4D PC MRI in the brain: basics and applications
Susanne Schnell1
1University of Greifswald, Greifswald, Germany

Synopsis

Phase-contrast MRI and its extension to 4D flow MRI will be explained. Flowing spins, for example from flowing blood, appear as an artifact in the image. However, by understanding the characteristics of flowing spins, their appearance can be utilized. Phase-contrast MRI is sensitized to flow by using a series of bipolar gradients affecting the phase signal of spins that flow with a uniform velocity in the direction parallel to the gradients. By utilizing ECG gating, fluid flow velocities can be measured in a time-resolved manner. After successful correction of phase errors and velocity aliasing, the fluid dynamics can be quantified.

TARGET AUDIENCE

Anyone who is interested in how we can measure blood flow and determine hemodynamic flow parameters in vivo using MRI. Basic post-processing of 2D PC and 4D flow MRI will be covered.

OUTCOME/OBJECTIVES

Learners will understand phase-contrast MRI (2D PC and 4D Flow MRI) and how to effectively acquire and analyze the data. Applications in the brain for vascular disease as well as cerebrospinal fluid will be shown.

PURPOSE

Phase-Contrast MR imaging will be discussed for its role in quantitative angiography in the brain and the assessment of CSF flow. Phase-contrast imaging is sensitized to blood flow velocity, affecting the phase signal of flowing spins. This encoding of velocity enables quantification of hemodynamics. Several quantitative measures that can be derived from velocity encoded MRI will be discussed such as peak velocity, flow rate, pressure drop, and wall shear stress.

METHODS

MRI techniques provide non-invasive and non-ionizing methods for the highly accurate anatomical depiction of vessels throughout the cardiac cycle. Also, the intrinsic sensitivity of MRI to motion offers the unique ability to acquire spatially registered blood flow simultaneously with the morphological data, within a single measurement. In clinical routine, flow MRI is typically accomplished using methods that resolve two spatial dimensions in individual planes and encode the time-resolved velocity in one principal direction, typically oriented perpendicular to the two-dimensional (2D) section. In this lecture, time-resolved 3D MRI flow techniques (4D Flow MRI) will be introduced. Emerging techniques and novel applications in the brain will be explored. Besides, applications of these new techniques for the improved evaluation of cerebrovascular disease will be presented.

CONCLUSIONS

In summary, flow imaging with MRI has undergone and continues to undergo a substantial transformation, from simple techniques measuring one-directional blood flow velocities at a specific location to a more compressive diagnostic tool that can assess 3D blood flow, or derive advanced metrics of cerebrovascular hemodynamics, such as pressure drop or WSS.

Acknowledgements

No acknowledgement found.

References

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Proc. Intl. Soc. Mag. Reson. Med. 29 (2021)