ct qa

Recognise the importance of quality assurance in CT to ensure accurate and reliable results.
Define the parameters that affect CT image quality, including:
  - Spatial resolution
  - Contrast resolution
  - Temporal resolution
  - Noise
Describe the purpose and objectives of a CT quality assurance program.
Identify the different types of phantoms used in CT quality assurance and explain their roles in testing image quality and dose.
Understand methods for measuring patient dose in CT and the importance of dose optimisation strategies.
Understand the principles of radiation safety in CT along with regulatory guidelines and standards associated with CT imaging.

Importance of Noise:
- Noise is identified as a significant adversary in CT imaging.
Quantum Mottle:
  - Causes a grainy, mottled appearance in images due to variations in Hounsfield units.
  - Results from an insufficient amount of signal during data acquisition.
  - Insufficient photons hitting detectors contribute to increased noise.
  - More true signal leads to reduced noise.
Signal to Noise Ratio (SNR):
- Higher SNR results in improved image quality.

Decreasing noise requires the following:
- Increased photons absorbed per voxel, which correlates with increased dose.
- This leads to a higher SNR and subsequently, better image quality.

High-Contrast Resolution:
- Ability to differentiate between two objects of different densities that are close to each other.
Low-Contrast Resolution:
- Ability to differentiate between two objects of similar densities.

Defined as the duration required for the acquisition of a single frame in a dynamic process.
Example in Cardiac CT:
- A temporal resolution of 250 ms implies that a single image is obtained over 250 ms of the cardiac cycle, obtaining 4 images at a heart rate of 60 bpm.

Field of View (FOV):
- Increasing FOV results in larger pixel size, which decreases spatial resolution.
Pixel Size:
- Smaller pixel size correlates with increased spatial resolution.
Focal Spot Size:
- Larger focal spot size leads to decreased spatial resolution.
Magnification:
- Increase in focal spot size results in decreased spatial resolution.
Motion Artifacts:
- Movement during imaging results in decreased spatial resolution.
Pitch:
- Increasing pitch leads to decreased spatial resolution.
Kernel:
- Use of sharp or edge-enhancing kernels increases spatial resolution.
Slice Thickness:
- Smaller slice thickness results in increased spatial resolution.
Detector Elements:
- Smaller detector elements yield higher resolution and reduced partial volume effect despite introducing more noise.

Noise:
- Increased noise results in a decrease in contrast differentiation.
Tube Current (mA):
- Lower tube current corresponds to increased noise.
Inherent Tissue Properties:
- The difference in linear attenuation coefficients of adjacent objects influences contrast.
Beam Strength (kV):
- Higher beam energy may lead to decreased contrast resolution beyond a specific threshold.
Kernel:
- Use of soft tissue kernels increases contrast resolution.
Contrast Media:
- Administration of contrast enhances contrast resolution.

Complicated Relationship:
- Protocol development must consider the clinical question.
- Image reconstruction algorithms and parameter adjustments during multiplanar reconstruction must strike a balance between spatial and contrast resolution.