Improving the image quality of 3D FLAIR with a spiral MRI technique.

Abstract

Fluid-attenuated inversion recovery (FLAIR) nulls the CSF signal and is widely used in neuro MRI exams. A 3D scan can provide high SNR, contiguous coverage, and reduced sensitivity to through-plane CSF flow. In this work, a 3D spiral FLAIR technique is proposed to improve the image quality of conventional 3D Cartesian FLAIR. The 3D spiral FLAIR sequence incorporated a spiral-in/out readout to preserve higher scan efficiency and eliminate off resonance-induced artifacts observed with a commonly implemented spiral-out readout, a compensation approach to minimize phase errors due to the concomitant fields accompanying the spiral gradient, and an adapted variable flip angle scheme to preserve scan efficiency and maintain a long and stable echo train. 3D Cartesian and spiral FLAIR (~6 min each) were acquired on a 3 Tesla scanner from 6 subjects (age range: 31-64 years; mean: 39.5). Two neuroradiologists rated the images in a blinded fashion on a 5-point scale. The noise performance was assessed quantitatively. Compared to 3D Cartesian FLAIR, 3D spiral FLAIR exhibits greater reduction of artifacts from CSF, especially anterior to the brain stem (rated better in 4 cases), artifacts attributed to blood/flow in the deep brain (better or much better in all 6 cases), and superior overall image quality (much better in 5 cases) despite residual susceptibility artifacts near the nasal cavity. Quantitative assessment demonstrates ~1.5× higher average SNR than Cartesian data. 3D spiral FLAIR achieves higher SNR, reduced CSF, and blood/flow artifacts, providing an alternative to 3D Cartesian FLAIR for neurological exams.