Shear rate estimation using a clinical ultrasound scanner

Area of Science:

• Cardiovascular Science
• Medical Imaging
• Biomedical Engineering

Background:

• Wall shear stress is implicated in atherogenesis and thrombus formation.
• Direct measurement of wall shear stress using ultrasonography is challenging.
• Shear rates offer an alternative metric for assessing blood flow dynamics.

Purpose of the Study:

• To evaluate the feasibility of estimating shear rates using clinical ultrasound.
• To compare shear rates in normal versus stenotic vessels both in vitro and in vivo.
• To investigate the relationship between shear rates and vessel stenosis.

Main Methods:

• Utilized a clinical ultrasound scanner (P700) with color M-mode imaging to obtain velocity profiles.
• Calculated maximum shear rates offline as maximum velocity gradients.
• Conducted in vitro studies using a flow phantom with a 50% stenosis model.
• Performed in vivo studies on the internal carotid artery of volunteers and patients with stenoses.

Main Results:

• In vitro: Shear rates within the stenosis were significantly higher (P < 0.00001) and more variable than outside.
• In vivo: Mean shear rate in normal internal carotid arteries was 414 s⁻¹ ± 154.5 s⁻¹.
• In vivo: Mean shear rate in stenotic internal carotid arteries was significantly higher at 687 s⁻¹ ± 263.5 s⁻¹ (P = 0.00017).

Conclusions:

• Clinical ultrasound, specifically color M-mode imaging, can effectively estimate shear rates.
• Estimated shear rates are significantly elevated in stenotic vessels compared to normal vessels, both in vitro and in vivo.
• Shear rate estimation via ultrasound provides a valuable, non-invasive method for assessing hemodynamic changes in vascular diseases.