Image Quality

Question 1

Contrast

Answer 1

Difference in signals between structures

Question 2

Factors that affect contrast

Answer 2

Tissue (thickness, density, composition/atomic number - inherent)
Beam quality (filtration)
Image (detector properties, image processing, viewing monitor)

Question 3

Spatial resolution

Answer 3

Ability to distinguish objects that are close together in space

Question 4

Factors that affect spatial resolution

Answer 4

Patient motion
Detector (size, light scatter in a phosphor layer)
Monitor (pixels)

Question 5

Noise

Answer 5

Unwanted information that degrades image quality.
Due to fluctuations or inconsistencies of photons read by the detector.
Optimised image can still have noise.

Question 6

Higher tube current (mA) results in (higher/lower) patient dose and (higher/lower) image quality due to (higher/lower) SNR

Answer 6

Higher mA = higher dose, higher image quality, higher SNR

Question 7

How does peak tube voltage (kVp) affect the image quality?

Answer 7

Higher kVp = higher electron stream energy = higher beam quality by affecting contrast

Question 8

How might the space charge effect influence image quality?

Answer 8

The space charge effect is a phenomenon where electrons accumulate in the cathode to form a cloud of negative charge, which means that this cloud of electrons can repel and prevent the electrons released by the cathode - lower image quality through less penetration.
Solved by applying high enough kVp to release these electrons.

Question 9

Anode

Answer 9

Positive electrode in the radiology context

Question 10

Line focus principle

Answer 10

In order to optimise image quality (having a small focal spot while having an area large enough for heat dissipation), the target face is slanted to achieve the above. Spatial resolution is maintained while allowing heat to dissipate (equipment durability).
Consider heel effect as a result - X ray intensity varies across the beam ie poorer field coverage.

Question 11

3 types of image acquisition

Answer 11

1. Film/screen - now replaced by digital imaging
2. Computed radiography - uses phosphor imaging plates to create a digital image of x-rays (becoming obsolete)
3. Direct digital radiography

Question 12

Name the materials involved in direct and indirect conversions in direct digital radiography (DDR)

Answer 12

Indirect conversion - scintillation phosphor and silicon with thin film transistors

Direct conversion - amorphous selenium and thin film transistors

Question 13

How does the indirect conversion in direct digital radiography (DDR) work?

Answer 13

X-rays interact with phosphor, which releases photoelectrons to cause a series of charged particle interactions. The electrons drop to ground state which causes fluorescence, and the resulting light is absorbed in the thin film transistors to be converted into electrical signals

Question 14

Which of direct or indirect conversion in DDR have better resolution?

Answer 14

Direct conversion, due to the resolution only being limited by dexel size as opposed to the resolution in indirect conversion being affected by the conversion process.