Fast Whole-Brain 4D Contrast-Enhanced MR Angiography with Velocity Encoding Using Undersampled Radial Acquisition and Highly Constrained Projection Reconstruction: Image-Quality Assessment in Volunteer Subjects: Fig 1.

Abstract

SUMMARYWe report on the image quality obtained by using fast contrast-enhanced whole-brain 4D radial MRA with 0.75-second temporal resolution, isotropic submillimeter spatial resolution, and velocity encoding (HYPRFlow). Images generated by HYPR-LR by using the velocity-encoded data as the constraining image were of diagnostic quality. In addition, we demonstrate that measurements of shear stress within the middle cerebral artery can be derived from the highresolution 3D velocity data.Whole-brain 4D contrast-enhanced MRA has been previously described by using Cartesian acquisitions, partial-Fourier encoding, and parallel imaging with multiple coils. [1][2][3] However, performing high-resolution whole-brain 4D contrast-enhanced MRA examinations is challenging using conventional imaging methods because acquisition time increases proportionally with matrix size. Radial acquisitions like 2D projection reconstruction [4][5][6]8 can be effective in accelerating MR angiography; however, image quality is limited by undersampling artifacts and decreased SNR at high acceleration factors. Innovative reconstruction algorithms, such as HYPR and HYPR-LR 9-11 ), which exploit prior information to constrain individual images, are able to reduce the severity of undersampling artifacts and SNR loss even at high levels of acceleration. Combining undersampled radial acquisition with HYPR reconstruction can dramatically improve frame rates and image coverage without degradation of image quality. 12 HYPRFlow is one of the hybrid HYPR techniques that uses the phase-contrast image from a separate scan as the vascular constraint to provide whole-brain 4D contrast-enhanced MRA with subsecond temporal resolution and submillimeter isotropic spatial resolution as well as flow dynamics. [12][13][14] In this article, we investigate the clinical utility of this technique by assessing the image quality of HYPRFlow and estimate WSS in the middle cerebral arteries by using the time-average velocity through a single cardiac cycle. TechniqueVolunteer studies were performed in compliance with the Health Insurance Portability and Accountability Act regulations and by using a protocol approved by the local institutional NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript review board. Eight adult subjects ranging from 24 to 40 years of age were imaged (4 women, 4 men) with a clinical 3T MR imaging system (Excite HD, TwinSpeed, Signa; GE Healthcare, Waukesha, Wisconsin) with an 8-channel head coil (HD Brain Coil, GE Healthcare). Each HYPRFlow study involved 2 encoding methods. First, during contrast injection, spatial encoding was performed by using a time-resolved multiecho 3D radial acquisition (CE-VIPR). 15 Subsequently, velocity encoding was performed by using a highresolution dual-echo 3D radial phase-contrast acquisition (PC-VIPR). The PC-VIPR data were used to form a composite image (angiographic constraint) for HYPR-LR reconstruction and for hemodynamic evaluation. MR Imaging ProtocolImaging parameters for CE-VIPR were th...

Measuring Pulsatile Flow in Cerebral Arteries Using 4D Phase-Contrast MR Imaging

“…8,9 This approach significantly eases the workflow, possibly reduces total scan time, and ensures the proper capture of all vessels in the prescribed imaging volume. Such 4D PCMRI techniques for intracranial measurements have been validated in vivo, 10,11 but evaluations regarding pulsatile hemodynamics are lacking.…”

Time-of-Arrival Parametric Maps and Virtual Bolus Images Derived From Contrast-Enhanced Time-Resolved Radial Magnetic Resonance Angiography Improve the Display of Brain Arteriovenous Malformation Vascular Anatomy

“…However, high temporal and spatial resolution is essential to properly identify components, especially within lesions with rapid arteriovenous shunting. In this report, we use a recently introduced method termed HYPRFlow (HFMRA) which employs undersampled radial acquisition and constrained reconstruction to overcome these limitations (9). HFMRA depicts small vessel structures with a spatial resolution of 0.68 mm isotropic voxels and a temporal resolution as high as 0.75 seconds.…”

Neurovascular 4DFlow MRI (Phase Contrast MRA): emerging clinical applications

“…One potential method for reducing scan times is to use non-Cartesian sampling trajectories which either collect more data per excitation, as in spiral [10] or allow greater under sampling of the imaging volume without obscuring artifacts, as in radial trajectories. Non-Cartesian imaging additionally allows for a reduction of the echo time [11,12], allowing improved imaging of complex flow and/or higher spatial resolution [13,14]. Another method commonly used to reduce scan time is to utilize a reconstruction which harnesses correlation in space and time [9,[15][16][17][18][19][20][21][22].…”