Ultrasound Image Optimization Settings

Image Optimization

• Image optimization involves adjusting settings to improve image quality
• Settings include output power, frequency, depth, zoom, gain, and focus

Output Power

• Adjusting output power varies sensitivity and detects weaker echoes
• Increasing output power:
  • Increases pulses and echo signals
  • Increases acoustical exposure (ALARA principle)
• Reducing output power:
  • Reduces intensity of pulses and energy transmitted to the patient
  • Reduces brightness of echoes visualized within the displayed image

Frequency

• Increasing frequency:
  • Increases resolution
  • Decreases penetration
• Multifrequency transducers are used for different applications:
  • Transabdominal: 3-5 MHz
  • Transvaginal: 5-20 MHz

Depth

• Depth of field of view varies with transducer type
• Increasing depth:
  • Increases far field and reduces near field
• Decreasing depth:
  • Focuses on superficial structures
  • Increases near field and reduces far field

Zoom

• Read zoom magnifies still image
• Write zoom magnifies live image
• Provides greater anatomical detail

Gain

• Echo signal amplification compensates for attenuation loss
• Increasing gain:
  • Brightens image
  • No change to amount of energy transmitted
  • High gain setting: noise and misdiagnosis
• Decreasing gain:
  • Darkens image
  • No change in energy transmitted
  • Low gain setting: misdiagnosis

Focus

• Focal zone can be single or multiple
• Decreases frame rate
• Artefacts can occur due to equipment malfunction, operator error, violation of assumptions, or physical principle

Artefacts

• Occur due to equipment malfunction, operator error, violation of assumptions, or physical principle
• Types of artefacts include:
  • Reverberation
  • Comet tail
  • Ring down
  • Mirror image
  • Shadowing
  • Enhancement

Reverberation Artefacts

• Produced due to repeated reflections
• Causes false echoes
• Characteristics:
  • Equally spaced echoes
  • Strong echoes due to high acoustic mismatch
  • Can be result of defective equipment or improper technique
  • Examples: biopsy needle, comet tail artefact

Comet Tail Artefact

• Type of reverberation artefact seen in US imaging of metallic objects
• Characteristics:
  • Single long hyperechoic echo
  • Parallel to sound of beams main axis
  • ‘Trails off’ distally
  • Examples: IUDs, surgical clips, needle tips

Ring Down Artefact

• Similar to comet tail artefact
• Typically occurs due to resonance of fluid trapped among gas bubbles after being insonated with ultrasound
• Characteristics:
  • Vibrations produce a continuous sound wave that is transmitted to the transducer

Mirror Image Artefact

• Created as sound reflects off strong reflector and is redirected towards object
• Characteristics:
  • Appears as second copy of object – deeper on image
  • Straight line: true reflector and artefact are equal distances from mirror

Shadowing Artefact

• Occurs when ultrasound beam meets reflector that causes almost total reflections
• Characteristics:
  • Everything posterior to reflector appears black – no energy

Enhancement Artefact

• Lower density mass – little attenuation
• Characteristics:
  • Increased through transmission amplitude of distal echo signal
  • Area of increased brightness relative to echoes from adjacent tissues
  • Examples: cystic/fluid masses