Second-order quadrupolar shifts as an NMR probe of fast molecular-scale dynamics in solids

Molecular-scale dynamics on the nanosecond timescale or faster can have a measurable influence on isotropic NMR frequencies of quadrupolar nuclei. Although previously studied in solution, where it is usually referred to as the ‘dynamic shift’, this effect is less well known in solids. Here we demonstrate that multiple-quantum NMR measurements of isotropic quadrupolar shifts are a simple way to probe nanosecond timescale motions in solids. We measure the <sup>11</sup>B (spin I = 3/2) shifts of the resolved boron sites in ortho-carborane as a function of temperature and interpret the results in terms of the known rapid tumbling dynamics

A fast method for the measurement of long spin-lattice relaxation times by Single Scan Inversion Recovery experiment

A new method of measuring long spin-lattice relaxation times ($T_1$) is proposed. Being a single scan technique, the method is at least one order of magnitude faster than the conventional technique. This method (Single-Scan or Slice Selected Inversion Recovery or SSIR) relies on the slice selection technique. The method is experimentally verified and compared with the time taken by the conventional measurement. Furthermore, it is shown that the conventional Inversion Recovery (IR) method which suffers from effects of r.f. inhomogeneity can also be improved by measuring the magnetization of only a central slice.Comment: 12 pages, 5 figures. Chemical Physics Letters, in pres

Magic angle spinning (MAS) NMR linewidths in the presence of solid-state dynamics

In solid-state NMR, the magic angle spinning (MAS) technique fails to suppress anisotropic spin interactions fully if reorientational dynamics are present, resulting in a decay of the rotational-echo train in the time-domain signal. We show that a simple analytical model can be used to quantify this linebroadening effect as a function of the MAS frequency, reorientational rate constant, and magnitude of the inhomogeneous anisotropic broadening. We compare this model with other theoretical approaches and with exact computer simulations, and show how it may be used to estimate rate constants from experimental NMR data

How does blood regulate cerebral temperatures during hypothermia?

AbstractMacro-modeling of cerebral blood flow can help determine the impact of thermal intervention during instances of head trauma to mitigate tissue damage. This work presents a bioheat model using a 3D fluid-porous domain coupled with intersecting 1D arterial and venous vessel trees. This combined vascular porous (VaPor) model resolves both cerebral blood flow and energy equations, including heat generated by metabolism, using vasculature extracted from MRI data and is extended using a tree generation algorithm. Counter-current flows are expected to increase thermal transfer within the brain and are enforced using either the vascular structure or flow reversal, represented by a flow reversal constant, C R . These methods exhibit larger average brain cooling (from 0.56 °C ± &lt;0.01 °C to 0.58 °C ± &lt;0.01 °C) compared with previous models (0.39 °C) when scalp temperature is reduced. An greater reduction in core brain temperature is observed (from 0.29 °C ± &lt;0.01 °C to 0.45 °C ± &lt;0.01 °C) compared to previous models (0.11 °C) due to the inclusion of counter-current cooling effects. The VaPor model also predicts that a hypothermic average temperature (&lt;36 °C) can be reached in core regions of neonatal models using scalp cooling alone.</jats:p

Quantitative magnetisation transfer imaging in relapsing-remitting multiple sclerosis: a systematic review and meta-analysis

Myelin-sensitive MRI such as magnetization transfer imaging has been widely used in multiple sclerosis. The influence of methodology and differences in disease subtype on imaging findings is, however, not well established. Here, we systematically review magnetization transfer brain imaging findings in relapsing-remitting multiple sclerosis. We examine how methodological differences, disease effects and their interaction influence magnetization transfer imaging measures. Articles published before 06/01/2021 were retrieved from online databases (PubMed, EMBASE and Web of Science) with search terms including ‘magnetization transfer’ and ‘brain’ for systematic review, according to a pre-defined protocol. Only studies that used human in vivo quantitative magnetization transfer imaging in adults with relapsing-remitting multiple sclerosis (with or without healthy controls) were included. Additional data from relapsing-remitting multiple sclerosis subjects acquired in other studies comprising mixed disease subtypes were included in meta-analyses. Data including sample size, MRI acquisition protocol parameters, treatments and clinical findings were extracted and qualitatively synthesized. Where possible, effect sizes were calculated for meta-analyses to determine magnetization transfer (i) differences between patients and healthy controls; (ii) longitudinal change and (iii) relationships with clinical disability in relapsing-remitting multiple sclerosis. Eighty-six studies met inclusion criteria. MRI acquisition parameters varied widely, and were also underreported. The majority of studies examined the magnetization transfer ratio in white matter, but magnetization transfer metrics, brain regions examined and results were heterogeneous. The analysis demonstrated a risk of bias due to selective reporting and small sample sizes. The pooled random-effects meta-analysis across all brain compartments revealed magnetization transfer ratio was 1.17 per cent units (95% CI −1.42 to −0.91) lower in relapsing-remitting multiple sclerosis than healthy controls (z-value: −8.99, P < 0.001, 46 studies). Linear mixed-model analysis did not show a significant longitudinal change in magnetization transfer ratio across all brain regions [β = 0.12 (−0.56 to 0.80), t-value = 0.35, P = 0.724, 14 studies] or normal-appearing white matter alone [β = 0.037 (−0.14 to 0.22), t-value = 0.41, P = 0.68, eight studies]. There was a significant negative association between the magnetization transfer ratio and clinical disability, as assessed by the Expanded Disability Status Scale [r = −0.32 (95% CI −0.46 to −0.17); z-value = −4.33, P < 0.001, 13 studies]. Evidence suggests that magnetization transfer imaging metrics are sensitive to pathological brain changes in relapsing-remitting multiple sclerosis, although effect sizes were small in comparison to inter-study variability. Recommendations include: better harmonized magnetization transfer acquisition protocols with detailed methodological reporting standards; larger, well-phenotyped cohorts, including healthy controls; and, further exploration of techniques such as magnetization transfer saturation or inhomogeneous magnetization transfer ratio