Photoacoustic Imaging for Monitoring Calcium Dynamics in the Heart.

Area of Science:

• Biomedical Imaging
• Physiology
• Biophysics

Background:

• Photoacoustic imaging (PAI) is a hybrid modality combining optical absorption and ultrasound detection.
• PAI offers deeper tissue visualization than fluorescence imaging but has not been practically applied for cardiac calcium dynamics.
• Conventional optical methods are limited by shallow penetration depth in deep organs like the heart.

Purpose of the Study:

• To implement and demonstrate a novel sectional excitation strategy for photoacoustic imaging of cardiac calcium dynamics.
• To achieve real-time visualization of calcium transients in deep cardiac tissue.
• To explore the potential of PAI for assessing physiological function beyond morphology.

Main Methods:

• Developed a sectional excitation strategy using a thin, sheet-shaped laser beam to confine optical excitation to specific tissue planes.
• Applied this method to photoacoustic imaging of a perfused bullfrog heart.
• Loaded the heart with liposome-encapsulated calcium-sensitive dye.
• Performed simultaneous electrocardiographic recordings to correlate signals with cardiac electrical activity.

Main Results:

• Successfully achieved real-time visualization of calcium dynamics within the atrial cross-section of the bullfrog heart.
• Demonstrated temporal correlation between photoacoustic signal fluctuations and cardiac electrical activity.
• Showcased PAI's capability for deep-tissue calcium imaging.

Conclusions:

• The sectional excitation PAI method enables less-invasive assessment of deep-tissue calcium transients.
• This approach broadens PAI applications from morphology to physiological function, particularly in cardiac imaging.
• PAI is a powerful tool for calcium imaging in physiological and pharmacological studies of deep-tissue organs.