Room temperature "optical nanodiamond hyperpolarizer": Physics, design, and operation

Dynamic Nuclear Polarization (DNP) is a powerful suite of techniques that deliver multifold signal enhancements in nuclear magnetic resonance (NMR) and MRI. The generated athermal spin states can also be exploited for quantum sensing and as probes for many-body physics. Typical DNP methods require the use of cryogens, large magnetic fields, and high power microwave excitation, which are expensive and unwieldy. Nanodiamond particles, rich in Nitrogen-Vacancy (NV) centers, have attracted attention as alternative DNP agents because they can potentially be optically hyperpolarized at room temperature. Here, unraveling new physics underlying an optical DNP mechanism first introduced by Ajoy et al. [Sci. Adv. 4, eaar5492 (2018)], we report the realization of a miniature "optical nanodiamond hyperpolarizer," where ¹³C nuclei within the diamond particles are hyperpolarized via the NV centers. The device occupies a compact footprint and operates at room temperature. Instrumental requirements are very modest: low polarizing fields, low optical and microwave irradiation powers, and convenient frequency ranges that enable miniaturization. We obtain the best reported optical ¹³C hyperpolarization in diamond particles exceeding 720 times of the thermal 7 T value (0.86% bulk polarization), corresponding to a ten-million-fold gain in averaging time to detect them by NMR. In addition, the hyperpolarization signal can be background-suppressed by over two-orders of magnitude, retained for multiple-minute long periods at low fields, and deployed efficiently even to ¹³C enriched particles. Besides applications in quantum sensing and bright-contrast MRI imaging, this work opens possibilities for low-cost room-temperature DNP platforms that relay the ¹³C polarization to liquids in contact with the high surface-area particles.

Amyloid oligomer formation probed by water proton magnetic resonance spectroscopy

Formation of amyloid oligomers, the most toxic species of amyloids in degenerative diseases, is critically coupled to the interplay with surrounding water. The hydrophobic force driving the oligomerization causes water removal from interfaces, changing the surface-hydration properties. Here, we show that such effects alter the magnetic relaxation response of local water in ways that may enable oligomer detection. By using water proton magnetic resonance spectroscopy, we measured significantly longer transverse magnetic relaxation (T(2)) times in mixtures of serum and amyloidogenic Aβ(1-42) peptides versus similar concentration solutions of serum and nonamyloidogenic scrambled Aβ(42-1) peptides. Immunochemistry with oligomer-specific antibodies, electron microscopy and computer simulations demonstrated that the hyperintense magnetic signal correlates with Aβ(1-42) oligomerization. Finding early biophysical markers of the oligomerization process is crucial for guiding the development of new noninvasive imaging techniques, enabling timely diagnosis of amyloid-related diseases and pharmacological intervention.

Error optimization of a three-dimensional magnetic resonance imaging tagging-based cartilage deformation technique

Three-dimensional strain fields in articular cartilage subjected to compressive loading can be determined using a recently developed MRI-based cartilage deformation by tag registration technique. The objective of this study was to determine the experimental variables that minimize the technique error, which has not been previously reported. Error (strain bias and precision) was determined using direct experiments and Monte Carlo simulations for four variables: spatial resolution, tag line spacing, applied nominal strain, and number of control points used to describe tag lines in a B-spline model. The important results include the following: (1) bias was not significantly different from zero, (2) precision increased with image resolution and with tag line spacing, (3) precision was independent of applied nominal strain, and (4) error was a minimum (absolute precision = 0.41% strain) for the following values: spatial resolution = 0.05 x 0.05 mm2; tag line spacing = 2.0 mm; control points = 6. With these results the technique can now be used in various applications while minimizing error.

Heterogeneous three-dimensional strain fields during unconfined cyclic compression in bovine articular cartilage explants

Articular cartilage provides critical load-bearing and tribological properties to the normal function of diarthrodial joints. The unique properties of cartilage, as well as heterogeneous deformations during mechanical compression, are due to the nonuniform microstructural organization of tissue components such as collagens and proteoglycans. A new cartilage deformation by tag registration (CDTR) technique has been developed by the authors to determine heterogeneous deformations in articular cartilage explants. The technique uses a combination of specialized MRI methods, a custom cyclic loading apparatus, and image processing software. The objective of this study was to use the CDTR technique to document strain patterns throughout the volume of normal bovine articular cartilage explants during cyclic unconfined compression at two physiologically-relevant applied normal stress levels (1.29 and 2.57 MPa). Despite simple uniaxial cyclic compressive loading with a flat, nonporous indenter, strain patterns were heterogeneous. Strains in the thickness direction (E(yy)) were compressive, varied nonlinearly with depth from the articular surface from a maximum magnitude of 11% at the articular surface, and were comparable despite a 2-fold increase in applied normal stress. Strains perpendicular to the thickness direction (E(xx) and E(zz)) were tensile, decreased linearly with depth from the articular surface from a maximum of 7%, and increased in magnitude 2.5-fold with a 2-fold increase in applied normal stress. Shear strains in the transverse plane (E(xz)) were approximately zero while shear strains in the other two planes were much larger and increased in magnitude with depth from the articular surface, reaching maximum magnitudes of 2% at the articular cartilage-subchondral bone interface. In general, strain patterns indicated that cartilage osteochondral explants exhibited depth-dependent nonisotropic behavior during uniaxial cyclic loading. These results are useful in verifying constitutive formulations of articular cartilage during cyclic unconfined compression and in characterizing the micromechanical environment likely experienced by individual chondrocytes throughout the tissue volume.

MRI-based technique for determining nonuniform deformations throughout the volume of articular cartilage explants

Articular cartilage is critical to the normal function of diarthrodial joints. Despite the importance of the tissue and the prevalence of cartilage degeneration (e.g., osteoarthritis), the technology required to noninvasively describe nonuniform deformations throughout the volume of the tissue has not been available until recently. The objectives of the work reported in this paper were to 1) describe a noninvasive technique (termed the cartilage deformation by tag registration (CDTR) technique) to determine nonuniform deformations in articular cartilage explants with the use of specialized MRI tagging and image processing methods, 2) evaluate the strain error of the CDTR technique using a custom MRI-compatible phantom material, and 3) demonstrate the applicability of the CDTR technique to articular cartilage by determining 3D strain fields throughout the volume of a bovine articular cartilage explant. A custom MRI pulse sequence was designed to tag and image articular cartilage explants at 7 Tesla in undeformed and deformed states during the application of multiple load cycles. The custom pulse sequence incorporated the "delays alternating with nutations for tailored excitation" (DANTE) pulse sequence to apply tags. This was followed by a "fast spin echo" (FSE) pulse sequence to create images of the tags. The error analysis using the phantom material indicated that deformations can be determined with an error, defined as the strain precision, better than 0.83% strain. When this technique was applied to a single articular cartilage explant loaded in unconfined compression, hetereogeneous deformations throughout the volume of the tissue were evident. This technique potentially can be applied to determine normal cartilage deformations, analyze degenerated cartilage, and evaluate cartilage surgical repair and treatment methodologies. In addition, this technique may be applied to other soft tissues that can be appropriately imaged by MR.

Use of speech production repair strategies to improve diver communication

The purpose of this investigation was to determine if speech intelligibility improved when divers made specific modifications to their speaking patterns while in a hyperbaric helium-oxygen (heliox) environment. Divers were trained to produce a variety of sentences using speech with three types of alterations: (1) slowed rate, (2) increased loudness, and (3) a combination of slightly slowed rate, a minimal increase in loudness, increased pause time, and greater mouth opening (composite strategy). Both diver and non-diver listeners judged these sentences for intelligibility. In addition, acoustic analysis of the cues for the identification of voicing, place, and manner of articulation was conducted to determine if such cues might become more audible in the speech signal when repair strategies were used. Both perceptual and acoustic results showed the composite method to be the best for natural-sounding, intelligible speech. It had the effect of slowing rate and increasing loudness just enough to increase intelligibility without causing distortion. It was concluded that teaching divers to produce speech using this method would be a worthwhile investment for improving speech intelligibility.

Dynamics of fluid/particulate mixtures in tube flow

Magnetic resonance imaging (MRI) techniques have been utilized to experimentally measure the velocity profile of fluid/particulate mixtures as a function of flow rate, particle loading, and particle size. The experimental velocity profiles in tube flow were described by a power law model; the power law parameter decreased as flow rate, particle loading, and particle size increase. This work is relevant to aseptic processing of particulate foods.

Speaker race identification from acoustic cues in the vocal signal

One-second acoustic samples were extracted from the mid-portion of sustained /a/ vowels produced by 50 black and 50 white adult males. Each vowel sample from a black subject was randomly paired with a sample from a white subject. From the tape-recorded samples alone, both expert and naive listeners could determine the race of the speaker with 60% accuracy. The accuracy of race identification was independent of the listener's own race, sex, or listening experience. An acoustic analysis of the samples revealed that, although within ranges reported by previous studies of normal voices, the black speakers had greater frequency perturbation, significantly greater amplitude perturbation, and a significantly lower harmonics-to-noise ratio than did the white speakers. The listeners were most successful in distinguishing voice pairs when the differences in vocal perturbation and additive noise were greatest and were least successful when such differences were minimal or absent. Because there were no significant differences in the mean fundamental frequency or formant structure of the voice samples, it is likely that the listeners relied on differences in spectral noise to discriminate the black and white speakers.

Black English in a Mississippi prison population

Nine linguistic features unique to Black English were examined in the speech of 87 Black and 77 White inmates of a Mississippi prison population. The purpose of the study was to determine whether Black inmates could be distinguished from White inmates by their use of the present progressive, final stops, distributive be, remote aspect been, noun plurals, third person singular present tense, possessives, consonant clusters, and the copula. Results showed that use of eight of the nine features accurately predicted the ethnicity of the subjects. Only remote aspect been failed to identify ethnic differences. Identification of dialect variation among minority populations and more specifically among prison populations is an important step toward providing effective remediation programs.

CO/N2/Ar orientational glass: magnetic resonance

The nmr lineshapes and linewidths of KCN/KBr, N2/Ar, and CO/N2/Ar are compared at corresponding states and are found to agree closely. This indicates a similar kind of orientational freezing, despite major differences in the anisotropic molecular interactions. The line narrowing and T2 data are explicable by two different theories. The one involves an orientation probability function, while the other invokes a broad homogeneous distribution of correlation times. Spin–lattice relaxation measurements indicate that T1 and dielectric loss are controlled at low temperatures by nearly π flips of CO molecules.

Flow velocity measurement with ac gradients

Two NMR experiments are described that use ac field gradients to measure flow velocities. Both experiments perform no spacial localization; instead, fluid velocity is converted to a resonance frequency shift. Thus, by Fourier transformation of a single FID or echo train the distribution of velocities is available. The first experiment uses only one rf pulse but requires a homogeneous static field. The second experiment uses the CPMG multiple-pulse sequence to refocus the effects of field inhomogeneity and chemical shifts. Results are shown for both experiments using a simple flowing phantom. Applications of the techniques to time-resolved blood flow measurement are discussed.