T1 Relaxation Values Research Articles

Unveiling the Exquisite Microstructural Details in Zebrafish Brain Non-Invasively Using Magnetic Resonance Imaging at 28.2 T

Zebrafish (Danio rerio) is an important animal model for a wide range of neurodegenerative diseases. However, obtaining the cellular resolution that is essential for studying the zebrafish brain remains challenging as it requires high spatial resolution and signal-to-noise ratios (SNR). In the current study, we present the first MRI results of the zebrafish brain at the state-of-the-art magnetic field strength of 28.2 T. The performance of MRI at 28.2 T was compared to 17.6 T. A 20% improvement in SNR was observed at 28.2 T as compared to 17.6 T. Excellent contrast, resolution, and SNR allowed the identification of several brain structures. The normative T1 and T2 relaxation values were established over different zebrafish brain structures at 28.2 T. To zoom into the white matter structures, we applied diffusion tensor imaging (DTI) and obtained axial, radial, and mean diffusivity, as well as fractional anisotropy, at a very high spatial resolution. Visualisation of white matter structures was achieved by short-track track-density imaging by applying the constrained spherical deconvolution method (stTDI CSD). For the first time, an algorithm for stTDI with multi-shell multi-tissue (msmt) CSD was tested on zebrafish brain data. A significant reduction in false-positive tracks from grey matter signals was observed compared to stTDI with single-shell single-tissue (ssst) CSD. This allowed the non-invasive identification of white matter structures at high resolution and contrast. Our results show that ultra-high field DTI and tractography provide reproducible and quantitative maps of fibre organisation from tiny zebrafish brains, which can be implemented in the future for a mechanistic understanding of disease-related microstructural changes in zebrafish models of various brain diseases.

Evolving Characteristics of Gadolinium-Based Contrast Agents for MR Imaging: A Systematic Review of the Importance of Relaxivity.

Gadolinium-based contrast agents (GBCAs) are widely and routinely used to enhance the diagnostic performance of magnetic resonance imaging and magnetic resonance angiography examinations. T1 relaxivity (r1) is the measure of their ability to increase signal intensity in tissues and blood on T1-weighted images at a given dose. Pharmaceutical companies have invested in the design and development of GBCAs with higher and higher T1 relaxivity values, and "high relaxivity" is a claim frequently used to promote GBCAs, with no clear definition of what "high relaxivity" means, or general concurrence about its clinical benefit. To understand whether higher relaxivity values translate into a material clinical benefit, well-designed, and properly powered clinical studies are necessary, while mere in vitro measurements may be misleading. This systematic review of relevant peer-reviewed literature provides high-quality clinical evidence showing that a difference in relaxivity of at least 40% between two GBCAs results in superior diagnostic efficacy for the higher-relaxivity agent when this is used at the same equimolar gadolinium dose as the lower-relaxivity agent, or similar imaging performance when used at a lower dose. Either outcome clearly implies a relevant clinical benefit. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 3.

Myocardial native T1 mapping at 3T cardiac magnetic resonance–closing the full-vendor reporting cycle of normal values

Cardiac magnetic resonance is currently an indispensable tool in the diagnosis of cardiac pathologies, with mapping techniques being one of the most recent advances in this area. T1 mapping is a robust tool that uses the T1 magnetic relaxation time as a quantitative marker of myocardial tissue composition. However, multiple T1 mapping sequences are used, and data comparing them, especially on different vendors, is limited. This study aims to determine the T1 relaxation values in the cardiac muscle of healthy individuals using GE's Discovery 3T scanner, allowing the use of the T1 mapping technique in patients on a sustained basis. Thirty-one healthy volunteers were submitted to T1 mapping at 3T magnetic resonance imaging (MRI) equipment, with 3 being excluded from the analysis (54% women; mean age: 39.2±13.9 years). The MOLLI 5(3)3 sequence was used, acquiring one short axis slice at midventricular level. Native T1 values were presented as means (± standard deviation), and t-student independent samples tests evaluated gender differences in T1 values. The results show an average global native T1 value of 1193±39 ms, with women's values being statistically higher than men (1211±40 vs 1173±27 ms, respectively, p<0.006). Gender remained the only determinant of native T1 times on a multiple linear regression model that included age, ejection fraction, and T2 status. This study has established one of the few native T1 values for a 3T GE Discovery scanner that are on par with those already reported by other vendors for a similar sequence, closing the circle in full-vendor reporting.

Identification of the reporter gene combination that shows high contrast for cellular level MRI.

Currently, we can label the certain cells by transducing specific genes, called reporter genes, and distinguish them from other cells. For example, fluorescent protein such as green fluorescence protein (GFP) is commonly used for cell labeling. However, fluorescent protein is difficult to observe in living animals. We can observe the reporter signals of the luciferin-luciferase system from the outside of living animals using in vivo imaging systems, although the resolution of this system is low. Therefore, in this study, we examined the reporter genes, which allowed the MRI-mediated observation of labeled cells in living animals. As a preliminary stage of animal study, we transduced some groups of plasmids that coded the protein that could take and store metal ions to the cell culture, added metal ions solutions, and measured their T1 or T2 relaxation values. Finally, we specified the best reporter gene combination for MRI, which was the combination of transferrin receptor, DMT1, and Ferritin-M6A for T1WI, and Ferritin-M6A for T2WI.

A Gd(III)-labelled self-assembling peptide as a potential pH-responsive MRI contrast agent.

A marine-derived peptide labelled with a Gd(III)-chelate was found to self-assemble depending on the solution pH, accompanied by changes in T1-relaxivity (r1) values when in the dispersed or self-assembled form. Such pH-responsive behavior can be advantageous in the development of macromolecular magnetic resonance imaging (MRI) contrast agents which monitor the tissue physiology.

Ultrasmall catechol-PEG-anchored ferrite nanoparticles for highly sensitive magnetic resonance angiography.

Highly sensitive iron oxide nanoparticles with stable, safe and efficient surface functionalization, as potential substitutes for gadolinium-based contrast agents (GBCAs) with increasing biosafety concerns, exhibit great potential for high-performance magnetic resonance angiography (MRA). Herein, we developed ultrasmall catechol-PEG-anchored ferrite nanoparticles (PEG-UMFNPs) for highly sensitive MRA. The obtained nanoprobe has a high T1 relaxivity value (7.2 mM-1 s-1) due to its ultrasmall size and Mn doping. It has a suitable hydrodynamic size of 20 nm, which prevents rapid vascular extravasation and renal clearance and prolongs its blood circulation time. In vivo MRA at 3.0 T using the nanoprobe shows that the arteries and veins of rats, even blood vessels as small as 0.32 mm, are distinctly visible, and the contrast enhancement can last for at least 1 h. In addition, due to the outstanding contrast enhancement and long circulation time, the stenosis and recanalization process of the rat's carotid artery can be continuously monitored with a single injection of the nanoprobe. Our study indicates that PEG-UMFNPs are outstanding MR imaging nanoprobes that can be used to diagnose vascular diseases without the biosafety issues of GBCAs.

Gestational age-related changes in relaxation times of neonatal brain by quantitative synthetic magnetic resonance imaging.

This study aimed to explore the correlation between T1 and T2 relaxation times of synthetic MRI (SyMRI) and gestational age (GA) in each hemisphere of preterm and term newborns at the initial 28 days of birth. Seventy preterm and full-term infants were prospectively included in this study. All subjects completed 3.0 T routine MRI and SyMRI (MAGiC) one-stop scanning within 28 days of birth (aged 34-42 W at examination). The SyMRI postprocessing software (v8.0.4) was used to measure the T1 and T2 relaxation values of each brain region. The linear regression equations of quantitative relaxation values with GA were established to compare the variation speed in each brain region. A significant linear and negative correlation was found between relaxation times and GA in the neonate cerebral cortex and subcortical gray and white matter regions (All p<.05). The relaxation time of the left centrum semiovale decreased with maximum variance with increasing GA among all white matter regions (T1: b = -51.45, β = -0.65, p < .0001; T2: b = -8.77, β = -0.71, p < .0001), whereas the right posterior limb of internal capsule showed minimal variance (T1: b = -27.94, β = -0.60, p < .0001; T2: b = -3.25, β = -0.68, p < .0001). Among all gray matter regions, the right globus pallidus and thalamus indicated the most significant decreasing degree of T1 and T2 relaxation values with GA (right globus pallidus T1: b = -33.14, β = -0.64, p < .0001; right thalamus T2: b = -3.94, β = -0.81, p < .0001), and the right and left occipital lobes indicated the least significant decreasing degree of T1 and T2 relaxation values with GA, respectively (right occipital lobes T1: b = -11.18, β = -0.26, p = .028; left occipital lobes T2: b = -1.22, β = -0.27, p = .024). SyMRI could quantitatively evaluate the linear changes of T1 and T2 relaxation values with GA in brain gray and white matter of preterm and term neonates.

Quantitative liver magnetic resonance imaging: correlation between conventional magnetic resonance imaging, laboratory values, and prognostic indices in Budd-Chiari syndrome.

In Budd-Chiari syndrome (BCS), unevenly distributed parenchymal changes and perfusion abnormalities occur due to hepatic venous outflow obstruction. This study aimed to evaluate the changes in the liver parenchyma in BCS using the quantitative magnetic resonance (MR) techniques of MR elastography, T1 and T2 mapping, and diffusion imaging and correlate the quantitative MR parameters through biochemical results and prognostic indices. Fourteen patients with BCS (seven men and seven women) were examined retrospectively. Liver stiffness (kPa), T1 relaxation times (ms) were achieved using the modified Look-Locker inversion recovery (MOLLI) 3(2)3(2)5 sequence and B1-corrected variable flip angle methods, T2 relaxation times (ms), and apparent diffusion coefficient (ADC) values (mm2/s) were measured using regions of interest placed in the same region in all quantitative methods. Measurements were repeated at the precontrast and postcontrast hepatobiliary phases. The reduction rate (RR; %) and adjusted postcontrast T1 (%) were calculated. The values obtained from different liver parenchyma areas (whole liver, caudate lobe, pathological T2 hyperintense tissue, and relatively preserved normal-appearing tissue) were compared using the Wilcoxon signed-rank test. Spearman's correlation coefficient was used to investigate the correlation between quantitative MR parameters and biochemical parameters/ prognostic scores (Child-Pugh score, Clichy score, and Rotterdam index). The parenchymal stiffness and precontrast T1 values of the caudate lobe were significantly lower than those of the remainder of the parenchyma, whereas the adjusted postcontrast T1 percentages (MOLLI) were significantly higher (P ≤ 0.027). The parenchymal stiffness value, T1 and T2 values, percentages of RR (MOLLI), and adjusted postcontrast T1 values for the pathological tissue and relatively normal tissue were significantly different (P < 0.028). No significant difference was found in terms of ADC values between any of the distinct regions of the liver. A strong correlation was detected between the Child-Pugh score, Clichy score, and precontrast T1 values obtained through the MOLLI sequence (r = 0.867, P = 0.012, r = 0.821, P = 0.023, respectively). No correlation was found between the whole liver stiffness values and the laboratory parameters, fibrosis markers, prognostic indices, or MR parameters. A significant correlation was identified between creatinine levels and several T1 parameters and the T2 relaxation time (r ≥ 0.661, P ≤ 0.052). Tissue stiffness and T1 relaxation values are high in the areas identified as fibrosis compared with those in the relatively preserved parenchyma. The T1 relaxation time can offer quantitative information for assessing segmental functional changes and prognosis in BCS.ion for assessing segmental functional changes and prognosis in BCS.

Engineered Protein-Driven Synthesis of Tunable Iron Oxide Nanoparticles as T1 and T2 Magnetic Resonance Imaging Contrast Agents.

Iron oxide nanoparticles (IONPs) have become one of the most promising nanomaterials for biomedical applications because of their biocompatibility and physicochemical properties. This study demonstrates the use of protein engineering as a novel approach to design scaffolds for the tunable synthesis of ultrasmall IONPs. Rationally designed proteins, containing different number of metal-coordination sites, were evaluated to control the size and the physicochemical and magnetic properties of a set of protein-stabilized IONPs (Prot-IONPs). Prot-IONPs, synthesized through an optimized coprecipitation approach, presented good T1 and T2 relaxivity values, stability, and biocompatibility, showing potential for magnetic resonance imaging (MRI) applications.

Quantitative imaging metrics derived from magnetic resonance fingerprinting using ISMRM/NIST MRI system phantom: An international multicenter repeatability and reproducibility study.

To compare the bias and inherent reliability of the quantitative (T1 and T2 ) imaging metrics generated from the magnetic resonance fingerprinting (MRF) technique using the ISMRM/NIST system phantom in an international multicenter setting. ISMRM/NIST MRI system phantom provides standard reference T1 and T2 relaxation values (vendor-provided) for each of the 14 vials in T1 and T2 arrays. MRF-SSFP scans repeated over 30days on GE 1.5 and 3.0T scanners at three collaborative centers. MRF estimated T1, and T2 values averaged over 30days were compared with the phantom vendor-provided and spin-echo (SE) based convention gold standard (GS) method. Repeatability and reproducibility were characterized by the within-case coefficient of variation (wCV) of the MRF data acquired over 30days, along with the biases. For the wide ranges of MRF estimated T1 values, vials #1-8 (T1 relaxation time between 2033 and 184ms) exhibited a wCV less than 3% and 4%, respectively, on 3.0 and 1.5T scanners. T2 values in vials #1-8 (T2 relaxation, 1044-45ms) have shown wCV to be <7% on both 3.0 and 1.5T scanners. A stronger linear correlation overall for T1 (R2 =0.9960 and 0.9963 at center-1 and center-2 on 3.0T scanner, and R2 =0.9951 and 0.9988 at center-1 and center-3 on 1.5T scanner) compared to T2 (R2 =0.9971 and 0.9972 at center-1 and center-2 on 3.0T scanner, and R2 =0.9815 and 0.9754 at center-1 and center-3 on 1.5T scanner). Bland-Altman (BA) analysis showed MRF based T1 and T2 values were within the limit of agreement (LOA) except for one data point. The mean difference or bias and 95% lower bound (LB) and upper bound (UB) LOA are reported in the format; mean bias: 95% LB LOA: 95% UB LOA. The biases for T1 values were 21.34: -50.00: 92.69, 21.32: -47.29: 89.94ms, and for T2 values were -19.88: -42.37: 2.61, -19.06: -43.58: 5.45ms on 3.0T scanner at center-1 and center-2, respectively. Similarly, on 1.5T scanner biases for T1 values were 26.54: -53.41: 106.50, 9.997: -51.94: 71.94ms, and for T2 values were -23.84: -135.40: 87.76, -37.30: 134.30: 59.73ms at center-1 and center-3, respectively. Additionally, the correlation between the SE based GS and MRF estimated T1 and T2 values (R2 =0.9969 and 0.9977) showed a similar trend as we observed between vendor-provided and MRF estimated T1 and T2 values (R2 =0.9963 and 0.9972). In addition to correlation, BA analysis showed that all the vials are within the LOA between the GS and vendor-provided for the T1 values and except one vial for T2 . All the vials are within the LOA between GS and MRF except one vial in T1 and T2 array. The wCV for reproducibility was <3% for both T1 and T2 values in vials #1-8, for all the 14 vials, wCV calculated for reproducibility was <4% for T1 values and <5% for T2 . This study shows that MRF is highly repeatable (wCV <4% for T1 and <7% for T2 ) and reproducible (wCV < 3% for both T1 and T2 ) in certain vials (vials #1-8).

Fe3O4@M nanoparticles for MRI-targeted detection in the early lesions of atherosclerosis

Atherosclerosis can lead to most cardiovascular diseases. Although some biomimetic nanomaterials coated by macrophage membranes have been reported in previous studies of atherosclerosis, to our knowledge, no studies regarding the detection of early lesions of atherosclerosis (foam cells) using such a strategy have yet been reported. In the present study, Fe3O4 biomimetic nanoparticles coated with a macrophage membrane (Fe3O4@M) were prepared to investigate the imaging effect on the early lesions of atherosclerosis (foam cells). The results showed that the Fe3O4@M particles are spheres with average diameters of approximately 300 nm. T1 and T2 relaxation values showed that the ratio of r2 to r1 was 26.09. The protein content accounted for approximately 27% of the total weight in Fe3O4@M, and Fe3O4@M nanoparticles exhibited high biosafety. Further testing showed that Fe3O4@M effectively targets early atherosclerotic lesions by the specific recognition of integrin α4β1 to VCAM-1. Taken together, Fe3O4@M is a promising contrast agent for the diagnosis of early stage atherosclerosis.

Repeatability and reproducibility of human brain morphometry using three-dimensional magnetic resonance fingerprinting.

Three‐dimensional (3D) Magnetic resonance fingerprinting (MRF) permits whole‐brain volumetric quantification of T1 and T2 relaxation values, potentially replacing conventional T1‐weighted structural imaging for common brain imaging analysis. The aim of this study was to evaluate the repeatability and reproducibility of 3D MRF in evaluating brain cortical thickness and subcortical volumetric analysis in healthy volunteers using conventional 3D T1‐weighted images as a reference standard. Scan‐rescan tests of both 3D MRF and conventional 3D fast spoiled gradient recalled echo (FSPGR) were performed. For each sequence, the regional cortical thickness and volume of the subcortical structures were measured using standard automatic brain segmentation software. Repeatability and reproducibility were assessed using the within‐subject coefficient of variation (wCV), intraclass correlation coefficient (ICC), and mean percent difference and ICC, respectively. The wCV and ICC of cortical thickness were similar across all regions with both 3D MRF and FSPGR. The percent relative difference in cortical thickness between 3D MRF and FSPGR across all regions was 8.0 ± 3.2%. The wCV and ICC of the volume of subcortical structures across all structures were similar between 3D MRF and FSPGR. The percent relative difference in the volume of subcortical structures between 3D MRF and FSPGR across all structures was 7.1 ± 3.6%. 3D MRF measurements of human brain cortical thickness and subcortical volumes are highly repeatable, and consistent with measurements taken on conventional 3D T1‐weighted images. A slight, consistent bias was evident between the two, and thus careful attention is required when combining data from MRF and conventional acquisitions.

Gadoxetic disodium-enhanced MRI to characterize T1 relaxation values and expression level of organic anion transporters and multidrug resistance protein on hepatocyte surface membrane of normal C57BL/6 mice

Objective: The characteristics of T1 relaxation values and the expression levels of organic anion transport system (OATP) and multidrug resistance protein carrier (MRP) on hepatocyte surface membrane were quantitatively studied to evaluate liver function in normal C57BL/6 mice with gadoxetic disodium-enhanced MRI. Methods: Ten 6-weeks-old, normal C57BL/6 mice were included in this study. Gadoxetic disodium- enhanced MRI examination was performed. Longitudinal relaxation time images before and 20 min after contrast injection (hepatobiliary-specific phase) were acquired. T1-relaxation time, T1 relaxation time decline rate (△T) and rapid initial enhancement slope percentage in the first-pass study of the liver parenchyma before and after administration of gadoxetate disodium were measured. Liver parenchyma specimens were detected by Western blotting and the values ​​of OATP1, MRP2, and MRP3 were recorded. Statistical results were expressed in mean. Results: The mean T1 relaxation time of 10 normal C57BL/6 mice before and after enhancement was 659.13 ± 24.07, and 408.87 ± 27.21 ms. The mean T1 relaxation time decline rate and rapid initial enhancement slope percentage in the first-pass study was 37.12% ± 4.95% and 4.14% ± 0.96% ms. Furthermore, the mean value of OATP1, MRP2 and MRP3 were 29 952.1 ± 11 475.2, 34 376.4 ± 33 228.4 and 357 308.9 ± 64 646.5. Conclusion: T1-relaxation values, T1 relaxation time decline rate and rapid initial enhancement slope percentage in the first-pass study before and after gadoxetic disodium-enhanced MRI were determined in normal C57BL/6 mice as well as quantitative values of OATP1, MRP2 and MRP3 at the molecular level on the hepatocyte surface membrane were helpful for liver injury model with control study.

THE RISE AND FALL OF DGEMRIC EVALUATION IN THE ADOLESCENT HIP

BACKGROUND: Delayed Gadolinium Enhanced Magnetic Resonance Imaging of Cartilage (dGEMRIC) was first introduced in 1996 by Bashir et al. as a method of indirectly evaluating glycosaminoglycan (GAG) changes in cartilage microstructure. Following publications originating from the Boston Children’s research group describing the association of early joint failure following periacetabular osteotomy (PAO) in patients with diminished preoperative cartilage T1 relaxation values, the interest in this imaging technique spread. dGEMRIC imaging was introduced into our clinical practice in 2013 with enrollment of both pediatric and adult patients. However, since the program’s apex in 2015, a marked decline in referral of adolescent patients for preoperative dGEMRIC imaging has occurred. Using data acquired during a quality analysis of the dGEMRIC program, this project was designed to investigate the utility of the dGEMRIC exam in our adolescent imaging cohort from 2013-2015 and to identify potential factors leading to decreased utilization from 2015-2018. METHODS: IRB approval was obtained for a HIPAA-compliant, retrospective cohort study which included all patients referred for dGEMRIC from May 2013- June 2015. 108 patients/112 exams/122 hips were identified. The study was designed in 4 parts including a. Blinded quantitative imaging review x 2 performed by 4 radiologists, b. Surgical review with 2 year post-operative follow-up completed July 2017, c. Patient phone interview, and d. Financial billing and reimbursement analysis. Subsequently, dGEMRIC utilization data from July 2015-May 2018 was compiled for comparative analysis of adolescent referral patterns. RESULTS: Of the 108 patients included in the comprehensive retrospective analysis, 56 were &lt; 19 years of age with 43% of the adolescent patients participating in sports at time of presentation. 4 patients were excluded as the dGEMRIC data was either incomplete or could not be reprocessed. 61 hips were evaluated in the remaining 52 patients. The following summary data was compiled during the 4 part analysis. From the radiologist review: Siemens MapIt® T1 measurement software performed well at both 1.5 T and 3 T with good to excellent within rater ICC (0.79-0.92) but the between rater agreement was lacking particularly at 3.0 T (0.45) compared to 1.5 T (0.77) (p&lt;0.05). Variability between sequential T1 measurements performed by the same radiologist at 2 different time points existed averaging 36-41 ms at 1.5 T and 76-84 ms at 3 T. From the surgical perspective: 17 hips in 16 patients were determined to have abnormally low T1 relaxation values when reprocessed by the 4 radiologists. 1 patient’s T1 values differed significantly after blinded review compared to the original interpretation. Of the 16 abnormal patients, 5 were referred for total hip arthroplasty. 7 patients underwent surgical intervention (2 PAO, 3 arthroscopic debridement/rim trim/chondroplasty/labral repair, 2 femoral/acetabular osteotomy). 1 patient was referred to rheumatology and 3 were lost to follow-up. After 2 year follow-up, all surgical patients reported decreased pain and improved function compared to presentation. From the patient perspective: 62 of the original 108 patients were contacted by phone with 60 (56%) participating in the phone survey. Patients described the dGEMRIC exam as a difficult procedure. The total time expenditure for the dGEMRIC exam averaged 3.5 hours in hospital with an average time in magnet of 107 minutes. 40% of patients reported significant pain with the pre-imaging exercise and 33% reported significant pain while in the MRI. Of 49 respondents who had undergone previous hip injections, 28 (57%) stated the dGEMRIC exam was as or more difficult than the injection. However, 50/57 (88%) stated they would undergo dGEMRIC again if the surgeon felt the information would be of added value in decision making. From the financial review, a lack of standardization of CPT codes billed was discovered resulting in discrepant billed charges varying by a factor &gt;10 ($2300-$24,000). Following completion of the quality analysis and review of the results with the referring orthopedists, only 17 dGEMRIC exams have been performed in the adolescent age group in the subsequent 36 months. CONCLUSIONS: While the dGEMRIC exam holds promise as a prognosticating tool to guide surgical planning, in the adolescent practice environment, our historical data reveals that even when faced with abnormal T1 relaxation values, surgeons may opt to proceed with hip sparing surgical procedures simply because of the young age of the patient. From the radiologist’s perspective, dGEMRIC reporting is clouded by measurement variability. Inherent variability in the numbers reported brings to question the wisdom of using absolute T1 numeric thresholds to prognosticate joint failure risk. From the patient’s perspective, this imaging test comes with significant cost measured by time, pain, and financial burden. For all these reasons, utilization of this imaging study should be limited to the select few adolescent patients in whom documentation of an abnormal cartilage T1 value alone could substantially impact the surgical plan.

Gray matter atrophy in multiple sclerosis despite clinical and lesion stability during natalizumab treatment.

BackgroundBrain volume loss is an important surrogate marker for assessing disability in MS; however, contribution of gray and white matter to the whole brain volume loss needs further examination in the context of specific MS treatment.ObjectivesTo examine whole and segmented gray, white, thalamic, and corpus callosum volume loss in stable patients receiving natalizumab for 2–5 years.MethodsThis was a retrospective study of 20 patients undergoing treatment with natalizumab for 24–68 months. Whole brain volume loss was determined with SIENA. Gray and white matter segmentation was done using FAST. Thalamic and corpus callosum volumes were determined using Freesurfer. T1 relaxation values of chronic hypointense lesions (black holes) were determined using a quantitative, in-house developed method to assess lesion evolution.ResultsOver a mean of 36.6 months, median percent brain volume change (PBVC) was -2.0% (IQR 0.99–2.99). There was decline in gray (p = 0.001) but not white matter (p = 0.6), and thalamic (p = 0.01) but not corpus callosum volume (p = 0.09). Gray matter loss correlated with PBVC (Spearman’s r = 0.64, p = 0.003) but not white matter (Spearman’s r = 0.42, p = 0.07). Age significantly influenced whole brain volume loss (p = 0.010, multivariate regression), but disease duration and baseline T2 lesion volume did not. There was no change in T1 relaxation values of lesions or T2 lesion volume over time. All patients remained clinically stable.ConclusionsThese results demonstrate that brain volume loss in MS is primarily driven by gray matter changes and may be independent of clinically effective treatment.

Cerebrospinal fluid-suppressed T2 -weighted MR imaging at 7 T for human brain.

PurposeT2‐weighted lesional imaging is most commonly performed using inversion recovery turbo spin echoes. At 7 T, however, this acquisition is limited for specific absorption rate and resolution. This work describes and implements a method to generate CSF‐suppressed T2‐weighted imaging.MethodsThe strategy uses a driven equilibrium spin‐echo preparation within an inversion recovery with multiple 3D gradient‐echo imaging blocks. Images are combined using the self‐normalization approach, which achieves CSF suppression through optimized timing of individual blocks and minimizes sources of variation due to coil receptivity, T2 *, and proton density. Simulations of the magnetization‐prepared fluid‐attenuated inversion recovery gradient‐echo (MPFLAGRE) method over T1 and T2 relaxation values are performed, and in vivo demonstrations using an 8 × 2 transceiver array in healthy controls are shown.ResultsThe specific absorption rate of the calculated MPFLAGRE sequence is 11.1 ± 0.5 W (n = 5 volunteers), which is 74 ± 2% of the US Food and Drug Administration guidelines. This method acquires both contrasts for CSF suppression with detection of long T2 components and T2‐weighted imaging in a single acquisition. In healthy controls, the former contrast generates increased signal in the cortical rim and ependyma. A comparison is shown with a conventional 3D SPACE fluid‐attenuated inversion recovery acquisition, and sensitivity to pathology is demonstrated in an epilepsy patient.ConclusionAs applied with the 8 × 2 transceiver, the MPFLAGRE sequence generates both whole‐brain contrast suitable for lesional and T2‐weighted imaging at 7 T in fewer than 10 minutes within the US Food and Drug Administration's specific absorption rate guidelines.

Revisiting Radiographic L5-S1 Parallelism Using MRI T1 Mapping.

Purpose:Thirty years ago, we reported that parallel aspect of the L5-S1 disc on a lateral view of the spine might be considered to be an initial stage of disk degeneration. The current study represents an attempt to increase the validity of parallel sign on conventional radiograph using MR real T1 mapping.Methods:Forty-four young asymptomatic volunteers (mean age 21.6 ± 2.3) underwent lumbar spine MRI, twice the same day, morning and afternoon. Dedicated sequences using the inversion-recovery technique were used to calculate the T1 relaxation time. A region of interest (ROI) representing the nucleus pulposus was defined in each disk. The volunteers were stratified according to the presence or absence of a parallel morphology of L5-S1. Correlation between endplates angles, sacral slopes and T1 values were then evaluated.Results:L5-S1 space looks parallel for angles <10° (mean value 6.9° ± 1.4°). Sacral slope was lower in parallel disks (31.7 ± 4.9° vs. 40.1 ± 5.6°), showing a significant difference of 8.4° (p < 0.05). The T1 relaxation values show a significant difference between the two groups (p < 0.05) with a difference of 96 ms for the morning (1090.9 ± 33.3 ms for the parallel group and 1186.9 ± 41.2 ms for the non-parallel) and 121.9 ms for the afternoon (respectively 1004.7 ± 22.2 ms and 1126.6 ± 12.9 ms).Conclusion:The difference between the two groups suggests that parallel morphology of the L5-S1 disk is associated with lower water content.

Gd-EOB-DTPA-enhanced T1 relaxometry for assessment of liver function determined by real-time 13C-methacetin breath test.

To determine whether liver function as determined by intravenous administration of 13C-methacetin and continuous real-time breath analysis can be estimated quantitatively from gadoxetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance (MR) relaxometry. Sixty-six patients underwent a 13C-methacetin breath test (13C-MBT) for evaluation of liver function and Gd-EOB-DTPA-enhanced T1-relaxometry at 3 T. A transverse 3D VIBE sequence with an inline T1 calculation based on variable flip angles was acquired prior to (T1 pre) and 20 min post-Gd-EOB-DTPA (T1 post) administration. The reduction rate of T1 relaxation time (rrT1) and T1 relaxation velocity index (∆R1) between pre- and post-contrast images was evaluated. 13C-MBT values were correlated with T1post, ∆R1 and rrT1, providing an MRI-based estimated 13C-MBT value. The interobserver reliability was assessed by determining the intraclass correlation coefficient (ICC). Stratified by three different categories of 13C-MBT readouts, there was a constant increase of T1 post with increasing progression of diminished liver function (p ≤ 0.030) and a constant significant decrease of ∆R1 (p ≤ 0.025) and rrT1 (p < 0.018) with progression of liver damage as assessed by 13C-methacetin breath analysis. ICC for all T1 relaxation values and indices was excellent (> 0.88). A simple regression model showed a log-linear correlation of 13C-MBT values with T1post (r = 0.57; p < 0.001), ∆R1 (r = 0.59; p < 0.001) and rrT1 (r = 0.70; p < 0.001). Liver function as determined using real-time 13C-methacetin breath analysis can be estimated quantitatively from Gd-EOB-DTPA-enhanced MR relaxometry. • Gd-EOB-DTPA-enhanced T1 relaxometry quantifies liver function • Gd-EOB-DTPA-enhanced MR relaxometry may provide parameters for assessing liver function before surgery • Gd-EOB-DTPA-enhanced MR relaxometry may be useful for monitoring liver disease progression • Gd-EOB-DTPA-enhanced MR relaxometry has the potential to become a novel liver function index.

Gadolinium(III)‐Based Porous Luminescent Metal–Organic Frameworks for Bimodal Imaging

GdIII -based metal-organic frameworks, Gd-pDBI-1 and Gd-pDBI-2, have been synthesized using the linker pDBI (pDBI=1,4-bis(5-carboxy-1H-benzimidazole-2yl)benzene). They exhibited structural diversity due to subtle change in reaction constituents. Owing to the judicious choice of the fluorescent linker, the materials could be used for bimodal imaging (fluorescent and magnetic resonance) and displayed a modest T1 relaxivity value.

Evolution of T1 Relaxation, ADC, and Fractional Anisotropy during Early Brain Maturation: A Serial Imaging Study on Preterm Infants.

The alteration of brain maturation in preterm infants contributes to neurodevelopmental disabilities during childhood. Serial imaging allows understanding of the mechanisms leading to dysmaturation in the preterm brain. The purpose of the present study was to provide reference quantitative MR imaging measures across time in preterm infants, by using ADC, fractional anisotropy, and T1 maps obtained by using the magnetization-prepared dual rapid acquisition of gradient echo technique. We included preterm neonates born at <30 weeks of gestational age without major brain lesions on early cranial sonography and performed 3 MRIs (3T) from birth to term-equivalent age. Multiple measurements (ADC, fractional anisotropy, and T1 relaxation) were performed on each examination in 12 defined white and gray matter ROIs. We acquired 107 MRIs (35 early, 33 intermediary, and 39 at term-equivalent age) in 39 cerebral low-risk preterm infants. Measures of T1 relaxation time showed a gradual and significant decrease with time in a region- and hemispheric-specific manner. ADC values showed a similar decline with time, but with more variability than T1 relaxation. An increase of fractional anisotropy values was observed in WM regions and inversely a decrease in the cortex. The gradual change with time reflects the progressive maturation of the cerebral microstructure in white and gray matter. Our study provides reference trajectories from 25 to 40 weeks of gestation of T1 relaxation, ADC, and fractional anisotropy values in low-risk preterm infants. We speculate that deviation thereof might reflect disturbed cerebral maturation; the correlation of this disturbed maturation with neurodevelopmental outcome remains to be addressed.