High‐resolution diffusion‐weighted imaging with interleaved variable‐density spiral acquisitions

Abstract

Purpose: To develop a multishot magnetic resonance imaging (MRI) pulse sequence and reconstruction algorithm for diffusion-weighted imaging (DWI) in the brain with submillimeter in-plane resolution. Materials and Methods:A self-navigated multishot acquisition technique based on variable-density spiral kspace trajectory design was implemented on clinical MRI scanners. The image reconstruction algorithm takes advantage of the oversampling of the center k-space and uses the densely sampled central portion of the k-space data for both imaging reconstruction and motion correction. The developed DWI technique was tested in an agar gel phantom and three healthy volunteers.Results: Motions result in phase and k-space shifts in the DWI data acquired using multishot spiral acquisitions. With the two-dimensional self-navigator correction, diffusion-weighted images with a resolution of 0.9 ϫ 0.9 ϫ 3 mm 3 were successfully obtained using different interleaves ranging from 8 -32. The measured apparent diffusion coefficient (ADC) in the homogenous gel phantom was (1.66 Ϯ 0.09) ϫ 10 -3 mm 2 /second, which was the same as measured with single-shot methods. The intersubject average ADC from the brain parenchyma of normal adults was (0.91 Ϯ 0.01) ϫ 10 -3 mm 2 /second, which was in a good agreement with the reported literature values. Conclusion:The self-navigated multishot variable-density spiral acquisition provides a time-efficient approach to acquire high-resolution diffusion-weighted images on a clinical scanner. The reconstruction algorithm based on motion correction in the k-space data is robust, and measured ADC values are accurate and reproducible.

White matter pathology isolates the hippocampal formation in Alzheimer's disease

“…Although advanced procedures were applied to address common concerns of diffusion imaging studies, further improvement is required in this field. Methods to enhance spatial [40,42,43] and angular [84,85] resolution will be necessary to fully exclude concerns about eddy current and susceptibility artifact distortions. Similarly, although the procedures used here are superior to standard linear transformations for registration of DTI data, the potential still exists for further refinement of DTI registration using the full tensor information [52].…”

High efficiency, low distortion 3D diffusion tensor imaging with variable density spiral fast spin echoes (3D DW VDS RARE)

“…All gradients are expressed in units of rad/(cm-sec) . This trajectory has previously been used for self-navigated interleaved spirals for DTI (Li et al, 2005; Liu et al, 2004). In the current implementation the magnetization was rewound after each shot by the addition of a numerically generated refocusing trajectory segment.…”

Human brain diffusion tensor imaging at submillimeter isotropic resolution on a 3 Tesla clinical MRI scanner

“…In addition to post-mortem human brain imaging, in vivo human brain DTI at high in-plane resolution (e.g., 0.5 × 0.5 × 6 mm 3 ) has also been achieved in studies using a number of 2D acquisitions, including interleaved echo-planar imaging (EPI) (Bammer, 2003; Chen et al, 2013; Jeong et al, 2013; Miller and Pauly, 2003; Van et al, 2009), interleaved spiral imaging (Butts et al, 1997; Li et al, 2005; Liu et al, 2004; Truong and Guidon, 2013), readout segmented EPI (Porter and Heidemann, 2009), short-axis PROPELLER EPI (Skare et al, 2006), and PROPELLER fast spin-echo pulse sequences (Pipe et al, 2002). However, because of the limited signal-to-noise ratio (SNR) and difficulty in effectively suppressing fat signals for thin slices (e.g., < 1.5 mm), it is challenging to achieve submillimeter isotropic resolution with 2D DTI protocols.…”