Chapter 12 Exam Flashcards
Which of the following will decrease the amount of scatter radiation produced?
a. Increasing the x-ray field size
b. Decreasing the x-ray field size
c. Increasing the grid ratio
d. Decreasing the grid ratio=
b. Decreasing the x-ray field size
Which of the following is not a type of beam restrictor?
a. Aperture diaphragm
b. Positive beam-limiting device
c. Cylinder
d. Lead shield
d. Lead shield
As collimation decreases, the quantity of scatter radiation decreases.
a. True
b. False
b. False
What type of beam-restricting device provides the most flexibility in adjusting the x-ray field size?
a. Cylinder
b. Aperture
c. Diaphragm
d. Cone
c. Diaphragm
What describes the number of lead lines per unit length?
a. Grid frequency
b. Grid pattern
c. Grid convergent point
d. Grid ratio
a. Grid frequency
A radiographic image was created using a 12:1 grid and 70 kVp at 10 mAs. What exposure technique change would maintain a similar exposure to the image receptor when converting to a 6:1 ratio grid?
a. 81 kVp at 5 mAs
b. 70 kVp at 16.7 mAs
c. 70 kVp at 6 mAs
d. 60 kVp at 20 mAs
c. 70 kVp at 6 mAs
What type of grid has lead strips running parallel to the long axis of the grid?
a. Focused
b. Short dimension
c. Cross hatched
d. Long dimension
d. Long dimension
Angling the x-ray tube along the long axis of a crossed grid would result in:
a. Increased scatter absorption
b. Grid cutoff
c. Moiré effect
d. Lateral decentering
b. Grid cutoff
For the air gap technique to be effective in reducing scatter radiation reaching the image receptor, what must be increased?
a. SID
b. Focal spot size
c. kVp
d. OID
d. OID
With exposure technique compensation, _____ the grid ratio will _____ patient radiation exposure.
a. Decreasing, increase
b. Increasing, decrease
c. Increasing, increase
d. Decreasing, will not affect
c. Increasing, increase
Related to the energy of the photon. As x-ray photon energy increases, the probability of that photon penetrating a given tissue without interaction increases. With this increase in photon energy, the likelihood of Compton interactions relative to photoelectric interactions also increases
Does not depend on the atomic number of atoms involved
compton scatter probability
The greater the volume of tissue irradiated because of part thickness or x-ray beam field size, the greater:
the amount of scatter radiation produced.
The higher the kVp used, the greater:
the energy of scattered x-rays exiting the patient
As collimation increases, the field size decreases and the quantity of scatter radiation ________
decreases
As collimation decreases, the field size increases and the quantity of scatter radiation ________
increases
what is the shape of the primary beam?
The unrestricted primary beam is cone shaped and projects a round field on the patient and IR
what happens if the primary beam is not restricted in some way?
goes beyond the boundaries of the anatomic are of interest and IR size, resulting in unnecessary patient exposure
what changes the shape and size of the primary beam?
beam restricting device
limits patient exposure and reduces the amount of scatter radiation produced within the patient, increases radiographic contrast
beam restriction
what word is beam restriction interchangeable with?
collimation
- Aka positive beam-limiting device (PBL) device
- Automatically limits the size and shape of the primary beam to the size and shape of the IR
- Mechanically adjusts the primary beam size and shape to the IR
Automatic collimator
Where’s the grid?
It is placed between the patient and the IR
When should we use a grid?
- When the anatomic part is 10 cm (4 inches) or greater in thickness and for imaging procedures requiring more than 60 kVp
- Consider contrast improvement, patient does, likelihood of grid cutoff
How do grids work?
They trap scattered radiation that would otherwise cause fog on the radiograph
Grids are made of what materials?
- Thin lead strips or lines
- Radiolucent interspace material separates the lead lines
- Lead lines and interspace material covered by an aluminum front and back panel
As grid ratio increases, radiation exposure to the IR ________; as grid ratio decreases, radiation exposure to the IR ________
decreases, increases
Grid ratio formula
Grid ratio = height/width of interspace
Grid ratio = h/D
h = height of lead strips
D = distance between lead strips
Non-focused grid:
lead lines run parallel
Focused grid:
lead lines are angled to match the angle of divergence of the primary beam
Used with a specific SID
Distance between the grid and the convergent line or point
It is used to determine the focal range of a focused grid
Focal distance (grid radius)
the recommended range of SIDs that can be used with a focused grid
focal range
- Part of the bucky, more accurately called the Potter-Bucky diaphragm
§ Located directly below the radiographic tabletop and just above the tray that holds the IR - Grid motion controlled electrically by the x-ray exposure switch
- Grid moves slightly back and forth in a lateral direction over the IR during the entire exposure
reciprocating grids
Why does the reciprocating grid move?
To blur the gird lines during the x-ray exposure
When a grid is added to the IR, mAs must be ________ by the factors indicated to maintain the same number of x-ray photons reaching the IR
increased
Grid Conversion Factor (GCF) formula
Grid conversion factor = mAs with grid/mAs without grid
a decrease in the number of transmitted photons that reach the image receptor because of some misalignment of the gird
grid cutoff
types of grid cutoff
upside-down focused grid
off-level grid
off-center grid
off-focus grid
Occurs when a focused grid is placed upside down on the IR, resulting in the grid lines going opposite the angle of divergence of the x-ray beam
Upside-down focused grid
Occurs when the x-ray beam is angle across the lead
Off-level grid
Occurs when the CR of the x-ray beam is not aligned from side to side with the center of a focused gird
Off-center grid
- Occurs when using an SID outside of the recommended focal range
- Gird cutoff occurs if the SID is less than or greater than the focal range
- Radiographically, both appear the same - that is, as a loss of exposure at the periphery of the image
Off-focus grid
- Is an artifact that can occur when a stationary grid is used during CR imaging
- If the grid frequency is similar to the laser scanning frequency during CR image processing then a zebra pattern can result on the digital image
- A visual perception that occurs when viewing a set of lines or dots that is superimposed on another set of lines or dots, where the sets differ in relative size, angle, or spacing
Moire’ effect (zebra pattern)
- Provides another method for limiting the scatter reaching the IR
- Based on the simple concept that much of the scatter will miss the IR if there is increased distance between the patient and IR (OID)
- The greater the gap, the greater the reduction in scatter reaching the IR
- Contrast is increased, the number of photons reaching the IR is reduced because less scatter reaches the IR, and the mAs must be increased to compensate
Air gap technique
Using an increased OID requires an increase in ___ to decrease unharness and increase spatial resolution
SID
what are some views you could use the air gap technique on?
Lateral c-spine, SI joints, odontoid, ribs
what projections have a significant amount of scatter and benefit from lead being placed behind the patient
lateral lumbar spine, lateral spot
what does placing a lead shield on the x-ray table close to the collimated edge of the area of interest do?
absorbs scatter radiation exiting the patient that could degrade image quality
What is the term for the process of reducing the intensity of the x-ray beam as it passes through tissue?
attenuation
What is the term for the process of converting x-ray energy into visible light?
Luminescence
Which type of x-ray interaction results in a change in direction but no change in energy of the x-ray photon?
Coherent scattering
Which type of x-ray interaction results in no change in direction or energy of the x-ray photon?
Annihilation
What is the term for the phenomenon where a material emits light when exposed to x-rays?
Fluorescence
What type of x-ray interaction is responsible for producing image contrast in radiography?
Photoelectric effect
Increasing kVp ______ the amount of scatter striking the image receptor
increases
As kVp increases, Compton scatter ______
increases
As mAs increases, Compton scatter _______
increases
As tissue thickness increases, Compton scatter_______
increases
As collimation decreases (field size increases), Compton scatter ________
increases
