Beam Restriction
What are 2 types of ancillary devices used to limit the beam?
Lead blockers
Lead masking
What factors affect shape distortion?
Tube angle
IR angle
Part Angle
An insufficient amount of mAs will produce and image with what artifact?
Quantum noise/mottle Underexposed
Decreasing focal spot size will do what to spatial resolution?
improve or increase spatial resolution
A radiographic exposure is taken on a high frequency unit. In order to maintain exposure using a single-phase full wave unit would require what technique changes?
double the mAs
A grid should be used if the body part measures more than:
10 cm
What are the 4 different types of beam restrictors?
1. Collimators
2. Cones and cylinders
3. Aperture diaphragm
4. Ancillary device
Tube angle will produce what type of shape distortion?
Elongation
What imaging error occurs when the imaging plate or flat panel detector is grossly over penetrated?
Saturation
The measure of the amount of detail in a digital image defines:
Spatial resolution
What is the voltage ripple for a single-phase system?
100%
What grid error is produced when a focused grid not placed right side up?
Upside down
What is the most common beam restricting device and what impact does it have on contrast and patient dose?
Collimators
Reduces patient dose
Increases contrast
In order to reduce size distortion what should be done to SID?
Increase SID to minimize magnification.
What is blurring at the periphery called and what is another name for it?
Penumbra
aka geometric blur
Geometric factors will reduce or increase penumbra/ geometric blur
reduce= long SID, Short OID, small focal spot size
What factor determines the filament size and essentially the focal spot size?
mA
How many diodes are used in a single-phase full wave rectified unit?
4 diodes
What grid error is produced when the grid is not perpendicular to the central ray?
Off-Level
What are the 3 main reasons for restricting the x-ray beam?
Decrease patient dose
Decrease occupational dose
Increase image quality
What combination of SID and OID will produce an image with the largest magnification?
Low/short SID and high/long OID
What are the geometric factors that influence spatial resolution?
Focal Spot Size
SID
OID
What technical factor controls the temperature of the cathode filament in the x-ray tube?
mA
The current produced in a high- frequency generator is accomplished by high-speed switches called:
Inverter Circuits
The ability of a grid to absorb scattered radiation after it exits the patient, is termed the:
Contrast improvement factor
What relationship do collimation and contrast have?
Direct
Increase collimation= decreasing field size= reduces scatter= increases contrast
What are the patient factors that influence spatial resolution?
Patient size
Patient movement
Describe the difference between image contrast and subject contrast:
Image contrast is the differences in grey on the display
and subject contrast is the differential absorption from the patient.
What are the ideal combination of settings for SID, OID and Focal spot size that will produce an image with the greatest spatial resolution?
Long SID
Short OID
Small focal spot
3-phase units consist of waveforms separated by how many degrees?
120 degrees
What grid error is produced when the grid is not placed directly under the central ray?
Off-Center