Pulse inversion ultrasound modulated optical tomography.

Area of Science:

• Biomedical Optics
• Acoustic Imaging
• Optical Tomography

Background:

• Pulse inversion acoustic imaging enables second harmonic imaging with short pulses, offering high axial resolution.
• This technique minimizes spectral overlap between fundamental and harmonic frequencies.
• Ultrasound modulated optical tomography (UMOT) is an emerging imaging modality.

Purpose of the Study:

• To demonstrate pulse inversion UMOT using an optical speckle-based detection method.
• To achieve enhanced second harmonic signal generation for improved imaging.
• To evaluate the imaging performance in optically scattering media.

Main Methods:

• Utilized pulse inversion acoustic pulses (inverted and non-inverted) with synchronized strobed illumination.
• Employed an optical speckle-based detection method with a camera.
• Acquired data by summing multiple pulses and repeating the process with a phase shift of π/2 for ultrasound.
• Combined camera frames to isolate the second harmonic signal.

Main Results:

• Successfully obtained a second harmonic signal using the pulse inversion UMOT technique.
• Observed a significant reduction in linewidth, indicating improved resolution.
• Achieved linewidths of 9.26 mm (DC), 4.02 mm (fundamental), and 2.43 mm (second harmonic).
• Demonstrated imaging of optically absorbing objects embedded within a scattering medium (thickness 16 mm, scattering coefficient 2.3 mm⁻¹, anisotropy factor 0.938).

Conclusions:

• Pulse inversion UMOT effectively generates second harmonic signals.
• The method provides superior axial resolution compared to fundamental imaging.
• This technique shows promise for high-resolution imaging in scattering biological tissues.