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Radiography Principles and Circuitry
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1
Question
What is the difference between the actual and effective focal spot in an x-ray tube?
Answer
Actual is on the anode, effective is measured beneath it.
2
Question
What causes off-focus radiation in x-ray production?
Answer
Rebounding electrons produce off-focus x-ray photons.
3
Question
How is tube loading quantified?
Answer
Tube heat units = mAs × kVp × generator factor.
4
Question
What is Ohm’s law?
Answer
V = IR, relating voltage, current, and resistance.
5
Question
How do series circuits distribute current and voltage?
Answer
Same current flows; voltages sum; resistances add.
6
Question
How do parallel circuits behave?
Answer
Current divides; voltage across components is equal.
7
Question
What is the purpose of the primary circuit in x-ray equipment?
Answer
To supply AC power to the step-up transformer.
8
Question
What role does the autotransformer play in x-ray circuits?
Answer
It adjusts incoming line voltage through self-induction.
9
Question
How does the step-up transformer function?
Answer
It increases voltage via mutual induction.
10
Question
What is the main function of the rectifiers in the secondary circuit?
Answer
Convert AC to DC for the tube.
11
Question
What does the filament circuit regulate?
Answer
Electron emission by controlling filament current.
12
Question
How does mA influence x-ray production?
Answer
Higher mA increases electron flow and x-ray intensity.
13
Question
Describe the effect of increasing exposure time?
Answer
Increases total mAs, producing more x-rays.
14
Question
What is the significance of kVp in x-ray imaging?
Answer
It accelerates electrons, influencing energy and quality of the x-ray beam.
15
Question
How does the 15% rule relate kVp and mAs?
Answer
+15% kVp halves mAs; -15% kVp doubles mAs.
16
Question
What is the inverse square law in radiography?
Answer
Intensity ∝ 1/distance², affecting exposure and dose.
17
Question
What is the purpose of automatic exposure control (AEC)?
Answer
To maintain consistent ir exposure by adjusting exposure time.
18
Question
What is the effect of increasing source-to-image distance (SID)?
Answer
Decreases intensity, ir exposure, and patient dose.
19
Question
How do grids improve image quality?
Answer
Absorb scatter, increase contrast, but raise patient dose.
20
Question
What causes grid cut-off artifacts?
Answer
Misalignment, improper SID, or upside-down placement.
21
Question
What is the law of reciprocity in radiography?
Answer
mA × s = mAs; exposure depends on product of current and time.
22
Question
How does the linear square law affect exposure when changing SID?
Answer
Maintain exposure by adjusting mAs proportionally to SID².
23
Question
What is the primary principle of computed radiography (CR)?
Answer
Stores latent image in a photostimulable phosphor within a cassette.
24
Question
How is a latent image captured in CR?
Answer
X-ray energy excites phosphor particles, storing energy.
25
Question
What component converts the stored energy in CR to a visible image?
Answer
The photomultiplier tube or CCD in the cassette reader.
26
Question
What does the histogram in digital radiography represent?
Answer
Distribution of pixel signal intensities in the image.
27
Question
Why is proper collimation important in digital imaging?
Answer
To reduce scatter, improve contrast, and avoid histogram errors.
28
Question
What is quantum mottle and how can it be minimized?
Answer
Noise from low IR exposure; increase mAs or kVp.
29
Question
How does the LUT modify the digital image?
Answer
Adjusts brightness and contrast during post-processing.
30
Question
What effect does increasing grid ratio have on image contrast?
Answer
It increases contrast by reducing scatter.