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Optimized quantification of spin relaxation times in the hybrid state.

ABSTRACT: PURPOSE:The optimization and analysis of spin ensemble trajectories in the hybrid state-a state in which the direction of the magnetization adiabatically follows the steady state while the magnitude remains in a transient state. METHODS:Numerical optimizations were performed to find spin ensemble trajectories that minimize the Cramér-Rao bound for T1 -encoding, T2 -encoding, and their weighted sum, respectively, followed by a comparison between the Cramér-Rao bounds obtained with our optimized spin-trajectories, Look-Locker sequences, and multi-spin-echo methods. Finally, we experimentally tested our optimized spin trajectories with in vivo scans of the human brain. RESULTS:After a nonrecurring inversion segment on the southern half of the Bloch sphere, all optimized spin trajectories pursue repetitive loops on the northern hemisphere in which the beginning of the first and the end of the last loop deviate from the others. The numerical results obtained in this work align well with intuitive insights gleaned directly from the governing equation. Our results suggest that hybrid-state sequences outperform traditional methods. Moreover, hybrid-state sequences that balance T1 - and T2 -encoding still result in near optimal signal-to-noise efficiency for each relaxation time. Thus, the second parameter can be encoded at virtually no extra cost. CONCLUSIONS:We provided new insights into the optimal encoding processes of spin relaxation times in order to guide the design of robust and efficient pulse sequences. We found that joint acquisitions of T1 and T2 in the hybrid state are substantially more efficient than sequential encoding techniques.

SUBMITTER: Asslander J

PROVIDER: S-EPMC7301573 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Optimized quantification of spin relaxation times in the hybrid state.

Assländer Jakob J Lattanzi Riccardo R Sodickson Daniel K DK Cloos Martijn A MA

Magnetic resonance in medicine 20190612 4

<h4>Purpose</h4>The optimization and analysis of spin ensemble trajectories in the hybrid state-a state in which the direction of the magnetization adiabatically follows the steady state while the magnitude remains in a transient state.<h4>Methods</h4>Numerical optimizations were performed to find spin ensemble trajectories that minimize the Cramér-Rao bound for T1 -encoding, T2 -encoding, and their weighted sum, respectively, followed by a comparison between the Cramér-Rao bounds obtained with ...[more]

PMID: 31189025

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Project description:ObjectiveTo explore whether subregional laminar femorotibial cartilage spin-spin relaxation time (T2) is associated with subsequent radiographic progression and cartilage loss and/or whether one-year change in subregional laminar femorotibial cartilage T2 is associated with concurrent progression in knees with established radiographic OA (ROA).MethodsIn this case-control study, Osteoarthritis Initiative (OAI) knees with medial femorotibial progression were selected based on one-year loss in both quantitative cartilage thickness Magnetic resonance imaging (MRI) and radiographic joint space width (JSW). Non-progressor knees were matched by sex, Body mass index (BMI), baseline Kellgren-Lawrence-grade (2/3), and pain. Baseline and one-year follow-up superficial and deep cartilage T2 was analyzed in 16 femorotibial subregions using multi-echo spin-echo MRI.Results37 knees showed medial femorotibial progression whereas 37 matched controls had no medial or lateral compartment progression. No statistically significant baseline differences between progressor and non-progressor knees in medial femorotibial cartilage T2 were observed in the superficial (48.9 ± 3.0 ms; 95% CI: [47.9, 49.9] vs 47.8 ± 3.6 ms; 95% CI: [46.6, 49.0], P = 0.07) or deep cartilage layer (40.8 ± 3.6 ms; 95% CI: [39.5, 42.0] vs 40.1 ± 4.7 ms; 95% CI: [38.5, 41.6], P = 0.29). Concurrent T2 change was more pronounced in the deep than the superficial cartilage layer. In the medial femorotibial compartment (MFTC), longitudinal change was greater in the deep layer of progressor than non-progressor knees (1.8 ± 4.5 ms; 95% CI: [0.3, 3.3] vs -0.2 ± 1.9 ms; 95% CI: [-0.8, 0.5], P = 0.02), whereas no difference was observed in the superficial layer.ConclusionMedial compartment cartilage T2 did not appear to be a strong prognostic factor for subsequent structural progression in the same compartment of knees with established ROA, when appropriately controlling for covariates. Yet, deep layer T2 change in the medial compartment occurred concurrent with medial femorotibial progression.

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Optimized quantification of spin relaxation times in the hybrid state.

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Optimized quantification of spin relaxation times in the hybrid state.

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