T1 Measurements Research Articles

Review of oxygen-enhanced lung mri: Pulse sequences for image acquisition and T1 measurement.

Oxygen-enhanced MR imaging (OE-MRI) is a special proton imaging technique that can be performed without modifying the scanner hardware. Many fundamental studies have been conducted following the initial reporting of this technique in 1996, illustrating the high potential for its clinical application. This review aims to summarise and analyse current pulse sequences and T1 measurement methods for OE-MRI, including fundamental theories, existing pulse sequences applied to OE-MRI acquisition and T1 mapping. Wash-in and wash-out time identify lung function and are sensitive to ventilation; thus, dynamic OE-MRI is also discussed in this review. We compare OE-MRI with the primary competitive technique, hyperpolarised gas MRI. Finally, an overview of lower-field applications of OE-MRI is highlighted, as relatively recent publications demonstrated positive results. Lower-field OE-MRI, which is lower than 1.5 T, could be an alternative modality for detecting lung diseases. This educational review is aimed at researchers who want a quick summary of the steps needed to perform pulmonary OE-MRI with a particular focus on sequence design, settings, and quantification methods.

T1 mapping in population ageing

Abstract Funding Acknowledgements Type of funding sources: None. Background The world’s population is ageing: every country is experiencing growth in both the size and the proportion of older people. Common health states in older age mainly include cardiovascular disease. To ensure that our health system is ready to face this demographic shift, we investigated native and post-contrast T1 mapping as a quantitative method to appraise its clinical potential in older people. Purpose This article aimed to provide reference values of T1 mapping for quantification of the expansion of the extracellular matrix in older people. Methods We retrospectively selected subjects ranged in age from 86 to 101 years old that underwent contrast cardiac magnetic resonance (CMR). All subjects were imaged on a 1.5 T system. T1 measurements were performed with a Modified Look Lockers Inversion (MOLLI) recovery sequence. Regions of interest (ROI) were drawn in the left ventricle for blood T1 measurement and in the interventricular septum. We used T1 data obtained before and after contrast injection. We also measured the volume and function of both ventricles. Rho di Spearman was used for correlations. Results We analysed 29 patients (mean age 88.58±3.13 years old). Mean value of T1 in the blood pool (T1bp) was 1647.43±107.66 before contrast and 357.18±63.94 after contrast. Mean value of T1 in the septum (T1s) was 1012.86±38.41 before contrast and 488.68±69.29 after contrast. Left ventricle (LV) EDVI was 48.11±15.29 ml/m2 and ESVI 16.49±8.59 ml/m2, LV ejection fraction (EF) and stroke volume (SV) were 66.38±9.65 % and 52.39±18.84 ml respectively. Right ventricle (RV) EDVI was 46.44±13.19 ml/m2 and ESVI 16.97±5.93 ml/m2, LV ejection fraction (EF) and stroke volume (SV) were 63.46±8.65 % and 49.29±18.63 ml respectively. A significant negative correlation was found between age and T1s before contrast (r=-0.405 and p = 0.015). Positive correlations were found also between T1s before contrast and LV volumes. Conclusions This study shows a correlation between T1 mapping and population ageing.

A deep learning approach for accurate and robust T1 estimation from cardiac magnetic resonance MOLLI sequences

Abstract Funding Acknowledgements Type of funding sources: None. Background T1 parametric maps of the myocardium are a recent development in cardiac Magnetic Resonance Imaging (MRI). They can be used to characterize the composition of the heart and identify alterations that can be indicative of a pathology. A common method of T1 estimation involves pixel-wise non-linear curve fitting from Modified Look-Locker Inversion Recovery (MOLLI) series [1]. Whilst relatively accurate, this method presents several drawbacks. Firstly, it assumes magnetization recovery to be a purely exponential process dependent on T1, thus neglecting other parameters such as T2 and B1 that can interfere in the process. Secondly, it does not consider that each acquisition during an inversion recovery experiment inverts the magnetization vector by a given angle and thus interferes with the recovery leading to the measurement of a shorter T1* rather than the actual T1 [2]. Additionally, since it considers each pixel individually, neglecting spatial information, it is sensitive to image quality [3]. Finally, since non-linear curve fitting is an iterative algorithm, it is computationally expensive and time-consuming. Methods To address these issues a convolutional neural network, DeepBLESS [4], and two spatially aware variants of it, were trained to predict T1, T2, and B1 with a dataset of MOLLI series simulated from experimental data. The simulation was performed using Bloch simulations and parameters extracted from a dataset composed of 27 single-slice MOLLI series acquired with the 5(3s)3 protocol using a b-SSFP readout at a main magnetic field strength of 3 Tesla. Thus, a dataset could be generated without relying on exponential fitting for ground truth generation. Results The exponential fitting of T1 was shown to consistently underestimate true T1 values by 138 +- 90 ms. In comparison, the spatially naïve DeepBLESS approach showed a mean absolute error of 14 +- 9 ms and the spatially aware DeepBLESS approach (Median-DeepBLESS) showed a mean absolute error of 13 +- 9 ms. As can be seen in Figure 1, Median-DeepBLESS also showed considerably more resilience to noise than exponential fitting and the spatially naïve version of DeepBLESS. Additionally, the deep learning approaches showcased promising results with regards to the estimation of T2 and B1 from MOLLI sequences (See Figure 2). Conclusions It was shown that the Deep Learning approaches eliminated the underestimation bias of exponential fitting with the spatially aware network Median-DeepBLESS being more robust to noise than both exponential fitting and the standard DeepBLESS network for myocardial T1 estimation. Relatively accurate estimation of T2 and B1 from MOLLI sequences was also accomplished through the Deep Learning approach, which may lead to simultaneous T1, T2, and B1 estimation in common clinical practice in the future.

Tissue characterisation of acute ablation lesions in the right atrium during CMR-guided atrial flutter ablation

Abstract Funding Acknowledgements Type of funding sources: None. Background Cardiac magnetic resonance (CMR)-guided ablation therapy offers a unique opportunity and incentive to investigate acute ablation lesions. Until present, human studies only used T2-weighted imaging (T2WI) and late gadolinium enhancement (LGE) to assess acute ablation lesions. Purpose To investigate the tissue characteristics of acute ablation lesions during CMR-guided atrial flutter ablation, by combining T2WI and LGE with first-pass perfusion and T1 mapping. Methods Thirteen patients with typical isthmus-dependent atrial flutter were prospectively enrolled and treated with CMR-guided ablation. Pre-ablation tissue characterisation consisted of T2WI and T1 mapping. Postablation imaging was performed directly after application of the primary ablation lesions and included T2WI (n=12), first-pass perfusion (n=9), LGE (n=9) and T1 mapping (n=7). For analysis of T2WI an edema ratio (ER; i.e. the signal intensity ratio between myocardium and reference skeletal muscle) > 2.0 was considered indicative of edema. Post-processing comprised native T1 measurements in three regions of the ablation line (near the tricuspid annulus, mid region, near the caval vein) on pre- and post-ablation images by two independent observers. For each region, the change in T1 value was expressed as the absolute increase (in ms) and the relative increase (in %). A third observer, blinded to the CMR results, reviewed which region(s) had required additional RF lesions after post-ablation CMR imaging. Results In 12 out of 13 patients CMR-guided atrial flutter ablation was successful, resulting in bidirectional conduction block. In 1 patient the ablation procedure was completed in the conventional electrophysiology lab, hampering acute post-ablation imaging. In all patients T2WI demonstrated edema in the ablation region. The ER increased from 1.6 ± 0.3 to 3.3 ± 0.5 post-ablation (p<0.001). Perfusion defects were present in 9/9 patients. The LGE images demonstrated hyperenhancement with a central area of hypo-enhancement in 9/9 patients, suggestive of ablation necrosis and previously reported areas of microvascular damage and hemorrhage. Right atrial T1 mapping was feasible in 20/21 regions (in 1 case artifacts from the adjacent catheter hampered analysis) and reproducible (r 0.981, ICC 0.939). The post-ablation increase in T1 value was significantly different between regions that did (n=10) and did not (n=10) require additional RF lesions, T1 increase was 46 ± 90ms versus 133 ± 69ms (p = 0.026), and 4.7 ± 9.1% versus 13.2 ± 6.8% (p = 0.028) respectively. Conclusion CMR tissue characterisation of acute ablation lesions during CMR-guided atrial flutter ablation demonstrates edema, perfusion defects, and necrosis with a core of microvascular damage. Atrial T1 mapping of the acute ablation lesion is feasible and reproducible, and might distinguish regions that require additional RF applications.

A Longitudinal Mediation Analysis of the Interrelations among Exclusionary Immigration Policy, Ethnic Identity, and Self-Esteem of Latinx Early Adolescents

Little is known about how exclusionary immigration laws affect ethnic identity and self-esteem among Latinx middle school students. Arizona’s SB 1070, which required local officers to verify the legal status of detained individuals, garnered national attention for its impact on immigrant and Latinx communities. This study tested a longitudinal parallel multiple mediation model where perceptions of the effects of an exclusionary immigration law (Arizona’s SB 1070) on self-esteem were mediated by dimensions of ethnic identity (ethnic centrality, ethnic private regard, ethnic public regard). Data were collected from a two-wave survey of 891 early adolescents ranging in age from 10 to 14 years (M = 12.09 years; SD = 0.99), a majority (71%) of whom were of Mexican descent. Analyses revealed an indirect effect of T1 perceptions of this law on T2 self-esteem (7 months later), holding T1 measures constant, with T2 ethnic centrality, private regard, and public regard acting as mediators. Perceived effects of this exclusionary law led to increased self-esteem through increased dimensions of ethnic identity. Results reveal how ethnic identity functions as a multidimensional construct in the process through which exclusionary immigration policy may impact the self-esteem of Latinx early adolescents.

The Landscape of Gold Nanocrystal Surface Chemistry.

ConspectusGold nanoparticles (AuNPs) exhibit unique size- and shape-dependent properties not obtainable at the macroscale. Gold nanorods (AuNRs), with their morphology-dependent optical properties, ability to convert light to heat, and high surface-to-volume ratios, are of great interest for biosensing, medicine, and catalysis. While the gold core provides many fascinating properties, this Account focuses on AuNP soft surface coatings, which govern the interactions of nanoparticles with the local environments. Postmodification of AuNP surface chemistry can greatly alter NP colloidal stability, nano-bio interactions, and functionality. Polyelectrolyte coatings provide controllable surface-coating thickness and charge, which impact the composition of the acquired corona in biological settings. Covalent modification, in which covalently bound ligands replace the original capping layer, is often performed with thiols and disulfides due to their ability to replace native coatings. N-heterocyclic carbenes and looped peptides expand the possible functionalities of the ligand layer.The characterization of surface ligands bound to AuNPs, in terms of ligand density and dynamics, remains a challenge. Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for understanding molecular structures and dynamics. Our recent NMR work on AuNPs demonstrated that NMR data were obtainable for ligands on NPs with diameters up to 25 nm for the first time. This was facilitated by the strong proton NMR signals of the trimethylammonium headgroup, which are present in a distinct regime from other ligand protons' signals. Ligand density analyses showed that the smallest AuNPs (below 4 nm) had the largest ligand densities, yet spin-spin T2 measurements revealed that these smallest NPs also had the most mobile ligand headgroups. Molecular dynamics simulations were able to reconcile these seemingly contradictory results.While NMR spectroscopy provides ligand information averaged over many NPs, the ligand distribution on individual particles' surfaces must also be probed to fully understand the surface coating. Taking advantage of improvements in electron energy loss spectroscopy (EELS) detectors employed with scanning transmission electron microscopy (STEM), a single-layer graphene substrate was used to calibrate the carbon K-edge EELS signal, allowing quantitative imaging of the carbon atom densities on AuNRs with sub-nanometer spatial resolution. In collaboration with others, we revealed that the mean value for surfactant-bilayer-coated AuNRs had 10-30% reduced ligand density at the ends of the rods compared to the sides, confirming prior indirect evidence for spatially distinct ligand densities.Recent work has found that surface ligands on nanoparticles can, somewhat surprisingly, enhance the selectivity and efficiency of the electrocatalytic reduction of CO2 by controlling access to the active site, tuning its electronic and chemical environment, or denying entry to impurities that poison the nanoparticle surface to facilitate reduction. Looking to the future, while NMR and EELS are powerful and complementary techniques for investigating surface coatings on AuNPs, the frontier of this field includes the development of methods to probe the surface ligands of individual NPs in a high-throughput manner, to monitor nano-bio interactions within complex matrices, and to study structure-property relationships of AuNPs in biological systems.

In vivo quantitative MRI: T1 and T2 measurements of the human brain at 0.064 T

ObjectiveTo measure healthy brain {T}_{1} and {T}_{2} relaxation times at 0.064 T.Materials and methods{T}_{1} and {T}_{2} relaxation times were measured in vivo for 10 healthy volunteers using a 0.064 T magnetic resonance imaging (MRI) system and for 10 test samples on both the MRI and a separate 0.064 T nuclear magnetic resonance (NMR) system. In vivo {T}_{1} and {T}_{2} values are reported for white matter (WM), gray matter (GM), and cerebrospinal fluid (CSF) for automatic segmentation regions and manual regions of interest (ROIs).Results{T}_{1} sample measurements on the MRI system were within 10% of the NMR measurement for 9 samples, and one sample was within 11%. Eight {T}_{2} sample MRI measurements were within 25% of the NMR measurement, and the two longest {T}_{2} samples had more than 25% variation. Automatic segmentations generally resulted in larger {T}_{1} and {T}_{2} estimates than manual ROIs.Discussion{T}_{1} and {T}_{2} times for brain tissue were measured at 0.064 T. Test samples demonstrated accuracy in WM and GM ranges of values but underestimated long {T}_{2} in the CSF range. This work contributes to measuring quantitative MRI properties of the human body at a range of field strengths.

Comparing CT and MR Properties of Artificial Thrombi According to Their Composition.

This study aims to determine whether and to what extent the structure and composition of thrombi can be assessed using NMR and CT measurements. Seven different thrombus models, namely, six RBC thrombi with hematocrit levels (HTs) of 0%, 20%, 40%, 60%, 80% and 100% and one platelet thrombus model, were analyzed using proton NMR at 100 MHz and 400 MHz, with measurements of T1 and T2 NMR relaxation times and measurements of the apparent diffusion coefficient (ADC). In addition, the thrombus models were CT-scanned in a dual-energy mode (80 kV and 140 kV) and in a single-energy mode (80 kV) to measure their CT numbers. The results confirmed that RBC thrombi can be distinguished from platelet thrombi by using ADC and CT number measurements in all three settings, while they cannot be distinguished by using T1 and T2 measurements. All measured parameters allowed for the differentiation of RBC thrombi according to their HT values, but the best sensitivity to HT was obtained with ADC and single-energy CT measurements. The importance of this study also lies in the potential application of its results for the characterization of actual thrombi in vivo.

Measurement of Tumor T2* Relaxation Times after Iron Oxide Nanoparticle Administration.

T2* relaxometry is one of the established methods to measure the effect of superparamagnetic iron oxide nanoparticles on tumor tissues with magnetic resonance imaging (MRI). Iron oxide nanoparticles shorten the T1, T2, and T2* relaxation times of tumors. While the T1 effect is variable based on the size and composition of the nanoparticles, the T2 and T2* effects are usually predominant, and T2* measurements are the most time-efficient in a clinical context. Here, we present our approach to measuring tumor T2* relaxation times, using multi-echo gradient echo sequences, external software, and a standardized protocol for creating a T2* map with scanner-independent software. This facilitates the comparison of imaging data from different clinical scanners, different vendors, and co-clinical research work (i.e., tumor T2* data obtained in mouse models and patients). Once the software is installed, the T2 Fit Map plugin needs to be installed from the plugin manager. This protocol provides step-by-step procedural details, from importing the multi-echo gradient echo sequences into the software, to creating color-coded T2* maps and measuring tumor T2* relaxation times. The protocol can be applied to solid tumors in any body part and has been validated based on preclinical imaging data and clinical data in patients. This could facilitate tumor T2* measurements for multi-center clinical trials and improve the standardization and reproducibility of tumor T2* measurements in co-clinical and multi-center data analyses.

Changes in CMR findings over time following acute Takotsubo cardiomyopathy

Takotsubo cardiomyopathy (TTS) is characterized by acute reversible left ventricular dysfunction showing typical left ventricular apical ballooning in the absence of obstructive coronary artery disease. Cardiac magnetic resonance (CMR) provides functional and inflammatory findings in contrast with the absence of late gadolinium enhancement (LGE). TTS generally heals within the first two weeks after the onset of symptoms, with the ECG and echocardiogram normalizing. However, data on CMR dynamics are scarce. In the present study, we aimed to describe how CMR findings change over time in acute TTS. Between December 2008 and May 2021, we retrospectively included all the patients hospitalized in the tertiary University Hospital of Angers, France who underwent CMR and received a diagnosis of acute TTS. Sixty-two patients fulfilled the diagnostic criteria from the 2018 ESC international expert consensus and underwent CMR. Patients were classified into three groups based on the delay between their first day of hospitalization and their assessment using CMR: less than five days (n = 31, 50%), between 5 and 15 days (n = 16, 25.8%), and more than 15 days [median 27 days (IQR: 20–36)] (n = 15, 24.2%). Compared to the 0–5 d group, the patients in the > 15 d group showed resolution of the LVEF alterations (55.9 ± 10.7 vs. 44.8 ± 13.3, P = 0.07), less apical akinesia (40% vs. 83%, P = 0.01) and normalized apical T2 values (44.5 ± 3.5 vs. 57 ± 2, P = 0.049). T1 and T2 quantitative measurements showed a base-to-apex gradient in 88.2% and 85.7% of patients, irrespective of the delay (P = 0.12 and P = 0.88). When CMR cannot be performed early after the onset of a suspected TTS, wall motion abnormalities disappear, and LVEF alteration resolve. However, a parametric assessment searching for a base-to-apex gradient in T1 and T2 values with higher apical values may be helpful to confirm the diagnosis. Main CMR findings at different time points (Fig. 1).

Adaptive model-based Magnetic Resonance.

Conventional sequences are static in nature, fixing measurement parameters in advance in anticipation of a wide range of expected tissue parameter values. We set out to design and benchmark a new, personalized approach-termed adaptive MR-in which incoming subject data is used to update and fine-tune the pulse sequence parameters in real time. We implemented an adaptive, real-time multi-echo (MTE) experiment for estimating T2 s. Our approach combined a Bayesian framework with model-based reconstruction. It maintained and continuously updated a prior distribution of the desired tissue parameters, including T2 , which was used to guide the selection of sequence parameters in real time. Computer simulations predicted accelerations between 1.7- and 3.3-fold for adaptive multi-echo sequences relative to static ones. These predictions were corroborated in phantom experiments. In healthy volunteers, our adaptive framework accelerated the measurement of T2 for n-acetyl-aspartate by a factor of 2.5. Adaptive pulse sequences that alter their excitations in real time could provide substantial reductions in acquisition times. Given the generality of our proposed framework, our results motivate further research into other adaptive model-based approaches to MRI and MRS.

MP-453088-9 THE SPATIAL VENTRICULAR GRADIENT IS ASSOCIATED WITH CARDIAC MAGNETIC RESONANCE MARKERS OF OF DIFFUSE MYOCARDIAL FIBROSIS

Cardiac MRI (CMR) markers of diffuse myocardial fibrosis are of prognostic importance in cardiomyopathies. However, CMR is expensive, time-consuming, and not readily available. An ECG correlate for diffuse fibrosis, via its effect on myocardial electrical heterogeneity, would be useful. The spatial ventricular gradient (SVG), a vectorcardiographic (VCG) measurement of myocardial electrical heterogeneity, is a promising ECG correlate of CMR detected diffuse fibrosis. To assess the relationship of the SVG to extracellular volume (ECV) and native T1 values in patients referred for CMR. Retrospective cohort study of all patients referred for CMR from 2015 to 2022 at a single academic medical center who had ECG(s) performed within 30 days of CMR. Median VCGs were constructed from the 12-lead ECGs, and SVG was calculated as the area under the X, Y, and Z median beats. ECV and native T1 values were regressed on SVG vector magnitude, QT interval, and QRS duration using linear regression. Median values were compared using the rank-sum test. We evaluated 679 patients who underwent CMR and had ECV and T1 measurements and a recent ECG. The sample was 60% male and the mean age was 55 +/- 16 years. The figure shows how SVG vector magnitude was inversely correlated with both T1 and ECV (p<0.001 for both). In the lowest and highest quartiles of both ECV (0.03-0.28 vs 0.35-0.68) and T1 (1041-1227 vs 1315-1535 ms), the median SVG magnitude was significantly lower: 48.7 vs 32.3 mv*ms for ECV, and 48.5 vs 30 mv*ms for T1 (p<0.001 for both). In a multivariable model, the SVG remained independently associated with ECV and T1 after adjustment for QT interval, QRS duration, age, and sex (p<0.001). SVG magnitude is independently associated with CMR measures of extracellular fibrosis. Patients with higher SVG magnitude are unlikely to have a significant burden of diffuse fibrosis.

Reducing Gadolinium Exposure in Patients Undergoing Monitoring for Meningiomas.

Background Due to the non-malignant and slow-growing nature of many meningiomas, surveillance with serial magnetic resonance imaging (MRI) serves as an acceptable management plan. However, repeated imaging with gold-standard contrast-based studies may lead to contrast-associated adverse effects. Non-gadolinium T2 sequences may serve as a suitable alternative without the risk of adverse effects of contrast. Thus, this study sought to investigate the agreement between post-contrast T1 and non-gadolinium T2 MRI sequences in the measurement of meningioma growth. Methodology The Virginia Commonwealth University School of Medicine (VCU SOM) brain tumor database was used to create a cohort of meningioma patients and determine the number of patients who had T1 post-contrast imaging accompanied by readily measurable imaging from either T2 fast spin echo (FSE) or T2 fluid-attenuated inversion recovery (FLAIR) sequences. Measurements of the largest axial and perpendicular diameters of each tumor were conducted by two independent observers using T1 post-contrast, T2 FSE, and T2 FLAIR imaging series.Lin's concordance correlation coefficient (CCC) was calculated to assess inter-rater reliability between observers and agreement between measurements of tumor diameter among the different imaging sequences. Results In total, 33 patients (average age = 72.1 ± 12.9 years, 90% female) with meningiomas were extracted from our database, with 22 (66.7%) undergoing T1 post-contrast imaging accompanied with readily measurable imaging from T2 FSE and/or T2 FLAIR sequences. The inter-rater reliability between the measurements of T1 axial and perpendicular diameters was 0.96 (95% confidence interval (CI) = 0.92-0.98) and 0.92 (95% CI = 0.83-0.97), respectively. The inter-rater reliability between the measurements of T2 axial perpendicular diameters was 0.93 (95% = CI 0.92-0.97) and 0.89 (95% CI = 0.74-0.95), respectively. The agreements between the measurement of T1 and T2 FSE axial diameter by each observer were 0.97 (95% CI = 0.93-0.98) and 0.92 (95% CI = 0.81-0.97). The agreements between the measurements of T1 and T2 FSE perpendicular diameter measurements by each observer were 0.98 (95% CI = 0.95-0.99) and 0.88 (95% CI = 0.73-0.95). Conclusions Two-thirds of our patients had meningiomas that were readily measurable on either T2 FSE or T2 FLAIR sequences. Additionally, there was excellent inter-rater reliability between the observers in our study as well as an agreement between individual measurements of T1 post-contrast and T2 FSE tumor diameters. These findings suggest that T2 FSE may serve as a safe and similarly effective surveillance method for the long-term management of meningioma patients.

An NMR study of hexamethylbenzene (HMB) incorporated in 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) framework

Molecular motion of hexamethylbenzene (HMB) incorporated in 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) was investigated by 1H NMR spin-lattice relaxation time T1 measurements. In the porous space of one-dimensional (1D) CLPOT nanochannels, HMB molecules reorientate more freely compared to bulk HMB crystals. With low concentrations x < 0.5 of CLPOT-(HMB)x, the distribution of HMB seems to be quite inhomogeneous in 1D nanochannel. The activation energy of the in-plane reorientation of HMB is 5 kJ mol−1 due to the interaction with nanochannel-wall and 10 - 18 kJ mol−1 depending on the separation distance when the interaction between the adjacent HMB molecules determines the activation energy.

MRI-based T1rho and T2 cartilage compositional imaging in osteoarthritis: what have we learned and what is needed to apply it clinically and in a trial setting?

Cartilage MRI-based T1rho and T2 compositional measurements have been developed to characterize cartilage matrix quality and diagnose cartilage damage before irreversible defects are found, allowing intervention at an early, potentially reversible disease stage. Over the last 2 decades, this technology was investigated in numerous studies and was validated using specimen studies and arthroscopy; and longitudinal studies documented its ability to predict progression of degenerative disease and radiographic osteoarthritis (OA). While T1rho and T2 measurements have shown promise in early disease stages, several hurdles have been encountered to apply this technology clinically. These include (i) challenges with cartilage segmentation, (ii) long image acquisition times, (iii) a lack of standardization of imaging, and (iv) an absence of reference databases and definitions of abnormal cut-off values. Progress has been made by developing deep-learning based automatic cartilage segmentation and faster imaging methods, enabling the feasibility of T1rho and T2 imaging for clinical and scientific trial applications. Also, the Radiological Society of North America (RSNA) Quantitative Imaging Biomarker Alliance mechanism was used to establish standardized profiles for compositional T1rho and T2 imaging, and multi-center feasibility testing is work in progress. The last hurdles are the development of reference databases and establishing a definition of normal versus abnormal cartilage T1rho and T2 values. Finally, effective treatments for prevention and slowing progression of OA are required in order to establish T1rho and T2 as imaging biomarkers for initiating and monitoring therapies, analogous to the role of dual X-ray absorptiometry (DXA) bone mineral density measurements in the management of osteoporosis. KEY POINTS: • T1rho and T2 cartilage measurements have been validated in characterizing cartilage degenerative change using histology and arthroscopy as a reference. • They have also been shown to predict progression of cartilage degeneration and incidence of radiographic OA. • Advances have been made to facilitate clinical and trial application of T1rho and T2 by improved standardization of imaging and by establishing deep learning-based automatic cartilage segmentation. • Effective treatments with disease-modifying OA specific drugs may establish T1rho and T2 cartilage compositional measurements as biomarkers to initiate and monitor treatment.

Single breath-hold three-dimensional whole-heart T2 mapping with low-rank plus sparse reconstruction.

The purpose of the current study was to develop and evaluate a three-dimensional single Breath-hOLd cardiac T2 mapping sequence (3D BOLT) with low-rank plus sparse (L + S) reconstruction for rapid whole-heart T2 measurement. 3D BOLT collects three highly accelerated electrocardiogram-triggered volumes with whole-heart coverage, all within a single 12-heartbeat breath-hold. Saturation pulses are performed every heartbeat to prepare longitudinal magnetization before T2 preparation (T2 -prep) or readout, and the echo time of T2 -prep is varied per volume for variable T2 weighting. Accelerated volumes are reconstructed jointly by an L + S algorithm. 3D BOLT was optimized and validated against gradient spin echo (GraSE) and a previously published approach (three-dimensional free-breathing cardiac T2 mapping [3DFBT2]) in both phantoms and human subjects (11 healthy subjects and 10 patients). The repeatability of 3D BOLT was validated on healthy subjects. Retrospective experiments indicated that 3D BOLT with 4.2-fold acceleration achieved T2 measurements comparable with those obtained with fully sampled data. T2 measured in phantoms using 3D BOLT demonstrated good accuracy and precision compared with the reference (R2 > 0.99). All in vivo imaging was successful and the average left ventricle T2 s measured by GraSE, 3DFBT2, and 3D BOLT were comparable and consistent for all healthy subjects (47.0± 2.3 vs. 47.7± 2.7 vs. 48.4± 1.8 ms) and patients (50.8± 3.0 vs. 48.6± 3.9 vs. 49.1 ± 3.7 ms), respectively. Myocardial T2 measured by 3D BOLT had excellent agreement with 3DFBT2 and there was no significant difference in mean, standard deviation, and coefficient of variation. 3D BOLT showed excellent repeatability (intraclass correlation coefficient: 0.938). The proposed 3D BOLT achieved whole-heart T2 mapping in a single breath-hold with good accuracy, precision, and repeatability on T2 measurements.

Measurement of crude oil emulsion instability using magnetic resonance and magnetic resonance imaging

Emulsion stability is important in many environmental and industrial applications. Unstable emulsions tend to have a layered structure which will evolve in space and time. Magnetic Resonance (MR) is a nondestructive method that can be used to study emulsion instability based on relaxation times (T1, T2), and/or diffusion (D). The bulk transverse relaxation lifetime (T2) is the most useful parameter for analysis. Since breaking of emulsions creates different layers and phases, spatially resolved T2 data is more valuable than bulk whole sample data. Previous literature studies were principally based on bulk T1, T2 or self-diffusion measurements without spatial resolution. In this study, for the first time, spatially resolved T2 distributions were used to examine oil and water behavior during emulsion breaking.Diluted bitumen was used as the oil phase in a synthetic emulsion. Measurements undertaken included spatially resolved T2 distribution measurements and T1-T2 relaxation correlation measurements. The results reveal changes in the relaxation times of oil and water caused by changes in the dynamics of the water and oil during emulsion breaking. In each layer of the sample, comparing peak T2 values with bulk T2 values of different components gives an insight into phase environments. Water and oil content in each layer was resolved by using peak areas of the T2 distribution. The results of T2 distribution imaging were consistent with optical microscopy images, which showed W/O emulsions in the oil dominant region and complex W/O/W emulsions in the water dominant region of the sample. With the above information one can obtain full spatial and temporal information on evolving phases as well as kinetics of phase dynamics in emulsion breaking.

Gastric digestion of whey protein gels: A randomized cross-over trial with the use of MRI

Food structure affects the breakdown kinetics of food. This has been extensively studied via in vitro digestion models. However, these in vitro findings need to be verified in vivo. Previously, we found that MRI parameters (T1 and T2 relaxation times) can serve as markers of protein digestion. Here, we assessed the effect of food hardness and protein content on gastric emptying as well as the application of these MRI parameters to monitor in vivo gastric digestion of solid foods. In a randomized cross-over trial, 18 healthy males (age: 27 ± 5 y; BMI 23 ± 1 kg/m2) ingested three gels: a soft gel with low protein content (Soft-LP), a hard gel with low protein content (Hard-LP), and a hard gel with high protein content (Hard-HP). Before and every 10 min after ingestion till 85 min, abdominal MRI scans were obtained to determine the gastric content volume and T1 and T2 of the gastric content. The decrease in gastric content volume differed among gels: Hard-HP < Hard-LP < Soft-LP. For all gels, mean T1 and T2 of the measured stomach content decreased directly after ingestion and then after 15 min gradually increased with Hard-HP < Hard-LP < Soft-LP. In conclusion, high protein content and high hardness slowed gastric emptying down. In addition, we show that T1 and T2 measurements provide extra information on the dilution and digestion of solid foods in the stomach. This underpins the potential of MRI to provide insights into in vivo protein digestion and link in vitro and in vivo digestion research.

Three techniques for measuring the transverse relaxation time of cesium atoms

The transverse relaxation time (T2) is an important indicator to determine the fundamental sensitivity limit of alkali-metal atomic magnetometers. We propose a method based on the principle of longitudinal field modulation that obtains T2 by scanning the transverse static magnetic field. The previous technique of extracting T2 from the linewidth of the modulation frequency and the traditional magnetic-resonance-broadening-fitting method are also described. The T2 measurements of Cesium (Cs) atoms are carried out through these three methods, whose operating environments are applicable to different atomic magnetometers, respectively. The method that we propose can be used for obtaining the T2 of Cs atoms as well as detecting the transverse static magnetic field and is customized for the study of the Cs–Xenon ensemble for the construction of nuclear magnetic resonance gyroscopes. Moreover, the relationship between the limit sensitivities and cell temperatures is further studied in the experiment.

Robust Assessment of Macromolecular Fraction (MMF) in Muscle with Differing Fat Fraction Using Ultrashort Echo Time (UTE) Magnetization Transfer Modeling with Measured T1.

Magnetic resonance imaging (MRI) is widely regarded as the most comprehensive imaging modality to assess skeletal muscle quality and quantity. Magnetization transfer (MT) imaging can be used to estimate the fraction of water and macromolecular proton pools, with the latter including the myofibrillar proteins and collagen, which are related to the muscle quality and its ability to generate force. MT modeling combined with ultrashort echo time (UTE-MT modeling) may improve the evaluation of the myotendinous junction and regions with fibrotic tissues in the skeletal muscles, which possess short T2 values and higher bound-water concentration. The fat present in muscle has always been a source of concern in macromolecular fraction (MMF) calculation. This study aimed to investigate the impact of fat fraction (FF) on the estimated MMF in bovine skeletal muscle phantoms embedded in pure fat. MMF was calculated for several regions of interest (ROIs) with differing FFs using UTE-MT modeling with and without T1 measurement and B1 correction. Calculated MMF using measured T1 showed a robust trend, particularly with a negligible error (<3%) for FF < 20%. Around 5% MMF reduction occurred for FF > 30%. However, MMF estimation using a constant T1 was robust only for regions with FF < 10%. The MTR and T1 values were also robust for only FF < 10%. This study highlights the potential of the UTE-MT modeling with accurate T1 measurement for robust muscle assessment while remaining insensitive to fat infiltration up to moderate levels.