Effect of Clutter Filter in High-Frame-Rate Ultrasonic Backscatter Coefficient Analysis

Area of Science:

• Biomedical Ultrasound
• Hemodynamics
• Medical Imaging

Background:

• High-frame-rate ultrasound with clutter filtering visualizes blood flow and distinguishes it from tissue signals.
• Previous in vitro studies suggested red blood cell (RBC) aggregation evaluation via backscatter coefficient (BSC) frequency dependence.
• In vivo applications necessitate clutter filtering for visualizing RBC echoes.

Purpose of the Study:

• To evaluate the impact of clutter filtering on ultrasonic BSC analysis for characterizing hemorheology.
• To assess the feasibility of in vitro and preliminary in vivo data analysis using clutter filtering.
• To investigate RBC aggregation by analyzing frequency-dependent BSC.

Main Methods:

• Coherently compounded plane wave imaging at 2 kHz frame rate.
• Singular value decomposition for clutter signal suppression in flow phantoms.
• Reference phantom method for BSC calculation (4-12 MHz), parametrized by spectral slope and mid-band fit (MBF).
• Block matching for velocity distribution and shear rate estimation.

Main Results:

• Saline samples showed a constant spectral slope around four (Rayleigh scattering), indicating no RBC aggregation.
• Plasma samples exhibited a lower spectral slope at low shear rates, increasing with shear rate as aggregations dispersed.
• Plasma sample MBF decreased from -36 to -49 dB with increasing shear rates (10-100 s⁻¹).
• Saline sample's BSC variations mirrored in vivo results from healthy human jugular veins.

Conclusions:

• Clutter filtering is effective for ultrasonic BSC analysis in hemorheology studies.
• Frequency-dependent BSC analysis, particularly spectral slope and MBF, can characterize RBC aggregation and dispersion.
• The method shows promise for in vivo hemorheological assessment in vessels like the jugular vein.