Ultrasound Probe Selection for Deep Structure Visualization
For visualizing deep structures in ultrasound, a lower frequency probe (2.0-5.0 MHz) should be used, as lower frequencies provide better depth penetration despite reduced resolution. 1
Physics of Ultrasound Penetration
The selection of ultrasound probe frequency involves a fundamental trade-off between resolution and penetration:
Lower frequency probes (2.0-5.0 MHz):
- Provide greater depth penetration
- Ideal for deep abdominal structures, large patients
- Can achieve depth of field up to 25 cm 1
- Sacrifice some resolution quality
Higher frequency probes (7.5-20 MHz):
- Offer superior spatial resolution
- Limited depth penetration
- Better for superficial structures (tendons, ligaments, small joints) 1
- Not suitable for deep structure visualization
Specific Probe Recommendations
For deep structure visualization:
- Curvilinear abdominal probe: 2.0-5.0 MHz with a mean of 3.5 MHz for adults 1
- Phased array cardiac probe: Similar frequency range (2.0-5.0 MHz)
- For extremely large patients: Use the lower end of the frequency range (2.0-3.0 MHz)
- For average-sized adults: 3.5 MHz is typically optimal 1
Technical Considerations
When imaging deep structures:
- Depth settings: Set depth of field up to 25 cm as needed 1
- Focus adjustments: Position focus at the level of the structure of interest
- Gain settings: May need to increase overall gain to compensate for attenuation
- Patient positioning: Consider positioning that brings the target structure closer to the surface when possible
Scientific Rationale
The physics of ultrasound dictate this relationship between frequency and penetration:
- Sound wave attenuation in tissue is directly related to frequency 2
- Higher frequencies experience greater attenuation, resulting in weaker return signals from deep structures 2
- The optimal frequency selection represents a compromise between resolution and adequate range 2
Common Applications for Deep Structure Imaging
- Abdominal organs: Liver, pancreas, kidneys, aorta
- Pelvic structures: Bladder, uterus, ovaries
- Cardiac imaging: Heart chambers, valves
- Deep vascular structures: Abdominal aorta, iliac vessels
Pitfalls to Avoid
- Using high-frequency probes for deep structures: Will result in poor penetration and inadequate visualization
- Excessive depth settings: Can reduce frame rate and overall image quality
- Inadequate acoustic coupling: Ensure proper gel application for optimal sound transmission
- Overlooking patient factors: Obesity may require even lower frequencies (2.0-3.0 MHz)
While higher frequency probes (7.5-20 MHz) provide superior resolution for superficial structures 1, 3, they cannot adequately penetrate to visualize deep structures. The optimal approach is to select the highest frequency that still allows adequate penetration to the depth required for your examination 2.