What is the typical cross-sectional beam dimension at a distance of 10 cm from the ultrasound (ultrasound) transducer?

Ultrasound Beam Dimensions at 10 cm from Transducer

At a distance of 10 cm from an ultrasound transducer, the beam typically diverges at an angle of 8-10° beyond the Fresnel zone, with the cross-sectional dimension determined by the formula sine = 0.6λ/r, where λ is wavelength and r is beam radius. 1

Beam Characteristics and Dimensions

The ultrasound beam's cross-sectional dimensions at 10 cm from the transducer depend on several factors:

• In the Fraunhofer zone (far zone), which occurs beyond the Fresnel zone, the ultrasound beam begins to diverge at an angle commonly between 8-10° 1
• The divergence of the ultrasound beam beyond the Fresnel zone can be described mathematically by the formula: sine = 0.6λ/r, where λ is the wavelength and r is the beam radius 1
• The beam profile at 10 cm depends on whether the transducer is planar or focused 1

Factors Affecting Beam Dimensions

Several key factors determine the actual cross-sectional dimensions at 10 cm:

• Transducer frequency: Higher frequencies produce narrower beams with better resolution but experience greater attenuation 2
• Transducer diameter: Larger diameter transducers produce more directional beams with less divergence 2, 3
• Transducer type: Focused transducers concentrate the beam energy differently than planar transducers 1
  • Focused transducers draw the focal zone inward compared to planar transducers of the same diameter 1
  • Within the focal zone of a focused transducer, acoustic intensity may increase by factors greater than 100 compared to outside the focal zone 1

Beam Zones and Their Characteristics

The ultrasound beam has distinct zones that affect its dimensions:

• Fresnel zone (near zone): Characterized by variable sonication pressure with unpredictable output pressure in cross-sectional planes 1
• Fraunhofer zone (far zone): The region beyond the Fresnel zone where ultrasound pressure stabilizes and the wavefront appears planar 1
• At 10 cm, depending on the transducer specifications, the beam may be in either the Fresnel or Fraunhofer zone, affecting its cross-sectional dimensions 1

Clinical Implications

Understanding beam dimensions at specific distances has important clinical implications:

• For ocular applications, focused transducers are often preferred as they minimize pressure experienced by non-target tissues, improving safety when the beam passes through delicate tissues such as the lens or cornea 1
• The focal length (distance of maximal acoustic intensity from the transducer surface) and focal area (cross-sectional area of the focal zone) are critical parameters for medical applications 1
• Proper understanding of beam dimensions helps prevent tissue damage in ultrasound-mediated drug delivery and other therapeutic applications 1

Practical Considerations

When working with ultrasound at specific distances:

• Empirical measurement of pressure output at the applied location using a hydrophone is more practical and reliable than theoretical modeling 1
• For optimal imaging and therapeutic applications, the highest frequency that permits adequate penetration depth should be selected 2
• The beam dimensions at 10 cm should be considered when positioning the transducer to ensure proper targeting of the intended tissue 1, 3