Improved 3D phase contrast MRI with off‐resonance corrected dual echo VIPR

Abstract

Phase contrast (PC) magnetic resonance imaging with a three-dimensional, radially undersampled acquisition allows for the acquisition of high resolution angiograms and velocimetry in dramatically reduced scan times. However, such an acquisition is sensitive to blurring and artifacts from offresonance and trajectory errors. A dual-echo trajectory is proposed with a novel trajectory calibration from prescan data coupled with a multi-frequency reconstruction to correct for these errors. Comparisons of phantom data and in vivo results from volunteer, and patients with arteriovenous malformations patients are presented with and without these corrections and show significant improvement of image quality when both corrections are applied. The results demonstrate significantly improved visualization of vessels, allowing for highly accelerated PC acquisitions without sacrifice in image quality. Volumetric phase contrast (PC) MR imaging with velocity encoding in three spatial dimensions holds the potential to be a comprehensive vascular imaging method; providing both anatomical and quantitative velocity measurements, all without the use of a contrast agent. As a lumenographic imaging tool, it has been effectively used for the identification of aneurysms, arteriovenous malformations (1), and vascular stenoses (2) in the cerebrovascular system, great vessels, and renal arteries. Additional hemodynamic information can be obtained through postprocessing of the acquired anatomical and velocity data, providing either velocity visualization and/or quantitative hemodynamic analysis. Visualization of complex velocity fields can be performed by flow vectors, streamlines, and particle traces to visually identify pathologic flow patterns (3). Quantitative flow measurements can be accomplished retrospectively with oblique reformats, avoiding difficulties of prospectively targeted two-dimensional (2D) PC measurements. Hemodynamic measures such as wall sheer stress and relative pressure can be determined directly from the velocity data (4,5). However, despite the plethora of diagnostic measures available from 3D PC, its clinical use has been hindered by relatively lengthy imaging times and the occurrence of flow related artifacts.For 3D PC to become a viable clinical solution, the scan time for images of diagnostic resolution must be reduced. This has been achieved through protocol optimization for vascular territories with larger vessels (6), which usually still results in extended imaging times. Parallel imaging techniques (7,8) can be used in conjunction with optimized protocols, but generally only allow accelerations on the order of 2-4 and can lead to additional signal-to-noise ratio (SNR) degradation. In addition to these accelerated imaging approaches, non-Cartesian trajectories may be used for more efficient sampling schemes, accelerated imaging by undersampling, and the reduction of flow related artifacts.We have previously introduced Vastly undersampled Isotropic PRojection (VIPR) imaging (9), a 3D radial trajectory with angul...

Volumetric velocity measurements in restricted geometries using spiral sampling: a phantom study

“…A major obstacle to wide-spread clinical use of 4D PC is the long acquisitions times. However, volumetric non-cartesian sequences in combination with PC (such as PC-VIPR) have been shown able to greatly reduce acquisition times compared to traditional Cartesian readout schemes, while maintaining accuracy in flow quantification [28,29], and 4D PC have also been successfully combined with spiral readouts for in-vivo measurements [30,31].…”

4D phase contrast MRI at 3 T: Effect of standard and blood‐pool contrast agents on SNR, PC‐MRA, and blood flow visualization

“…However, most PC-MRA implementations used nongated data acquisition, which can result in artifacts for pulsatile blood flow. Further drawbacks of the PC-MRA method are long scan times and lack of respiration control, which limited most applications of 3D PC-MRA to static regions with low pulsatile flow such as the cranial vessels (12,13).…”

Flow Imaging: Cardiac Applications of 3D Cine Phase-Contrast MRI

“…Different research groups use their own approaches and adapt them for different applications (10)(11)(12)(13)(14)(15)(16). Differences exist in temporal coverage, spatial coverage, acquisition time, and data quality.…”

“…Minimizing the imaged field-of-view can further reduce the imaging time, such as focusing the acquisition on the left ventricle, but most cardiac applications require coverage of the complete left side or the whole heart(15,17-20). Other techniques can be used to further decrease the scan time, either by use of parallel imaging, data-driven sparse sampling, efficient noncartesian k-space trajectories, or combinations of these (14,(21)(22)(23). It is important to realize the cost associated with all of these trade-offs, in order to ensure sufficient data quality.…”

“…Typical acquisition times are currently too long to be added to a standard cardiac MRI protocol or to justify its use in clinical practice. The usage of parallel imaging, data-driven sparse sampling, or efficient non-cartesian kspace trajectories (14,(21)(22)(23) can decrease the scan time, but at the cost of data quality. Even though recently important improvements in the analysis process have been reported, further studies are necessary in order to adapt the analyses method to the question at hand.…”