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Tissue-mimicking materials (TMMs) are now essential reference objects for quality control, development and training in all medical imaging modalities. This review aims to provide a comprehensive synthesis of materials used in the fabrication of TMMs for MRI phantoms, focusing on their composition, fabrication methods, and relaxation properties (T1 and T2). A systematic review was conducted, covering articles published between 1980 and 2023. Inclusion criteria encompassed studies involving physical MRI phantoms with measured T1 and T2 relaxation times. Exclusion criteria filtered out non-MRI studies, and digital/computational models. The review identifies and categorizes TMMs based on their primary gelling agents: agar, carrageenan, gelatin, polyvinyl alcohol (PVA), and other less common gels. Agar emerged as the most frequently used gelling agent due to its versatility and favorable MRI signal properties. Carrageenans, noted for their strength and minimal impact on T2 values, are often used in combination with agar. Gelatin, PVA, and other materials like Polyvinyl chloride (PVC) and PolyvinylPyrrolidone (PVP) also demonstrate unique advantages for specific applications. The review also highlights the challenges in phantom stability and the impact of various additives on the relaxation properties. This synthesis provides a valuable guide for the fabrication of MRI phantoms tailored to desired T1 and T2 relaxation times, facilitating the development of more accurate and reliable imaging tools. Understanding the detailed properties of TMMs is fundamental to improve the quality control and educational applications of MRI technologies, especially with the advent of new magnetic field strengths and parametric imaging techniques. As experts in MRI systems, radiographers, educators, and researchers need to understand TMM compositions and methods of fabrications to develop MRI phantoms for educational tools and research purposes. This review serves as a valuable resource to guide them in these efforts. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to assess how T2 heterogeneity biases IMPULSED‐derived metrics of tissue microstructure in solid tumors and evaluate the potential of estimating multi‐compartmental T2 and microstructural parameters simultaneously. Methods: This study quantifies the impact of T2 relaxation on IMPULSED‐derived microstructural parameters using computer simulations and in vivo multi‐TE IMPULSED MRI in five tumor models, including brain, breast, prostate, melanoma, and colon cancer. A comprehensive T2 + IMPULSED method was developed to fit multi‐compartmental T2 and microstructural parameters simultaneously. A Bayesian model selection approach was carried out voxel‐wisely to determine if the T2 heterogeneity needs to be included in IMPULSED MRI in cancer. Results: Simulations suggest that T2 heterogeneity has a minor effect on the estimation of d in tissues with intermediate or high cell density, but significantly biases the estimation of vin$$ {v}_{in} $$ with low cell density. For the in vivo animal experiments, all IMPULSED metrics except vin$$ {v}_{in} $$ are statistically independent on TE. For B16 tumors, the IMPULSED‐derived vin$$ {v}_{in} $$ exhibited a notable increase with longer TEs. For MDA‐MB‐231 tumors, IMPULSED‐derived vin$$ {v}_{in} $$ showed a significant increase with increasing TEs. The T2 + IMPULSED‐derived T2in$$ {T}_2^{in} $$ of all five tumor models are consistently smaller than T2ex$$ {T}_2^{ex} $$. Conclusions: The findings from this study highlight two key observations: (i) TE has a negligible impact on IMPULSED‐derived cell sizes, and (ii) the TE‐dependence of IMPULSED‐derived intracellular volume fractions used in T2 + IMPULSED modeling to estimate T2in$$ {T}_2^{in} $$ and T2ex$$ {T}_2^{ex} $$. These insights contribute to the ongoing development and refinement of non‐invasive MRI techniques for measuring cell sizes. [ABSTRACT FROM AUTHOR]

PurposeUsing ultrashort echo time (UTE) MRI, we determined prevalence of abnormal cartilaginous endplate (CEP), and the relationship between CEP and disc degeneration in human lumbar spines.Materials and methodsLumbar spines from 71 cadavers (age 14-74 years) were imaged at 3 T using sagittal UTE and spin echo T2 map sequences. On UTE images, CEP morphology was defined as "normal" with linear high signal intensity or "abnormal" with focal signal loss and/or irregularity. On spin echo images, disc grade and T2 values of the nucleus pulposus (NP) and annulus fibrosus (AF) were determined. 547 CEPs and 284 discs were analysed. Effects of age, sex, and level on CEP morphology, disc grade, and T2 values were determined. Effects of CEP abnormality on disc grade, T2 of NP, and T2 of AF were also determined.ResultsOverall prevalence of CEP abnormality was 33% and it tended to increase with older ages (p = 0.08) and at lower spinal levels of L5 than L2 or L3 (p = 0.001). Disc grades were higher and T2 values of the NP were lower in older spines (p

Degradation of articular cartilage (AC) due to injury to the knee joint may initiate post-traumatic osteoarthritis (PTOA). Failure to diagnose the onset of the disease at an early stage makes the cure ineffective for PTOA. This study investigated the consequences of a mechanical injury to the knee in a rabbit model using microscopic magnetic resonance imaging (µMRI) at high resolution. A mechanical injury was induced to the knee joints of 12 rabbits. Cartilage blocks were extracted from the non-impacted and impacted knee joints after 2 and 14 weeks post-impact. The specimens were studied using µMRI T2 relaxation and inductively coupled plasma analysis to determine the early degradation of the articular cartilage. The data established a connection between T2 relaxation time and the early progression of knee PTOA after an impact injury. T2 values were found to be higher in the impacted cartilage at both 2 and 14 weeks, in particular, T2–55° values in the impacted samples displayed a significant rise of 6.93% after 2 weeks and 20.02% after 14 weeks. Lower glycosaminoglycan measurement and higher water content in the impacted cartilage confirmed the µMRI results. This µMRI T2 study was able to detect cartilage damage in the impacted knees. In addition, greater degradation in the affected knees at 14 weeks than at 2 weeks indicated the progressive nature of cartilage deterioration over time. The µMRI results were in accord with the biochemical analysis, indicating the detection of early structural damage in the cartilage. [ABSTRACT FROM AUTHOR]

ABSTRACT: Relationships between texture measurements and meat water properties were investigated in raw intact broiler breast fillets with the wooden breast (WB) condition. Texture measurements included subjective WB scores and blunt Meullenet-Owens Razor Shear (BMORS). Water properties were determined with low-field nuclear magnetic resonance (LF-NMR). Spearman correlation was used to estimate relationships between WB scores and water properties, while Pearson correlation was used for relationships between BMORS force and water properties. LF-NMR measurements exhibited 3 water components: protein-associated or hydration water T2b, intra-myofibrillar water or immobilized water T21, and extra-myofibrillar water or free water T22 in chicken breast meat. Significant and strong Spearman correlations were found between the WB scores and T21 time constant, the abundance (normalized areas) of T22, and the proportion of T21 and T22 (rs > 0.60, P < 0.001). Strong Pearson correlations (r = 0.72) were noted only between the T21 time constant and BMORS force. These results demonstrate that water may contribute to the specific texture characteristics measured with subjective WB scoring (palpable hardness and rigidity) and BMORS (hardness and share force) in raw broiler breast fillets with the WB condition.

Aging is a known risk factor for Osteoarthritis (OA), however, relations between cartilage composition and aging remain largely unknown in understanding human OA. T2 imaging provides an approach to assess cartilage composition. Whether these T2 relaxation times in the joint contact region change with time during gait remain unexplored. The study purpose was to demonstrate a methodology for linking dynamic joint contact mechanics to cartilage composition as measured by T2 relaxometry. T2 relaxation times for unloaded cartilage were measured in a 3T General Electric magnetic resonance (MR) scanner in this preliminary study. High-speed biplanar video-radiography (HSBV) was captured for five 20–30-year-old and five 50–60-year-old participants with asymptomatic knees. By mapping the T2 cartilages to the dynamic contact regions, T2 values were averaged over the contact area at each measurement within the gait cycle. T2 values demonstrated a functional relationship across the gait cycle. There were no statistically significant differences between 20- and 30-year-old and 50–60-year-old participant T2 values at first force peak of the gait cycle in the medial femur (p = 1.00, U = 12) or in the medial tibia (p = 0.31, U = 7). In the medial and lateral femur in swing phase, the joint moved from a region of high T2 values at 75% of gait to a minimum at 85–95% of swing. The lateral femur and tibia demonstrated similar patterns to the medial compartments but were less pronounced. This research advances understanding of the linkage between cartilage contact and cartilage composition. The change from a high T2 value at ~ 75% of gait to a lower value near the initiation of terminal swing (90% gait) indicates that there are changes to T2 averages corresponding to changes in the contact region across the gait cycle. No differences were found between age groups for healthy participants. These preliminary findings provide interesting insights into the cartilage composition corresponding to dynamic cyclic motion and inform mechanisms of osteoarthritis. [ABSTRACT FROM AUTHOR]

Axon radius is a potential biomarker for brain diseases and a crucial tissue microstructure parameter that determines the speed of action potentials. Diffusion MRI (dMRI) allows non-invasive estimation of axon radius, but accurately estimating the radius of axons in the human brain is challenging. Most axons in the brain have a radius below one micrometer, which falls below the sensitivity limit of dMRI signals even when using the most advanced human MRI scanners. Therefore, new MRI methods that are sensitive to small axon radii are needed. In this proof-of-concept investigation, we examine whether a surface-based axonal relaxation process could mediate a relationship between intra-axonal T2 and T1 times and inner axon radius, as measured using postmortem histology. A unique in vivo human diffusion-T1-T2 relaxation dataset was acquired on a 3T MRI scanner with ultra-strong diffusion gradients, using a strong diffusion-weighting (i.e., b = 6,000 s/mm²) and multiple inversion and echo times. A second reduced diffusion-T2 dataset was collected at various echo times to evaluate the model further. The intra-axonal relaxation times were estimated by fitting a diffusionrelaxation model to the orientation-averaged spherical mean signals. Our analysis revealed that the proposed surface-based relaxation model effectively explains the relationship between the estimated relaxation times and the histological axon radius measured in various corpus callosum regions. Using these histological values, we developed a novel calibration approach to predict axon radius in other areas of the corpus callosum. Notably, the predicted radii and those determined from histological measurements were in close agreement. [ABSTRACT FROM AUTHOR]

This study applied partial least squares (PLS) regression to nuclear magnetic resonance (NMR) relaxation curves to quantify the free base of an active pharmaceutical ingredient powder. We measured the T 2 relaxation of intact and moisture-absorbed physical mixtures of tetracaine free base (TC) and its hydrochloride salt (TC·HCl). The obtained T 2 relaxation curves were analyzed by two methods, one using a previously reported T 2 relaxation time (T 2), and the other using PLS regression. The accuracy of estimating TC was inadequate when using previous T 2 values because the moisture-absorbed physical mixtures showed biphasic T 2 relaxation curves. By contrast, the entire measured whole of the T 2 relaxation curves was used as input variables and analyzed by PLS regression to quantify the content of TC in the moisture-absorbed TC/TC·HCl. Based on scatterplots of theoretical versus predicted TC, the obtained PLS model exhibited acceptable coefficients of determination and relatively low root mean squared error values for calibration and validation data. The statistical values confirmed that an accurate and reliable PLS model was created to quantify TC in even moisture-absorbed TC/TC·HCl. The bench-top low-field NMR instrument used to apply PLS regression to the T 2 relaxation curve may be a promising tool in process analytical technology. [ABSTRACT FROM AUTHOR]

Axon radius is a potential biomarker for brain diseases and a crucial tissue microstructure parameter that determines the speed of action potentials. Diffusion MRI (dMRI) allows non-invasive estimation of axon radius, but accurately estimating the radius of axons in the human brain is challenging. Most axons in the brain have a radius below one micrometer, which falls below the sensitivity limit of dMRI signals even when using the most advanced human MRI scanners. Therefore, new MRI methods that are sensitive to small axon radii are needed. In this proof-of-concept investigation, we examine whether a surface-based axonal relaxation process could mediate a relationship between intra-axonal T2 and T1 times and inner axon radius, as measured using postmortem histology. A unique in vivo human diffusion-T1-T2 relaxation dataset was acquired on a 3T MRI scanner with ultra-strong diffusion gradients, using a strong diffusion-weighting (i.e., b = 6,000 s/mm2) and multiple inversion and echo times. A second reduced diffusion-T2 dataset was collected at various echo times to evaluate the model further. The intra-axonal relaxation times were estimated by fitting a diffusion-relaxation model to the orientation-averaged spherical mean signals. Our analysis revealed that the proposed surface-based relaxation model effectively explains the relationship between the estimated relaxation times and the histological axon radius measured in various corpus callosum regions. Using these histological values, we developed a novel calibration approach to predict axon radius in other areas of the corpus callosum. Notably, the predicted radii and those determined from histological measurements were in close agreement.

Introduction:Estimation of intervertebral disc degeneration on magnetic resonance imaging (MRI) is challenging. Qualitative schemes used in clinical practice correlate poorly with pain and quantitative techniques have not entered widespread clinical use. Methods:As part of a prior study, 25 New Zealand white rabbits underwent annular puncture to induce disc degeneration in 50 noncontiguous lumbar discs. At 16 weeks, the animals underwent multi-echo T2 MRI scanning and were euthanized. The discs were stained and examined histologically. Quantitative T2 relaxation maps were prepared using the nonlinear least squares method. Decay Variance maps were created using a novel technique of aggregating the deviation in the intensity of each echo signal from the expected intensity based on the previous rate of decay. Results:Decay Variance maps showed a clear and well demarcated nucleus pulposus with a consistent rate of decay (low Decay Variance) in healthy discs that showed progressively more variable decay (higher Decay Variance) with increasing degeneration. Decay Variance maps required significantly less time to generate (1.0 ± 0.0 second) compared with traditional T2 relaxometry maps (5 (±0.9) to 1788.9 (±116) seconds). Histology scores correlated strongly with Decay Variance scores (r = 0.82, P

High‐resolution mapping of magnetic resonance imaging (MRI)'s transverse relaxation time (T2) can benefit many clinical applications by offering improved anatomic details, enhancing the ability to probe tissues' microarchitecture, and facilitating the identification of early pathology. Increasing spatial resolutions, however, decreases data's signal‐to‐noise ratio (SNR), particularly at clinical scan times. This impairs imaging quality, and the accuracy of subsequent radiological interpretation. Recently, principal component analysis (PCA) was employed for denoising diffusion‐weighted MR images and was shown to be effective for improving parameter estimation in multiexponential relaxometry. This study combines the Marchenko–Pastur PCA (MP‐PCA) signal model with the echo modulation curve (EMC) algorithm for denoising multiecho spin‐echo (MESE) MRI data and improving the precision of EMC‐generated single T2 relaxation maps. The denoising technique was validated on simulations, phantom scans, and in vivo brain and knee data. MESE scans were performed on a 3‐T Siemens scanner. The acquired images were denoised using the MP‐PCA algorithm and were then provided as input for the EMC T2‐fitting algorithm. Quantitative analysis of the denoising quality included comparing the standard deviation and coefficient of variation of T2 values, along with gold standard SNR estimation of the phantom scans. The presented denoising technique shows an increase in T2 maps' precision and SNR, while successfully preserving the morphological features of the tissue. Employing MP‐PCA denoising as a preprocessing step decreases the noise‐related variability of T2 maps produced by the EMC algorithm and thus increases their precision. The proposed method can be useful for a wide range of clinical applications by facilitating earlier detection of pathologies and improving the accuracy of patients' follow‐up. [ABSTRACT FROM AUTHOR]

Diabetes patients often rely on tailored insulin therapies, necessitating precise blends of various insulin types to achieve optimal pharmacokinetic profiles, including the quantity and action duration of insulin absorption into the bloodstream. This study aimed to develop an accurate quantification method for mixed insulin preparations, consisting of Insulin-NPH and Insulin Regular in ratios varying between 0:100–100:0. Time Domain NMR (TD-NMR) techniques, T 2 relaxation times, and T 1 T 2 maps were used to analyze the mixtures. Individually, neither technique provided a reliable determination of insulin ratios. However, the integration of both methods through chemometrics has been proven to be a synergistic approach, yielding a robust quantification technique suitable for quality control in the assessment of mixed insulin drugs. This innovative combined TD-NMR method is non-invasive, cost-effective, and user-friendly, offering at the same time a significant potential for preventing health complications associated with improper insulin dosing. Furthermore, our work elucidates the broader applicability of converging multiple TD-NMR techniques for analyzing intricate mixtures. [Display omitted] • Insulin drugs were mixed in various ratios to achieve distinct pharmacokinetic profiles. • The measurements were conducted by integrating T 2 relaxation and T 1 T 2 maps using MLR. • The integrated TD-NMR method demonstrated high predictability for mixture ratios. • TD-NMR is proposed as a low-cost, non-invasive method for the pharmaceutical industry. • This serves as a quality control method to prevent health issues related to dosage miscalculations. [ABSTRACT FROM AUTHOR]

Background: Currently, the gadolinium retention in the brain after the use of contrast agents is studied by T1‐weighted magnetic resonance imaging (MRI) (T1w) and T1 mapping. The former does not provide easily quantifiable data and the latter requires prolonged scanning and is sensitive to motion. T2 mapping may provide an alternative approach. Animal studies of gadolinium retention are complicated by repeated intravenous (IV) dosing, whereas intraperitoneal (IP) injections might be sufficient. Hypothesis: T2 mapping will detect the changes in the rat brain due to gadolinium retention, and IP administration is equivalent to IV for long‐term studies. Study Type: Prospective longitudinal. Animal Model: A total of 31 Sprague–Dawley rats administered gadodiamide IV (N = 8) or IP (N = 8), or saline IV (N = 6) or IP (N = 9) 4 days per week for 5 weeks. Field strength/sequences: A 7 T, T1w, and T2 mapping. Assessment: T2 relaxation and image intensities in the deep cerebellar nuclei were measured pre‐treatment and weekly for 5 weeks. Then brains were assessed for neuropathology (N = 4) or gadolinium content using inductively coupled plasma mass spectrometry (ICP‐MS, N = 12). Statistical tests: Repeated measures analysis of variance with post hoc Student–Newman–Keuls tests and Hedges' effect size. Results: Gadolinium was detected by both approaches; however, T2 mapping was more sensitive (effect size 2.32 for T2 vs. 0.95 for T1w), and earlier detection (week 3 for T2 vs. week 4 for T1w). ICP‐MS confirmed the presence of gadolinium (3.076 ± 0.909 nmol/g in the IV group and 3.948 ± 0.806 nmol/g in the IP group). There was no significant difference between IP and IV groups (ICP‐MS, P = 0.109; MRI, P = 0.696). No histopathological abnormalities were detected in any studied animal. Conclusion: T2 relaxometry detects gadolinium retention in the rat brain after multiple doses of gadodiamide irrespective of the route of administration. Evidence Level 1 Technical Efficacy: Stage 1 [ABSTRACT FROM AUTHOR]

Purpose: While diffusion and T2 relaxation are intertwined, little or no correlation exists between diffusion and T2 relaxation of intracellular metabolites in the rodent brain, as measured by diffusion‐weighted MRS at different TEs. However, situation might be different for lactate, since it is present in both extracellular and intracellular spaces, which exhibit different diffusion properties and may also exhibit different T2. Such a TE dependence would be crucial to account for when interpreting or modeling lactate diffusion. Here we propose to take advantage of a new diffusion sequence, where J‐modulation of lactate is canceled even at long TE, thus retaining excellent signal, to assess potential T2 dependence on diffusion of lactate in the mouse brain. Methods: Using a frequency‐selective diffusion‐weighted spin‐echo sequence that removes J‐modulation at 1.3 ppm, thus preserving lactate signal even at long TE, we investigate the effect of TE between 50.9 and 110.9 ms (while keeping diffusion time constant) on apparent diffusivity and kurtosis in the mouse brain. Results: Regardless of the metabolites, no difference appears for the diffusion‐weighted signal attenuation with increasing TE. For lactate, apparent diffusivity and kurtosis remain unchanged as TE increases. Conclusion: No significant TE dependence of diffusivity and kurtosis is measured for lactate in the 50–110 ms TE range, confirming that potential T2 effects can be ignored when interpreting or modeling lactate diffusion. [ABSTRACT FROM AUTHOR]

Starch is a major contributor to the carbohydrate portion of our diet. When it is present with water, it undergoes several transformations during heating and/or cooling making it an essential structure‐forming component in starch‐rich food systems (e.g., bread and cake). Time domain proton nuclear magnetic resonance (TD 1H NMR) is a useful technique to study starch–water interactions by evaluation of molecular mobility and water distribution. The data obtained correspond to changes in starch structure and the state of water during or resulting from processing. When this technique was first applied to starch(‐rich) foods, significant challenges were encountered during data interpretation of complex food systems (e.g., cake or biscuit) due to the presence of multiple constituents (proteins, carbohydrates, lipids, etc.). This article discusses the principles of TD 1H NMR and the tools applied that improved characterization and interpretation of TD NMR data. More in particular, the major differences in proton distribution of various dough and cooked/baked food systems are examined. The application of variable‐temperature TD 1H NMR is also discussed as it demonstrates exceptional ability to elucidate the molecular dynamics of starch transitions (e.g., gelatinization, gelation) in dough/batter systems during heating/cooling. In conclusion, TD NMR is considered a valuable tool to understand the behavior of starch and water that relate to the characteristics and/or quality of starchy food products. Such insights are crucial for food product optimization and development in response to the needs of the food industry. [ABSTRACT FROM AUTHOR]

Multi-Dynamic Multi-Echo (MDME) Sequence is a new method which can acquire various contrast-weighted images using quantitative relaxometric parameters measured from multicontrast images. The purpose of our study was to investigate the effect of scan parameters of MDME Sequence on measured T1, T2 values of phantoms at 3.0 T MRI scanner. Gray matter, white matter and cerebrospinal fluid simulation phantoms with different relaxation times (named GM, WM, CSF, respectively) were used in our study. All the phantoms were scanned 9 times on different days using MDME sequence with variations of echo train length, matrix, and acceleration factor. The T1, T2 measurements were acquired after each acquisition. The repeatability was characterized as the intragroup coefficient of variation (CV) of measured values over 9 times, and the discrepancies of measurements across different groups were characterized as intergroup CVs. The highest intragroup CVs of T1-GM, T2-GM, T1-WM, T2-WM, T1-CSF, T2-SCF were 1.36%, 1.75%, 0.74%, 1.41%, 1.70%, 7.79%, respectively. The highest intergroup CVs of T1-GM, T2-GM, T1-WM, T2-WM, T1-CSF, T2-SCF were 0.54%, 1.86%, 1.70%, 0.94%, 1.00%, 2.17%, respectively. Quantitative T1, T2 measurements of gray matter, white matter and cerebrospinal fluid simulation phantoms derived from the MDME sequence were not obviously affected by variations of scanning parameters, such as echo train length, matrix, and acceleration factor on 3T scanner. [ABSTRACT FROM AUTHOR]

The free water elimination (FWE) model and its kurtosis variant (DKI-FWE) can separate tissue and free water signal contributions, thus providing tissue-specific diffusional information. However, a downside of these models is that the associated parameter estimation problem is ill-conditioned, necessitating the use of advanced estimation techniques that can potentially bias the parameter estimates. In this work, we propose the T2-DKI-FWE model that exploits the T2 relaxation properties of both compartments, thereby better conditioning the parameter estimation problem and providing, at the same time, an additional potential biomarker (the T2 of tissue). In our approach, the T2 of tissue is estimated as an unknown parameter, whereas the T2 of free water is assumed known a priori and fixed to a literature value (1573 ms). First, the error propagation of an erroneous assumption on the T2 of free water is studied. Next, the improved conditioning of T2-DKI-FWE compared to DKI-FWE is illustrated using the Cramér-Rao lower bound matrix. Finally, the performance of the T2-DKI-FWE model is compared to that of the DKI-FWE and T2-DKI models on both simulated and real datasets. The error due to a biased approximation of the T2 of free water was found to be relatively small in various diffusion metrics and for a broad range of erroneous assumptions on its underlying ground truth value. Compared to DKI-FWE, using the T2-DKI-FWE model is beneficial for the identifiability of the model parameters. Our results suggest that the T2-DKI-FWE model can achieve precise and accurate diffusion parameter estimates, through effective reduction of free water partial volume effects and by using a standard nonlinear least squares approach. In conclusion, incorporating T2 relaxation properties into the DKI-FWE model improves the conditioning of the model fitting, while only requiring an acquisition scheme with at least two different echo times.

Relationships between texture measurements and meat water properties were investigated in raw intact broiler breast fillets with the wooden breast (WB) condition. Texture measurements included subjective WB scores and blunt Meullenet-Owens Razor Shear (BMORS). Water properties were determined with low-field nuclear magnetic resonance (LF-NMR). Spearman correlation was used to estimate relationships between WB scores and water properties, while Pearson correlation was used for relationships between BMORS force and water properties. LF-NMR measurements exhibited 3 water components: protein-associated or hydration water T 2b , intra-myofibrillar water or immobilized water T 21, and extra-myofibrillar water or free water T 22 in chicken breast meat. Significant and strong Spearman correlations were found between the WB scores and T 21 time constant, the abundance (normalized areas) of T 22 , and the proportion of T 21 and T 22 (r s > 0.60, P < 0.001). Strong Pearson correlations (r = 0.72) were noted only between the T 21 time constant and BMORS force. These results demonstrate that water may contribute to the specific texture characteristics measured with subjective WB scoring (palpable hardness and rigidity) and BMORS (hardness and share force) in raw broiler breast fillets with the WB condition. [ABSTRACT FROM AUTHOR]

Microstructural abnormalities in the white matter (WM) are implicated in the pathophysiology of psychosis. In vivo magnetic resonance spectroscopy (MRS) can probe the brain's intracellular microenvironment through the measurement of transverse relaxation and diffusion of neurometabolites and possibly provide cell-specific information. In our previous studies, we observed differential metabolite signal abnormalities in first episode and chronic stages of psychosis. In the present work, longitudinal data were presented for the first time on white matter cell-type specific abnormalities using a combination of diffusion tensor spectroscopy (DTS), T2 MRS, and diffusion tensor imaging (DTI) from a group of 25 first episode psychosis patients and nine matched controls scanned at baseline and one and two years of follow-up. We observed significantly reduced choline ADC in the year 1 of follow-up (0.194 µm2/ms) compared to baseline (0.229 µm2/ms), followed by a significant increase in NAA ADC in the year 2 follow-up (0.258 µm2/ms) from baseline (0.222 µm2/ms) and year 1 follow-up (0.217 µm2/ms). In contrast, NAA T2 relaxation, reflecting a related but different aspect of microenvironment from diffusion, was reduced at year 1 follow-up (257 ms) compared to baseline (278 ms). These abnormalities were observed in the absence of any abnormalities in water relaxation and diffusion at any timepoint. These findings indicate that abnormalities are seen in in glial-enriched (choline) signals in early stages of psychosis, followed by the subsequent emergence of neuronal-enriched (NAA) diffusion abnormalities, all in the absence of nonspecific water signal abnormalities. [ABSTRACT FROM AUTHOR]

Fat unsaturation and poly-unsaturation measures can be obtained in vivo with magnetic resonance spectroscopy (MRS) through the olefinic (≈5.4 ppm) and diallylic (≈2.8 ppm) resonances, respectively. Long echo time (TE) MRS sequences have been previously optimized for olefinic/methylene (≈1.3 ppm) or olefinic/methyl (≈0.9 ppm) measures. The objectives of this work, using a Point RESolved Spectroscopy (PRESS) sequence, are to: 1) Investigate olefinic, methyl and methylene resonance decay in subcutaneous, tibial, and breast adipose tissue to determine if a direct comparison of unsaturation measures can be made without correction for T 2 losses. 2) Assess intra-individual fat unsaturation and poly-unsaturation measures in the three adipose tissues. 3) Estimate correction factors for olefinic to methylene ratios to compensate for J-coupling and T 2 relaxation losses that take place when increasing PRESS TE from 40 ms to 200 ms (previously optimized long-TE). 4) Investigate the utility of an inversion recovery for resolving the olefinic resonance from water in adipose tissue. PRESS spectra were acquired from the three adipose regions (breast in female only) in healthy volunteers at 3 T. It was found that olefinic and methyl signal decays faster in breast tissue compared to in tibial bone marrow. Poly-unsaturation measures (diallylic/methylene) differ for tibial bone marrow compared to subcutaneous and breast adipose tissue, with average values of 1.7 ± 0.4, 2.2 ± 0.4, and 2.3 ± 0.8%, respectively. PRESS (TE = 40 ms) with an inversion recovery resolves the olefinic and water resonances in breast tissue with a signal to noise ratio approximately six times greater than that using PRESS with a TE of 200 ms. Stimulated Echo Acquisition Mode (STEAM) with a TE of 20 ms (mixing time of 20 ms) was also combined with IR to resolve the olefinic resonance from that of water is spinal bone marrow. [ABSTRACT FROM AUTHOR]

Multiple echo-time arterial spin labelling (multi-TE ASL) offers estimation of blood–tissue exchange dynamics by probing the T2 relaxation of the labelled spins. In this study, we provide a recipe for robust assessment of exchange time (Texch) as a proxy measure of blood–brain barrier (BBB) integrity based on a test-retest analysis. This includes a novel scan protocol and an extension of the two-compartment model with an "intra-voxel transit time" (ITT) to address tissue transit effects. With the extended model, we intend to separate the underlying two distinct mechanisms of tissue transit and exchange. The performance of the extended model in comparison with the two-compartment model was evaluated in simulations. Multi-TE ASL sequence with two different bolus durations was used to acquire in vivo data (n = 10). Cerebral blood flow (CBF), arterial transit time (ATT) and Texch were fitted with the two models, and mean grey matter values were compared. Additionally, the extended model also extracted ITT parameter. The test-retest reliability of Texch was assessed for intra-session, inter-session and inter-visit pairs of measurements. Intra-class correlation coefficient (ICC) and within-subject coefficient of variance (CoV) for grey matter were computed to assess the precision of the method. Mean grey matter Texch and ITT values were found to be 227.9 ± 37.9 ms and 310.3 ± 52.9 ms, respectively. Texch estimated by the extended model was 32.6 ± 5.9% lower than the two-compartment model. A significant ICC was observed for all three measures of Texch reliability (P < 0.05). Texch intra-session CoV, inter-session CoV and inter-visit CoV were found to be 6.6%, 7.9%, and 8.4%, respectively. With the described improvements addressing intra-voxel transit effects, multi-TE ASL shows good reproducibility as a non-invasive measure of BBB permeability. These findings offer an encouraging step forward to apply this potential BBB permeability biomarker in clinical research. [ABSTRACT FROM AUTHOR]

To in situ and noninvasively monitor the biofilm development process by low-field nuclear magnetic resonance (NMR), experiments should be made to determine the mechanisms responsible for the T2 signals of biofilm growth. In this paper, biofilms were cultivated in both fluid media and saturated porous media. T2 relaxation for each sample was measured to investigate the contribution of the related processes to T2 relaxation signals. In addition, OD values of bacterial cell suspensions were measured to provide the relative number of bacterial cells. We also obtained SEM photos of the biofilms after vacuum freeze-drying the pure sand and the sand with biofilm formation to confirm the space within the biofilm matrix and identify the existence of biofilm formation. The T2 relaxation distribution is strongly dependent on the density of the bacterial cells suspended in the fluid and the stage of biofilm development. The peak time and the peak percentage can be used as indicators of the biofilm growth states. [ABSTRACT FROM AUTHOR]

Multi-echo T2 magnetic resonance images contain information about the distribution of T2 relaxation times of compartmentalized water, from which we can estimate relevant brain tissue properties such as the myelin water fraction (MWF). Regularized non-negative least squares (NNLS) is the tool of choice for estimating non-parametric T2 spectra. However, the estimation is ill-conditioned, sensitive to noise, and highly affected by the employed regularization weight. The purpose of this study is threefold: first, we want to underline that the apparently innocuous use of two alternative parameterizations for solving the inverse problem, which we called the standard and alternative regularization forms, leads to different solutions; second, to assess the performance of both parameterizations; and third, to propose a new Bayesian regularized NNLS method (BayesReg). The performance of BayesReg was compared with that of two conventional approaches (L-curve and Chi-square (X2) fitting) using both regularization forms. We generated a large dataset of synthetic data, acquired in vivo human brain data in healthy participants for conducting a scan-rescan analysis, and correlated the myelin content derived from histology with the MWF estimated from ex vivo data. Results from synthetic data indicate that BayesReg provides accurate MWF estimates, comparable to those from L-curve and X2, and with better overall stability across a wider signal-to-noise range. Notably, we obtained superior results by using the alternative regularization form. The correlations reported in this study are higher than those reported in previous studies employing the same ex vivo and histological data. In human brain data, the estimated maps from L-curve and BayesReg were more reproducible. However, the T2 spectra produced by BayesReg were less affected by over-smoothing than those from L-curve. These findings suggest that BayesReg is a good alternative for estimating T2 distributions and MWF maps.

Multiple echo-time arterial spin labelling (multi-TE ASL) offers estimation of blood–tissue exchange dynamics by probing the T2 relaxation of the labelled spins. In this study, we provide a recipe for robust assessment of exchange time (Texch) as a proxy measure of blood–brain barrier (BBB) integrity based on a test-retest analysis. This includes a novel scan protocol and an extension of the two-compartment model with an “intra-voxel transit time” (ITT) to address tissue transit effects. With the extended model, we intend to separate the underlying two distinct mechanisms of tissue transit and exchange. The performance of the extended model in comparison with the two-compartment model was evaluated in simulations. Multi-TE ASL sequence with two different bolus durations was used to acquire in vivo data (n = 10). Cerebral blood flow (CBF), arterial transit time (ATT) and Texch were fitted with the two models, and mean grey matter values were compared. Additionally, the extended model also extracted ITT parameter. The test-retest reliability of Texch was assessed for intra-session, inter-session and inter-visit pairs of measurements. Intra-class correlation coefficient (ICC) and within-subject coefficient of variance (CoV) for grey matter were computed to assess the precision of the method. Mean grey matter Texch and ITT values were found to be 227.9 ± 37.9 ms and 310.3 ± 52.9 ms, respectively. Texch estimated by the extended model was 32.6 ± 5.9% lower than the two-compartment model. A significant ICC was observed for all three measures of Texch reliability (P < 0.05). Texch intra-session CoV, inter-session CoV and inter-visit CoV were found to be 6.6%, 7.9%, and 8.4%, respectively. With the described improvements addressing intra-voxel transit effects, multi-TE ASL shows good reproducibility as a non-invasive measure of BBB permeability. These findings offer an encouraging step forward to apply this potential BBB permeability biomarker in clinical research.

Background: Schizophrenia (SZ) and bipolar disorder (BD) are characterized by white matter (WM) abnormalities, however, their relationship with illness presentation is not clear. Sleep disturbances are common in both disorders, and recent evidence suggests that sleep plays a critical role in WM physiology. Therefore, it is plausible that sleep disturbances are associated with impaired WM integrity in these disorders. To test this hypothesis, we examined the association of self-reported sleep disturbances with WM transverse (T2) relaxation times in patients with SZ spectrum disorders and BD with psychotic features., Methods: 28 patients with psychosis (17 BD-I, with psychotic features and 11 SZ spectrum disorders) were included. Metabolite and water T2 relaxation times were measured in the anterior corona radiata at 4T. Sleep was evaluated using the Pittsburgh Sleep Quality Index., Results: PSQI total score showed a moderate to strong positive correlation with water T2 (r = 0.64, p<0.001). Linear regressions showed that this association was specific to sleep disturbance but was not a byproduct of exacerbation in depressive, manic, or psychotic symptoms. In our exploratory analysis, sleep disturbance was correlated with free water percentage, suggesting that increased extracellular water may be a mechanism underlying the association of disturbed sleep and prolonged water T2 relaxation., Conclusion: Our results highlight the connection between poor sleep and WM abnormalities in psychotic disorders. Future research using objective sleep measures and neuroimaging techniques suitable to probe free water is needed to further our insight into this relationship., Competing Interests: Disclosure Statement The authors declare no conflict of interest.

Although the central role of adequate blood flow and oxygen delivery is known, the lack of optimized imaging modalities to study placental structure has impeded our understanding of its vascular function. Magnetic resonance imaging is increasingly being applied in this field, but gaps in knowledge remain, and further methodological developments are needed. In particular, the ability to distinguish maternal from fetal placental perfusion and the understanding of how individual placental lobules are functioning are lacking. The potential clinical benefits of developing noninvasive tools for the in vivo assessment of blood flow and oxygenation, two key determinants of placental function, are tremendous. Here, we summarize a number of structural and functional magnetic resonance imaging techniques that have been developed and applied in animal models and studies of human pregnancy over the past decade. We discuss the potential applications and limitations of these approaches. Their combination provides a novel source of contrast to allow analysis of placental structure and function at the level of the lobule. We outline the physiological mechanisms of placental T2 and T2* decay and devise a model of how tissue composition affects the observed relaxation properties. We apply this modeling to longitudinal magnetic resonance imaging data obtained from a preclinical pregnant nonhuman primate model to provide initial proof-of-concept data for this methodology, which quantifies oxygen transfer and placental structure across and between lobules. This method has the potential to improve our understanding and clinical management of placental insufficiency once validation in a larger nonhuman primate cohort is complete., (© The Author(s) 2024. Published by Oxford University Press on behalf of Society for the Study of Reproduction.)

The anisotropy of brain white matter microstructure manifests itself in orientational-dependence of various MRI contrasts, and can result in significant quantification biases if ignored. Understanding the origins of this orientation-dependence could enhance the interpretation of MRI signal changes in development, ageing and disease and ultimately improve clinical diagnosis. Using a novel experimental setup, this work studies the contributions of the intra- and extra-axonal water to the orientation-dependence of one of the most clinically-studied parameters, apparent transverse relaxation T2. Specifically, a tiltable receive coil is interfaced with an ultra-strong gradient MRI scanner to acquire multidimensional MRI data with an unprecedented range of acquisition parameters. Using this setup, compartmental T2 can be disentangled based on differences in diffusional-anisotropy, and its orientation-dependence further elucidated by re-orienting the head with respect to the main magnetic field B→0. A dependence of (compartmental) T2 on the fibre orientation w.r.t. B→0 was observed, and further quantified using characteristic representations for susceptibility- and magic angle effects. Across white matter, anisotropy effects were dominated by the extra-axonal water signal, while the intra-axonal water signal decay varied less with fibre-orientation. Moreover, the results suggest that the stronger extra-axonal T2 orientation-dependence is dominated by magnetic susceptibility effects (presumably from the myelin sheath) while the weaker intra-axonal T2 orientation-dependence may be driven by a combination of microstructural effects. Even though the current design of the tiltable coil only offers a modest range of angles, the results demonstrate an overall effect of tilt and serve as a proof-of-concept motivating further hardware development to facilitate experiments that explore orientational anisotropy. These observations have the potential to lead to white matter microstructural models with increased compartmental sensitivity to disease, and can have direct consequences for longitudinal and group-wise T2- and diffusion-MRI data analysis, where the effect of head-orientation in the scanner is commonly ignored.

MRI's transverse relaxation time (T2) is sensitive to tissues' composition and pathological state. While variations in T2 values can be used as clinical biomarkers, it is challenging to quantify this parameter in vivo due to the complexity of the MRI signal model, differences in protocol implementations, and hardware imperfections. Herein, we provide a detailed analysis of the echo modulation curve (EMC) platform, offering accurate and reproducible mapping of T2 values, from 2D multi‐slice multi‐echo spin‐echo (MESE) protocols. Computer simulations of the full Bloch equations are used to generate an advanced signal model, which accounts for stimulated echoes and transmit field (B1+) inhomogeneities. In addition to quantifying T2 values, the EMC platform also provides proton density (PD) maps, and fat‐water fraction maps. The algorithm's accuracy, reproducibility, and insensitivity to T1 values are validated on a phantom constructed by the National Institute of Standards and Technology and on in vivo human brains. EMC‐derived T2 maps show excellent agreement with ground truth values for both in vitro and in vivo models. Quantitative values are accurate and stable across scan settings and for the physiological range of T2 values, while showing robustness to main field (B0) inhomogeneities, to variations in T1 relaxation time, and to magnetization transfer. Extension of the algorithm to two‐component fitting yields accurate fat and water T2 maps along with their relative fractions, similar to a reference three‐point Dixon technique. Overall, the EMC platform allows to generate accurate and stable T2 maps, with a full brain coverage using a standard MESE protocol and at feasible scan times. The utility of EMC‐based T2 maps was demonstrated on several clinical applications, showing robustness to variations in other magnetic properties. The algorithm is available online as a full stand‐alone package, including an intuitive graphical user interface. [ABSTRACT FROM AUTHOR]

The purpose of our study was to assess whether T2 MRI identifies the infarcted myocardium or the true area-at-risk (AAR) and whether edema is present in the salvageable region following acute myocardial infarction (MI). The study involved a porcine model of MI with a coronary occlusion model of either 60 min or 90 min. Imaging was performed on a 3T MRI pre-occlusion and at day 3 post-MI. Prior-MI, myocardial perfusion territory (MPT) maps were obtained under MRI via direct intracoronary injection of contrast agent. Post-MI, edema extent was quantified by T2 mapping while infarction and microvascular obstruction (MVO) were assessed by late gadolinium enhancement (LGE). Anatomically registered short-axis slices were analyzed for MPT, T2-AAR and infarct areas and T2 relaxation values. Animals were divided into groups with (MVO+) and without MVO (MVO-). T2-AAR area was significantly greater than infarct area in both groups. In the MVO+ group, T2-AAR and MPT were comparable and highly correlated, whereas, in the MVO- group, T2-AAR significantly underestimated MPT without any trend. T2 values in the salvageable myocardium were found to be significantly higher than those in remote myocardium. Our methodology offers the advantage that all images are acquired within the same MRI reference as opposed to complex co-registration with gross pathology. Our study suggests that edema may expand beyond the infarct zone over the entire ischemic bed. T2-AAR may be more clinically relevant than true AAR by perfusion territory since it identifies the "salvageable" myocardium. [ABSTRACT FROM AUTHOR]

Abstract Background Magnetic resonance imaging (MRI) T2 and T1ρ relaxation are increasingly being proposed as imaging biomarkers potentially capable of detecting biochemical changes in articular cartilage before structural changes are evident. We aimed to: 1) summarize MRI methods of published studies investigating T2 and T1ρ relaxation time in participants at risk for but without radiographic knee OA; and 2) compare T2 and T1ρ relaxation between participants at-risk for knee OA and healthy controls. Methods We conducted a systematic review of studies reporting T2 and T1ρ relaxation data that included both participants at risk for knee OA and healthy controls. Participant characteristics, MRI methodology, and T1ρ and T2 relaxation data were extracted. Standardized mean differences (SMDs) were calculated within each study. Pooled effect sizes were then calculated for six commonly segmented knee compartments. Results 55 articles met eligibility criteria. There was considerable variability between scanners, coils, software, scanning protocols, pulse sequences, and post-processing. Moderate risk of bias due to lack of blinding was common. Pooled effect sizes indicated participants at risk for knee OA had lengthened T2 relaxation time in all compartments (SMDs from 0.33 to 0.74; p

Clinical magnetic resonance spectroscopy (MRS) mainly concerns itself with the quantification of metabolite concentrations. Metabolite relaxation values, which reflect the microscopic state of specific cellular and sub‐cellular environments, could potentially hold additional valuable information, but are rarely acquired within clinical scan times. By varying the flip angle, repetition time and echo time in a preset way (termed a schedule), and matching the resulting signals to a pre‐generated dictionary – an approach dubbed magnetic resonance fingerprinting – it is possible to encode the spins' relaxation times into the acquired signal, simultaneously quantifying multiple tissue parameters for each metabolite. Herein, we optimized the schedule to minimize the averaged root mean square error (RMSE) across all estimated parameters: concentrations, longitudinal and transverse relaxation time, and transmitter inhomogeneity. The optimal schedules were validated in phantoms and, subsequently, in a cohort of healthy volunteers, in a 4.5 mL parietal white matter single voxel and an acquisition time under 5 minutes. The average intra‐subject, inter‐scan coefficients of variation (CVs) for metabolite concentrations, T1 and T2 relaxation times were found to be 3.4%, 4.6% and 4.7% in‐vivo, respectively, averaged over all major singlets. Coupled metabolites were quantified using the short echo time schedule entries and spectral fitting, and reliable estimates of glutamate+glutamine, glutathione and myo‐inositol were obtained. [ABSTRACT FROM AUTHOR]

Background: Neurodegeneration is a complex cellular process linked to prompt changes in myelin integrity and gradual neuron loss. Current imaging techniques offer estimations of myelin volumes in lesions/remyelinated areas but are limited to detect subtle injury. Purpose: To investigate whether measurements detected by a signal hierarchically isolated as a function of time‐to‐echo (SHIFT) MRI technique can determine changes in myelin integrity and fiber axolemma. Study Type: Prospective animal model. Animal Model: Surgically demyelinated spinal cord (SC) injury model in rodents (n = 6). Field Strength/Sequence: Gradient‐echo spin‐echo at 3T. Assessment: Multicompartment T2 relaxations were computed by SHIFT MRI in 75‐microns‐resolution images of the SC injury penumbra region 2 weeks post‐trauma. G‐ratio and axolemma delamination were assessed by transmission electron microscopy (TEM) in intact and injured samples. SC myelinated nerve fraction was computed by SHIFT MRI prospectively and assessed histologically. Statistical Tests: Relations between SHIFT‐isolated T2‐components and TEM measurements were studied using linear regression and t‐tests. Pearson's correlation and significance were computed to determine the SHIFT's sensitivity to detect myelinated fibers ratio in gray matter. Regularized least‐squares‐based ranking analysis was employed to determine SHIFT MRI's ability to discern intact and injured myelinated nerves. Results: Biexponential signals isolated by SHIFT MRI for intact vs. lesion penumbra exhibited changes in T2, shifting from intermediate components (25 ± 2 msec) to long (43 ± 11 msec) in white matter, and similarly in gray matter regions‐of‐interest (31 ± 2 to 46 ± 16 msec). These changes correlated highly with TEM g‐ratio and axon delamination measurements (P < 0.05). Changes in short T2 components were observed but not statistically significant (8.5 ± 0.5 to 7 ± 3 msec, P = 0.445, and 4.0 ± 0.9 to 7 ± 3 msec, P = 0.075, respectively). SHIFT MRI's ability to detect myelinated fibers within gray matter was confirmed (P < 0.001). Data Conclusion: Changes detected by SHIFT MRI are associated with abnormal intermembrane spaces formed upon mild injury, directly correlated with early neuro integrity loss. Level of Evidence 1 Technical Efficacy Stage 2 [ABSTRACT FROM AUTHOR]

Introduction: Multi‐component T2 mapping using a gradient‐ and spin‐echo (GraSE) acquisition has become standard for myelin water imaging at 3 T. Higher magnetic field strengths promise signal‐to‐noise ratio benefits but face specific absorption rate limits and shortened T2 times. This study investigates compartmental T2 times in vivo and addresses advantages and challenges of multi‐component T2 mapping at 7 T. Methods: We acquired 3D multi‐echo GraSE data in seven healthy adults at 7 T, with three subjects also scanned at 3 T. Stimulated echoes arising from B1+ inhomogeneities were accounted for by the extended phase graph (EPG) algorithm. We used the computed T2 distributions to determine T2 times that identify different water pools and assessed signal‐to‐noise and fit‐to‐noise characteristics of the signal estimation. We compared short T2 fractions and T2 properties of the intermediate water pool at 3 T and 7 T. Results: Flip angle mapping confirmed that EPG accurately determined the larger B1+ inhomogeneity at 7 T. Multi‐component T2 analysis demonstrated shortened T2 times at 7 T compared with 3 T. Fit‐to‐noise and signal‐to‐noise ratios were improved at 7 T but depended on B1+ homogeneity. Adjusting the shortest T2 to 8 ms and the T2 threshold that separates different water compartments to 20 ms yielded short T2 fractions at 7 T that conformed to 3 T data. Short T2 fractions in myelin‐rich white matter regions were lower at 7 T than at 3 T, and higher in iron‐rich structures. Discussion: Adjusting the T2 compartment boundaries was required due to the shorter T2 relaxation times at 7 T. Shorter echo spacing would better sample the fast decaying signal but would increase peripheral nerve stimulation. Multi‐channel transmission will improve T2 measurements at 7 T. Conclusion: We used a multi‐echo 3D GraSE sequence to characterize the multi‐exponential T2 decay at 7 T. We adapted T2 parameters for evaluation of the short T2 fraction. Obtained 7 T multi‐component T2 maps were in good agreement with 3 T data. [ABSTRACT FROM AUTHOR]

A series of poly(sodium methacrylate) hydrogels, also called superabsorbents, having a theoretical degree of neutralization of 100 mol%, and degree of crosslinking varying from 0.6 to 20 mol%, are synthesized via conventional free radical polymerization. The networks are characterized in detail by inverse size‐exclusion chromatography and 1H‐NMR relaxometry in order to place particular emphasis on the investigation of the pore size distribution (PSD) and the chain mobility, respectively. The two previously mentioned parameters are compared to understand the correlation between the elastic chain mobilities and the average pore size of the hydrogel. From the resulting data, a new empirical equation is proposed, which is valid under the given experimental conditions and permits a rough estimation of the average PSD from the relaxation data. Thus, the equation permits to reduce the number of analytical techniques needed for the characterization of complex systems such as polymer networks. [ABSTRACT FROM AUTHOR]

Background: Previous in vivo proton MR spectroscopy (MRS) studies have demonstrated the possibility of quantifying amide groups of conjugated bile acids (NHCBA), olefinic lipids and cholesterol (OLC), choline-containing phospholipids (CCPLs), taurine and glycine conjugated bile acids (TCBA, GCBA), methylene group of lipids (ML), and methyl groups of bile acids, lipids, and cholesterol (BALC1.0, BALC0.9, and TBAC) in the gallbladder, which may be useful for the study of cholestatic diseases and cholangiopathies. However, these studies were performed at 1.5T and 3T, and higher magnetic fields may offer improved spectral resolution and signal intensity.Purpose: To develop a method for gallbladder MRS at 7T.Study Type: Retrospective, technical development.Population: Ten healthy subjects (five males and five females), two patients with primary biliary cholangitis (PBC) (one male and one female), and one patient with primary sclerosing cholangitis (PSC) (female).Field Strength/sequence: Free-breathing single-voxel MRS with a modified stimulated echo acquisition mode (STEAM) sequence at 7T.Assessment: Postprocessing was based on the T2 relaxation of water in the gallbladder and in the liver. Concentrations of biliary components were calculated using water signal. All data were corrected for T2 relaxation times measured in healthy subjects.Statistical Tests: The range of T2 relaxation time and concentration per bile component, and the resulting mean and standard deviation, were calculated.Results: The concentrations of gallbladder components in healthy subjects were: NHCBA: 93 ± 66 mM, OLC: 154 ± 124 mM, CCPL: 42 ± 17 mM, TCBA: 48 ± 35 mM, GCBA: 67 ± 32 mM, ML: 740 ± 391 mM, BALC1.0: 175 ± 92 mM, BALC0.9: 260 ± 138 mM, and TBAC: 153 ± 90 mM. Mean concentrations of all bile components were found to be lower in patients.Data Conclusion: This work provides a protocol for designing future MRS investigations of the bile system in vivo.Evidence Level: 2 TECHNICAL EFFICACY STAGE: 1. [ABSTRACT FROM AUTHOR]

Objective: To develop and validate a 3D registration approach by which double echo steady state (DESS) MR images with cartilage thickness segmentations are used to extract the cartilage transverse relaxation time (T2) from multi-echo-spin-echo (MESE) MR images, without direct segmentations for MESE. Materials and methods: Manual DESS segmentations of 89 healthy reference knees (healthy) and 60 knees with early radiographic osteoarthritis (early ROA) from the Osteoarthritis Initiative were registered to corresponding MESE images that had independent direct T2 segmentations. For validation purposes, (a) regression analysis of deep and superficial cartilage T2 was performed and (b) between-group differences between healthy vs. early ROA knees were compared for registered vs. direct MESE analysis. Results: Moderate to high correlations were observed for the deep (r = 0.80) and the superficial T2 (r = 0.81), with statistically significant between-group differences (ROA vs. healthy) of + 1.4 ms (p = 0.002) vs. + 1.3 ms (p < 0.001) for registered vs. direct T2 segmentation in the deep, and + 1.3 ms (p = 0.002) vs. + 2.3 ms (p < 0.001) in the superficial layer. Discussion: This registration approach enables extracting cartilage T2 from MESE scans using DESS (cartilage thickness) segmentations, avoiding the need for direct MESE T2 segmentations. [ABSTRACT FROM AUTHOR]

Neurite orientation dispersion and density imaging (NODDI) has become a popular diffusion MRI technique for investigating microstructural alternations during brain development, maturation and aging in health and disease. However, the NODDI model of diffusion does not explicitly account for compartment-specific T2 relaxation and its model parameters are usually estimated from data acquired with a single echo time (TE). Thus, the NODDI-derived measures, such as the intra-neurite signal fraction, also known as the neurite density index, could be T2-weighted and TE-dependent. This may confound the interpretation of studies as one cannot disentangle differences in diffusion from those in T2 relaxation. To address this challenge, we propose a multi-TE NODDI (MTE-NODDI) technique, inspired by recent studies exploiting the synergy between diffusion and T2 relaxation. MTE-NODDI could give robust estimates of the non-T2-weighted signal fractions and compartment-specific T2 values, as demonstrated by both simulation and in vivo data experiments. Results showed that the estimated non-T2 weighted intra-neurite fraction and compartment-specific T2 values in white matter were consistent with previous studies. The T2-weighted intra-neurite fractions from the original NODDI were found to be overestimated compared to their non-T2-weighted estimates; the overestimation increases with TE, consistent with the reported intra-neurite T2 being larger than extra-neurite T2. Finally, the inclusion of the free water compartment reduces the estimation error in intra-neurite T2 in the presence of cerebrospinal fluid contamination. With the ability to disentangle non-T2-weighted signal fractions from compartment-specific T2 relaxation, MTE-NODDI could help improve the interpretability of future neuroimaging studies, especially those in brain development, maturation and aging.

Fragile X syndrome (FXS) is the most commonly inherited form of intellectual disability ascribed to the autism spectrum disorder. Studies with FXS patients have reported altered white matter volume compared to controls. The Fmr1 knockout (KO) mouse, a model for FXS, showed evidence of delayed myelination during postnatal brain development. In this study, we examined several white matter regions in the male Fmr1 KO mouse brain compared to male wild-type (WT) mice at postnatal days (PND) 18, 21, 30, and 60, which coincide with critical stages of myelination and postnatal brain development. White matter volume, T2 relaxation time, and magnetization transfer ratio (MTR) were measured using magnetic resonance imaging and myelin content was determined with histological staining of myelin. Differences in the developmental accumulation of white matter and myelin between Fmr1 KO and WT mice were observed in the corpus callosum, external and internal capsules, cerebral peduncle, and fimbria. Alterations were more predominant in the external and internal capsules and fimbria of Fmr1 KO mice, where the MTR was lower at PND 18, then elevated at PND 30, and again lower at PND 60 compared to the corresponding regions in WT mice. The pattern of changes in MTR were similar to those observed in myelin staining and could be related to the altered protein synthesis that is a hallmark of FXS. While no significant changes in white matter volumes and T2 relaxation time between the Fmr1 KO and WT mice were observed, the altered pattern of myelin staining and MTR, particularly in the external capsule, reflecting the abnormalities associated with myelin content is suggestive of a developmental delay in the white matter of Fmr1 KO mouse brain. These early differences in white matter during critical developmental stages may contribute to altered brain networks in the Fmr1 KO mice. [ABSTRACT FROM AUTHOR]

Purpose: Myelin water imaging (MWI) provides a valuable biomarker for myelin, but clinical application has been restricted by long acquisition times. Accelerating the standard multi‐echo T2 acquisition with gradient echoes (GRASE) or by 2D multi‐slice data collection results in image blurring, contrast changes, and other issues. Compressed sensing (CS) can vastly accelerate conventional MRI. In this work, we assessed the use of CS for in vivo human MWI, using a 3D multi spin‐echo sequence. Methods: We implemented multi‐echo T2 relaxation imaging with compressed sensing (METRICS) and METRICS with partial Fourier acceleration (METRICS‐PF). Scan‐rescan data were acquired from 12 healthy controls for assessment of repeatability. MWI data were acquired for METRICS in 9 m:58 s and for METRICS‐PF in 7 m:25 s, both with 1.5 × 2 × 3 mm3 voxels, 56 echoes, 7 ms ΔTE, and 240 × 240 × 170 mm3 FOV. METRICS was compared with a novel multi‐echo spin‐echo gold‐standard (MSE‐GS) MWI acquisition, acquired for a single additional subject in 2 h:2 m:40 s. Results: METRICS/METRICS‐PF myelin water fraction had mean: repeatability coefficient 1.5/1.1, coefficient of variation 6.2/4.5%, and intra‐class correlation coefficient 0.79/0.84. Repeatability metrics comparing METRICS with METRICS‐PF were similar, and both sequences agreed with reference values from literature. METRICS images and quantitative maps showed excellent qualitative agreement with those of MSE‐GS. Conclusion: METRICS and METRICS‐PF provided highly repeatable MWI data without the inherent disadvantages of GRASE or 2D multi‐slice acquisition. CS acceleration allows MWI data to be acquired rapidly with larger FOV, higher estimated SNR, more isotropic voxels and more echoes than with previous techniques. The approach introduced here generalizes to any multi‐component T2 mapping application. [ABSTRACT FROM AUTHOR]

Background: The interpretation system for prostate MRI is largely based on qualitative image contrast of different tissue types. Therefore, a fast, standardized, and robust quantitative technique is necessary. Synthetic MRI is capable of quantifying multiple relaxation parameters, which might have potential applications in prostate cancer (PCa).Purpose: To investigate the use of quantitative relaxation maps derived from synthetic MRI for the diagnosis and grading of PCa.Study Type: Prospective.Subjects: In all, 94 men with pathologically confirmed PCa or benign pathological changes.Field Strength/sequence: T1 -weighted imaging, T2 -weighted imaging, diffusion-weighted imaging, and synthetic MRI at 3.0T.Assessment: Four kinds of tissue types were identified on pathology, including PCa, stromal hyperplasia (SH), glandular hyperplasia (GH), and noncancerous peripheral zone (PZ). PCa foci were grouped as low-grade (LG, Gleason score ≤6) and intermediate/high-grade (HG, Gleason score ≥7). Regions of interest were manually drawn by two radiologists in consensus on parametric maps according to the pathological results.Statistical Tests: Independent sample t-test, Mann-Whitney U-test, and receiver operating characteristic curve analysis.Results: T1 and T2 values of PCa were significantly lower than SH (P = 0.015 and 0.002). The differences of T1 and T2 values between PCa and noncancerous PZ were also significant (P ≤ 0.006). The area under the curve (AUC) of the apparent diffusion coefficient (ADC) value was significantly higher than T1 , T2 , and proton density (PD) values in discriminating PCa from SH and noncancerous PZ (P ≤ 0.025). T2 , PD, and ADC values demonstrated similar diagnostic performance in discriminating LG from HG PCa (AUC = 0.806 [0.640-0.918], 0.717 [0.542-0.854], and 0.817 [0.652-0.925], respectively; P ≥ 0.535).Data Conclusion: Relaxation maps derived from synthetic MRI were helpful for discriminating PCa from other benign pathologies. But the overall diagnostic performance was inferior to the ADC values. T2 , PD, and ADC values performed similarly in discriminating LG from HG PCa lesions.Level Of Evidence: 2 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2020;52:552-564. [ABSTRACT FROM AUTHOR]

Purpose: To assess the utility of Laplacian fitting to describe the differences in hyperpolarized [13C, 15N]urea T2 relaxation in ischemic and healthy rodent kidneys. Methods: Six rats with unilateral renal ischemia were investigated. [13C, 15N]Urea T2 mapping was undertaken with a radial fast spin echo method, with subsequent postprocessing performed with regularized Laplacian fitting. Results: Simulations showed that Laplacian fitting was stable down to a signal‐to‐noise ratio of 20. In vivo results showed a significant increase in the mono‐ and decrease in biexponential pools in ischemia reperfusion injury kidneys, in comparison to healthy (14 ± 10% versus 4 ± 2%, 85 ± 10% versus 95 ± 3%; P <.05). Conclusion: We demonstrate, for the first time, the differences in multiexponential behavior of [13C, 15N]urea between the healthy and ischemic rodent kidney. The distribution of relaxation pools were found to be both visually and numerically significantly different. The ability to improve the information level in hyperpolarized MR, by using the relaxation contrast mechanisms is an appealing option, that can easily be adopted in large animals and even in clinical studies in the near future. [ABSTRACT FROM AUTHOR]

Purpose: Dynamic glucose enhanced (DGE) MRI has shown potential for imaging glucose delivery and blood–brain barrier permeability at fields of 7T and higher. Here, we evaluated issues involved with translating d‐glucose weighted chemical exchange saturation transfer (glucoCEST) experiments to the clinical field strength of 3T. Methods: Exchange rates of the different hydroxyl proton pools and the field‐dependent T2 relaxivity of water in d‐glucose solution were used to simulate the water saturation spectra (Z‐spectra) and DGE signal differences as a function of static field strength B0, radiofrequency field strength B1, and saturation time tsat. Multislice DGE experiments were performed at 3T on 5 healthy volunteers and 3 glioma patients. Results: Simulations showed that DGE signal decreases with B0, because of decreased contributions of glucoCEST and transverse relaxivity, as well as coalescence of the hydroxyl and water proton signals in the Z‐spectrum. At 3T, because of this coalescence and increased interference of direct water saturation and magnetization transfer contrast, the DGE effect can be assessed over a broad range of saturation frequencies. Multislice DGE experiments were performed in vivo using a B1 of 1.6 µT and a tsat of 1 second, leading to a small glucoCEST DGE effect at an offset frequency of 2 ppm from the water resonance. Motion correction was essential to detect DGE effects reliably. Conclusion: Multislice glucoCEST‐based DGE experiments can be performed at 3T with sufficient temporal resolution. However, the effects are small and prone to motion influence. Therefore, motion correction should be used when performing DGE experiments at clinical field strengths. [ABSTRACT FROM AUTHOR]

A technique is presented for performing T2 spectroscopy in magnetic resonance imaging (MRI). It is based on a weighted linear combination of T2 decay data. The data is combined in a manner that acts like a filter on the T2 spectrum. The choice of weighting coefficients determines the filter specifications (e.g. passband/stopband locations, stopband suppression factors). To perform spectroscopy, a series of filters are designed with narrow passbands centered about consecutive regions of the T2 spectrum. This provides an estimate of every region of the spectrum. Taken together, an initial estimate of the full T2 spectrum is thus obtained. However, the filtering process causes a distortion of the estimate relative to the true spectrum. To reduce this distortion, deconvolution is performed. The characteristics of the technique are first evaluated through simulation. The technique is then applied to experimental MRI data to demonstrate practical feasibility. T2 spectroscopy falls into a class of problems requiring inverse transformation with a set of exponential basis functions (i.e. the Laplace Transform). It is demonstrated how the present technique may be applied to problems involving non-exponential basis functions as well. [ABSTRACT FROM AUTHOR]

To develop technical recommendations on the acquisition and post-processing of renal longitudinal (T1) and transverse (T2) relaxation time mapping. A multidisciplinary panel consisting of 18 experts in the field of renal T1 and T2 mapping participated in a consensus project, which was initiated by the European Cooperation in Science and Technology Action PARENCHIMA CA16103. Consensus recommendations were formulated using a two-step modified Delphi method. The first survey consisted of 56 items on T1 mapping, of which 4 reached the pre-defined consensus threshold of 75% or higher. The second survey was expanded to include both T1 and T2 mapping, and consisted of 54 items of which 32 reached consensus. Recommendations based were formulated on hardware, patient preparation, acquisition, analysis and reporting. Consensus-based technical recommendations for renal T1 and T2 mapping were formulated. However, there was considerable lack of consensus for renal T1 and particularly renal T2 mapping, to some extent surprising considering the long history of relaxometry in MRI, highlighting key knowledge gaps that require further work. This paper should be regarded as a first step in a long-term evidence-based iterative process towards ever increasing harmonization of scan protocols across sites, to ultimately facilitate clinical implementation. [ABSTRACT FROM AUTHOR]

Radiation therapy (RT) has been widely used as a powerful treatment tool to address cancerous tissues because of its ability to control cell growth. Its ionizing radiation damages the DNA of cancerous tissues, leading to cell death. Medical imaging, however, still has limitations regarding the reliability of its assessment of tissue response and in predicting the treatment effect because of its inability to provide contrast information on the gradual, minute tissue changes after RT. A recently developed magnetic resonance (MR)-based conductivity imaging method may provide direct, highly sensitive information on this tissue response because its contrast mechanism is based on the concentration and mobility of ions in intracellular and extracellular spaces. In this feasibility study, we applied T2-weighted, diffusion-weighted, and electrical conductivity imaging to mouse brain, thus, using the MR imaging to map the tissue response after radiation exposure. To evaluate the degree of response, we measured the T2 relaxation, apparent diffusion coefficient (ADC), and electrical conductivity of brain tissues before and after irradiation. The conductivity images, which showed significantly higher sensitivity than other MR imaging methods, indicated that the contrast is distinguishable in different ways at different areas of the brain. Future studies will focus on verifying these results and the long-term evaluation of conductivity changes using various irradiation methods for clinical applications. [ABSTRACT FROM AUTHOR]

Objective: To determine T1 and T2 relaxation times of healthy pancreas parenchyma at 7 T using a multi-transmit system. Materials and methods: Twenty-six healthy subjects were scanned with a 7 T MR system using eight parallel transceiver antennas, each with two additional receive loops. A Look-Locker sequence was used to obtain images for T1 determination, while T2 was obtained from spin-echo images and magnetic resonance spectroscopy measurements with different echo times. T1 and T2 times were calculated using a mono-exponential fit of the average magnitude signal from a region of interest in the pancreas and were tested for correlation with age. Results: The age range of the included subjects was 21–72 years. Average T1 and T2 relaxation times in healthy pancreas were 896 ± 149 ms, and 26.7 ± 5.3 ms, respectively. No correlation with age was found. Conclusion: T1 and T2 relaxation times of the healthy pancreas were reported for 7 T, which can be used for image acquisition optimization. No significant correlations were found between age and T1 or T2 relaxation times of the pancreas. Considering their low standard deviation and no observable age dependence, these values may be used as a baseline to study potentially pancreatic tissue affected by disease. [ABSTRACT FROM AUTHOR]