Dynamic Ultrasound Localization Microscopy Without ECG-Gating.

Area of Science:

• Biomedical Engineering
• Medical Imaging
• Ultrasound Technology

Background:

• Dynamic Ultrasound Localization Microscopy (DULM) enables non-invasive pulsatility measurements in the rodent brain by tracking microbubbles (MBs).
• Traditional DULM methods require ECG-gating, which limits applications and increases acquisition time.
• There is a need for DULM techniques that do not rely on external synchronization signals.

Purpose of the Study:

• To eliminate the requirement for ECG-gating in Dynamic Ultrasound Localization Microscopy (DULM) experiments.
• To introduce a novel motion-matching method for accurate time registration in DULM.
• To enable DULM on a wider range of datasets without compromising data quality.

Main Methods:

• Developed a motion-matching algorithm utilizing tissue Doppler signals to leverage inherent cyclic brain tissue motion.
• Estimated tissue Doppler for frame groups at locations of local maxima on the skull's surface.
• Time-registered frame groups by aligning their tissue Doppler signals to a reference group, synchronizing with the cardiac cycle.

Main Results:

• The motion-matching method was successfully validated in rat, mice (2D), and feline (3D) models.
• Results from motion-matching time registration were comparable to those obtained using ECG-gating.
• Demonstrated the extraction of dynamic velocity and density cine-loops and estimation of pulsatility index without ECG data.

Conclusions:

• DULM can be performed effectively without external gating, broadening its applicability to any ultrasound localization microscopy dataset with sufficient microbubble detection.
• Motion-matching for time registration significantly advances DULM by simplifying experimental procedures and increasing accessibility.
• This technique enhances the utility of DULM for non-invasive hemodynamic assessments in various animal models.