Chapter 3- Image Formation and Radiographic Quality Flashcards
Anatomic tissues absorb and transmit x-rays differently based on their composition (atomic number and tissue density)
Differential Absorption
______ absorbs more x-rays than muscle?
Bone
The primary x-ray beam loses some of its energy (number of photons) as its interacts with anatomic tissue.
Attenuation
What are the two types of attenuation?
Absorption and scattering
Complete absorption of the incoming photon
Photoelectric effect
During absorption, the energy of the _______ beam is deposited within the atoms comprising the tissue
Primary
What are effects of photoelectric
X-ray ionizes atom
low energy secondary x-ray photon created
probability of photoelectric effect dependent on the energy of the incoming x-ray photon and tissue atomic number
Occurs when an incoming photon loses some but not all of its energy, then changes its direction
The Compton effect (Scattering)
* It can occur within all diagnostic x-ray energies and is dependent only on the energy of the incoming photon, not the atomic number of tissue
- Higher KVP reduces the number of interactions, but the the Compton interactions increases in comparison to the number of photoelectric interactions
Factors affecting beam attenuation: (att)
Tissue thickness- reduce by 50% for each 4 to 5cm
Type of tissue- higher atomic # will increase beam att.
Tissue density- increase compactness of atomic particles will increase beam att.
X-ray beam quality- higher KVP increases the energy of the x-ray beam will decrease beam att
Scatter radiation reaching the image receptor creates _______ exposure called ______
Unwanted
Fog
______ or exit radiation is composed and transmitted and ________ radiation
Remnant
Scattered
What radiation creates an image that structurally represents that anatomic area of interest?
Transmitted and Absorbed (Exit Radiation)
X-ray beam passes through matter there is a gradual reduction in the number of photons, what is this called?
Absorption or Attenuation
What does an x-ray beam produce on a image receptor?
Latent Image
What is an excellent demonstration of the different absorption characteristics
CT
Dense structures and those of high atomic number appear _______ areas on the image
lighter
_____ and _______ appear as dark areas on the image
Air (low density)
Fat (low atomic #)
Dense and high atomic numbers appear _______ shadow on the film and are usually ________?
Light
Bone
What are technical factors radiation therapist use for differential absorption on the film?
KVP or MA
_______ structures represent areas of _______ atomic numbers
Dark
Low
_______ structures represent tissue that is dense with ______ atomic numbers
Light
High
Density = __________
Darkness
_______ radiation reacts with an image receptor such as film screen system to create latent image until processed to produce the manifest or the _______ image.
Exit
visible
Low Density = ____________
Brightness
______ radiation creates higher brightness or low density on the displayed image
Absorbed
________ radiation creates lower brightness or high density on the displayed image
Transmitted
The various shades of gray recorded in the image make atomic tissue _________.
Visible
Visibility of anatomic structures
Density
Contrast
Accuracy of structural lines (sharpness)
Resolution or recorded detail
Distortion
True of False- A quality radiographic image accurately represents the anatomic area of interest, and its information is well visualized for diagnosis.
True
A film image is evaluated by the amount of ________ or overall blackness after processing
Density
A digital image is evaluated by the amount of _______ or ______ (Light emission)
Brightness
Luminescence
The range of brightness levels are a result of the tissues _______ _______ of the x-ray photons
Differential Absorption
Ex: Barium (contrast material)
True or False- The ability to distinguish among types of tissues is determined by the difference in brightness levels or densities in the image or contrast
True
Gray scale is?
The number of different shades of gray that can be stored and displayed in a digital image
Scale of contrast is?
The range of densities visible on film
_______ resolution describes and imaging receptors ability to distinguish between objects similar in subject contrast?
Contrast
True or False- Anatomic details do not have to be recorded accurately?
False- They must be, with the greatest amount of sharpness
_______ resolution refers to the smallest object that can be detected in a digital image?
Spatial
_______ detailed refers to the distinctness or sharpness of the structural lines that make up the recorded film image?
Recorded
True of False- All radiographic images have some degree of unsharpness
True
Size distortion or magnification is an _______ in the objects image _____ compared to its true or actual _______.
Increase
Size
Size
True or False- Shape distortion is a representation of an object’s image shape
False- Its a misrepresentation
- Elongation and foreshortening
- Central ray (CR) alignment of the x-ray tube, part and image receptor affect distortion
Does scatter and fog decrease image contrast?
YES
True or False: Digital image receptors can detect lower levels of radiation intensity and therefore are less sensitive to scatter?
False- They are MORE sensitive to scatter
Visible as brightness or density fluctuations and is photon dependent
Quantum Noise
- Provides no useful information
- More visible in digital imaging
- Too few x-ray photons result in increase
Classified as plus density and minus density
Image Artifact
In digital imaging what is the column and the rows called
Matrix
What are the small boxes in a digital image called
Pixel- picture element or smallest component of matrix
Recorded a single numerical value representing a brightness level on a display monitor
Matrix
True or False: Location of pixel in the matrix corresponds to an area within the patient or volume of tissue
True
True or False: If the Matrix size is smaller the greater number of smaller pixels?
False: the quality is improved with a larger matrix. This will increase digital storage, processing time and network transmission time.
Numerical value assigned to a _______ is determined by the relative attenuation of x-rays passing through the volume of the tissue
Pixel
What determines the shade of gray in image
pixel bit depth or number of bits (2”) determines the number of gray that can be displayed
Active layer of film that contains the crystals that serve as latent imaging centers?
Film Emulsion
Used to convert exit radiation intensities to visible light and expose the emulsion crystals
Intensifying Screens
Is chemically processed to display the range of densities created as a result of the x-ray attenuation characteristics of anatomic structures
Film
_______ _________ image receptors have a limited dynamic range that vary greatly in x-ray attenuation
Film Screen
Receptors have a wide dynamic range, and therefore anatomic areas of widely different attenuation properties can be more easily visualized on a digital image.
Digital Image
The range of exposure intensities an image receptor can accurately detect
Dynamic Range
