High-frequency harmonic imaging of the eye

Area of Science:

• Ophthalmology
• Biomedical Ultrasound
• Medical Imaging

Background:

• Harmonic imaging is established for ultrasound below 10 MHz.
• Ophthalmology utilizes fundamental frequencies from 20 MHz to 50 MHz.
• Generating harmonics in this high-frequency range for ophthalmic applications is unexplored.

Purpose of the Study:

• To investigate harmonic generation in the 20-50 MHz range.
• To create harmonic ultrasound images of the eye.
• To assess the feasibility and potential of high-frequency harmonic imaging in ophthalmology.

Main Methods:

• Harmonic presence was measured in water and vitreous using pulse/echo and hydrophone techniques.
• Measurements were taken at varying intensities and frequencies, including focal, near-, and far-field zones.
• Analog filtering and digital post-processing were used to generate harmonic images of rabbit eyes.

Main Results:

• Harmonics were generated similarly in water and vitreous.
• Maximum second harmonic levels were -5 dB (hydrophone) and -15 dB (pulse/echo) relative to the fundamental.
• Harmonics were detected in the far-field but not the near-field.
• Generated harmonic images of the anterior eye segment demonstrated enhanced resolution.

Conclusions:

• Harmonics are readily generated at high frequencies (20-50 MHz) within FDA-compliant power levels.
• High-frequency harmonic imaging offers potential for improved resolution in ophthalmic ultrasound.
• This technique may significantly enhance the diagnosis of retinal diseases, particularly in the macular region.