Transverse Relaxation Research Articles

Anisotropic longitudinal water proton relaxation in white matter investigated ex vivo in porcine spinal cord with sample rotation

A variation of the longitudinal relaxation time T1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{1}$$\\end{document} in brain regions that differ in their main fiber direction has been occasionally reported, however, with inconsistent results. Goal of the present study was to clarify such inconsistencies, and the origin of potential T1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{1}$$\\end{document} orientation dependence, by applying direct sample rotation and comparing the results from different approaches to measure T1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{1}$$\\end{document}. A section of fixed porcine spinal cord white matter was investigated at 3 T with variation of the fiber-to-field angle θFB\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ heta_{{{\ ext{FB}}}}$$\\end{document}. The experiments included one-dimensional inversion-recovery, MP2RAGE, and variable flip-angle T1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{1}$$\\end{document} measurements at 22 °C and 36 °C as well as magnetization-transfer (MT) and diffusion-weighted acquisitions. Depending on the technique, different degrees of T1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{1}$$\\end{document} anisotropy (between 2 and 10%) were observed as well as different dependencies on θFB\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ heta_{{{\ ext{FB}}}}$$\\end{document} (monotonic variation or T1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{1}$$\\end{document} maximum at 30–40°). More pronounced anisotropy was obtained with techniques that are more sensitive to MT effects. Furthermore, strong correlations of θFB\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ heta_{{{\ ext{FB}}}}$$\\end{document}-dependent MT saturation and T1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{1}$$\\end{document} were found. A comprehensive analysis based on the binary spin-bath model for MT revealed an interplay of several orientation-dependent parameters, including the transverse relaxation times of the macromolecular and the water pool as well as the longitudinal relaxation time of the macromolecular pool.

Mapping vascular network architecture in primate brain using ferumoxytol-weighted laminar MRI.

Mapping the vascular organization of the brain is of great importance across various domains of basic neuroimaging research, diagnostic radiology, and neurology. However, the intricate task of precisely mapping vasculature across brain regions and cortical layers presents formidable challenges, resulting in a limited understanding of neurometabolic factors influencing the brain's microvasculature. Addressing this gap, our study investigates whole-brain vascular volume using ferumoxytol-weighted laminar-resolution multi-echo gradient-echo imaging in macaque monkeys. We validate the results with published data for vascular densities and compare them with cytoarchitecture, neuron and synaptic densities. The ferumoxytol-induced change in transverse relaxation rate (ΔR2*), an indirect proxy measure of cerebral blood volume (CBV), was mapped onto twelve equivolumetric laminar cortical surfaces. Our findings reveal that CBV varies 3-fold across the brain, with the highest vascular volume observed in the inferior colliculus and lowest in the corpus callosum. In the cerebral cortex, CBV is notably high in early primary sensory areas and low in association areas responsible for higher cognitive functions. Classification of CBV into distinct groups unveils extensive replication of translaminar vascular network motifs, suggesting distinct computational energy supply requirements in areas with varying cytoarchitecture types. Regionally, baseline R2* and CBV exhibit positive correlations with neuron density and negative correlations with receptor densities. Adjusting image resolution based on the critical sampling frequency of penetrating cortical vessels, allows us to delineate approximately 30% of the arterial-venous vessels. Collectively, these results mark significant methodological and conceptual advancements, contributing to the refinement of cerebrovascular MRI. Furthermore, our study establishes a linkage between neurometabolic factors and the vascular network architecture in the primate brain.

Dielectric microwave resonator with large optical apertures for spin-based quantum devices

We demonstrate a low-loss dielectric microwave resonator with an internal quality factor of 2.30×104 while accommodating optical apertures with a diameter of 8 mm. The two seemingly conflicting requirements, high quality factor and large optical apertures, are satisfied, thanks to the large dielectric constant of rutile (TiO2). The quality factor is limited by radiation loss, and we confirmed by numerical simulation that this radiation loss can be suppressed by extending the enclosure height of the resonator; the resonator can potentially achieve a dielectric loss-limited quality factor, exceeding 106. Using this resonator, we performed both continuous-wave (cw) and pulse electron spin resonance (ESR) spectroscopy on 2,2-diphenyl-1-picrylhydrazyl (DPPH) crystalline powder and P1 centers in a diamond crystal in a dilution refrigerator. The cw ESR spectroscopy demonstrated high-cooperativity and strong spin-resonator coupling with the DPPH and P1 centers, respectively, while the pulse ESR spectroscopy successfully measured longitudinal and transverse relaxation times. This optically accessible low-loss microwave resonator enables the implementation of a spin-based quantum device, such as a microwave-optical photon transducer.

Multiparametric-magnetic resonance imaging (mp-MRI) of the prostate and Urolift: Identifying artefact size, location and clinical implications.

We sought to define the degree of artefact caused by prostatic urethral lift (PUL) on multiparametric-magnetic resonance imaging (mp-MRI) to determine the location, size of artefact and if the device could potentially obscure a diagnosis of prostate cancer. Ten patients were prospectively enrolled to undergo PUL for treatment of benign prostatic hyperplasia and follow-up imaging. A standard mp-MRI protocol using a 3.0 Tesla scanner was performed prior to and following Urolift insertion. Pre- and post-PUL images were compared to measure maximum artefact diameter around each implant in each MRI parameter. A transverse relaxation time weighted (T2) artefact reduction protocol was also evaluated. The location of each artefact was then compared to a separate database of 225 consecutive patients who underwent magnetic resonance guided prostate biopsies. Artefact occurred around the stainless steel urethral implant component only. Mean T2 artefact maximum diameter was 7.7mm (sd = 1.71 mm), with an artefact reduction protocol reducing this to 5.4mm (sd = 1.43). Mean dynamic-contrast-enhancement artefact was 10mm (sd = 2.5mm), and mean diffusion-weighted-imaging artefact was 28.2mm (sd = 7.8mm). All artefacts were confined to the posterior transition zone only. In the 225 consecutive patients who had undergone magnetic resonance guided prostate biopsies, there were 55 positive biopsies with prostate cancer, with 13 cases found in the transition zones and no cancer identified solely in the posterior transitional zone. The stainless steel urethral component of the PUL does cause artefact, which is confined to the posterior transition zone only. PUL artefact occurs in an area of the prostate that has a very low incidence of a single focus of prostate cancer. If there is concern for prostate cancer in the posterior TZ (e.g. if every other area is clear with a high PSA), this area can undergo targeted biopsy.

Anterior cruciate ligament injury and age affect knee cartilage T2 but not thickness

ObjectiveTo investigate the effect of unilateral anterior cruciate ligament (ACL) injury on cartilage thickness and composition, specifically laminar transverse relaxation time (T2) by magnetic resonance imaging (MRI), in younger and older participants and to compare within-person side differences in these parameters between ACL-injured and healthy controls. DesignQuantitative double-echo steady-state (qDESS) 3 Tesla MRI-sequences were acquired in both knees of 85 participants in four groups: 20–30 years: healthy, HEA20–30, n=24; ACL-injured, ACL20–30, n=23; 40–60 years: healthy, HEA40–60, n=24; ACL-injured, ACL40–60, n=14 (ACL injury 2–10 years prior to study inclusion). Weight-bearing femorotibial cartilages were manually segmented; cartilage T2 and thickness were computed using custom software. Mean and side difference in subregional cartilage thickness, superficial and deep cartilage T2 were compared within and between groups using non-parametric statistics. ResultsCartilage thickness did not differ within or between groups. Only the side difference in medial femorotibial cartilage thickness was greater in ACL20–30 than in HEA20–30. Deep zone T2 was longer in the ACL-injured than in the contralateral uninjured knees and than in healthy controls, especially in the lateral compartment. Most ACL-injured participants had side differences in femorotibial deep zone T2 above the threshold derived from controls. ConclusionIn the ACL-injured knee, early compositional differences in femorotibial cartilage (T2) appear to occur in the deep zone and precede cartilage thickness loss. These results suggest that monitoring laminar T2 after ACL injury may be useful in the diagnosing and monitoring early articular cartilage changes.

A fast and effective way to measure the inner pore size distributions of wetted cotton fibers and their pretreatment performance using time-domain nuclear magnetic resonance

This study reports the findings from using time-domain nuclear magnetic resonance (TD-NMR) to analyze the pore structures of cotton fibers. Cotton fibers, which swell and soften in water, present challenges for conventional pore measurement techniques. TD-NMR overcomes these by measuring the transverse relaxation time (T2) of water protons within the fibers, indicative of internal pore sizes. We established a T2-to-pore size conversion equation using mixed cellulose ester membranes. This enabled differentiation between strongly bound, loosely bound, and free water within the fibers, and detailed the water distribution. A method for measuring the pore size distribution of wet cotton fiber was developed using TD-NMR. We then examined how various pretreatments affect the fibers' internal pores by comparing their pore size distribution and porosity. Specifically, caustic mercerization primarily enlarges the porosity and size of larger pores, while liquid ammonia treatment increases porosity but reduces the size of smaller pores. This research confirms TD-NMR's utility in assessing cotton fabrics' wet processing performance.

Ready-to-print alginate inks: The effect of different divalent cations on physico-chemical properties of 3D printable alginate hydrogels

Studies about the use of different divalent cations to produce 3D printed scaffolds are almost limited to their application as secondary crosslinking agents after the printing of alginate. For this reason, this research aims to demonstrate the possibility to develop alginate hydrogel-inks for 3D-printing application, exploiting the ionotropic gelation in a preprint step, by paying attention to the role of divalent cations on hydrogel-inks properties. The investigation of transversal relaxation time highlighted differences among inks (barium-ink 90.04 ms, calcium-ink 84.33 ms, and zinc-ink 75.05 ms) suggesting a potential influence of different cations. If all the inks showed a shear thinning behaviour with similar flowability index (0.153±0.018), they were characterised by different consistency index (from 2420 to 574 Pa•s), extrudability and homogeneity, parameters that influence the printing setup. In fact, to reach the same flowability and thus low deviation in the layer width for all inks, a variation in printing pressure and speed was necessary. Overall, it can be deduced that alginate inks preparation following a preprint crosslinking approach could be a valid method to overcome the alginate printability issues underlining the possibility to select the crosslinking cation according to the technological properties wanted for the final matrix.

Influence of linearly polarized light on the transverse relaxation of ground-state 133Cs atoms

In order to obtain an understanding of the relationship between the optical absorption and the transverse relaxation, the influences of linearly polarized light respectively at 133Cs D1 and D2 lines on the transverse relaxation of ground-state 133Cs atoms are studied. Under different vapor temperatures, light intensities and light frequencies, transverse spin relaxation times are separately measured for 133Cs atoms in different hyperfine levels. For theoretically analyzing the measuring results, especially for an unusual trend that the transverse spin relaxation time rises with the increase of light intensity, photon absorption cross-sections of linearly polarized light by 133Cs atoms are simulated. The experimental results show that through influencing the optical absorption and spin-exchange collisions, the linearly polarized light plays a remarkable role in the transverse spin relaxation. The results obtained by this paper can provide a guide to find the optimal intensity and frequency of linearly polarized light in practical applications for decreasing the influences of linearly polarized light on the transverse relaxation.

Nanoparticulated Bimodal Contrast Agent for Ultra-High-Field Magnetic Resonance Imaging and Spectral X-ray Computed Tomography.

Bimodal medical imaging based on magnetic resonance imaging (MRI) and computed tomography (CT) is a well-known strategy to increase the diagnostic accuracy. The most recent advances in MRI and CT instrumentation are related to the use of ultra-high magnetic fields (UHF-MRI) and different working voltages (spectral CT), respectively. Such advances require the parallel development of bimodal contrast agents (CAs) that are efficient under new instrumental conditions. In this work, we have synthesized, through a precipitation reaction from a glycerol solution of the precursors, uniform barium dysprosium fluoride nanospheres with a cubic fluorite structure, whose size was found to depend on the Ba/(Ba + Dy) ratio of the starting solution. Moreover, irrespective of the starting Ba/(Ba + Dy) ratio, the experimental Ba/(Ba + Dy) values were always lower than those used in the starting solutions. This result was assigned to lower precipitation kinetics of barium fluoride compared to dysprosium fluoride, as inferred from the detailed analysis of the effect of reaction time on the chemical composition of the precipitates. A sample composed of 34 nm nanospheres with a Ba0.51Dy0.49F2.49 stoichiometry showed a transversal relaxivity (r2) value of 147.11 mM-1·s-1 at 9.4 T and gave a high negative contrast in the phantom image. Likewise, it produced high X-ray attenuation in a large range of working voltages (from 80 to 140 kVp), which can be attributed to the presence of different K-edge values and high Z elements (Ba and Dy) in the nanospheres. Finally, these nanospheres showed negligible cytotoxicity for different biocompatibility tests. Taken together, these results show that the reported nanoparticles are excellent candidates for UHF-MRI/spectral CT bimodal imaging CAs.

Assessment of water relaxometry of meat under different ageing processes using time domain nuclear magnetic resonance relaxometry

This study assessed water relaxometry of beef exposed to different ageing techniques by examining the inner and surface regions using time-domain nuclear magnetic resonance (TD-NMR) relaxometry. Beef strip loins were aged under vacuum (Wet), under vacuum using moisture absorbers (Abs), under vacuum using moisture absorbers and with mechanical tenderisation (AbsTend), or without any packaging (Dry). The ageing technique significantly influenced various meat parameters, including dehydration, total loss, and the moisture content of the meat surface. The transverse (T2) relaxation times provided a more sensitive indicator of the changes in meat water relaxometry than the longitudinal (T1) relaxation times. The Dry samples exhibited distinct differences in the T2 signals between the surface and inner regions of the meat. In particular, for the inner region, there were significant differences in signal areas between the Wet and Dry samples, and the Abs and AbsTend samples were positioned closely together between the Dry and Wet samples. The principal component analysis supported these findings: it indicated some differentiation among the ageing techniques in the score plot, but the differentiation was more pronounced when analysing the surface region. Additionally, there was a strong correlation between dehydration and the T2 values, leading to a clustering of the samples based on the ageing technique. The overlap between the Abs and AbsTend samples, situated between the Dry and Wet samples, suggests the potential of these treatments to produce meat with properties that are intermediate to Wet and Dry meat. Furthermore, tenderisation did not lead to greater dehydration.

Dynamic monitoring soft tissue healing via visualized Gd-crosslinked double network MRI microspheres

By integrating magnetic resonance-visible components with scaffold materials, hydrogel microspheres (HMs) become visible under magnetic resonance imaging(MRI), allowing for non-invasive, continuous, and dynamic monitoring of the distribution, degradation, and relationship of the HMs with local tissues. However, when these visualization components are physically blended into the HMs, it reduces their relaxation rate and specificity under MRI, weakening the efficacy of real-time dynamic monitoring. To achieve MRI-guided in vivo monitoring of HMs with tissue repair functionality, we utilized airflow control and photo-crosslinking methods to prepare alginate-gelatin-based dual-network hydrogel microspheres (G-AlgMA HMs) using gadolinium ions (Gd (III)), a paramagnetic MRI contrast agent, as the crosslinker. When the network of G-AlgMA HMs degrades, the cleavage of covalent bonds causes the release of Gd (III), continuously altering the arrangement and movement characteristics of surrounding water molecules. This change in local transverse and longitudinal relaxation times results in variations in MRI signal values, thus enabling MRI-guided in vivo monitoring of the HMs. Additionally, in vivo data show that the degradation and release of polypeptide (K2 (SL)6 K2 (KK)) from G-AlgMA HMs promote local vascular regeneration and soft tissue repair. Overall, G-AlgMA HMs enable non-invasive, dynamic in vivo monitoring of biomaterial degradation and tissue regeneration through MRI, which is significant for understanding material degradation mechanisms, evaluating biocompatibility, and optimizing material design.

DNA-Mediated Magnetic-Dimer Assembly for Fault-Free Ultra-High-Field Magnetic Resonance Imaging of Tumors.

Ultra-high-field (UHF) magnetic resonance imaging (MRI) stands as a pivotal cornerstone in biomedical imaging, yet the challenge of false imaging persists, constraining its full potential. Despite the development of dual-mode contrast agents improving conventional MRI, their effectiveness in UHF remains suboptimal due to the high magnetic moment, resulting in diminished T1 relaxivity and excessively enhanced T2 relaxivity. Herein, we report a DNA-mediated magnetic-dimer assembly (DMA) of iron oxide nanoparticles that harnesses UHF-tailored nanomagnetism for fault-free UHF-MRI. DMA exhibits a dually enhanced longitudinal relaxivity of 4.42 mM-1·s-1 and transverse relaxivity of 26.23 mM-1·s-1 at 9 T, demonstrating a typical T1-T2 dual-mode UHF-MRI contrast agent. Importantly, DMA leverages T1-T2 dual-modality image fusion to achieve artifact-free breast cancer visualization, effectively filtering interference from hundred-micrometer-level false-positive signals with unprecedented precision. The UHF-tailored T1-T2 dual-mode DMA contrast agents hold promise for elevating the accuracy of MR imaging in disease diagnosis.

Interactions of cumulative load with biomarkers of cartilage turnover predict knee cartilage change over 2 years: data from the osteoarthritis initiative.

The purpose was to investigate relationships of cumulative load and cartilage turnover biomarkers with 2-year changes in cartilage in knee osteoarthritis. From participants with Kellgren-Lawrence (KL) grades of 1 to 3, cartilage thickness and transverse relaxation time (T2) were computed from 24-month (baseline) and 48-month magnetic resonance images. Cumulative load was the interaction term of the Physical Activity Scale for the Elderly (PASE) and body mass index (BMI). Serum cartilage oligomeric matrix protein (COMP) and the nitrated form of type II collagen (Coll2-1 NO2) were collected at baseline. Multiple regressions (adjusted for baseline age, KL grade, cartilage measures, pain, comorbidity) evaluated the relationships of cumulative load and biomarkers with 2-year changes. In 406 participants (63.7 (8.7) years), interactions of biomarkers with cumulative load weakly predicted 2-year cartilage changes: (i) COMP × cumulative load explained medial tibia thickness change (R2 increased 0.062 to 0.087, p < 0.001); (ii) Coll2-1 NO2 × cumulative load explained central medial femoral T2 change (R2 increased 0.177 to 0.210, p < 0.001); and (iii) Coll2-1 NO2 × cumulative load explained lateral tibia T2 change (R2 increased 0.166 to 0.188, p < 0.001). Moderate COMP or Coll2-1 NO2 at baseline appeared protective. High COMP or Coll2-1 NO2, particularly with high BMI and low PASE, associated with worsening cartilage. Moderate serum concentrations of cartilage turnover biomarkers, at high and low physical activity, associated with maintained cartilage outcomes over 2 years. In conclusion, high concentrations of cartilage turnover biomarkers, particularly with high BMI and low physical activity, associated with knee cartilage thinning and increasing T2 over 2 years. Key Points • Higher quality cartilage may be better able to tolerate a larger cumulative load than poor quality cartilage. • Among participants enrolled in the Osteoarthritis Initiative Biomarkers Consortium Project, a representation of cumulative load exposure and its interaction with cartilage turnover biomarkers were weakly related with 2-year change in knee cartilage. • These findings suggest that cartilage turnover is a factor that modifies the relationship between loading exposure and cartilage loss in knee OA.

Longitudinal myelin content measures of slowly expanding lesions using 7T MRI in multiple sclerosis.

Slowly expanding lesions (SELs) are thought to represent a subset of chronic active lesions and have been associated with clinical disability, severity, and disease progression. The purpose of this study was to characterize SELs using advanced magnetic resonance imaging (MRI) measures related to myelin and neurite density on 7Tesla (T) MRI. The study design was retrospective, longitudinal, observational cohort with multiple sclerosis (n=15). Magnetom 7T scanner was used to acquire magnetization-prepared 2 rapid acquisition gradient echo and advanced MRI including visualization of short transverse relaxation time component (ViSTa) for myelin, quantitative magnetization transfer (qMT) for myelin, and neurite orientation dispersion density imaging (NODDI). SELs were defined as lesions showing ≥12% of growth over 12months on serial MRI. Comparisons of quantitative measures in SELs and non-SELs were performed at baseline and over time. Statistical analyses included two-sample t-test, analysis of variance, and mixed-effects linear model for MRI metrics between lesion types. A total of 1075 lesions were evaluated. Two hundred twenty-four lesions (21%) were SELs, and 216 (96%) of the SELs were black holes. At baseline, compared to non-SELs, SELs showed significantly lower ViSTa (1.38vs. 1.53, p<.001) and qMT (2.47vs. 2.97, p<.001) but not in NODDI measures (p>.27). Longitudinally, only ViSTa showed a greater loss when comparing SEL and non-SEL (p=.03). SELs have a lower myelin content relative to non-SELs without a difference in neurite measures. SELs showed a longitudinal decrease in apparent myelin water fraction reflecting greater tissue injury.

A Novel Positive-Contrast Magnetic Resonance Imaging Line Marker for High-Dose-Rate (HDR) MRI-Assisted Radiosurgery (MARS).

Magnetic resonance imaging (MRI) can facilitate accurate organ delineation and optimal dose distributions in high-dose-rate (HDR) MRI-Assisted Radiosurgery (MARS). Its use for this purpose has been limited by the lack of positive-contrast MRI markers that can clearly delineate the lumen of the HDR applicator and precisely show the path of the HDR source on T1- and T2-weighted MRI sequences. We investigated a novel MRI positive-contrast HDR brachytherapy or interventional radiotherapy line marker, C4:S, consisting of C4 (visible on T1-weighted images) complexed with saline. Longitudinal relaxation time (T1) and transverse relaxation time (T2) for C4:S were measured on a 1.5 T MRI scanner. High-density polyethylene (HDPE) tubing filled with C4:S as an HDR brachytherapy line marker was tested for visibility on T1- and T2-weighted MRI sequences in a tissue-equivalent female ultrasound training pelvis phantom. Relaxivity measurements indicated that C4:S solution had good T1-weighted contrast (relative to oil [fat] signal intensity) and good T2-weighted contrast (relative to water signal intensity) at both room temperature (relaxivity ratio > 1; r2/r1 = 1.43) and body temperature (relaxivity ratio > 1; r2/r1 = 1.38). These measurements were verified by the positive visualization of the C4:S (C4/saline 50:50) HDPE tube HDR brachytherapy line marker on both T1- and T2-weighted MRI sequences. Orientation did not affect the relaxivity of the C4:S contrast solution. C4:S encapsulated in HDPE tubing can be visualized as a positive line marker on both T1- and T2-weighted MRI sequences. MRI-guided HDR planning may be possible with these novel line markers for HDR MARS for several types of cancer.

Analyzing coherent and incoherent optical susceptibilities in four-wave mixing: stochasticity, symmetry, and intramolecular coupling

The nonlinear optical susceptibilities are analyzed in their optical propagation length considering the incoherent-coherent contributions with the dependence on the relaxation times. In addition, some symmetry properties of the Four-Wave mixing (FWM) signal concerning the frequency detuning exchange are used in the study, without restricting ourselves to the maxima of population oscillations. We analyze the behaviors of these optical responses in a vibronic coupling scheme using a molecule model consisting of two coupled harmonic curves of electronic energies with displaced minima in position and nuclear energies. The solvent effect in our model is treated through the natural Bohr frequency shift to a time-dependent function, with explicit manifestations in its comparison as if the upper state were broadened. Our results for both FWM signal propagation and nonlinear optical susceptibilities are sensitive to the intramolecular coupling parameters, solvent stochasticity, and perturbation order for the treatment of the weak probe beam. The consideration of a second-order probe beam in FWM would not represent a significant contribution to the predicted results, since its percentage contribution is negligible within the model development framework; however, this contribution becomes important when increasing the ratio between longitudinal and transverse relaxation times.

Dosimetry with the TruView gel on a 0.35 T MR-Linac: A feasibility study

The purpose of this work is to assess the feasibility of performing dosimetry with the TruView (ModusQA, London, Ontario, Canada) MTB Fricke gel by MRI reading on a low field MR-Linac (0.35 T). Radiochromic TruView gels were manufactured at IRSN. A 4 echoes time (TE) single-shot fast spin echo sequence (HASTE) was used for 2D images acquisitions. Raw MRI images were denoised (MP-PCA) and transversal relaxation rates (R2) maps were extracted using a homemade Matlab routine. Temperature influences on R2 as well as gel homogeneity were investigated. A dosimetric evaluation of the TruView gel was conducted implying four gels made from the same batch, with three of them dedicated to calibration, and the fourth one received a simple dosimetric plan. Results showed the TruView gel to be sensitive to temperature drift. A protocol was thus developed to ensure thermal stability with the use of a dedicated temperature-controlled water bath. An inhomogeneity that manifests as a R2 increase near the air/gel interface was found to cause a 4% amplitude deviation in R2 along unirradiated gels. Air sealing drastically reduced the inhomogeneity. Dose versus R2 calibration was established. TruView gel sensitivity was found to be low (0.0093 Gy−1 s−1). 1D and 2D comparison to planned dose distribution displayed overall agreement with global gamma index (5%/3 mm) evaluation with an 87 % passing rate. Main discrepancies in the low and gradient dose regions were attributable to the calibration range and diffusion effects. This study demonstrated the feasibility of using the TruView gel for dosimetric evaluation on a low field MR-Linac. The protocol developed needs to be extended to a full 3D evaluation to enable patient QA and may require modifications to the gel formulation to increase its overall sensitivity and ensure limited dependence on temperature drift.

Suppressing effect of shortening vapor cell stem on polarization-induced magnetic gradient relaxation of Xe in NMR co-magnetometers

The Rb polarization-induced magnetic field gradient is one of the crucial sources of Xe spin relaxation in NMR co-magnetometers. The additional volume of the atomic vapor cell stem can enhance the effective magnetic field gradient through the diffusion effect of the optically polarized-Rb atoms, which affects the spin relaxation properties of Xe and degrades the long-term stability of NMR co-magnetometers. Based on the discrete steps random walk diffusion model, the magnetic gradient relaxation properties of Xe diffusing in an asymmetric cell composed of a cubic part and a cylindrical tube (stem) are characterized. Simulation results indicate that a shorter stem can effectively prolong the nuclear spin relaxation time under a constant magnetic field gradient. To verify this conclusion, a cell stem truncating actuator is developed using a high-power CO2 laser to shorten the cell stem, and the magnetic field gradient coil is used to perform the gradient compensation to examine the impact of various stem lengths on the spin relaxation rate. Experiments indicate that under the influence of atomic diffusive motions, shortening the stem length can effectively suppress the polarization-induced magnetic gradient and increase the 129Xe transverse relaxation time from 4.5 s to 21 s. The study posts practical applications for vapor cells with a stem, which is expected to enhance the performance of atomic spin co-magnetometers.

Quantitative MRI imaging of parenchyma and venation networks in Brassica napus leaves: effects of development and dehydration

BackgroundCharacterisation of the structure and water status of leaf tissues is essential to the understanding of leaf hydraulic functioning under optimal and stressed conditions. Magnetic Resonance Imaging is unique in its capacity to access this information in a spatially resolved, non-invasive and non-destructive way. The purpose of this study was to develop an original approach based on transverse relaxation mapping by Magnetic Resonance Imaging for the detection of changes in water status and distribution at cell and tissue levels in Brassica napus leaves during blade development and dehydration.ResultsBy combining transverse relaxation maps with a classification scheme, we were able to distinguish specific zones of areoles and veins. The tissue heterogeneity observed in young leaves still occurred in mature and senescent leaves, but with different distributions of T2 values in accordance with the basipetal progression of leaf blade development, revealing changes in tissue structure. When subjected to severe water stress, all blade zones showed similar behaviours.ConclusionThis study demonstrates the great potential of Magnetic Resonance Imaging in assessing information on the structure and water status of leaves. The feasibility of in planta leaf measurements was demonstrated, opening up many opportunities for the investigation of leaf structure and hydraulic functioning during development and/or in response to abiotic stresses.

A sensitive Ag+-mediated magnetic relaxation and colorimetry dual-mode sensing platform

To address the relatively low sensitivity of current redox reagent-mediated magnetic relaxation sensing methods, we present a novel Ag+-mediated magnetic sensing platform that enhances the sensitivity by three orders of magnitude. The new sensing platform is based on Ag+-catalyzed oxidation of Mn2+ to KMnO4, accompanied by a distinct color change, which facilitates colorimetric detection. In the case of insufficient Ag+ ions, MnO2 is an additional oxidation product and the KMnO4/MnO2 ratio is dependent on the concentration of Ag+. When combined with a specific quantity of reducing agent, both KMnO4 and MnO2 are reduced to Mn2+ with a large relaxivity, and the concentration of Mn2+ in the resultant solution inversely correlates with the amount of KMnO4 since KMnO4 consumes more reductant during reduction. Consequently, the transverse relaxation rate of the solution exhibits a negative correlation with the Ag+ concentration. Thus, by coupling this Ag+-mediated Mn2+ to KMnO4 transformation with reactions that modulate Ag+ concentration, a dual-mode sensing platform for magnetic relaxation and colorimetry can be realized. Herein, we take H2O2 as an example to verify the detection performance of this sensing platform since H2O2 can oxidize Ag0 in Ag@Fe3O4 nanoparticles to Ag+. Experimental findings demonstrate detection limits of 10 nM and 20 nM for the magnetic relaxation and colorimetry modes, respectively, affirming the excellent sensitivity and the potential practical application of this strategy.