Quantitative magnetization transfer imaging of the human locus coeruleus.

The locus coeruleus (LC) is the major origin of norepinephrine in the central nervous system, and is subject to age-related and neurodegenerative changes, especially in disorders such as Parkinson's disease and Alzheimer's disease. Previous studies have shown that neuromelanin (NM)-sensitive MRI can be used to visualize the LC, and it is hypothesized that magnetization transfer (MT) effects are the primary source of LC contrast. The aim of this study was to characterize the MT effects in LC imaging by applying high spatial resolution quantitative MT (qMT) imaging to create parametric maps of the macromolecular content of the LC and surrounding tissues. Healthy volunteers (n = 26; sex = 17 F/9M; age = 41.0 ±â€¯19.1 years) underwent brain MRI on a 3.0 T scanner. qMT data were acquired using a 3D MT-prepared spoiled gradient echo sequence. A traditional NM scan consisting of a T1-weighted turbo spin echo sequence with MT preparation was also acquired. The pool-size ratio (PSR) was estimated for each voxel using a single-point qMT approach. The LC was semi-automatically segmented on the MT-weighted images. The MT-weighted images provided higher contrast-ratio between the LC and surrounding pontine tegmentum (PT) (0.215 ±â€¯0.031) than the reference images without MT-preparation (-0.005 ±â€¯0.026) and the traditional NM images (0.138 ±â€¯0.044). The PSR maps showed significant differences between the LC (0.090 ±â€¯0.009) and PT (0.188 ±â€¯0.025). The largest difference between the PSR values in the LC and PT was observed in the central slices, which also correspond to those with the highest contrast-ratio. These results highlight the role of MT in generating NM-related contrast in the LC, and should serve as a foundation for future studies aiming to quantify pathological changes in the LC and surrounding structures in vivo.

Longitudinal atlas for normative human brain development and aging over the lifespan using quantitative susceptibility mapping.

Longitudinal brain atlases play an important role in the study of human brain development and cognition. Existing atlases are mainly based on anatomical features derived from T1-and T2-weighted MRI. A 4D developmental quantitative susceptibility mapping (QSM) atlas may facilitate the estimation of age-related iron changes in deep gray matter nuclei and myelin changes in white matter. To this end, group-wise co-registered QSM templates were generated over various age intervals from age 1-83 years old. Registration was achieved by combining both T1-weighted and QSM images. Based on the proposed template, we created an accurate deep gray matter nuclei parcellation map (DGM map). Notably, we segmented thalamus into 5 sub-regions, i.e. the anterior nuclei, the median nuclei, the lateral nuclei, the pulvinar and the internal medullary lamina. Furthermore, we built a "whole brain QSM parcellation map" by combining existing cortical parcellation and white-matter atlases with the proposed DGM map. Based on the proposed QSM atlas, the segmentation accuracy of iron-rich nuclei using QSM is significantly improved, especially for children and adolescent subjects. The age-related progression of magnetic susceptibility in each of the deep gray matter nuclei, the hippocampus, and the amygdala was estimated. Our automated atlas-based analysis provided a systematic confirmation of previous findings on susceptibility progression with age resulting from manual ROI drawings in deep gray matter nuclei. The susceptibility development in the hippocampus and the amygdala follow an iron accumulation model; while in the thalamus sub-regions, the susceptibility development exhibits a variety of trends. It is envisioned that the newly developed 4D QSM atlas will serve as a template for studying brain iron deposition and myelination/demyelination in both normal aging and various brain diseases.

Quantitative susceptibility mapping (QSM) as a means to monitor cerebral hematoma treatment.

BACKGROUND: Quantitative susceptibility mapping (QSM) offers a consistent hemorrhage volume measurement independent of imaging parameters. PURPOSE: To investigate the magnetic susceptibility of intracerebral hemorrhage (ICH) as a quantitative measurement for monitoring treatment in hematoma patients. STUDY TYPE: Prospective. POPULATION: Twenty-six patients with acute ICH were recruited and enrolled in treatment including surgery or medication (mannitol) for 1 week. FIELD STRENGTH/SEQUENCE: A 3D gradient echo sequence at 3.0T. ASSESSMENT: The hematoma volumes on computed tomography (CT) and QSM were calculated and used for correlation analysis. Magnetic susceptibility changes from pre- to posttreatment were calculated and compared to the National Institutes of Health stroke scale (NIHSS) measure of neurological deficit for each patient. STATISTICAL TESTS: Mean susceptibility values were calculated over each region of interest (ROI). A one-sample t-test was used to assess the changes of total volumes and mean magnetic susceptibility of ICH identified between pre- and posttreatment images (P < 0.05 was considered significant) and the Bland-Altman analysis with 95% limits of agreement (average difference, ±1.96 SD of the difference). Regression of volume measurements on QSM vs. CT and fitted linear regression of mean susceptibility vs. CT signal intensity for hematoma regions were conducted in all patients. RESULTS: Good correlation was found between hemorrhage volumes calculated from CT and QSM (CT volume = 0.94*QSM volume, r = 0.98). Comparison of QSM pre- and posttreatment showed that the mean ICH volume was reduced by a statistically insignificant amount from 5.74 cm3 to 5.45 cm3 (P = 0.21), while mean magnetic susceptibility was reduced significantly from 0.48 ppm to 0.38 ppm (P = 0.004). A significant positive association was found between changes in magnetic susceptibility values and NIHSS following hematoma treatment (P < 0.01). DATA CONCLUSIONS: QSM in hematoma assessment, as compared with CT, offers a comparably accurate volume measurement; however, susceptibility measurements may enable improved monitoring of ICH treatment compared to volume measurements alone. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:907-915.

Exploring the origins of echo-time-dependent quantitative susceptibility mapping (QSM) measurements in healthy tissue and cerebral microbleeds.

Quantitative susceptibility mapping (QSM) is increasingly used to measure variation in tissue composition both in the brain and in other areas of the body in a range of disease pathologies. Although QSM measurements were originally believed to be independent of the echo time (TE) used in the gradient-recalled echo (GRE) acquisition from which they are derived; recent literature (Sood et al., 2016) has shown that these measurements can be highly TE-dependent in a number of brain regions. In this work we systematically investigate possible causes of this effect through analysis of apparent frequency and QSM measurements derived from data acquired at multiple TEs in vivo in healthy brain regions and in cerebral microbleeds (CMBs); QSM data acquired in a gadolinium-doped phantom; and in QSM data derived from idealized simulated phase data. Apparent frequency measurements in the optic radiations (OR) and central corpus callosum (CC) were compared to those predicted by a 3-pool white matter model, however the model failed to fully explain contrasting frequency profiles measured in the OR and CC. Our results show that TE-dependent QSM measurements can be caused by a failure of phase unwrapping algorithms in and around strong susceptibility sources such as CMBs; however, in healthy brain regions this behavior appears to result from intrinsic non-linear phase evolution in the MR signal. From these results we conclude that care must be taken when deriving frequency and QSM measurements in strong susceptibility sources due to the inherent limitations in phase unwrapping; and that while signal compartmentalization due to tissue microstructure and content is a plausible cause of TE-dependent frequency and QSM measurements in healthy brain regions, better sampling of the MR signal and more complex models of tissue are needed to fully exploit this relationship.

Rapid whole-brain quantitative magnetization transfer imaging using 3D selective inversion recovery sequences.

Selective inversion recovery (SIR) is a quantitative magnetization transfer (qMT) method that provides estimates of parameters related to myelin content in white matter, namely the macromolecular pool-size-ratio (PSR) and the spin-lattice relaxation rate of the free pool (R1f), without the need for independent estimates of ∆B0, B1+, and T1. Although the feasibility of performing SIR in the human brain has been demonstrated, the scan times reported previously were too long for whole-brain applications. In this work, we combined optimized, short-TR acquisitions, SENSE/partial-Fourier accelerations, and efficient 3D readouts (turbo spin-echo, SIR-TSE; echo-planar imaging, SIR-EPI; and turbo field echo, SIR-TFE) to obtain whole-brain data in 18, 10, and 7 min for SIR-TSE, SIR-EPI, SIR-TFE, respectively. Based on numerical simulations, all schemes provided accurate parameter estimates in large, homogenous regions; however, the shorter SIR-TFE scans underestimated focal changes in smaller lesions due to blurring. Experimental studies in healthy subjects (n = 8) yielded parameters that were consistent with literature values and repeatable across scans (coefficient of variation: PSR = 2.2-6.4%, R1f = 0.6-1.4%) for all readouts. Overall, SIR-TFE parameters exhibited the lowest variability, while SIR-EPI parameters were adversely affected by susceptibility-related image distortions. In patients with relapsing remitting multiple sclerosis (n = 2), focal changes in SIR parameters were observed in lesions using all three readouts; however, contrast was reduced in smaller lesions for SIR-TFE, which was consistent with the numerical simulations. Together, these findings demonstrate that efficient, accurate, and repeatable whole-brain SIR can be performed using 3D TFE, EPI, or TSE readouts; however, the appropriate readout should be tailored to the application.

Quantifying MRI frequency shifts due to structures with anisotropic magnetic susceptibility using pyrolytic graphite sheet.

Magnetic susceptibility is an important source of contrast in magnetic resonance imaging (MRI), with spatial variations in the susceptibility of tissue affecting both the magnitude and phase of the measured signals. This contrast has generally been interpreted by assuming that tissues have isotropic magnetic susceptibility, but recent work has shown that the anisotropic magnetic susceptibility of ordered biological tissues, such as myelinated nerves and cardiac muscle fibers, gives rise to unexpected image contrast. This behavior occurs because the pattern of field variation generated by microstructural elements formed from material of anisotropic susceptibility can be very different from that predicted by modelling the effects in terms of isotropic susceptibility. In MR images of tissue, such elements are manifested at a sub-voxel length-scale, so the patterns of field variation that they generate cannot be directly visualized. Here, we used pyrolytic graphite sheet which has a large magnetic susceptibility anisotropy to form structures of known geometry with sizes large enough that the pattern of field variation could be mapped directly using MRI. This allowed direct validation of theoretical expressions describing the pattern of field variation from anisotropic structures with biologically relevant shapes (slabs, spherical shells and cylindrical shells).

Longitudinal data for magnetic susceptibility of normative human brain development and aging over the lifespan.

The data presented in this article accompany the research article entitled "Longitudinal Atlas for Normative Human Brain Development and Aging over the Lifespan using Quantitative Susceptibility Mapping" (Zhang et al., 2018) [1]. The longitudinal evolution of magnetic susceptibility in human brain indicates critical characteristics of normal brain development and aging. In the corresponding research article, we build longitudinal QSM atlases over various age intervals using 166 healthy subjects (83F/69M) with an age range of 1-83 years old. Based on the newly built atlases, we investigate the regional evolutions of magnetic susceptibility in the brain. In this article, we report anatomical evolutions of the age-specific QSM atlases in deep gray matter nuclei and in two selected white matter fiber bundles. In addition to iron-rich brain nuclei, the evolution patterns of the magnetic susceptibility in the amygdala and hippocampus are also presented.

Histological Basis of Laminar MRI Patterns in High Resolution Images of Fixed Human Auditory Cortex.

Functional magnetic resonance imaging (fMRI) studies of the auditory region of the temporal lobe would benefit from the availability of image contrast that allowed direct identification of the primary auditory cortex, as this region cannot be accurately located using gyral landmarks alone. Previous work has suggested that the primary area can be identified in magnetic resonance (MR) images because of its relatively high myelin content. However, MR images are also affected by the iron content of the tissue and in this study we sought to confirm that different MR image contrasts did correlate with the myelin content in the gray matter and were not primarily affected by iron content as is the case in the primary visual and somatosensory areas. By imaging blocks of fixed post-mortem cortex in a 7 T scanner and then sectioning them for histological staining we sought to assess the relative contribution of myelin and iron to the gray matter contrast in the auditory region. Evaluating the image contrast in [Formula: see text]-weighted images and quantitative [Formula: see text] maps showed a reasonably high correlation between the myelin density of the gray matter and the intensity of the MR images. The correlation with T1-weighted phase sensitive inversion recovery (PSIR) images was better than with the previous two image types, and there were clearly differentiated borders between adjacent cortical areas in these images. A significant amount of iron was present in the auditory region, but did not seem to contribute to the laminar pattern of the cortical gray matter in MR images. Similar levels of iron were present in the gray and white matter and although iron was present in fibers within the gray matter, these fibers were fairly uniformly distributed across the cortex. Thus, we conclude that T1- and [Formula: see text]-weighted imaging sequences do demonstrate the relatively high myelin levels that are characteristic of the deep layers in primary auditory cortex and allow it and some of the surrounding areas to be reliably distinguished.

Comparison of two over-the-counter tooth whitening products using a novel system.

Tooth whitening is one of the most widely accepted esthetic procedures in dentistry. Various treatment options include in-office and prescribed at-home bleaching procedures, over-the-counter bleaching kits, and whitening dentifrices. This study evaluated and compared a 6% hydrogen peroxide tooth bleaching gel delivered on polyethylene film (HP) with an 18% carbamide peroxide brush-applied liquid gel (CP). A total of 59 subjects completed this 2-week, examiner blind, randomized, parallel group study. Both treatments were applied twice daily for 2 weeks according to the manufacturer's instructions. Evaluations for oral safety and Vita tooth shade were conducted by a dental examiner at baseline and 2 weeks after product use. In addition, the ShadeVision System was used to determine changes in Vita shade and L*a*b* values. Based on both the examiner and ShadeVision System assessments, both treatments significantly improved tooth shade. Improvements in Vita tooth shade based on the adjusted mean for HP were 2.64 (P < 0.001) and 2.33 (P < 0.001) for the examiner and ShadeVision System assessments, respectively, compared with improvements of 1.04 (P = .004) and 0.42 (P = 0.029) for CP users, respectively. The difference between treatments was found to be significant for both the examiner (P = .005) and ShadeVision (P = .001) assessments. Findings from the L*a*b* data derived from the ShadeVision System were in agreement with Vita assessments, with significant differences for changes in L*, a*, and b* in favor of HP users (P = .001). In this study, the ShadeVision method of color analysis was relatively easy to use and demonstrated significant differences between 2 OTC whitening products using both Vitapan and L*a*b* means of assessment.

A 30-day clinical comparison of a novel interdental cleaning device and dental floss in the reduction of plaque and gingivitis.

OBJECTIVE: To compare the safety and efficacy of a novel battery-operated interdental cleaning device (Oral-B Hummingbird) [ID], fitted with either a flossette or pick attachment, versus hand-held dental floss in the reduction of plaque and gingivitis when combined with manual tooth brushing over a 30-day period. METHODOLOGY: This randomized, examiner blind, parallel group study assessed three treatment groups: ID/flossette (ID/F), ID/pick (ID/P), and unwaxed manual dental floss. All groups used the same soft manual toothbrush and toothpaste. The 84 subjects were stratified to treatment groups based on initial whole mouth mean plaque scores, gingivitis scores, and gender. Subjects were instructed to brush twice daily and use their assigned interdental method once daily in the evening before brushing. Gingivitis, gingival bleeding, and plaque were evaluated at baseline and Day 30. RESULTS: A total of 78 subjects completed all aspects of the study and were included in the analyses. There was no significant difference between treatment groups in baseline plaque, gingivitis, and bleeding scores. After 30 days, statistically significant reductions from baseline gingivitis and bleeding scores were found for all groups (p < 0.0001), but there were no significant statistical differences among groups. Whole mouth and approximal plaque scores were significantly reduced from baseline in the manual floss and ID/F groups after 30 days of product use, with no significant difference between groups. Plaque reduction for both the manual floss and ID/F groups was significantly greater than the ID/P group. All interdental cleaning methods were safe as used in the study, with no evidence of oral hard or soft tissue trauma. CONCLUSION: The Oral-B Hummingbird was safe and effective in reducing approximal plaque and gingival inflammation, and provides a useful alternative device for interdental cleaning.

A clinical study of plaque removal with an advanced rechargeable power toothbrush and a battery-operated device.

PURPOSE: To compare the safety and efficacy of two recently introduced modern power toothbrushes with different characteristics. MATERIALS AND METHODS: This was a single-blind, randomized, crossover study which compared the ability of two power toothbrushes to remove plaque during a 2-minute brushing period. The two brushes were the Braun Oral-B 3D Excel (D17), a rechargeable toothbrush with an oscillating/rotating/pulsating action and the Colgate Actibrush, a battery-operated device with an oscillating/rotating action. Seventy-four healthy subjects from a general population who met the inclusion/exclusion criteria used the two brushes on alternate days for a period of familiarization before returning to the test facility. At this visit, subjects with a whole mouth mean Proximal/Marginal Plaque Index of > or = 2.20 after 23-25 hours of no oral hygiene were randomly assigned to one of two treatment sequences, D17/Actibrush and Actibrush/D17, balanced for age and gender. Subjects brushed with their assigned toothbrush after which post-brushing plaque scores were recorded. After a 2-week washout phase subjects returned to the test facility and brushed with the alternate toothbrush as described. Data from the two visits were pooled, after which plaque removal efficacies were compared. Change from prebrushing treatment means were compared using ANOVA with models appropriate for the crossover design. RESULTS: Both toothbrushes were found to be safe and both significantly reduced plaque levels (P < or = 0.0001), but the D17 was significantly more effective than the Actibrush for the whole mouth and for approximal sites. Plaque reductions for the D17 were 46.5%, 55.2% and 42.9% for whole mouth, marginal and approximal sites, respectively while reductions for the Actibrush for the whole mouth, marginal, and approximal sites, were 41.5%, 52.5% and 36.8% respectively. It is concluded that the Braun Oral-B D17 may offer advantages in terms of plaque removal over the battery-powered Actibrush, particularly at hard to reach approximal sites.