Abstract
ObjectSodium magnetic resonance imaging (23Na-MRI) of the brain has shown changes in 23Na signal as a hallmark of various neurological diseases such as stroke, Alzheimer’s disease, Multiple Sclerosis and Huntington’s disease. To improve scan times and image quality, we have implemented the 3D-Cones (CN) sequence for in vivo 23Na brain MRI.Materials and methodsUsing signal-to-noise (SNR) as a measurement of sequence performance, CN is compared against more established 3D-radial k-space sampling schemes featuring cylindrical stack-of-stars (SOS) and 3D-spokes kooshball (KB) trajectories, on five healthy volunteers in a clinical setting. Resolution was evaluated by simulating the point-spread-functions (PSFs) and experimental measures on a phantom.ResultsAll sequences were shown to have a similar SNR arbitrary units (AU) of 6–6.5 in brain white matter, 7–9 in gray matter and 17–18 AU in cerebrospinal fluid. SNR between white and gray matter were significantly different for KB and CN (p = 0.046 and <0.001 respectively), but not for SOS (p = 0.1). Group mean standard deviations were significantly smaller for CN (p = 0.016). Theoretical full-width at half-maximum linewidth of the PSF for CN is broadened by only 0.1, compared to 0.3 and 0.8 pixels for SOS and KB respectively. Actual image resolution is estimated as 8, 9 and 6.3 mm for SOS, KB and CN respectively.ConclusionThe CN sequence provides stronger tissue contrast than both SOS and KB, with more reproducible SNR measurements compared to KB. For CN, a higher true resolution in the same amount of time with no significant trade-off in SNR is achieved. CN is therefore more suitable for 23Na-MRI in the brain.
Highlights
Background23Na-MRI of the brain has been used to show changes in total tissue sodium concentration (TSC) in stroke [1], Alzheimer’s disease [2], Multiple Sclerosis [3,4,5] and Huntington’s disease [6]
The CN sequence provides stronger tissue contrast than both SOS and KB, with more reproducible signal-to-noise ratio (SNR) measurements compared to KB
Signal-to-noise (SNR) for each sequence is given in Table 2, for each volunteer, in addition to the mean and standard deviations (SD) in gray matter (GM), white matter (WM), cerebrospinal fluid (CSF) and the two phantoms
Summary
Background23Na-MRI of the brain has been used to show changes in total tissue sodium concentration (TSC) in stroke [1], Alzheimer’s disease [2], Multiple Sclerosis [3,4,5] and Huntington’s disease [6]. Lesions and pathologies can be detected in these diseases using 23Na-MRI, complimentary to information obtained by 1H-MRI, as well as statistically significant changes in tissue that appears otherwise normal on 1H-images [3,4,5]. Applications of 23Na-MRI are not limited to the brain, changes in the cartilage of the knee that relate to osteoarthritis onset have been demonstrated [7]. To capture the entirety of the sodium signal, it is necessary to use ultra-short echo time (UTE) acquisition strategies, featuring radial or spiral free induction decay (FID) k-space sampling, rather than spin or gradient echoes as commonly used in 1H-MRI. UTE sampling increases the signal-to-noise ratio (SNR) significantly over standard spin and gradient echo sequences. The increase in SNR can in turn be used to shorten scan times or to achieve higher resolutions
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