Phase Contrast: Flow Quantification

Imaging Sequence Type:

  • Gradient Echo
  • Acquisition occurs over several heartbeats, but generally within a breathhold

Acquisition Mode:

  • Single slice, multiphase (i.e. one slice location is acquired per breath hold)
  • Each acquisition results in the reconstruction two cines, a phase-cine (above upper) and a magnitude-cine (above lower).
  • Although it is possible to measure the blood velocity simultaneously in all three dimensions, in clinical practice usually only the velocity component in the through-plane direction is determined for flow quantification.
  • The phase-cine is comprised of a series of gray scale velocity image where low velocities are shown as gray and high velocities are shown as either black or white (depending on the direction of the through-plane flow. Note that in the phase cine above, the ascending aorta is principally black and the descending aorta is principally white because the blood is flowing through the image in opposite directions. Also, note that in regions where there is no signal (e.g. the air in the lungs and outside the body), the velocity signal is speckled, reflecting the fact that there is insufficient signal to accurately determine the velocity for these pixels.
  • For every phase image there is a corresponding magnitude image. The magnitude-cine image shows the anatomy within the slice without any velocity information. When quantifying blood flow, typically the user uses the magnitude image to draw a region of interest (ROI) around the vessel of interest. The computer software then uses the velocities on the corresponding pixels in the phase image to determine the magnitude of the blood flow.

Image Contrast:

  • Bright blood
  • Does not require intravenous gadolinium contrast
  • T1 weighted

Imaging Options: Must set the maximum velocity that can be acquired without aliasing (Venc)

Clinical Utility:

Determines instantaneous velocity to quantify through-plane blood flow. Most common clinical applications include quantification of:

  • Intracardiac shunts (e.g. Qp/Qs in atrial septal defect, ventricular septal defect, patent ductus arteriosus, and/or partial anomalous pulmonary venous return)
  • Regurgitant volumes in valvular disease
  • Transvalvular pressure gradients  (e.g. aortic stenosis)