MRI phase contrast velocity and flow errors in turbulent stenotic jets

Area of Science:

• Cardiovascular Imaging
• Medical Physics
• Hemodynamics

Background:

• Doppler echocardiography is standard for assessing valvular heart disease.
• MRI phase contrast (PC) offers a non-invasive alternative for blood flow quantification.
• Accurate measurement of high-velocity turbulent jets in stenotic valvular disease remains a challenge.

Purpose of the Study:

• To evaluate the accuracy of MRI phase contrast (PC) for measuring stroke volume (SV) in patients with aortic stenosis (AS).
• To compare PC-derived SV with ventricular SV in vivo.
• To investigate the impact of flow characteristics and sequence parameters on PC accuracy.

Main Methods:

• In vivo comparison of PC aortic SV with ventricular SV in 31 patients with moderate to severe AS.
• In vitro experiments using pipe models to simulate stenotic and non-stenotic turbulent flows.
• Analysis of errors in relation to Doppler peak velocities, echo times (TE), and signal loss.

Main Results:

• Significant underestimation of in vivo SV by PC in the left-ventricular outflow tract (-24%) and aortic root (-41%).
• Errors were greatest in patients with higher peak velocities.
• In vitro stenotic flow measurements showed substantial errors, which decreased with shorter echo times (TEs).
• Signal loss in flow-compensated magnitude images correlated with flow errors in both in vivo and in vitro stenotic jets.

Conclusions:

• Signal loss is a key factor contributing to inaccurate flow quantification in stenotic jets using MRI phase contrast.
• Current clinical PC pulse sequences with echo times (TE) exceeding 2 msec may not accurately quantify blood flow in severe aortic stenosis.
• Further optimization of PC sequences is needed for reliable assessment of high-velocity stenotic lesions.