in scatter ↑ in fog =

short scale contrast

higher contrast & ↑ absorption ↑ more white =