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 off-resonance 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.

Figure 1

Pulse sequence diagram for dual-echo PC VIPR, consisting of a combined bipolar/prewinder, dual-echo readout, and gradient rewinders and spoilers. Gradient spoiling is applied consistently on the z-gradient with x and y gradients are rewound back to the center of k-space.

Figure 2

Zeroeth (top) and first (bottom) moment trajectory of the dual echo readout. The 0^th moment trajectory, show along starts at the edge of k-space, passes through the center, changes angles and proceeds back to the edge of k-space. The 1^st moment of this trajectory, shown applied along the k_r (projection) direction, is flow compensated with first moments equally minimized.

Figure 3

Comparison of trajectory deviations along the x-axis when two trapezoid gradients are played (1) together within one acquisition and (2) individually in two successive acquisitions. The system is well approximated with linear assumptions, shown by the agreement between the calculated deviation by adding gradients A and B and that actually measured with both gradients on.

Figure 4

Magnitude images of a phantom: uncorrected (A), trajectory corrected (B), off-resonance corrected (C), and with both corrections (D). Neither trajectory nor off-resonance corrections alone where successful in producing a high quality image, however, when both correction schemes are applied the image quality is significantly improved.

Figure 5

Representative coronal, sagittal, and axial full volume MIP images from a cranial PC VIPR exam, demonstrating the extensive coverage and excellent spatial resolution. Small arteries are well visualized with almost complete background subtraction.

Figure 6

Limited axial and sagittal MIP images from a cranial PC VIPR exam with no corrections (left), with off-resonance corrections alone (middle), and with both off-resonance and trajectory corrections (right). Only when all corrections are applied do images show clear delineation of small vessels above the nasal cavity.

Figure 7

Limited axial(left), coronal(middle), and sagittal(right) mips of a patient with an AVM in the anterior left lobe. Images show excellent delineation of both the feeding arteries/veins and nidus. Arrows point to a the nidus (left) and main draining vein (middle).