We introduce a new two-dimensional nuclear quadrupole resonance experiment, in which the first time period (t1) is the duration of the radiofrequency exciting pulse; and the second (t2) is the normal free precession of a quadrupolar nucleus at zero field. After double Fourier transformation, the result is a 2D spectrum in which the first frequency dimension is the nutation spectrum for the quadrupolar nucleus at zero field. For single crystals, this spectrum contains narrow lines, whose frequency, for axially symmetric tensors, is proportional to sin θ, where θ is the angle between the unique axis of the quadrupolar tensor and that of the transmitter/receiver coil. For polycrystalline samples we obtain powder line shapes which are reminiscent of high-field nuclear magnetic resonance (NMR) powder patterns, and which allow determination of the asymmetry parameter η, which has previously only been obtainable using Zeeman perturbed nuclear quadrupole resonance (NQR) methods. Both theoretical spectra and several experimental examples are presented.

Evidence mounts that the steady-state cellular water efflux (unidirectional) first-order rate constant (k io [s À1 ]) magnitude reflects the ongoing, cellular metabolic rate of the cytolemmal Na + , K + -ATPase (NKA), c MR NKA (pmol [ATP consumed by NKA]/s/cell), perhaps biology's most vital enzyme. Optimal 1 H 2 O MR k io determinations require paramagnetic contrast agents (CAs) in model systems. However, results suggest that the homeostatic metabolic k io biomarker magnitude in vivo is often too large to be reached with allowable or possible CA living tissue distributions. Thus, we seek a noninvasive (CA-free) method to determine k io in vivo. Because membrane water permeability has long been considered important in tissue water diffusion, we turn to the well-known diffusion-weighted MRI (DWI) modality. To analyze the diffusion tensor magnitude, we use a parsimoniously primitive model featuring Monte Carlo simulations of water diffusion in virtual ensembles comprising water-filled and -immersed randomly sized/shaped contracted Voronoi cells. We find this requires two additional, cytometric properties: the mean cell volume (V [pL]) and the cell number density (ρ [cells/μL]), important biomarkers in their own right. We call this approach metabolic activity diffusion imaging (MADI).We simulate water molecule displacements and transverse MR signal decays covering the entirety of b-space from pure water (ρ = V = 0; k io undefined; diffusion coefficient, D 0 ) to zero diffusion. The MADI model confirms that, in compartmented spaces with semipermeable boundaries, diffusion cannot be described as Gaussian: the nanoscopic D (D n ) is diffusion time-dependent, a manifestation of the "diffusion dispersion". When the "well-mixed" (steady-state) condition is reached, diffusion becomes limited, mainly by the probabilities of (1) encountering (ρ, V), and (2) permeating (k io ) cytoplasmic membranes, and less so by D n magnitudes. Importantly, for spaces with large area/volume (A/V; claustrophobia) ratios, this can happen in less than a millisecond. The model matches literature experimental data well, with implications for DWI interpretations.

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T 1ρ relaxation imaging is a quantitative imaging technique that has been used to assess cartilage integrity, liver fibrosis, tumors, cardiac infarction, and Alzheimer's disease. T 1 , T 2 , and T 1ρ relaxation time constants have each demonstrated different degrees of sensitivity to several markers of fibrosis and inflammation, allowing for a potential multi-parametric approach to tissue quantification. Traditional magnetic resonance fingerprinting (MRF) has been shown to provide quick, quantitative mapping of T 1 and T 2 relaxation time constants. In this study, T 1ρ relaxation is added to the MRF framework using spin lock preparations. An MRF sequence involving an RFspoiled sequence with T R , flip angle, T 1ρ , and T 2 preparation variation is described.The sequence is then calibrated against conventional T 1 , T 2 , and T 1ρ relaxation mapping techniques in agar phantoms and the abdomens of four healthy volunteers.Strong intraclass correlation coefficients (ICC > 0.9) were found between conventional and MRF sequences in phantoms and also in healthy volunteers (ICC > 0.8).The highest ICC correlation values were seen in T 1 , followed by T 1ρ and then T 2 . In this study, T 1ρ relaxation has been incorporated into the MRF framework by using spin lock preparations, while still fitting for T 1 and T 2 relaxation time constants. The acquisition of these parameters within a single breath hold in the abdomen alleviates the issues of movement between breath holds in conventional techniques. K E Y W O R D Sbody, quantitation, relaxometry, sampling strategies 1 | INTRODUCTION T 1ρ relaxation imaging is a quantitative imaging technique that has been used to assess cartilage integrity, 1-4 liver fibrosis, 5 tumors, 6 cardiac infarction, 7 and Alzheimer's disease. 8 T 1ρ relaxation has also been shown to correlate with large molecules that tumble at low frequencies, including proteoglycans in ex vivo bovine 9,10 and human 11,12 cartilage experiments, demonstrating a decrease in T 1ρ relaxation time as the proteoglycan concentration decreases. However, T 1ρ is highly correlated with T 1 and T 2 relaxation, with the relationship being dependent on the strength of the spin locking RF pulse. Therefore, by measuring T 1 , T 2 , and T 1ρ , the effects of T 1 and T 2 relaxation can be accounted for and the unique chemical exchange component of T 1ρ can potentially be isolated. In addition, these relaxation parameters have been found to correlate to separate portions of the unique aspects of the extracellular matrix. For example, in ex vivo articular cartilage, T 1 and T 1ρ have been shown to correlate more strongly with proteoglycans while T 2 relaxation correlates more strongly with collagen. [11][12][13][14] In cartilage degeneration and liver fibrosis, T 1ρ has been shown to correlate more strongly with fibrosis than T 1 or T 2 relaxation. [15][16][17] Therefore, acquiring all of these parameters could allow for a more comprehensive view of the biochemical structure of the tissue. Abbreviations: FA, flip angle; ICC, intracla...

Deuterium relaxation experiments have been carried out at 38.4 MHz from 29.9 to 44.3 °C on p-butoxybenzylidene-p-n-octylaniline (40⋅8), a smectic B liquid crystal, which had been deuterated in the aniline ring and along the octyl chain. The Jeener–Broekaert pulse sequence was used to determine the spectral densities of motion J1(ω) and J2(ω), and by rotating the sample such that the optic axis was oriented at three different angles to the external magnetic field we are able to obtain information about the frequency dependence not just of J1 and J2 but also of J0. We report here the first measurements of the latter parameter at frequencies other than zero.