Fauber Ch. 3: Radiographic Image Formation

Tissue

IR

To produce a radiographic image, x-ray photons must pass through _______ and interact with an _____.

Image Receptor (IR)

a device that receives the radiation leaving the patient

Thickness

Atomic Number

Tissue Density

The absorption characteristics of the anatomic part are determined by its ________, _________ ________ of the atoms contained within it, and _______ __________.

Latent (invisible)

Radiation that exits the patient is composed of varying energies and interacts with the IR to form a ______/________ image.

Differential Absorption

A process whereby some amount of the x-ray beam is absorbed in the tissue and some passes through the anatomic part.

Bone

Air

Anatomic parts composed of _____ absorb more x-ray photons than parts filled with ______.

Energy (intensity)

As the primary x-ray beam passes through anatomic tissue, it loses some of its _____ (________)

Attenuation

The reduction in the intensity or number of photons in the primary x-ray beam after it interacts with anatomic tissue

Absorption and Scattering

2 Distinct processes occur during beam attenuation:

Absorption

Complete _______ of the incoming x-ray photon occurs when it has enough energy to remove an inner-shell electron.

Photoelectron

The ejected electron is called a _____________

Tissues

The ejected electron (photoelectron) quickly loses energy by interacting with nearby ________.

Ionization

The ability to remove (eject) electrons

Photoelectric Effect

Ionization in the diagnostic range is also known as:

Electron Hole

With the photoelectric effect, an ionized atom has a _______ ______ in its inner shell.

Outer Shell

In Photoelectric Effect, An electron from ____ _____ drops down to fill the electron hole.

Secondary

In Photoelectric Effect, Because of the difference in binding energies between the two electron shells, a ________ x-ray photon is emitted.

Low

Unlikely

A Secondary x-ray photon typically has a very _____ energy and is _____ to exit the patient.

Photoelectric Effect

During attenuation of the x-ray beam, the ________________ _______ is responsible for the total absorption of the incoming x-ray photon.

Scattering

Some incoming photons are not absorbed but instead lose energy during interactions with the atoms of the tissue.

Compton Effect

The interaction between diagnostic x-rays and matter.

Outer-shell electron

The loss of energy of the incoming photon occurs when its ejects an _______-_______ ______ from a tissue atom.

Compton Electron or Secondary Electron

The ejected electron is called:

Compton Effect

During attenuation of the x-ray beam, the incoming x-ray photon may lose energy and change direction as a result of the _______ ______.

In Compton Effect

probability is the # of electrons per gram.

Coherent Scattering

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

Excited

Direction

In coherent scattering, the incoming photon interacts with the atom, causing it to become _________.

The X-ray does not loose energy it just changes ________.

Photoelectric Effect

*An incoming photon has sufficient energy to eject an inner-shell electron and be completely absorbed.

*An electron from an upper-level shell fills the electron hole or vacancy

*A secondary photon is created because of the difference in the electrons' binding energies.

*The probability of the effect depends on the energy of the incoming x-ray photon and the composition of the anatomic tissue.

*Fewer photon interactions occur at the higher kVp, but of those interactions, a smaller percentage are photoelectric interaction.

Compton Effect

*An incoming photon loses energy when it ejects an outer shell electron and changes direction.

*The scattered photon may be absorbed within the patient tissues, leave the anatomic part, interact with the image receptor, or expose anyone near the patient.

*Scattered photons that strike the image receptor provide no useful information.

*The probability of the effect depends on the energy of the incoming x-ray photon but not on the composition of the anatomic tissue.

*Fewer photon interactions occur at a higher kVp, but a greater percentage of those interactions are Compton interactions.

Fewer

More

_______ X-rays: Thinner Part

_______ X-rays: Thicker Part

Atomic Particles

Higher atomic number of the tissue means there are _____ __________ for interactions with x-ray photons

Bone

Muscle

Fat

Air

Four substances account for most of the beam attenuation in the human body:

4-5

X-rays are exponentially attenuated and generally reduced by approximately 50% for each _______cm

Higher kVp

Photoelectric Scatter is less than Compton

(LESS interaction total)

Transmission is HIGHER

this is good

Lower kVp

Photoelectric Scatter is greater than Compton

(greater interaction total)

Transmission is Smaller

this is not good

Decreases

Increases

Beam attenuation ________ with a higher energy X-ray beam and ______ with a lower energy X-ray beam.

Transmission

The incoming x-ray photon passes through the anatomic part without any interaction with the atomic structures.

Exit/Remnant Radiation

When the attenuated x-ray beam leaves the patient, the remaining x-ray beam.

*composed of both transmitted and scatter radiation

Fog

Scatter radiation creates unwanted exposure on the image called:

Absorption

Scattering

Transmission

When the diagnostic primary x-ray beam interacts with anatomic tissues, 3 processes occur:

White or Clear

The areas within the anatomic tissue that ABSORB incoming x-ray photons create the __________ areas on the image.

Black

The incoming c-ray photons that are TRANSMITTED create ______ areas on the image.

5%

Less than ________% of the primary x-ray beam interacting with the anatomic part actually reaches the IR.

Latent/Invisible Image

The exit radiation interacting with an image receptor.

Manifest/Visible Image

The processed latent image.

Visibility

Accuracy

The _________ of the anatomic structures and the ______ of their recorded structural lines determine the overall quality of the radiographic image.

Brightness

Contrast

The visibility of the recorded detail refers to the ________ and ______ of the image.

Spatial Resolution

Distortion

The accuracy of the structural lines is achieved by maximizing the amount of ________ _______ and minimizing the amount of _______.

Brightness

the amount of luminance of a display monitor

Density

the amount of overall blackness on the processed film image.

Brightness

A radiographic image must have sufficient ________ to visualize the anatomic structures of interest.

Contrast

the combined result of multiple factors associated with the anatomic structure, radiation quality, image-receptor capabilities, and in Digital imaging: Computer processing and display.

Subject contrast

the absorption characteristics of the anatomic tissue imaged and the quality of the x-ray beam.

low

Anatomic tissues that attenuate the beam similarly have _____ subject contrast.

high

Anatomic tissues that attenuate the beam very differently have _____ subject contrast.

Radiographic/Image Contrast

term used to describe variations in brightness and density.

Gray Scale

In digital imaging, the number of different shades of gray that can be stored and displayed by a computer system.

Contrast Resolution

used to describe the ability of an imaging receptor to distinguish between objects having similar subject contrast.

Scale of Contrast

the range of visible densities.

High contrast (short-scale contrast)

A film image with a few visible densities but great differences among them.

Low Contrast (long-scale contrast)

A radiograph with a large number of densities but few differences among them.

Spatial Resolution

the smallest object that can be detected in an image.

Spatial Resolution

The accuracy of the anatomic structural lines recorded in the radiographic image is determined by its ________ _______.

Distortion

Results form the radiographic misrepresentation of either the size (magnification) or the shape of the anatomic part.

Size distortion/Magnification

refers to an increase in the image size of an object compared with its true or actual size.

SID and OID

play important roles in minimizing the amount of size distortion of the radiographic image.

Elongation

refers to images of objects that appear longer than the true objects.

Foreshortening

refers to images that appear shorter than the true objects.

CR

Part

IR

Shape distortion can occur from inaccurate ____ alignment of the tube, the _____ being radiographed, or the ______.

Image Noise

contributes no useful diagnostic information and serves only to detract from the quality of an image.

Quantum Noise

*a concern in digital imaging and is photon dependent.

*visible as brightness or density fluctuations in the image.

Quantum Mottle

the term typically used when referring to noise on a film image.

Increase

Decreasing the number of photons reaching the IR may _______ the amount of quantum noise.

Decrease

Increasing the number of photons reaching the iR may _______ the amount of quantum noise

Digital Imaging

Quantum noise is more likely to occur in ____ _________

Dynamic Range

The range of exposure intensities an image receptor can accurately detect.