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Uniform Depth Channel Flow

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Uniform depth channel flow keeps fluid depth consistent along channels such as irrigation canals. In natural channels, such as rivers, approximate uniform flow is often assumed. This condition occurs when the channel’s bottom slope matches the energy slope, balancing potential energy lost from gravity with head loss due to shear stress. This balance prevents depth changes along the channel length, resulting in a steady, uniform flow.Uniform flow in open channels with a constant cross-section...
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Related Experiment Video

Updated: Jul 17, 2025

Blood Flow Imaging with Ultrafast Doppler
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Highly accelerated free-breathing real-time 2D flow imaging using compressed sensing and shared velocity encoding.

Fei Xiong1,2, Tilman Emrich2,3,4, U Joseph Schoepf5

  • 1Siemens Medical Solutions USA Inc, Cardiovascular MR R&D, Chicago, IL, USA.

European Radiology
|September 2, 2023
PubMed
Summary

Compressed sensing real-time (CS RT) phase-contrast MRI accurately measures blood flow beat-to-beat without breath-holding. This technique is feasible for patients with arrhythmias or poor respiratory control, showing excellent agreement with conventional methods.

Keywords:
ArrhythmiasCardiacHumansMagnetic resonance imagingPhantoms

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Area of Science:

  • Cardiovascular MRI
  • Flow Quantification
  • Medical Imaging

Background:

  • Conventional phase-contrast (PC) MRI faces challenges with irregular heartbeats and respiratory motion.
  • Real-time (RT) PC MRI offers a promising alternative for accurate flow measurements.
  • Accelerated techniques are needed to improve the temporal resolution of RT-PC MRI.

Purpose of the Study:

  • To evaluate a prototype compressed sensing (CS)-accelerated 2D RT-PC MRI technique.
  • To assess the accuracy of shared velocity encoding (SVE) for beat-to-beat flow measurements.
  • To compare the performance of CS RT-PC MRI against conventional and fully sampled PC sequences.

Main Methods:

  • Implementation of a CS RT-PC technique using a single-shot fast gradient echo with SVE.
  • Acquisition with high temporal resolution (51-56.5 ms) over 1-5 heartbeats.
  • Studies conducted in an aortic dissection phantom (n=8) and healthy volunteers (n=7) on a 3T MRI system.
  • Comparison using peak velocity, peak flow rate, net flow rate, and maximum velocity calculations.
  • Statistical analysis included linear regression, intraclass correlation (ICC), and Bland-Altman analysis.

Main Results:

  • Excellent correlation (R² ≥ 0.93) and agreement (ICC ≥ 0.97) in phantom studies.
  • Good correlation (R² ≥ 0.80) and agreement (ICC ≥ 0.90) in healthy volunteers.
  • Slight underestimation (~12%) of maximum velocities and flow rates observed with CS RT-PC MRI in volunteers.

Conclusions:

  • The highly accelerated CS RT-PC MRI technique with SVE is feasible for beat-to-beat flow evaluation without breath-holding.
  • The prototype CS RT-PC technique provides reliable flow measurements comparable to conventional PC MRI.
  • This free-breathing technique offers improved temporal resolution and image quality, beneficial for patients with arrhythmias.