Ultrasound: Probe orientation

Transducers

• Increasing frequency improves resolution but decreases penetration
  • Low-frequency transducers: deep structures
  • High-frequency transducers: superficial structures

Transducer types

• Curvilinear: large “footprint”, best resolution centralized
• Use for abdominal, FAST exam
• Phased array: all waves originate from a single point. used to view deep structures.
  • Use for smaller spaces (between ribs, to look at lungs, heart, etc.)
  • Use if available for Cardiac
• Linear: no array of waves, waves are spread out evenly. used to view superficial structures
  • Use for soft tissue, vascular access, musculoskeletal, lungs

Frequency

• Each transducer has a range of frequencies. You can select higher or lower frequency for each probe

on the ultrasound machine.

• RES = Resolution = Highest end of the probe’s frequency range
  • Better Picture, lower penetration
• PEN = Penetration = Lowest end of the probe’s frequency range
  • Higher penetration, worse picture
• GEN = General = Middle of the probe’s frequency range

Transducer indicator and orientation

• Sagittal: indicator to patient’s head. Probe placed vertically along body to create a sagittal view with probe marker pointing to patient's head
  
• Transverse: indicator to patient’s right. Probe placed across body right to left to create an axial view with probe marker pointing to patient's right
  
• Coronal: indicator to patient’s head, but probe on lateral side of body. Top of screen is lateral, bottom is medial
  

Artifacts

Images on ultrasound that ARE NOT REAL.

• High-attenuation: Objects decrease the sound wave
  • A shadow results behind a high-attenuating object.This makes the objects behind less visible
• Low-attenuation: sound passes through object very easily.
  • Low-attenuating tissue causes everything behind it to appear HYPERechoic or more visible
    
• Mirror image: sound bounces off diaphragm, returning to trasnducer with a longer time of flight. Machine interprets this as more liver tissue across the diaphragm. A mirror image of the liver or spleen across the diaphragm is normal

See Also

• Ultrasound (main)