Cyclic changes in blood echogenicity under pulsatile flow are frequency dependent

Area of Science:

• Biomedical Ultrasound
• Hemodynamics
• Biophysics

Background:

• Previous studies show conflicting results regarding blood echogenicity variations under pulsatile flow at physiological rates.
• Discrepancies may stem from the use of different ultrasound frequencies in prior in vitro and in vivo research.
• Understanding these variations is crucial for interpreting ultrasound signals in blood flow analysis.

Purpose of the Study:

• To investigate the effect of ultrasound frequency on the detection of cyclic blood echogenicity variations.
• To determine if physiological stroke rates (20-70 BPM) exhibit measurable echogenicity changes.
• To compare the sensitivity of different ultrasound frequencies in characterizing red blood cell (RBC) aggregation.

Main Methods:

• Porcine blood samples (normal and with dextran-induced hyperaggregating RBCs) were analyzed in a pulsatile Couette flow apparatus.
• Cyclic shear rate changes simulating stroke rates from 20 to 70 BPM were applied.
• Echogenicity was measured using single-element transducers at 10 MHz and 35 MHz, with spectral analysis confirming cyclic variations.

Main Results:

• Cyclic variations in backscatter were observed at 35 MHz across all tested stroke rates (20-70 BPM).
• At 10 MHz, these variations were only detected at 20 BPM.
• The magnitude of cyclic variations was generally higher at 35 MHz, indicating increased sensitivity to RBC aggregation changes.

Conclusions:

• Cyclic variations in RBC aggregation occur at physiological stroke rates, observable with higher ultrasound frequencies (35 MHz).
• The 35 MHz frequency offers enhanced sensitivity for characterizing RBC aggregation dynamics compared to 10 MHz.
• Findings align with in vivo observations using high-frequency intravascular ultrasound, supporting the clinical relevance of these echogenicity changes.