Imaging (Unit 1)

Scatter Radiation

Causes image fog and reduces diagnostic clarity.

Patient Dose

Increased due to scatter radiation exposure.

Dynamic Range

Enhances visualization of soft and bony structures.

Digital Imaging

Improves image quality through extended dynamic range.

Artifact

Unwanted brightness level on X-ray image

Attenuation

Reduction in energy or number of photons in primary x-ray Scatter absorption help

Brightness

Amount of luminance (light emission) of display monitor

Contrast

Differences in brightness levels the anatomic tissues

Differential absorption

Difference btwn x-ray photons absorbed photoelectrically & those that penetrate the body

Exit radiation

beam leaving the pt, has both transmitted & scattered radiation

Fog

Scatter radiation that creates unwanted exposure

Latent image

Invisible immage that exits on IR before it's processed

Manifest image

Visible image on exposed detector after processing

Remnant radiation

Attenuated beam leaving pt , composed of transmitted & X - ray Scattered radiation Exit Radiation

Transmission

X - ray photon passes through any anatomic part without interaction with anatomic structures

Coherent scattering

Interaction that occurs with low-energy x-rays, typically below the diagnostic range

• Incident photon interacts with K & L electron, giving all energy & ejecting electron
• Ejected electron imparts the atom w / energy equal to excess of electron's binding energy
• Vacancy in the inner orbital shell (K & L), must be filled; Next electron in outer shell fills void
• Electron drops to void , at may shed excess energy as secondary photon

Explain the concept of photoelectric effect

• Photon interacts with outer orbital electron, importing some energy to electron, ejecting from orbit
• Ejected electron leaves atom with energy equal to excess imparted by photore
• Photon continues on altered path, scattered with less energy than before collision

Compton effect

1. Incident photon interacts with inner-shell electron of tissue atom; removes orbit
2. Incident photon expends all energy & is totally absorbed

State which interactions occur above diagnostic range

Photoelectric

which interaction occur within diagnostic range or low energy photons

• Tissue Thickness; atomic #; Tissue density; X-ray beam Quality

Factors affecting Beam Attenuation

Brighter image

Higher atomic # =

Differential absorption

Shades of grey

Less than 5%

Amount of primary beam reaches IR

Allow for better visualization of soft tissue and bony structures

State the relationship between Brightness and image quality

Wont allow for visualization of structures of the anatomic part; Image Bright

Increased Brightness

Decreased Brightness

Anatomic part not well visualized; Image dark

Long scale contrast

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

Short scale contrast

Clear image of anatomy on radiograph showing the differences in density

Beam Attenuation: ⬆️ Absorption: ⬆️ Transmission: ⬇️

Increase Tissue Thickness

Beam Attenuation: ⬇️ Absorption: ⬇️ Transmission: ⬆️

Decrease tissue thickness

Beam Attenuation: ⬆️ Absorption: ⬆️ Transmission: ⬇️

Increasing Atomic #

Beam Attenuation: ⬇️ Absorption: ⬇️ Transmission: ⬆️

Decreasing Atomic #

Beam Attenuation: ⬆️ Absorption: ⬆️ Transmission: ⬇️

Increase Tissue Density

Beam Attenuation: ⬇️ Absorption: ⬇️ Transmission: ⬆️

Decrease Tissue Density

Beam Attenuation: ⬇️ Absorption: ⬇️ Transmission: ⬆️

Increase Beam Quality

Beam Attenuation: ⬆️ Absorption: ⬆️ Transmission: ⬇️

Decrease Beam Quality

Pixel

Single numeric value representing brightness

Bit Depth

# of bits that determines # of shades of grey

Ionization

Ejects electron out of orbit

Coherent Scatter

Gets excited➡️Photon In➡️Scatter photon out

20-120 kV

Diagnostic Range

energy of the incoming photon

Probability depends on

13.8

Atomic # of bone

7.4

Atomic # of muscle

6.3

Atomic # of fat

1850

Tissue Density: Bone

1000

Tissue Density: Muscle

910

Tissue Density: Fat

Absorption

X-ray photons removed from x-ray beam as result of uptake of their energy

Compton electron

Electron ejected from atom during Compton scattering event

Secondary Electron

Ejected electron resulting from Compton effect interaction; Compton electron

Contrast resolution

Ability of imaging system to distinguish btwn small objects that attenuate x-ray beam

Fluoroscopy

Use of continuous beam of x-rays to create dynamic images of internal structures

Image receptor

Device that receives radiation leaving pt

Photoelectron

Electron ejected from atom during photoelectric interaction

Scattering

Incoming photons not absorbed but lose energy during interactions

Tissue Density

Matter per unit volume, or compactness of atomic particles composing anatomic part