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Purpose: Measure the changes in relative lung water density (rLWD), lung volume, and total lung water content as a function of time after supine body positioning. Methods: An efficient ultrashort-TE pulse sequence with a yarnball k-space trajectory was used to measure water density-weighted lung images for 25 min following supine body positioning (free breathing, 74-s acquisitions, 3D images at functional residual capacity, 18 time points) in 9 healthy volunteers. Global and regional (10 chest-to-back positions) rLWD, lung volume, and total lung water volume were measured in all subjects at all time points. Volume changes were validated with a nitrogen washout study in 3 participants. Results: Global rLWD increased significantly (p=0.001) from 31.8±5.5% to 34.8±6.8%, while lung volumes decreased significantly (p<0.001) from 2390±620mL to 2130±630mL over the same 25-min interval. Total lung water volume decreased slightly from730±125mL to 706±126mL (p=0.028). There was a significant chest-to-back gradient in rLWD (20.7±4.6% to 39.9±6.1%) at all time points with absolute increases of 1.8±1.2% at the chest and 5.4±1.9% at the back. Nitrogen washout studies yielded a similar reduction in lung volume (12.5±0.9%) and time course following supine positioning. Conclusion: Lung volumes during tidal breathing decrease significantly over tens of minutes following supine body positioning, with corresponding increases in lung water density (9.2±4.4% relative increase). The total volume of lung water is slightly reduced over this interval (3.3±4.0% relative change). Evaluation of rLWD should take time after supine positioning, and more generally, all sources of lung volume changes should be taken into consideration to avoid significant bias. [ABSTRACT FROM AUTHOR]

Postural orthostatic tachycardia syndrome (POTS) is characterized by an excessive heart rate (HR) response upon standing and symptoms indicative of inadequate cerebral perfusion. We tested the hypothesis that during lower body negative pressure (LBNP), individuals with POTS would have larger decreases in cardiac and cerebrovascular function measured using magnetic resonance (MR) imaging. Eleven patients with POTS and 10 healthy controls were studied at rest and during 20 min of −25 mmHg LBNP. Biventricular volumes, stroke volume (SV), cardiac output (Qc), and HR were determined by cardiac MR. Cerebral oxygen uptake (VO2) in the superior sagittal sinus was calculated from cerebral blood flow (CBF; MR phase contrast), venous O2 saturation (SvO2; susceptometry‐based oximetry), and arterial O2 saturation (pulse oximeter). Regional cerebral perfusion was determined using arterial spin labelling. HR increased in response to LBNP (p < 0.001) with no group differences (HC: +9 ± 8 bpm; POTS: +13 ± 11 bpm; p = 0.35). Biventricular volumes, SV, and Qc decreased during LBNP (p < 0.001). CBF and SvO2 decreased with LBNP (p = 0.01 and 0.03, respectively) but not cerebral VO2 (effect of LBNP: p = 0.28; HC: −0.2 ± 3.7 mL/min; POTS: +1.1 ± 2.0 mL/min; p = 0.33 between groups). Regional cerebral perfusion decreased during LBNP (p < 0.001) but was not different between groups. These data suggest patients with POTS have preserved cardiac and cerebrovascular function. [ABSTRACT FROM AUTHOR]

Three‐dimensional fast spin echo imaging with long echo trains combines high resolution with reasonable acquisition times and reduced specific absorption rate due to low refocusing flip angles. Typically, an entire volume is encoded (nonselective excitation) or localization can be performed with slab select excitation, which uses a long 90° pulse for precise localization, followed by a preliminary nonselective 180° pulse bounded by spoiler gradients to destroy signal outside of the volume of interest. Subsequent flip angles in the train are nonselective and identical between the two methods. The inclusion of the initial selective pulse and spoiler gradients results in a signal‐to‐noise ratio (SNR) penalty for slab selection, beyond the slice‐averaging dependence, arising from a loss of stimulated echoes. SNR differences are explored using Bloch equation simulations of a T2‐weighted 96 echo train sequence with varying parameters including T2, T1, and B1+ and compared with phantom and in vivo brain, neck, and knee experiments. In vivo SNR measurements in the three regions showed a maximum decrease of selective SNR by 29% (gastrocnemius muscle), 25% (pons), and 22% (globus pallidus), despite similar experimental parameters to nonselective experiments. Decreased SNR was compounded by B1+ variation affecting prescribed flip angles with further smaller reductions with T2 and T1 times. In conclusion, the elimination of coherences via the preliminary nominal 180° pulse and spoiler gradients in addition to the extended echo timing from the long excitation pulse resulted in a reduction in SNR compared with the nonselective case. Consideration of the required SNR and chosen anatomy as well as sequence restrictions should be weighed before choosing slab‐selective excitation. [ABSTRACT FROM AUTHOR]

T2 mapping from 2D proton density and T2–weighted images (PD‐T2) using Bloch equation simulations can be time consuming and introduces a latency between image acquisition and T2 map production. A fast T2 mapping reconstruction method is investigated and compared with a previous modeling approach to reduce computation time and allow inline T2 maps on the MRI console. Brain PD‐T2 images from five multiple sclerosis patients were used to compare T2 map reconstruction times between the new subtraction method and the Euclidean norm minimization technique. Bloch equation simulations were used to create the lookup table for decay curve matching in both cases. Agreement of the two techniques used Bland–Altman analysis for investigating individual subsets of data and all image points in the five volumes (meta‐analysis). The subtraction method resulted in an average reduction of computation time for single slices from 134 s (minimization method) to 0.44 s. Comparing T2 values between the subtraction and minimization methods resulted in a confidence interval ranging from −0.06 to 0.06 ms (95% of values were within ± 0.06 ms between the techniques). Using identical reconstruction code based on the subtraction method, inline T2 maps were produced from PD‐T2 images directly on the scanner console. The excellent agreement between the two methods permits the subtraction technique to be interchanged with the previous method, reducing computation time and allowing inline T2 map reconstruction based on Bloch simulations directly on the scanner. [ABSTRACT FROM AUTHOR]

Iron concentration in the human brain plays a crucial role in several neurodegenerative diseases and can be monitored noninvasively using quantitative susceptibility mapping (QSM) and effective transverse relaxation rate (R2*) mapping from multiecho T2*‐weighted images. Large population studies enable better understanding of pathologies and can benefit from pooling multisite data. However, reproducibility may be compromised between sites and studies using different hardware and sequence protocols. This work investigates QSM and R2* reproducibility at 3 T using locally optimized sequences from three centers and two vendors, and investigates possible reduction of cross‐site variability through postprocessing approaches. Twenty‐four healthy subjects traveled between three sites and were scanned twice at each site. Scan‐rescan measurements from seven deep gray matter regions were used for assessing within‐site and cross‐site reproducibility using intraclass correlation coefficient (ICC) and within‐subject standard deviation (SDw) measures. In addition, multiple QSM and R2* postprocessing options were investigated with the aim to minimize cross‐site sequence‐related variations, including: mask generation approach, echo‐timing selection, harmonizing spatial resolution, field map estimation, susceptibility inversion method, and linear field correction for magnitude images. The same‐subject cross‐site region of interest measurements for QSM and R2* were highly correlated (R2 ≥ 0.94) and reproducible (mean ICC of 0.89 and 0.82 for QSM and R2*, respectively). The mean cross‐site SDw was 4.16 parts per billion (ppb) for QSM and 1.27 s−1 for R2*. For within‐site measurements of QSM and R2*, the mean ICC was 0.97 and 0.87 and mean SDw was 2.36 ppb and 0.97 s−1, respectively. The precision level is regionally dependent and is reduced in the frontal lobe, near brain edges, and in white matter regions. Cross‐site QSM variability (mean SDw) was reduced up to 46% through postprocessing approaches, such as masking out less reliable regions, matching available echo timings and spatial resolution, avoiding the use of the nonconsistent magnitude contrast between scans in field estimation, and minimizing streaking artifacts. [ABSTRACT FROM AUTHOR]

Purpose: The transmit field B1+ at 3 T in brain affects the spatial uniformity and contrast of most image acquisitions. Here, B1+ spatial variation in brain at 3 T is characterized in a large healthy population. Methods: Bloch‐Siegert B1+ maps were acquired at 3 T from 385 healthy subjects aged 5–90 years on a single MRI system. After transforming all B1+ maps to a standard brain atlas space, region‐of‐interest analysis was performed, and intersubject voxel‐wise coefficient of variation was calculated across the whole brain. The B1+ variability due to age and brain size was studied separately in males and females, along with B1+ variability due to nonideal transmit calibration. Results: The voxel‐based mean coefficient of variation was 4.0% across all subjects, and the difference in B1+ between central (left thalamus) and outer regions (left frontal gray matter) was 24.2% ± 2.3%. The least intersubject variability occurred in central regions, whereas regions toward brain edges increased markedly in variation. The B1+ variability with age was mostly attributed to lifespan changes in CSF volume (which alters brain conductivity) and head orientation. Larger brain size correlated with more B1+ inhomogeneity (p <.001). Varying head position and anatomy resulted in an inaccurate transmit calibration. Conclusion: In standard atlas space, intersubject B1+ variability at 3 T was relatively small in a large population aged 5–90 years. The B1+ varied with age‐related changes of CSF volume and head orientation, as well as differences in brain size and transmit calibration. [ABSTRACT FROM AUTHOR]

Putative MRI markers of iron in deep gray matter have demonstrated age related changes during discrete periods of healthy childhood or adulthood, but few studies have included subjects across the lifespan. This study reports both transverse relaxation rate (R2*) and quantitative susceptibility mapping (QSM) of four primary deep gray matter regions (thalamus, putamen, caudate, and globus pallidus) in 498 healthy individuals aged 5–90 years. In the caudate, putamen, and globus pallidus, increases of QSM and R2* were steepest during childhood continuing gradually throughout adulthood, except caudate susceptibility which reached a plateau in the late 30s. The thalamus had a unique profile with steeper changes of R2* (reflecting additive effects of myelin and iron) than QSM during childhood, both reaching a plateau in the mid‐30s to early 40s and decreasing thereafter. There were no hemispheric or sex differences for any region. Notably, both R2* and QSM values showed more inter‐subject variability with increasing age from 5 to 90 years, potentially reflecting a common starting point in iron/myelination during childhood that diverges as a result of lifestyle and genetic factors that accumulate with age. [ABSTRACT FROM AUTHOR]

Background: Texture analysis (TA) is an image-analysis technique that detects complex intervoxel statistical patterns. 3D TA has shown potential in detecting cerebral degeneration not perceptible to the human eye in many neurological disorders. The reliability of this method's application in a multicenter study is unknown.Purpose: To assess the intrasite and intersite reliability of a novel 3D TA method from data acquired systematically from the Canadian ALS Neuroimaging Consortium (CALSNIC).Study Type: Prospective multicenter data with harmonized MR sequence parameters acquired from five sites.Population: Six healthy subjects.Field Strength: 3T 3D-MPRAGE and 3D-SPGR T1 -weighted MRI of the brain.Assessment: Voxel-based 3D TA was performed on the whole brain to produce texture maps.Statistical Tests: Intra- and intersite reliability of texture features was assessed using a two-way mixed-effects model for intraclass correlation coefficients (ICC). ICCs were calculated in a region-of-interest (ROI) analysis of predetermined anatomically relevant areas. A voxelwise approach was used to assess the whole brain.Results: In the ROI analyses, intrasite reliability was excellent (ICC > 0.75) across most regions and texture features (autocorrelation [autoc], contrast [contr], energy [energ]). Intersite reliability was excellent for most regions with autoc, ranging from fair to excellent for contr, and ICCs ranging from poor to good (<0.40-0.75) for energ. Voxelwise analyses revealed a large range in ICC across the brain for both intrasite and intersite ICCs (0.0-0.90), with higher reliability in the cortical gray matter compared with deeper subcortical structures.Data Conclusion: Overall, the reliability of 3D TA was highly dependent on texture feature, region studied, and method of analysis (ROI or voxelwise). Intrasite reproducibility was good to excellent, and better than intersite. ROI-based analyses present higher reliability in comparison with voxelwise analyses. Autoc has overall excellent reliability. These factors might be considered when designing future 3D TA studies.Level Of Evidence: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2020;51:1200-1209. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate whether textures computed from T1‐weighted (T1W) images of the corticospinal tract (CST) in amyotrophic lateral sclerosis (ALS) are associated with degenerative changes evaluated by diffusion tensor imaging (DTI). Nineteen patients with ALS and 14 controls were prospectively recruited and underwent T1W and diffusion‐weighted magnetic resonance imaging. Three‐dimensional texture maps were computed from T1W images and correlated with the DTI metrics within the CST. Significantly correlated textures were selected and compared within the CST for group differences between patients and controls using voxel‐wise analysis. Textures were correlated with the patients' clinical upper motor neuron (UMN) signs and their diagnostic accuracy was evaluated. Voxel‐wise analysis of textures and their diagnostic performance were then assessed in an independent cohort with 26 patients and 13 controls. Results showed that textures autocorrelation, energy, and inverse difference normalized significantly correlated with DTI metrics (p < .05) and these textures were selected for further analyses. The textures demonstrated significant voxel‐wise differences between patients and controls in the centrum semiovale and the posterior limb of the internal capsule bilaterally (p < .05). Autocorrelation and energy significantly correlated with UMN burden in patients (p < .05) and classified patients and controls with 97% accuracy (100% sensitivity, 92.9% specificity). In the independent cohort, the selected textures demonstrated similar regional differences between patients and controls and classified participants with 94.9% accuracy. These results provide evidence that T1‐based textures are associated with degenerative changes in the CST. [ABSTRACT FROM AUTHOR]

Objective: To evaluate cerebral degenerative changes in ALS and their correlates with survival using 3D texture analysis. Methods: A total of 157 participants were included in this analysis from four neuroimaging studies. Voxel‐wise texture analysis on T1‐weighted brain magnetic resonance images (MRIs) was conducted between patients and controls. Patients were divided into long‐ and short‐survivors using the median survival of the cohort. Neuroanatomical differences between the two survival groups were also investigated. Results: Whole‐brain analysis revealed significant changes in image texture (FDR P < 0.05) bilaterally in the motor cortex, corticospinal tract (CST), insula, basal ganglia, hippocampus, and frontal regions including subcortical white matter. The texture of the CST correlated (P < 0.05) with finger‐ and foot‐tapping rate, measures of upper motor neuron function. Patients with a survival below the media of 19.5 months demonstrated texture change (FDR P < 0.05) in the motor cortex, CST, basal ganglia, and the hippocampus, a distribution which corresponds to stage 4 of the distribution TDP‐43 pathology in ALS. Patients with longer survival exhibited texture changes restricted to motor regions, including the motor cortex and the CST. Interpretation: Widespread gray and white matter pathology is evident in ALS, as revealed by texture analysis of conventional T1‐weighted MRI. Length of survival in patients with ALS is associated with the spatial extent of cerebral degeneration. [ABSTRACT FROM AUTHOR]

Research in amyotrophic lateral sclerosis (ALS) suggests that executive dysfunction, a prevalent cognitive feature of the disease, is associated with abnormal structural connectivity and white matter integrity. In this exploratory study, we investigated the white matter constructs of executive dysfunction, and attempted to detect structural abnormalities specific to cognitively impaired ALS patients. Eighteen ALS patients and 22 age and education matched healthy controls underwent magnetic resonance imaging on a 4.7 Tesla scanner and completed neuropsychometric testing. ALS patients were categorized into ALS cognitively impaired (ALSci, n = 9) and ALS cognitively competent (ALScc, n = 5) groups. Tract-based spatial statistics and connectomics were used to compare white matter integrity and structural connectivity of ALSci and ALScc patients. Executive function performance was correlated with white matter FA and network metrics within the ALS group. Executive function performance in the ALS group correlated with global and local network properties, as well as FA, in regions throughout the brain, with a high predilection for the frontal lobe. ALSci patients displayed altered local connectivity and structural integrity in these same frontal regions that correlated with executive dysfunction. Our results suggest that executive dysfunction in ALS is related to frontal network disconnectivity, which potentially mediates domain-specific, or generalized cognitive impairment, depending on the degree of global network disruption. Furthermore, reported co-localization of decreased network connectivity and diminished white matter integrity suggests white matter pathology underlies this topological disruption. We conclude that executive dysfunction in ALSci is associated with frontal and global network disconnectivity, underlined by diminished white matter integrity. Hum Brain Mapp 38:1249-1268, 2017. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Different lines of evidence suggest an abnormal cerebral energy metabolism as being critical to the pathophysiology of schizophrenia. However, it is unknown as to whether levels of creatine (Cr) would be involved in these anomalies. The study involved 33 unmedicated first episode psychosis patients and 41 healthy controls. Proton magnetic resonance spectroscopy (1H-MRS) was performed at 3 T using a long TE (TE/TM/TR of 240/27/3000 ms) such that within the total phosphocreatine (PCr) plus Cr signal (tCr240), mainly Cr was detectable. The target region was an 18 cm3 prefrontal volume. A negative association was found between age of patients and tCr240 levels referenced to internal water, with 20% of the variance in tCr240 accounted for by Age. A secondary finding revealed 16% reduction of tCr240 levels in patients, solely when comparing participants older than the median age of patients. No association existed between tCr240 levels and clinical variables. These findings support previous data reporting abnormalities in brain creatine kinase isoenzymes involved with the maintenance of energy pools in schizophrenia. The implications of using a long TE are discussed in terms of the relative proportions of Cr and PCr within the tCr240 signal, and of potential group differences in T2 times. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A pressure ulcer is a medical complication that arises in persons with decreased mobility and/or sensation. Deep pressure ulcers starting at the bone-muscle interface are the most dangerous, as they can cause extensive damage before showing any signs at the skin surface. We previously proposed a novel intervention called intermittent electrical stimulation (IES) for the prevention of deep tissue injury (DTI). In this study, we tested the effects of four paradigms of IES and one conventional pressure relief paradigm in preventing the formation of deep pressure ulcers in rats. Loading equivalent to 18, 28, or 38% of the body weight (BW) of each rat was applied to the triceps surae muscle in one hind limb. Treatment groups received IES every 10 min for either (i) 5 or 10 s with moderate or maximal contraction, or (ii) complete pressure removal every 10 min for 10 s (conventional pressure relief). The results showed that conventional pressure relief, emulating a wheelchair push-up every 10 min, was inadequate for the prevention of DTI. In contrast, all IES paradigms were equally effective in significantly reducing the extent of deep muscle damage caused by 28 or 38% BW pressure application. These findings suggest that, in conjunction with existing techniques, IES may be an effective intervention for the prophylactic prevention of DTI. [ABSTRACT FROM AUTHOR]

A new 1H-MRS filtering strategy for selective measurement of glycine (Gly) in human brain in vivo at 3.0T is proposed. Investigation of multiple refocusing following a 90° excitation pulse indicated that triple refocusing is most effective for suppression of the strongly coupled resonances of myo-inositol (mI) at the Gly 3.55-ppm resonance. The echo times of the triple refocusing were optimized, with numerical analysis of the filtering performance, as {TE1, TE2, TE3} = {67, 62, 69} ms. Compared with the 90°-acquired mI signal the mI suppression ratios of the filter were 170 and 1000, in terms of peak amplitude and area, respectively, between 3.51 and 3.59 ppm. From LCModel analyses, using density-matrix calculated spectra as basis functions, the concentration of Gly in parieto-occipital cortex of healthy adults was estimated to be 0.5 ± 0.1 mM (mean ± SD, n = 6), with reference to creatine at 8 mM. Magn Reson Med, 2007. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]