Multi-Wavelength Photoacoustic Visualization of High Intensity Focused Ultrasound Lesions

Area of Science:

• Biomedical Engineering
• Medical Imaging
• Acoustic Physics

Background:

• High-intensity focused ultrasound (HIFU) therapies require advanced image guidance for precise lesion targeting.
• Current imaging methods struggle to accurately delineate HIFU-induced thermal lesions.
• Previous single-wavelength photoacoustic (PA) imaging showed contrast but lacked sufficient lesion extent assessment.

Purpose of the Study:

• To demonstrate the feasibility of characterizing in vitro HIFU ablation lesion dimensions using 3D multi-wavelength PA imaging.
• To assess the capability of multi-wavelength PA imaging in differentiating ablated from native tissues.
• To compare PA imaging-based lesion assessment with stained gross pathology.

Main Methods:

• Porcine cardiac and liver tissues were ablated using a 2.5 MHz small-animal HIFU system.
• 2D and 3D multi-wavelength photoacoustic-ultrasonic (PAUS) scans were performed in the near-infrared (NIR) range.
• Ablated tissue spectra were analyzed, and PAUS findings were compared to stained gross pathology.

Main Results:

• Multi-wavelength PA imaging revealed spectral changes in ablated tissue, lacking the deoxy-hemoglobin peak near 760 nm.
• 2D tissue characterization map (TCM) images, reconstructed from 3D TCM volumes, accurately characterized lesion area.
• PAUS imaging showed >70% area agreement with stained gross pathology for lesion extent.
• PA signal exhibited temperature-dependent spectral changes during controlled heating experiments.

Conclusions:

• 3D multi-wavelength PA imaging is feasible for accurate characterization of HIFU ablation lesion dimensions.
• This technique offers improved assessment of lesion margins and extent compared to single-wavelength methods.
• Multi-wavelength PA imaging holds potential for enhanced image guidance in clinical HIFU treatments.