Quality Assurance chapter 22

Quality Assurance in Imaging Systems

  • Routine evaluation of VIS system is conducted to maintain optimal image quality.
  • Devices:
    • Tissue equivalent Phantoms are used to evaluate characteristics such as:
    • Gray scale
    • Tissue texture
    • Multifocus and adjustable focus phased transducers
    • Speed of sound, attenuation, scattering
    • Echogenicity

Performance Measurements

  • Sensitivity: Ability to display low-level echoes in two forms:

    1. Normal Sensitivity: Accurate display of solid masses and cystic structures in test phantoms.
    2. Max Sensitivity: Output power amps of the system set to practical maximum levels, assessed by adjusting echo brightness saturation.

  • Dead Zone: Region near the transducer with inaccurate images due to:

    • Transducer ring time.
    • Higher frequencies correspond to thinner dead zones.

Registration Accuracy

  • Vertical Depth Calibration: Ensures proper positioning of reflections based on depth.
  • Horizontal Calibration: Ensures echoes are placed in the correct horizontal position, affecting distance measurement accuracy.

Focal Zone and Resolutions

  • Focal Zone: Depth of highest intensity where the beam is narrowest.
  • Axial Resolution: Smallest distance where two structures parallel to the sound beam are identified separately.
  • Lateral Resolution: Minimum distance at which two side-by-side pins are displayed distinctly.

System Operation and Display

  • Compensation Operation (Uniformity): Ability to display reflectors with similar brightness.
  • Gray Scale Dynamic Range: Adjusting the power affects gray scale display.
  • Hardcopy Output: Relationship between screen images and outputs to other devices (e.g., remote viewing stations).