Photoacoustic speckle tracking for motion estimation and flow analysis

Area of Science:

• Biomedical Optics
• Medical Imaging
• Fluid Dynamics

Background:

• Ultrasound (US) speckle tracking faces limitations in signal-to-noise ratio (SNR) and contrast for submicrometer particles.
• Current photoacoustic (PA) flow imaging methods have limitations such as directional dependence and restricted fields of view.
• Accurate velocimetry is crucial for diagnosing conditions like ventricular shunt malfunction.

Purpose of the Study:

• To introduce and validate a novel photoacoustic (PA) speckle tracking method for flow characterization.
• To overcome the limitations of existing ultrasound (US) and PA flow imaging techniques.
• To demonstrate the feasibility of PA speckle tracking for medical applications, such as diagnosing shunt malfunction.

Main Methods:

• Developed a PA-based speckle tracking algorithm utilizing block matching of PA and US signals.
• Estimated the velocity of optically absorbing particles within a shunt catheter under various flow rates.
• Compared the performance of PA speckle tracking against US speckle tracking in challenging low-contrast conditions.

Main Results:

• The PA speckle tracking method demonstrated feasibility in characterizing flow, particularly where US imaging struggled due to low SNR and contrast.
• Accurate velocimetry was achieved for optically absorbing particles, indicating the method's potential for submicrometer particle tracking.
• The technique successfully estimated particle velocities across a range of flow rates in a simulated shunt environment.

Conclusions:

• Photoacoustic speckle tracking presents a viable and potentially more accurate alternative to US speckle tracking for flow characterization.
• This method overcomes key limitations of Doppler imaging and current PA correlation-based techniques.
• PA speckle tracking shows significant promise for minimally invasive diagnostic applications, especially in scenarios with poor US imaging quality.