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Cardiovascular MRI technique Development

Dual VENC Phase Contrast MRI

 

4D flow MR imaging combines ECG-synchronized 3D phase-contrast (PC) MRI with advanced post-processing strategies for the in vivo assessment of 3D blood flow with full volumetric coverage of the vascular region of interest. Several applications of 4D flow MRI demand the measurement of flow velocities with a high dynamic range (e.g. slow venous and fast arterial flow in the brain, near static velocities alongside high emptying jets in the aorta). However, current 4D flow MRI techniques assess blood velocity based on a single, pre-defined velocity sensitivity encoding (venc), which is usually set above the maximum expected velocity. As the velocity noise (dv) is directly related to the velocity sensitivity (dv ~ venc/SNRmag), a high venc can substantially limit the assessment of vascular regions with low flow velocities (v << venc). Previous applications of 4D flow MRI were limited by its inability to fully capture the wide range of velocities related to many pathologic hemodynamic patterns (e.g. aneurysms, where there is high flow jet entering the aneurysm alongside low unstable flow, vortex and helix type flow). We have developed a dual-venc sequence with shared reference scan and k-t acceleration for improved scan efficiency, allowing the acquisition of both low- and high-venc data within a single scan. The resulting high-venc data can be used for complete anti-aliasing of the low-venc data while maintaining the favorable velocity to noise ratio (VNR) of the low-venc data. Validation and evaluation of the sequence showed that e.g. with a low- and high- venc setting of 100cm/s and 200cm/s we observe an expected 200% VNR improvement. The sequence has been systematically evaluated in vivo with both steady-flow rotation phantom experiments as well as with a pulsatile, 3D printed, aorta phantom. We have also applied this dual-venc sequence to healthy volunteers and a variety of patients, for imaging of the intracranial vessels, thoracic aorta, and left atrium.  These experiments have demonstrated improved 3D flow assessment of small intracranial vessels and veins, as well as improved visualization of aortic and intracardiac hemodynamics.

Investigators: Susanne Schnell (PhD), Liliana Ma

Funding: American Heart Association, National Heart, Lung, and Blood Institute of the NIH.

Publications:

  1. Ma LE, Markl M, Chow K, Vali A, Wu C, Schnell S. Efficient triple-VENC phase-contrast MRI for improved velocity dynamic range. Magn Reson Med. 2019 Aug 18. [Pubmed Link]

  2. Ma, Liliana E., et al. “Aortic 4D flow MRI in 2 minutes using compressed sensing, respiratory controlled adaptive k‐space reordering, and inline reconstruction.” Magnetic resonance in medicine. 81.6 (2019): 3675-3690. [Pubmed Link]

  3. Schnell S, Ansari SA, Wu C, Garcia J, Murphy IG, Rahman OA, et al. Accelerated dual-venc 4d flow mri for neurovascular applications. Journal of Magnetic Resonance Imaging. 2017;46:102-114. [Pubmed Link]

  4. Schnell, S., et al., Improved assessment of aortic hemodynamics by kt accelerated dual-venc 4D flow MRI in pediatric patients. Journal of Cardiovascular Magnetic Resonance, 2016. 18(1): p. 1. [Pubmed Link]