The hippocampus is a structure in the medial temporal lobe which serves multiple cognitive functions. While important, the development of the hippocampus in the formative period of childhood and adolescence has not been extensively investigated, with most contemporary research focusing on macrostructural measures of volume. Thus, there has been little research on the development of the micron-scale structures (i.e., microstructure) of the hippocampus, which engender its cognitive functions. The current study examined age-related changes of hippocampal microstructure using diffusion MRI data acquired with an ultra-strong gradient (300 mT/m) MRI scanner in a sample of children and adolescents (N=88; 8-19 years). Surface-based hippocampal modelling was combined with established microstructural approaches, such as Diffusion Tensor Imaging (DTI) and Neurite Orientation Dispersion Density Imaging (NODDI), and a more advanced gray matter diffusion model Soma And Neurite Density Imaging (SANDI). No significant changes in macrostructural measures (volume, gyrification, and thickness) were found between 8-19 years, while significant changes in microstructure measures related to neurites (from NODDI and SANDI), soma (from SANDI), and mean diffusivity (from DTI) were found. In particular, there was a significant increase across age in neurite MR signal fraction and a significant decrease in extracellular MR signal fraction and mean diffusivity across the hippocampal subfields and long-axis. A significant negative correlation between age and MR apparent soma radius was found in the subiculum and CA1 throughout the anterior and body of the hippocampus. Further surface-based analyses uncovered variability in age-related microstructural changes between the subfields and long-axis, which may reflect ostensible developmental differences along these two axes. Finally, correlation of hippocampal surfaces representing age-related changes of microstructure with maps derived from histology allowed for postulation of the potential underlying microstructure that diffusion changes across age may be capturing. Overall, distinct neurite and soma developmental profiles in the human hippocampus during late childhood and adolescence are reported for the first time.

UNASSIGNED: Human brain organoids are 3-dimensional cellular models that mimic architectural features of a developing brain. Generated from human induced pluripotent stem cells, these organoids offer an unparalleled physiologically relevant in vitro system for disease modeling and drug screening. In the current study, we sought to establish a foundation for a magnetic resonance imaging (MRI)-based, label-free imaging system that offers high-resolution capabilities for deep tissue imaging of whole organoids.
UNASSIGNED: An 11.7T Bruker/89 mm microimaging system was used to collect high-resolution multishell 3-dimensional diffusion images of 2 induced pluripotent stem cell-derived human hippocampal brain organoids. The MRI features identified in the study were interpreted on the basis of similarities with immunofluorescence microscopy.
UNASSIGNED: MRI microscopy at ≤40 μm isotropic resolution provided a 3-dimensional view of organoid microstructure. T2-weighted contrast showed a rosette-like internal structure and a protruding spherical structure that correlated with immunofluorescence staining for the choroid plexus. Diffusion tractography methods can be used to model tissue microstructural features and possibly map neuronal organization. This approach complements traditional immunohistochemistry imaging methods without the need for tissue clearing.
UNASSIGNED: This proof-of-concept study shows, for the first time, the application of high-resolution diffusion MRI microscopy to image 2-mm diameter spherical human brain organoids. Application of ultrahigh-field MRI and diffusion tractography is a powerful modality for whole organoid imaging and has the potential to make a significant impact for probing microstructural changes in brain organoids used to model psychiatric disorders, neurodegenerative diseases, and viral infections of the human brain, as well as for assessing neurotoxicity in drug screening.
Versace et al. present a groundbreaking approach using ultrahigh-resolution MRI (11.7T) for deep tissue imaging of whole human brain organoids. These 3D miniature brains mimic the developing brain’s architecture and hold promise for disease modeling and drug discovery. This label-free MRI approach offers the potential to characterize microstructural features in human brain organoids modeling psychiatric disorders, neurodegenerative diseases, viral infections, and/or drug-induced neurotoxicity.

Imaging of rheumatologic diseases has historically been performed using conventional radiography. MRI offers an opportunity for detection of altered marrow signal in early disease that is not visible on other imaging modalities such as radiography, computed tomography, or sonography. This review describes the advantages of current MRI techniques in the diagnosis and treatment monitoring of rheumatologic diseases. In addition, this review discusses novel MRI techniques at high-field magnetic strength which may be deployed in the future to allow for improved imaging resolution and quantitative assessment of both axial and peripheral joints.

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Atherosclerosis and resulting cardiovascular disease are the leading causes of death in the US. Hyperhomocysteinemia (HHcy), or the accumulation of the intermediate amino acid homocysteine, is an independent risk factor for atherosclerosis, but the intricate biological processes mediating this effect remain elusive. Several factors regulate homocysteine levels, including the activity of several enzymes and adequate levels of their coenzymes, including pyridoxal phosphate (vitamin B6), folate (vitamin B9), and methylcobalamin (vitamin B12). To better understand the biological influence of HHcy on the development and progression of atherosclerosis, apolipoprotein-E-deficient (apoE-/- mice), a model for human atherosclerosis, were fed a hyperhomocysteinemic diet (low in methyl donors and B vitamins) (HHD) or a control diet (CD). After eight weeks, the plasma, aorta, and liver were collected to quantify methylation metabolites, while plasma was also used for a broad targeted metabolomic analysis. Aortic plaque burden in the brachiocephalic artery (BCA) was quantified via 14T magnetic resonance imaging (MRI). A severe accumulation of plasma and hepatic homocysteine and an increased BCA plaque burden were observed, thus confirming the atherogenic effect of the HHD. Moreover, a decreased methylation capacity in the plasma and aorta, indirectly assessed by the ratio of S-adenosylmethionine to S-adenosylhomocysteine (SAM:SAH) was detected in HHD mice together with a 172-fold increase in aortic cystathionine levels, indicating increased flux through the transsulfuration pathway. Betaine and its metabolic precursor, choline, were significantly decreased in the livers of HHD mice versus CD mice. Widespread changes in the plasma metabolome of HHD mice versus CD animals were detected, including alterations in acylcarnitines, amino acids, bile acids, ceramides, sphingomyelins, triacylglycerol levels, and several indicators of dysfunctional lipid metabolism. This study confirms the relevance of severe HHcy in the progression of vascular plaque and suggests novel metabolic pathways implicated in the pathophysiology of atherosclerosis.

OBJECTIVE: The use of intraoperative techniques to detect residual tumors has recently become increasingly important. Intraoperative MRI has long been considered the gold standard; however, it is not widely used because of high equipment costs and long acquisition times. Consequently, real-time intraoperative ultrasound (ioUS), which is much less expensive than MRI, has gained popularity. The aim of the present study was to evaluate the capacity of ioUS to accurately determine the primary tumor volume and detect residual tumors.
METHODS: A prospective study of adult patients who underwent surgery for intra-axial brain tumors between November 2017 and October 2020 was performed. Navigated intraoperative ultrasound (nioUS) of the brain was used to guide tumor resection and to detect the presence of residual disease. Both convex (5-8 MHz) and linear array (6-13 MHz) probes were used. Tumor volume and residual disease were measured with nioUS and compared with MR images. A linear regression model based on a machine learning pipeline and a Bland-Altman analysis were used to assess the accuracy of nioUS versus MRI.
RESULTS: Eighty patients (35 females and 45 males) were included. The mean age was 58 years (range 25-80 years). A total of 88 lesions were evaluated; there were 64 (73%) gliomas, 19 (21.6%) metastases, and 5 (5.7%) other tumors, mostly located in the frontal (41%) and temporal (27%) lobes. Most of the tumors (75%) were perfectly visible on ioUS (grade 3, Mair grading system), except for those located in the insular lobe (grade 2). The regression model showed a nearly perfect correlation (R2 = 0.97, p < 0.001) between preoperative tumor volumes from both MRI and nioUS. Ultrasonographic visibility significantly influenced this correlation, which was stronger for highly visible (grade 3) tumors (p = 0.01). For residual tumors, the correlation between postoperative MRI and nioUS was weaker (R2 = 0.78, p < 0.001) but statistically significant. The Bland-Altman analysis showed minimal bias between the two techniques for pre- and postoperative scenarios, with statistically significant results for the preoperative concordance.
CONCLUSIONS: The authors\' findings show that most brain tumors are well delineated by nioUS and almost perfectly correlated with MRI-based measurements both pre- and postoperatively. These data support the hypothesis that nioUS is a reliable intraoperative technique that can be used for real-time monitoring of brain tumor resections and to perform volumetric analysis of residual disease.

Parallel transmit MRI at 7 T has increasingly been adopted in research projects and provides increased signal-to-noise ratios and novel contrasts. However, the interactions of fields in the body need to be carefully considered to ensure safe scanning. Recent advances in physically flexible body coils have allowed for high-field abdominal imaging, but the effects of increased variability on energy deposition need further exploration. The aim of this study was to assess the impact of subject geometry, respiration phase and coil positioning on the specific absorption rate (SAR). Ten healthy subjects (body mass index [BMI] = 25 ± 5 kg m-2 ) were scanned (at 3 T) during exhale breath-hold and images used to generate body models. Seven of these subjects were also scanned during inhale. Simplifications of the coil and body models were first explored, and then finite-difference time-domain simulations were run with a typical eight-channel parallel transmit coil positioned over the abdomen. Simulations were used to generate 10 g averaged SAR (SAR10g ) maps across 100,000 phase settings, and the worst-case scenario 10 g averaged SAR (wocSAR10g ) was identified using trigonometric maximisation. The average maximum SAR10g across the 10 subjects with 1 W input power per channel was 1.77 W kg-1 . Hotspots were always close to the body surface near the muscle wall boundary. The wocSAR10g across the 10 subjects ranged from 2.3 to 3.2 W kg-1 and was inversely correlated to fat volume percentage (R = 8) and BMI (R = 0.6). The coefficient of variation values in SAR10g due to variations in subject geometry, respiration phase and realistic coil repositioning were 12%, 4% and 12%, respectively. This study found that the variability due to realistic coil repositioning was similar to the variability due to differing healthy subject geometries for abdominal imaging. This is important as it suggests that population-based modelling is likely to be more useful than individual modelling in setting safe thresholds for abdominal imaging.

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