Scatter Control
Any individual in the radiographic room during an exposure must:
Wear a lead apron
What is “pitting” the anode?
Happens with very high exposures, causing melted spots on the anode.
What does window width adjust?
The radiographic contrast
Ionization chamber systems are what type of device?
Entrance type
What are the primary parts of a cassette-based system?
Cassette, Photostimulable phosphor (PSP) plate, Plate reader, and Computer workstation
What are two characteristics of an unrestricted beam?
1. Cone-shaped
2. Projects a round field onto the patient and IR.
What is “sun-tanning” and what problems can it cause?
As the tube ages, vaporized tungsten from the filament deposits on the inside of the glass and causes a bronze discoloration. This can cause problems with arching and damage.
What is resolution expressed in?
Line pairs per millimeter (Lp/mm)
What is the most critical aspect of using AEC?
Patient centering
What moves the plate through the laser scanning process?
A drive mechanism
The grid conversion factor (GCF) can be expressed mathematically by:
Grid Conversion Factor (GCF) = mAs with grid/mAs without grid
What are factors that can shorten x-ray tube life and are within the radiographers control?
1. Frequent use of high or maximum exposure factors.
2. Use of lower, but very long exposure factors.
3. Overloading the filament.
What is the smallest component in the matrix and has a recorded value as a single numeric value?
Pixel
Which type of cast would require an increase in exposure factors?
Plaster casts
What is a histogram?
A graphic representation of the data set
What is the moiré effect?
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.
What are heat units and how are they calculated?
A measure of the amount of heat stored in a particular device. They are calculated by: kVp x mA x s x c
The number of different shades of gray that can be stored and displayed by a computer system is?
Grayscale
What is the minimum response time with modern AEC systems?
1ms
How many of the electrons are trapped in the conduction band as the latent image?
50%
The air-gap technique is based on:
Compensating for loss of recorded detail from an increase in OID, with increasing SID.
What is the anode heel effect?
The anode heel effect is simply caused by photons produced on the anode side, which must penetrate the heel of the target before exiting the tube. This causes some photons to be weakened and some to be absorbed. The net effect is a reduced intensity of the beam on the anode side.
What is the number of bits that determine the gray level that can be assigned to a pixel?
Bit depth
What happens in ionization chambers?
When exposed to radiation, the air in the chambers become ionized, creating an electrical charge.
The primary factor influencing contrast with digital radiography is?
The lookup table (LUT)