Background
Magnetic resonance fingerprinting (MRF) techniques have been recently described for simultaneous multiparameter cartilage mapping of the knee although investigation of their ability to ...detect early cartilage degeneration remains limited.
Purpose
To investigate age‐dependent changes in knee cartilage T1, T2, and T1p relaxation times measured using a three‐dimensional (3D) MRF sequence in healthy volunteers.
Study Type
Prospective.
Subjects
The study group consisted of 24 healthy asymptomatic human volunteers (15 males with mean age 34.9 ± 14.4 years and 9 females with mean age 44.5 ± 13.1 years).
Field Strength/Sequence
A 3.0 T gradient‐echo‐based 3D‐MRF sequence was used to simultaneously create proton density‐weighted images and T1, T2, and T1p maps of knee cartilage.
Assessment
Mean global cartilage and regional cartilage (lateral femur, lateral tibia, medial femur, medial tibia, and patella) T1, T2, and T1ρ relaxation times of the knee were measured.
Statistical Tests
Kruskal–Wallis tests were used to compared cartilage T1, T2, and T1ρ relaxation times between different age groups, while Spearman correlation coefficients was used to determine the association between age and cartilage T1, T2, and T1ρ relaxation times. The value of P < 0.05 was considered statistically significant.
Results
Higher age groups showed higher global and regional cartilage T1, T2, and T1ρ. There was a significant difference between age groups in global cartilage T2 and T1ρ but no significant difference (P = 0.13) in global cartilage T1. Significant difference was also present between age groups in cartilage T2 and T1ρ for medial femur cartilage and medial tibia cartilage. There were significant moderate correlations between age and T2 and T1ρ for global cartilage (R2 = 0.63–0.64), medial femur cartilage (R2 = 0.50–0.56), and medial tibia cartilage (R2 = 0.54–0.66).
Conclusion
Cartilage T2 and T1p relaxation times simultaneously measured using a 3D‐MRF sequence in healthy volunteers showed age‐dependent changes in knee cartilage, primarily within the medial compartment.
The cover image is based on the Research Article Quantitative platform for accurate and reproducible assessment of transverse (T2) relaxation time by Dvir Radunsky et al., ...https://doi.org/10.1002/nbm.4537.
•Futility of the Fuoss-Kirkwood relation proven by impedance parity with reason outlined.•Complex-valued distribution of relaxation times (DRT) using the Hilbert integral transform.•Inversion of DRT ...impedance by Mellin integral transform possible.
The Fuoss-Kirkwood (FK) relation is used to derive analytical expressions for the distribution of uncorrelated relaxation times (DRT), particularly of probed biochemical and electrochemical systems, often without scrutiny. Its futility is proven simply by using the parity of impedance with complex frequencies. However, given the futile nature of the FK relation, these expressions are not suitable for validation of computed DRT spectra. Despite this, the need for such expressions persists. Addressing this need and the oversight of the dependency of the DRT value on the underlying data, the DRT is extended into the complex plane using the Hilbert transform (HT). It makes the DRT universal for any complex-valued quantity to not only quantify the extent of relaxations but also to assess their nature. keyword: distribution; integral transforms; relaxation time; superposition.
A key challenge in textile sensors is to adequately solve the hysteresis for more broad and exacting applications. Unlike the conventional strategy in integrating elastic polymers into the textile, ...the hysteretic issue is critically addressed here through the structural design of yarns to provide a twisting force. The underlying mechanism is fully discussed based on theory and modeling, which are in good agreement with experimental data. Impressively, the pressure sensor outperforms almost all reported textile‐based sensors in terms of recovery index, which refers to the ability to overcome the lagged deformation reflected by the hysteresis (5.3%) and relaxation time (2 ms). Besides, the sensor superiority is also demonstrated by way of its ultrafast response time (2 ms). Thanks to these merits, this pressure sensor is demonstrated to be capable of monitoring epidermal pulses and meanwhile shows great potential to advance the standardization and modernization of pulse palpation in traditional Chinese medicine.
Hysteresis is a critical issue existing in textiles sensors. Distinct from the conventional methods, in this work, a biomimetic DNA‐like double‐helix structure is introduced into a textile‐based pressure sensor, providing a twisting force to allow quick and sufficient recovery from the deformation. Ultimately, the hysteresis is largely inhibited together with an improved response/relaxation time.
It is highly nontrivial to what extent we can deduce the relaxation behavior of a quantum dissipative system from the spectral gap of the Liouvillian that governs the time evolution of the density ...matrix. We investigate the relaxation processes of a quantum dissipative system that exhibits the Liouvillian skin effect, which means that the eigenmodes of the Liouvillian are localized exponentially close to the boundary of the system, and find that the timescale for the system to reach a steady state depends not only on the Liouvillian gap Δ , but also on the localization length ξ of the eigenmodes. In particular, we show that the longest relaxation time τ that is maximized over initial states and local observables is given by τ ∼ Δ − 1 ( 1 + L / ξ ) with L being the system size. This implies that the longest relaxation time can diverge for L → ∞ without gap closing.
Purpose
Relaxation times can contribute to spectral assignment. In this study, effective T2 relaxation times (T2eff) of macromolecules are reported for gray and white matter–rich voxels in the human ...brain at 9.4 T. The T2eff of macromolecules are helpful to understand their behavior and the effect they have on metabolite quantification. Additionally, for absolute quantification of metabolites with magnetic resonance spectroscopy, appropriate T2 values of metabolites must be considered. The T2 relaxation times of metabolites are calculated after accounting for TE/sequence‐specific macromolecular baselines.
Methods
Macromolecular and metabolite spectra for a series of TEs were acquired at 9.4 T using double inversion–recovery metabolite‐cycled semi‐LASER and metabolite‐cycled semi‐LASER, respectively. The T2 relaxation times were calculated by fitting the LCModel relative amplitudes of macromolecular peaks and metabolites to a mono‐exponential decay across the TE series. Furthermore, absolute concentrations of metabolites were calculated using the estimated relaxation times and internal water as reference.
Results
The T2eff of macromolecules are reported, which range from 13 ms to 40 ms, whereas, for metabolites, they range from 40 ms to 110 ms. Both macromolecular and metabolite T2 relaxation times are observed to follow the decreasing trend, with increasing B0. The linewidths of metabolite singlets can be fully attributed to T2 and B0 components. However, in addition to these components, macromolecule linewidths have contributions from J‐coupling and overlapping resonances.
Conclusion
The T2 relaxation times of all macromolecular and metabolite peaks at 9.4 T in vivo are reported for the first time. Metabolite relaxation times were used to calculate the absolute metabolite concentrations.
Magnetic resonance fingerprinting (MRF) is an emerging imaging technique for rapid and simultaneous quantification of multiple tissue properties. The technique has been developed for quantitative ...imaging of different organs. The obtained quantitative measures have the potential to improve multiple steps of a typical radiotherapy workflow and potentially further improve integration of magnetic resonance imaging guided clinical decision making. In this review paper, we first provide a technical overview of the MRF method from data acquisition to postprocessing, along with recent development in advanced reconstruction methods. We further discuss critical aspects that could influence its usage in radiation therapy, such as accuracy and precision, repeatability and reproducibility, geometric distortion, and motion robustness. Finally, future directions for MRF application in radiation therapy are discussed.
PDF
