Portable NMR Research Articles

Gel Cleaning in Heritage: Comparison of the Water Release among Gels and Traditional Pads

Water release is a crucial aspect when considering cleaning effects on water-sensitive materials. In conservation practice, a water-based cleaning method which limits water release is very often needed. Unfortunately, this is not accompanied by an appropriate measure of the effectively released water. In this paper, water release has been measured by comparing traditional cleaning formulations, such as paper pulp and sepiolite, with several gar gel formulations, used by both Italian and European conservators. The assessment has been carried out by the gravimetric method, using three different stone material specimens as reference: Noto calcarenite, Manciano sandstone and Black Bergamo limestone, whose porosity values and distributions are known. Moreover, water distribution has been evaluated by portable NMR tests. Different commercial agar gel products (Bresciani, CTS, Sigma), having different concentrations (3, 4, and 5%), application modes (rigid at room T or fluid warm gels, with and without inserting Japanese tissue paper), and geometry (horizontal in gravity force direction or vertical), have been compared to obtain a full scenario among different water release mechanisms present in real conservation works. The paper faces the important issue of preparing reproducible chemical or water pads as well, useful for further research aimed at comparing cleaning effects in heritage conservation. The most interesting quantitative results can be summarized as follows. The water release measured from paper pulp and sepiolite was found to be 2 to 4 times higher than from any tested agar gel. Water release decreases by increasing agar concentration; an increase in the agar concentration by 1% induces a decrease in water release in the range 16.98–66.88 g depending on the stone; the increase from 4% to 5% is more obvious with respect to that from 3% to 4%. It is possible to assess the effect of the presence of Japanese paper, which is able to reduce the water release from 18 to 76%, depending on the stone and on the agar used. The gravimetric results were also used in the preliminary calibration tests of a contact probe named System Unit Salinity Index (SUSI), recently patented and useful in providing humidity and salinity indexes in a given porous material.

Quantitative measurement of mammographic density in breast-tissue explants using portable NMR: Precision and accuracy.

Single-sided portable NMR (pNMR) has previously been demonstrated to be suitable for quantification of mammographic density (MD) in excised breast tissue samples. Here we investigate the precision and accuracy of pNMR measurements of MD ex vivo as compared with the gold standards. Forty-five breast-tissue explants from 9 prophylactic mastectomy patients were measured. The relative tissue water content was taken as the MD-equivalent quantity. In each sample, the water content was measured using some combination of three pNMR techniques (apparent T2, diffusion, and T1 measurements) and two gold-standard techniques (computed microtomography [μCT] and hematoxylin and eosin [H&E] histology). Pairwise correlation plots and Bland-Altman analysis were used to quantify the degree of agreement between pNMR techniques and the gold standards. Relative water content measured from both apparent T2 relaxation spectra, and diffusion decays exhibited strong correlation with the H&E and μCT results. Bland-Altman analysis yielded average bias values of -0.4, -2.6, 2.6, and 2.8 water percentage points (pp) and 95% confidence intervals of 13.1, 7.5, 11.2, and 11.8 pp for the H&E - T2, μCT - T2, H&E - diffusion, and μCT - diffusion comparison pairs, respectively. T1-based measurements were found to be less reliable, with the Bland-Altman confidence intervals of 27.7 and 33.0 pp when compared with H&E and μCT, respectively. Apparent T2-based and diffusion-based pNMR measurements enable quantification of MD in breast-tissue explants with the precision of approximately 10 pp and accuracy of approximately 3 pp or better, making pNMR a promising measurement modality for radiation-free quantification of MD.

Multimodal spectroscopic assessment of mechanical and chemical properties of ABS objects in cultural heritage preservation

The 1960s saw the emergence of plastic as an indispensable component in various fields, including art and design. Acrylonitrile-butadiene-styrene (ABS) is widely used by artists and designers for a range of applications including sculptures and decorative pieces. Consequently, the necessity to conserve ABS from deterioration is a crucial issue in the field of cultural heritage preservation. Many studies have highlighted the criticality of the stability of the polybutadiene component when exposed to light. We propose a new multimodal spectroscopic approach to assess the conservation status of plastic design objects. This non-destructive approach combines correlative Brillouin and Raman micro-spectroscopy (BRaMS), external reflection IR spectroscopy and portable NMR relaxometry. BRaMS is a novel non-destructive technique in the field of heritage conservation, allowing simultaneous monitoring of chemical and mechanical changes occurring at the sample surface. The present study focused on photochemically aged LEGO® bricks made of ABS and aimed to i) correlate chemical and mechanical changes induced by light exposure and ii) introduce a surface degradation index (SDI), measurable in situ by external reflection IR spectroscopy, to assess the state of conservation of plastic artefacts. Finally, non-invasive investigations were carried out on real design objects using the MObile LABoratory (MOLAB) platform.

Portable NMR for the investigation of models of mammographic density ex vivo: Androgens antagonise the promotional effect of oestrogen

Background: Increased mammographic density (MD) is a strong and independent risk factor for breast cancer. Lifetime oestrogenic exposure is associated with increased MD, however androgenic effects on MD have not been widely investigated. Methods: We studied the effect of 17 β-oestradiol (E2) alone or in combination with an androgen receptor (AR) agonist ( 5 α-dihydrotestosterone [DHT]) or a selective AR modulator (Enobosarm), in modulating MD as measured via single-sided Portable NMR in a patient-derived explant (PDE) model of normal human mammary tissue. Results: We observed an upward trend in explants treated with E2 alone in 3/6 cases, an effect which appeared to be somewhat influenced by menopausal status. Co-treatment of E2 with the AR agonists DHT or Enobosarm however effected a downward trend in regards to MD. E2 significantly upregulated the ER regulated genes (ERGs) CELSR2 and AR, and the AR regulated genes SEC14L2 and GRPC5A, whereas E2 in combination with AR agonist Enobosarm downregulated ERGs SERPINA3, ATP6V1B1, TFF1 and PR regulated gene RANK. Only GREB1 and CLIC6 were upregulated by E2 and downregulated by the combination of E2 with Enobosarm. DHT + E2 exhibited no significant difference in expression of ER, AR or PR genes examined, compared with the effect of E2 alone. A negative trend was observed between ER protein levels and MD increase in PDEs. Since ER protein gets degraded upon hormone activation, this observation supports active ER signalling in the promotion of MD. Conclusions: Collectively, these findings supports the utility of single-sided Portable NMR for the measurement of MD in explanted human mammary tissue to detect MD change in response to exogenous hormone treatments. A mechanism through which activation of AR may reduce MD as a potential mechanism for reducing breast cancer risk associated to high MD is discussed.

An easy-built Halbach magnet for LF-NMR with high homogeneity using optimized target-field passive shimming method

The aim of this work is to develop a Halbach magnet that possesses characteristics such as easy-built, low cost and high homogeneity for use in a portable low-field NMR (LF-NMR) system. Considering portability, a 4-ring Halbach magnet was designed through simulation and mechanical modelling, which was successfully constructed in a general laboratory setting. The obtained field strength (B0) was 0.169 T, with an initial homogeneity of 8204 ppm within a sphere with a diameter of 20 mm. To enhance robustness, efficiency and effectiveness of shimming, an optimized target-field passive shimming method was proposed. Subsequently, the homemade spectrometer was used to run NMR experiments on the Halbach magnet. The 1H NMR linewidths of water samples became significantly narrower after passive shimming, e.g., the linewidth of a sample with a diameter of 3 mm and a length of 3 mm reduced from 452.3 Hz (62.5 ppm) to 12.9 Hz (1.8 ppm), which was much less than 102 Hz. The NMR results demonstrate that the proposed passive shimming method can achieve high homogeneity, and the developed Halbach magnet is capable of satisfying numerous LF-NMR applications.

A Portable Chip-Based NMR Relaxometry System With Arbitrary Phase Control for Point-of-Care Blood Analysis.

In this article, we present a portable NMR relaxometry system optimized for the point-of-care analysis of body liquids such as blood. The presented system is centered on an NMR-on-a-chip transceiver ASIC, a reference frequency generator with arbitrary phase control, and a custom-designed miniaturized NMR magnet with a field strength of 0.29 T and a total weight of 330 g. The NMR-ASIC co-integrates a low-IF receiver, a power amplifier, and a PLL-based frequency synthesizer on a total chip area of 1100 × 900 μm 2. The arbitrary reference frequency generator enables the use of conventional CPMG and inversion sequences, as well as modified water-suppression sequences. Moreover, it is used to implement an automatic frequency lock to correct temperature-induced magnetic field drifts. Proof-of-concept measurements on NMR phantoms and human blood samples show an excellent concentration sensitivity of v[Formula: see text] = 2.2 mM/[Formula: see text]. This very good performance renders the presented system an ideal candidate for the future NMR-based point-of-care detection of biomarkers such as the blood glucose concentration.

A pulsed current-mode class-D low-voltage high-bandwidth power amplifier for portable NMR systems

Low-field NMR has seen growing interest in recent years, especially for portable applications. The lower homogeneity magnets used for portable applications require short RF pulses to ensure enough transmit bandwidth to excite the sample volume and also support short echo periods. Furthermore, the preferred use of a high-Q coil to improve signal-to-noise ratio (SNR) prolongs the pulse transients. Thus, at such low Larmor frequencies, the excitation pulse transients become comparable or longer than the pulse length, such that the transmit bandwidth begins to limit measurement SNR. This paper describes the design of a pulsed current-mode class-D power (PCMCD) transmitter that addresses this issue by generating high power in a tuned sample coil while maintaining short transients, thus resulting in high output bandwidth. The transmitter also uses a charge recycling mechanism to maximize power efficiency for RF train excitation, which also results in faster pulse repetition rate and reduces allowable echo time. Experimental results from a small form-factor PCMCD transmitter are presented. This design generates a peak RF power of 240 W into a 9.16 μH coil at 4 MHz while operating off a single 12 V power supply. NMR measurement results using the transmitter are also described, showing minimum achievable echo time of 70 μs and 25 μs depending on the transmitter mode of operation.

Theoretical foundation for designing multilayer Halbach array magnets for benchtop NMR and MRI

Multilayer Halbach array magnets support portable NMR and MRI, but optimizing their design to maximize performance and minimize the use of expensive magnet materials is challenging. This is partly because our theoretical understanding of such arrays is incomplete and computationally intensive. Here we provide a theoretical description of the magnetic field distribution and we demonstrate that inhomogeneity is greatest along the z axis in multilayer Halbach array magnets. This allows the configuration of the multilayer Halbach array magnets to be optimized in a way that takes into account homogeneity, magnet volume, and magnetic flux density. At the same time, our description simplifies the design of multilayer array magnets, while accommodating the possibility of different outer radii, lengths for each layer array, or the presence of separation between the rings. We validated the theoretical description in simulations of a three-layer Halbach array magnet, then with a prototype three-layer 1-T Halbach array magnet. After adjusting the position of magnet blocks in the neighboring rings, we achieved homogeneity of 220 ppm for a standard 5 mm NMR tube while the inner diameter of the magnet is 20 mm. Our work provides a theoretical foundation for designing multilayer Halbach array magnets to maximize homogeneity and minimize the use of magnet materials.

Portable NMR for quantification of breast density in vivo: Proof-of-concept measurements and comparison with quantitative MRI

Mammographic Density (MD) is the degree of radio-opacity of the breast in an X-ray mammogram. It is determined by the Fibroglandular: Adipose tissue ratio. MD has major implications in breast cancer risk and breast cancer chemoprevention. This study aimed to investigate the feasibility of accurate, low-cost quantification of MD in vivo without ionising radiation.We used single-sided portable nuclear magnetic resonance (“Portable NMR”) due to its low cost and the absence of radiation-related safety concerns. Fifteen (N = 15) healthy female volunteers were selected for the study and underwent an imaging routine consisting of 2D X-ray mammography, quantitative breast 3T MRI (Dixon and T1-based 3D compositional breast imaging), and 1D compositional depth profiling of the right breast using Portable NMR. For each participant, all the measurements were made within 3–4 h of each other. MRI-determined tissue water content was used as the MD-equivalent quantity. Portable NMR depth profiles of tissue water were compared with the equivalent depth profiles reconstructed from Dixon and T1-based MR images, which were used as the MD-equivalent reference standard.The agreement between the depth profiles acquired using Portable NMR and the reconstructed reference-standard profiles was variable but overall encouraging. The agreement was somewhat inferior to that seen in breast tissue explant measurements conducted in vitro, where quantitative micro-CT was used as the reference standard. The lower agreement in vivo can be attributed to an uncertainty in the positioning of the Portable NMR sensor on the breast surface and breast compression in Portable NMR measurements.The degree of agreement between Portable NMR and quantitative MRI is encouraging. While the results call for further development of quantitative Portable NMR, they demonstrate the in-principle feasibility of Portable NMR-based quantitative compositional imaging in vivo and show promise for the development of safe and low-cost protocols for quantification of MD suitable for clinical applications.

Dynamic mechanical analysis with portable NMR

Dynamic mechanical analysis (DMA) is an umbrella term for a variety of rheological experiments in which the response of a sample subjected to an oscillatory force is measured to characterize its dynamic properties. In this work, we present a method for DMA that employs a small unilateral three magnet array with an extended constant gradient to measure the velocity of a vibrating sample. By orienting the vibrations in the direction of the gradient, we use the motion-sensitized phase accumulation to determine the velocity. By implementing delays into the pulse sequence, we measure the phase at evenly spaced points in the vibration cycle, allowing for the acquisition of a complete velocity waveform. Using velocity waveforms, samples are characterized through differences in amplitude and phase, providing information on the magnitude of the dynamic modulus and loss-angle, respectively.

Decay of a Roman age pine wood studied by micro magnetic resonance imaging, diffusion nuclear magnetic resonance and portable nuclear magnetic resonance

Wood is a hygroscopic biodegradable porous material widely used by men in the past to create artworks. Its total preservation over time is quite rare and one of the best preservation modalities is waterlogging. Observing the anatomy of waterlogged archaeological wood could also be complicated because of its bacterial degradation. However, the characterization of wood morphology and conservation state is a fundamental step before starting any restoration intervention as it allows to extract information about past climatic conditions and human activities. In this work, a micro-invasive approach based on the combined use of high-resolution magnetic resonance imaging (MRI) and diffusion-nuclear magnetic resonance (NMR) was tested both on a modern and an ancient pine wood sample. Furthermore, a completely non-invasive analysis was performed by using portable NMR. This multi-analytical NMR approach allowed to highlight the effect of decay on the wood microstructure, through alterations in the pores size, tortuosity, and images contrast of the ancient pine compared to the modern one. This work pointed out the different but complementary multi-parametric information that can be obtained by using NMR and tested the potential of high-field MRI and low-field portable NMR in the detection of wood diagnostic features.

Dynamics of Diffusion, Evaporation, and Retention of Organic Solvents in Paints by Portable Nmr and Hr-Mas Nmr Spectroscopy

Dynamics of Diffusion, Evaporation, and Retention of Organic Solvents in Paints by Portable Nmr and Hr-Mas Nmr Spectroscopy

Non-Invasive Assessment of PVA-Borax Hydrogel Effectiveness in Removing Metal Corrosion Products on Stones by Portable NMR

Non-Invasive Assessment of PVA-Borax Hydrogel Effectiveness in Removing Metal Corrosion Products on Stones by Portable NMR

Studies of periodic seawater spray icing with unilateral NMR

Sea water ice has a complicated pore structure consisting of brine-filled pockets within a solid ice matrix. In this work, an unilateral Nuclear Magnetic Resonance instrument was used to characterize the evolution of sea-ice brine inclusions in two types of ice: stationary seawater ice and seawater spray ice formed by periodic spraying on horizontal and vertical surfaces. The portable unilateral NMR was capable of measuring very low amounts of brine (<10% of the water-filled volume). CPMG experiments were performed to extract the information on brine content and T2 distribution at temperatures between −6 °C and −16 °C. 1D imaging was used to spatially resolve the ice brine accumulation. The results show that the seawater spray ice growth, brine content (greater for the horizontal orientation than for the vertical one), and T2 distribution (unimodal for stationary ice and bimodal for spray ice) depend on temperature and surface orientation.

Portable CMOS NMR System With 50-kHz IF, 10-μs Dead Time, and Frequency Tracking

In this work, we report the portable NMR system which provides solutions to the existing problems in miniature CMOS NMR systems. First, a higher IF of 50 kHz is achieved by exploiting separate frequencies for sample excitation and LO, thereby having higher immunity to 1/f noise. The proposed phase detector circuit aligns the experiment trigger with the constant phase difference between two frequencies. It maintains the constant RX output phase in every experiment, allowing the direct signal averaging without extra phase correction. In addition, 40X faster RX recovery with RX BW switching enables the signal acquisition with the dead time of 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> . Fast settling improves the acquisition sensitivity. Lastly, a frequency calibration method based on signal peak detection is proposed. Combining the techniques with the fully integrated NMR transceivers, the system demonstrates the NMR experiments to measure the decaying time constant of less than 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> . Furthermore, NMR diffusion experiments are performed with the echo spacing of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.2\sim 8$ </tex-math></inline-formula> ms.

Combined use of rheology and portable low-field NMR in cystic fibrosis patients

BackgroundAs most cystic fibrosis (CF) patients progress to respiratory failure, lung functionality assessment is pivotal. We previously developed a test that indirectly monitors airways (inflammation/functional test) by measuring the spin-spin relaxation time (T2m) of the water hydrogens present in CF sputum. Here the T2m significance in the monitoring of CF lung disease was further investigated by studying the correlation of T2m with: 1) sputum viscoelasticity, 2) mucociliary clearability index (MCI)/cough clearability index (CCI) and 3) sputum average mesh-size. MethodsSputum samples from 25 consenting CF subjects were analyzed by rheology tests (elastic modulus G and zero shear viscosity η0) and Low Field Nuclear Magnetic (LF-NMR) resonance (T2m). MCI/CCI were calculated from the rheological parameters. The average mesh-size (ξ) of the sputum structure was then evaluated by rheology/LF-NMR, together with FEV1 for each patient. ResultsThere was an inverse correlation between G and η0 versus T2m, indicating that a worsening of the lung condition (T2m-FEV1 drop) is paralleled by an increase in sputum viscoelasticity (G and η0) favoring mucus stasis/inflammation. A direct correlation was also observed between T2m and MCI/CCI, showing that T2m provides information as to airway mucus clearing. Moreover, there was a direct correlation between T2m and the average sputum mesh size (ξ). ConclusionsWe demonstrated a correlation between T2m (measured in CF patient's sputum) and the sputum viscoelasticity/average mesh-size and with MCI/CCI, parameters related to airway mucus clearing. Thus, the present data strengthen the potential of our test to provide indirect monitoring of airway disease course in CF patients as T2m depends on mucus solid concentration and nanostructure.

Testing 1D and 2D single-sided NMR on Roman age waterlogged woods

Waterlogged archaeological wood can provide information on past human activities and technology but its structure may be modified due to microbial deterioration. Knowing its conservation state is fundamental for its restoration. Aim of this work was to test the use of non-destructive portable NMR for the microstructural characterization and preservation state of three archaeological wood samples (Roman age, 5th century AD). 1D T1 and T2 relaxation time distributions, as well as 2D T1-T2 and D-T2 distributions were measured by single-sided NMR and interpreted with the help of high resolution magnetic resonance imaging (MRI) and optical microscopy. Due to the complexity of the ancient wood samples, in this first study a multi-analytical approach was required. It allowed the characterization of both waterlogged softwood (spruce) and hardwood (chestnut and maple) by quantifying relaxation times and diffusion water components affected by the presence of degradation products such as fungi, paramagnetic agents, and microstructural changes. Optical microscopy was needed to investigate the sub-microscopic wood elements not resolved by MRI and validate indirect single-sided NMR investigations. Observations and results of this study will allow the improvement of single-sided NMR protocols for the analyses of archaeological wood in situ with portable NMR.

Single-Sided Portable NMR Investigation to Assess and Monitor Cleaning Action of PVA-Borax Hydrogel in Travertine and Lecce Stone

Single-Sided Portable NMR Investigation to Assess and Monitor Cleaning Action of PVA-Borax Hydrogel in Travertine and Lecce Stone

Trapped field evaluation of ring-shaped GdBCO bulk magnet excited by pulsed field magnetization

Recently, physical and mechanical properties of REBCO bulk are improved, and, accordingly, various practical applications are considered. As one of them, a portable bulk NMR system has been developed, and, then, the improvement of the system for practical use are progressing. In that system, 6 stacked bulks were magnetized by a superconducting magnet for NMR, resulting that the magnetic field of 4.74 T and inhomogeneity of 6.9 ppm were achieved. In this paper, we fabricated the bulk magnet with the room-temperature bore specialized in pulsed-field magnetization. The ring-shaped bulk was activated by pulsed-field magnetization, and, magnetic fields on the bulk surface and in the room-temperature bore of bulk magnet were evaluated. In the bore, the trapped field was approximately 0.79 T and homogeneity was over 150000 ppm.

Alginate-biocide hydrogel for the removal of biofilms from calcareous stone artworks

One aspect of heritage science is to examine and, if possible, reduce the chemical and physical interactions between the restoration products and artworks’ constituent materials. This research aims to identify an alternative process to minimize the impact on materials and health risk for users when hypochlorite is used as biocide on stone materials. In this study, we tested a hydrogel comprised of sodium alginate as an inert matrix and hypochlorite ions as biocide agents for the removal of biological patinas from calcarenite Lecce samples. These biofilms resulted formed mainly by filamentous cyanobacteria and green microalgae. We carried out 1H-NMR T2 relaxation measurements to check the hydrogel’s cleaning efficacy on artificially bio-deteriorated samples through a portable NMR equipment. Simultaneously, optical microscopy and colorimetric measurements allowed the establishment of color differences induced by treatments. Our biocide hydrogel proved to be effective in removing microbial colonization from the surface of Lecce stone specimens and from a section of an altar rail in the rupestrian Church of San Pietro Barisano, located in the “Sassi of Matera”.