Spiral Time of Flight MRA with Dixon Water and Fat Separation

Nicholas R. Zwart^{1}, Dinghui Wang^{1}, and James G. Pipe^{1}

*Scan Parameters:* The proposed method was compared to conventional
cartesian methods for 3D multi-slab imaging of the circle of Willis and 2D
multi-slice imaging of the carotid bifurcation. All scans were performed on
a volunteer using a 3T Philips Ingenia system with a 15 channel head coil.

*3D ToF:* The standard cartesian parameters used were: TR/TE = 23/3.5
msec, 16 x 16 cm field of view (FOV), 18˚ flip angle, a sampling window (tau)
of 5.7 msec and a partial echo acquisition of 65% in the readout direction for
a scan time of 5:25 min. The proposed spiral scan parameters were: TR =
21 msec, TEs = 1.24/1.99/2.74 msec, 24 x 24 cm FOV, 18˚ flip angle, tau =
7.2 msec, and 40 spiral interleaves per kz-encoding (fully sampled) for a scan
time of 4:02 min. Both sequences had a 1.4 mm slice thickness, 19 slices per
slab with an overlap of 9 slices for 5 slabs, flow compensation gradients and
a venous saturation pulse.

*2D ToF:* The cartesian scan parameters used were: TR/TE = 16/3.5
msec, 22 x 22 cm FOV, 30˚ flip angle, tau = 3.6 msec, and a partial echo
of 65%, for a scan time of 4:46 min. The proposed spiral scan parameters
were: TR = 25 msec, TEs = 2.5/3.25/4 msec, 35˚ flip angle, tau = 8.8 msec,
and 28 spiral interleaves per slice (fully sampled) for a scan time of 3:34 min.
The parameters used in both techniques were: 3 mm slice thickness with an
overlap of 1 mm, flow compensation and a venous saturation pulse.

*Reconstruction:* The reconstruction for the proposed 2D and 3D spiral
methods was implemented and processed in GPI [8]. In each reconstruction,
the three point Dixon method was used to calculate the B0 field maps. The
field maps are then used to reconstruct the three echo sets in a joint conjugate
gradient deblurring and water-fat separation [9].

[1] A Grayev et al. “Improved time-of-flight magnetic resonance angiography with IDEAL water-fat separation”. In: Journal of Magnetic Resonance Imaging 29.6 (2009), pp. 1367–1374.

[2] D Wang et al. “Analytical three-point Dixon method: With applications for spiral water–fat imaging”. In: Magnetic Resonance in Medicine (2015).

[3] QS Xiang. “Two-point water-fat imaging with partially-opposed-phase (POP) acquisition: An asymmetric Dixon method”. In: Magnetic resonance in medicine 56.3 (2006), pp. 572–584.

[4] J Berglund et al. “Three-point dixon method enables whole-body water and fat imaging of obese subjects”. In: Magnetic Resonance in Medicine 63.6 (2010), pp. 1659–1668.

[5] SB Reeder et al. “Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL): application with fast spin-echo imaging”. In: Magnetic resonance in medicine 54.3 (2005), pp. 636–644.

[6] QS Xiang and L An. “Water-fat imaging with direct phase encoding”. In: Journal of Magnetic Resonance Imaging 7.6 (1997), pp. 1002–1015.

[7] JG Pipe and NR Zwart. “Spiral trajectory design: A flexible numerical algorithm and base analytical equations”. In: Magnetic Resonance in Medicine 71.1 (2014), pp. 278–285.

[8] NR Zwart and JG Pipe. “Graphical programming inter- face: a development environment for MRI methods”. In: Magnetic Resonance in Medicine (2014).

[9] NR Zwart, D Wang, and JG Pipe. “Spiral CG deblurring and fat-water separation using a multi-peak fat model”. In: Proceedings of the Joint Annual Meeting of ISMRM-ESMRMB, Milan, Italy. 2014.

[10] CH Meyer et al. “Fast spiral coronary artery imaging”. In: Magnetic Resonance in Medicine 28.2 (1992), pp. 202–213.

Figure 1: Axial 10-slice MIP images of the cartesian TOF on the left, the spiral
water image in the middle and a single slice spiral fat image on the right (representing the center image of the 10 slice MIPs). The ophthalmic arteries are more
easily distinguished in the water image.

Figure 2: MIP images in the coronal, sagittal and axial directions for 3D cartesian
ToF on the left and 3D spiral-Dixon ToF on the right.

Figure 3: Coronal MIPs centered on the carotid bifurcation (conventional 2D ToF
on the left and the 2D spiral-Dixon ToF on the right).

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)

1834