期刊
MAGNETIC RESONANCE IN MEDICINE
卷 75, 期 2, 页码 688-700出版社
WILEY-BLACKWELL
DOI: 10.1002/mrm.25631
关键词
diffusion imaging; diffusion gradients; axon diameter; oscillating gradient spin-echo; pulsed gradient spin-echo
资金
- Leverhulme Trust Foundation
- EPSRC [EP/G007748, EP/I027084/01, EP/H046410/01]
- Engineering and Physical Sciences Research Council [EP/H046410/1, EP/L022680/1, EP/M020533/1, EP/G007748/1, EP/I027084/1, EP/M00855X/1, EP/M029778/1, EP/N018702/1] Funding Source: researchfish
- International Spinal Research Trust [IMG006] Funding Source: researchfish
- Medical Research Council [MR/M009106/1] Funding Source: researchfish
- EPSRC [EP/L022680/1, EP/I027084/1, EP/M020533/1, EP/N018702/1, EP/M00855X/1, EP/M029778/1, EP/G007748/1, EP/H046410/1] Funding Source: UKRI
- MRC [MR/M009106/1] Funding Source: UKRI
Purpose: To identify optimal pulsed gradient spin-echo (PGSE) and oscillating gradient spin-echo (OGSE) sequence settings for maximizing sensitivity to axon diameter in idealized and practical conditions. Methods: Simulations on a simple two-compartment white matter model (with nonpermeable cylinders) are used to investigate a wide space of clinically plausible PGSE and OGSE sequence parameters with trapezoidal diffusion gradient waveforms. Signal sensitivity is measured as a derivative of the signal with respect to axon diameter. Models of parallel and dispersed fibers are investigated separately to represent idealized and practical conditions. Results: Simulations show that, for the simple case of gradients perfectly perpendicular to straight parallel fibers, PGSE always gives maximum sensitivity. However, in real-world scenarios where fibers have unknown and dispersed orientation, low-frequency OGSE provides higher sensitivity. Maximum sensitivity results show that on current clinical scanners (G(max) = 60 mT/m, signal to noise ratio (SNR) = 20) axon diameters below 6 mu m are indistinguishable from zero. Scanners with stronger gradient systems such as the Massachusetts General Hospital (MGH) Connectom scanner (G(max) = 300 mT/m) can extend this sensitivity limit down to 2-3 mu m, probing a much greater proportion of the underlying axon diameter distribution. Conclusion: Low-frequency OGSE provides additional sensitivity to PGSE in practical situations. OGSE is particularly advantageous for systems with high performance gradients. (C) 2015 Wiley Periodicals, Inc.
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