Neuroimaging at 7 Tesla: a pictorial narrative review

Neuroimaging using the 7-Tesla (7T) human magnetic resonance (MR) system is rapidly gaining popularity after being approved for clinical use in the European Union and the USA. This trend is the same for functional MR imaging (MRI). The primary advantages of 7T over lower magnetic fields are its higher signal-to-noise and contrast-to-noise ratios, which provide high-resolution acquisitions and better contrast, making it easier to detect lesions and structural changes in brain disorders. Another advantage is the capability to measure a greater number of neurochemicals by virtue of the increased spectral resolution. Many structural and functional studies using 7T have been conducted to visualize details in the white matter and layers of the cortex and hippocampus, the subnucleus or regions of the putamen, the globus pallidus, thalamus and substantia nigra, and in small structures, such as the subthalamic nucleus, habenula, perforating arteries, and the perivascular space, that are difficult to observe at lower magnetic field strengths. The target disorders for 7T neuroimaging range from tumoral diseases to vascular, neurodegenerative, and psychiatric disorders, including Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, epilepsy, major depressive disorder, and schizophrenia. MR spectroscopy has also been used for research because of its increased chemical shift that separates overlapping peaks and resolves neurochemicals more effectively at 7T than a lower magnetic field. This paper presents a narrative review of these topics and an illustrative presentation of images obtained at 7T. We expect 7T neuroimaging to provide a new imaging biomarker of various brain disorders

Denoising approach with deep learning-based reconstruction for neuromelanin-sensitive MRI: image quality and diagnostic performance

[Purpose]Neuromelanin-sensitive MRI (NM-MRI) has proven useful for diagnosing Parkinson’s disease (PD) by showing reduced signals in the substantia nigra (SN) and locus coeruleus (LC), but requires a long scan time. The aim of this study was to assess the image quality and diagnostic performance of NM-MRI with a shortened scan time using a denoising approach with deep learning-based reconstruction (dDLR).[Materials and methods]We enrolled 22 healthy volunteers, 22 non-PD patients and 22 patients with PD who underwentNM-MRI, and performed manual ROI-based analysis. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in ten healthy volunteers were compared among images with a number of excitations (NEX) of 1 (NEX1), NEX1 images with dDLR (NEX1+dDLR) and 5-NEX images (NEX5). Acquisition times for NEX1 and NEX5 were 3 min 12 s and 15 min 58 s, respectively. Diagnostic performances using the contrast ratio (CR) of the SN (CR_SN) and LC (CR_LC) and those by visual assessment for diferentiating PD from non-PD were also compared between NEX1 and NEX1+dDLR.[Results]Image quality analyses revealed that SNRs and CNRs of the SN and LC in NEX1+dDLR were signifcantly higherthan in NEX1, and comparable to those in NEX5. In diagnostic performance analysis, areas under the receiver operating characteristic curve (AUC) using CR_SN and CR_LC of NEX1+dDLR were 0.87 and 0.75, respectively, which had no signifcant diference with those of NEX1. Visual assessment showed improvement of diagnostic performance by applying dDLR.[Conclusion]Image quality for NEX1+dDLR was comparable to that of NEX5. dDLR has the potential to reduce scan time of NM-MRI without degrading image quality. Both 1-NEX NM-MRI with and without dDLR showed high AUCs for diagnosing PD by CR. The results of visual assessment suggest advantages of dDLR. Further tuning of dDLR would be expected to provide clinical merits in diagnosing PD

The association between clinical symptoms of lumbar spinal stenosis and MRI axial imaging findings

Purpose: In diagnosing lumbar spinal stenosis (LSS), Magnetic Resonance Imaging (MRI) is appropriate to confirm the presence of anatomical stenosis of the spinal canal or compression of the nerve roots. However, it is known that morphological LSS is often present in asymptomatic subjects. There is still controversy about the relationship between anatomical LSS and symptomatic LSS. The aim of this study was to assess the association between qualitative imaging findings on MRI of the lumbar spine and symptomatic LSS. Patients and methods: This was a cross-sectional study of 239 volunteers from an epidemiological survey that included 1,862 participants in total. MRI of the lumbar spine was evaluated in four categories: morphological grading of central stenosis and lateral recess stenosis, presence of the sedimentation sign, and severity of facet joint effusion. The relationship between these morphological evaluations and typical LSS symptoms as assessed by the self-administered, self-reported history questionnaire for lumbar spinal stenosis (LSS-SSHQ) was investigated by multiple logistic regression analysis. Results: The odds ratio of the most severe central stenosis to no stenosis was 15.5 (95%CI: 1.4-164.9). Only the most severe central stenosis was associated with typical LSS symptoms, but not all cases with typical LSS symptoms were due to severe central stenosis. Conclusion: Extreme severe central stenosis was strongly related to typical LSS symptoms. However, although subjects with severe central stenosis showed symptoms suggestive of LSS, these subjects did not always show typical LSS symptoms

Evaluation of Heterogeneity in Thickness of Passive Films on Pure Iron by Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) was applied to evaluate the heterogeneity of a passive film formed on a pure iron electrode in deaerated pH 8.4 borate solution. A probe current image of SECM was measured with a tip-generation/substrate-collection (TG/SC) mode in deaerated pH 8.4 borate solution containing 0.03 mol dm-3 Fe(CN)64- as a mediator. The difference in thickness of passive films formed on two iron plates at different potentials could be evaluated from the probe current image. The probe current image of the passivated iron surface with distinctive crystal grains was composed of the patch patterns, the shapes of which coincided completely with the shapes of the substrate crystal grains. The probe current flowed above the grain surface oriented to {100} plane was less than that above the grain surface oriented to {110} or {111} plane. The grain orientation dependence of probe current was ascribed to the difference in thickness of passive films formed on the crystal grains

Aggregation-induced emission of a Eu(III) complex via ligand-to-metal charge transfer

Aggregation-induced emission (AIE) of a Eu(III) complex using ligand-to-metal charge transfer band is demonstrated. The Eu(III) complex comprises three anionic 2,2,6,6-tetramethyl-3,5-heptanedionate (tmh) ligands and one large p-conjugated neutral dipyrido[3,2-f:2',3'-h]quinoxaline (dpq) ligand. Crystalline H-aggregates of the Eu(III) complex were characterized by X-ray crystal structure analysis. H-aggregation-induced emission (H-AIE) properties were evaluated using emission spectra, emission lifetime, and quantum yields. The energy transfer efficiency of the H-aggregate in the solid state is five times larger than that of the isolated Eu(III) complex in solution