Acquisition Duration Research Articles

Towards guidelines to harmonize textural features in PET: Haralick textural features vary with image noise, but exposure-invariant domains enable comparable PET radiomics.

Image texture is increasingly used to discriminate tissues and lesions in PET/CT. For quantification or in computer-aided diagnosis, textural feature analysis must produce robust and comparable values. Because statistical feature values depend on image count statistics, we investigated in depth the stability of Haralick features values as functions of acquisition duration, and for common image resolutions and reconstructions. A homogeneous cylindrical phantom containing 9.6 kBq/ml Ge-68 was repeatedly imaged on a Siemens Biograph mCT, with acquisition durations ranging from three seconds to three hours. Images with 1.5, 2, and 4 mm isometrically spaced voxels were reconstructed with filtered back-projection (FBP), ordered subset expectation maximization (OSEM), and the Siemens TrueX algorithm. We analysed Haralick features derived from differently quantized (3 to 8-bit) grey level co-occurrence matrices (GLCMs) as functions of exposure E, which we defined as the product of activity concentration in a volume of interest (VOI) and acquisition duration. The VOI was a 50 mm wide cube at the centre of the phantom. Feature stability was defined for df/dE → 0. The most stable feature values occurred in low resolution FBPs, whereas some feature values from 1.5 mm TrueX reconstructions ranged over two orders of magnitude. Within the same reconstructions, most feature value-exposure curves reached stable plateaus at similar exposures, regardless of GLCM quantization. With 8-bit GLCM, median time to stability was 16 s and 22 s for FBPs, 18 s and 125 s for OSEM, and 23 s, 45 s, and 76 s for PSF reconstructions, with longer durations for higher resolutions. Stable exposures coincided in OSEM and TrueX reconstructions with image noise distributions converging to a Gaussian. In FBP, the occurrence of stable values coincided the disappearance of negatives image values in the VOI. Haralick feature values depend strongly on exposure, but invariance exists within defined domains of exposure. Here, we present an easily replicable procedure to identify said stable exposure domains, where image noise does not substantially add to textural feature values. Only by imaging at predetermined feature-invariant exposure levels and by adjusting exposure to expected activity concentrations, can textural features have a quantitative use in PET/CT. The necessary exposure levels are attainable by modern PET/CT systems in clinical routine.

ROLE OF CONTRAST ENHANCED DIGITAL MAMMOGRAPHY IN BREAST LESIONS

Back ground: Breast cancer in women is major public health problem throughout the world, Mammography is basic breast imaging modality for early detection and diagnosis of breast cancer, mammography has its own limitations so contrast enhanced digital mammography is new advanced application using intravenous injection of contrast under development of subtraction and dual energy technique to improve detection of breast cancer. Aim of the Work: To investigate the potential of using intravenous contrast material with full field digital mammography to facilitate the detection and characterization of lesions in the breast. Patients and Methods: This study was conducted on 40 patients with mammographic clinical findings that warranted biopsy recruited from department of Radio-Diagnosis, Ain Shams University hospitals. A technique for demonstrating breast cancers, dualenergy contrast agent–enhanced digital subtraction mammography, was performedfor the 40female patients. The technique consists of high energy and low-energy digital mammography after administration of iodinated contrast agent. Weighted subtraction of the logarithmic transform of these images is then performed to obtain an image that preferentially shows iodine. Results: Of the40 subjects, twenty eight of these tumors enhanced strongly, proved carcinoma, in the other 12 patients, benign tissue enhanced diffusely in two and weakly ocally in two. These results indicate that the technique is feasible and worthy of further study. Conclusion: Contrast-enhanced digital mammography is a new breast imaging technique using full-field digital mammography in conjunction with the injection of an iodinated contrast medium. Dualenergy CEDM also allows shorter acquisition duration and does notrequire prolonged breast compression. This could result in better acceptance from patients and fewer technical problems, such as misregistration of subtracted images.

Imaging Performance of a Multimodal Module to Enhance Preclinical Irradiator Capabilities

This article highlights the performance measurements of an optical device which aims at upgrading preclinical irradiators. The evaluated device allows acquiring X-ray as well as bioluminescence images with a single sensor. The latter consists of a supercooled camera equipped with a 1024x1024 charge coupling device (each element measuring 13x13µm²). X-ray imaging is feasible, thanks to a conversion phosphor screen. Phantom acquisitions revealed a spatial resolution of 2.5 line pairs per millimetre (0.2mm) for Xray imaging and between 0.4 and 0.7mm for bioluminescence images. Image homogeneity was 0.8 for radiographic images with preclinical imaging parameters and higher than 0.9 for optical images. For functional imaging, contrast to noise ratio (CNR) ranged from 1.3 (for contrast of 2:1 and 0.1s acquisition) up to 253 (for contrast of 32:1 and 5s acquisition). CNR was related to acquisition duration. The device’s overall performance revealed that it is suitable to upgrade existing irradiators and improve laboratory capabilities toward image-guided radiotherapy.

Characterization of Neutron Detection Systems with Confidence via Statistical Parameter Correction

Neutron detection systems utilize statistical alarm techniques where a measured false alarm rate (FAR) can vary drastically from the FAR predicted by a theoretical model. The ability to set an alarm threshold that results in a practically controlled FAR is crucial to characterize detector sensitivity with both accuracy and precision. A generalized and automated method is presented to statistically evaluate FAR performance by assuming that the FAR itself is not deterministic, but a normal stochastic process over a specific parameter to be corrected that will hereafter be referred to as the correction. In this manner, a specific correction results in not only a point estimate of FAR, but also a confidence interval. The central objective is focused exclusively on characterization assuming that experiments are executed in a tightly controlled environment so that an accurate comparison is enabled across detectors. Once a correction is calculated, the estimated FAR is only assumed accurate in a similar environment for sensitivity evaluation. Initially, the calculated correction factor was used to compare FARs across various distributions including normal, corrected normal, Poisson, and a simplified normal distribution. Later verification data sets were used to empirically demonstrate the rate of containment of measured confidence coefficients using two detectors of different technology. A second application uses the correction method to improve the signal-to-noise ratio metric to agree more with dynamic sensitivity results. Finally, a third application studies the effect of altering the duration of background acquisition on FAR performance.

Smartphone interfaced handheld echocardiography for focused assessment of ventricular function and structure in children: A pilot study.

Miniaturized echocardiographic machines improve availability and portability and can be particularly useful for underserved and resource-limited settings. The goal of this study was to compare left ventricular fractional shortening (FS) and left ventricular ejection fraction (LVEF) obtained by a newer handheld echo (HHE) machine to standard transthoracic echocardiogram (TTE) in children. Pediatric outpatients (Birth-18years) undergoing TTE were prospectively enrolled. HHE protocol included 2D and M-mode images from the parasternal long, short, and apical-4 chamber views. HHE and TTE measurements were reviewed for agreement. Kappa statistic was used to analyze qualitative indices while FS and LVEF were analyzed with Lin's concordance correlation coefficient (CCC) and Bland-Altman limits of agreement (loa). Sixty children were enrolled; 55 were included in the quantitative analysis. Mean age was 7.5±5.5years; 67% males; median HHE image acquisition duration was 2.3(1-5) minutes. Fractional shortening and EF by HHE showed good agreement with TTE [CCC=0.82, 95%CI (0.73,0.90), mean bias -3.18%, loa (-7.00,6.44%) vs CCC=0.81 (0.72,0.90), mean bias -0.87%, loa (-6.94,5.17%], respectively. In children ≤5years, HHE FS (n=20) and EF (n=21) agreed with TTE measurement [0.59 (0.31, 0.88), mean bias 0.30%, loa (-8.5, 9.1%); 0.79 (0.63, 0.96), mean bias 0.10%, loa (-5.99, 6.14)]. Kappa values for RV size, function, and LV function were 1.00 (P<.05); 0.75 for LV size (P<.05) and 0.66 for pericardial effusion (P<.05). Handheld echo demonstrates good correlation with standard TTE for focused assessment of ventricular chamber sizes and function in children.

Number of subjects required in common study designs for functional GABA magnetic resonance spectroscopy in the human brain at 3 Tesla.

Magnetic resonance spectroscopy (MRS) is a research tool for measuring the concentration of metabolites such as γ‐aminobutyric acid (GABA) and glutamate in the brain. MEGA‐PRESS has been the preferred pulse sequence for GABA measurements due to low physiological GABA concentrations, hence low signal. To compensate, researchers incorporate long acquisition durations (7–10 min) making functional measurements of this metabolite challenging. Here, the acquisition duration and sample sizes required to detect specific concentration changes in GABA using MEGA‐PRESS at 3 T are presented for both between‐groups and within‐session study designs. 75 spectra were acquired during rest using MEGA‐PRESS from 41 healthy volunteers in 6 different brain regions at 3 T with voxel sizes between 13 and 22 cm3. Between‐group and within‐session variance was calculated for different acquisition durations and power calculations were performed to determine the number of subjects required to detect a given percentage change in GABA/NAA signal ratio. Within‐subject variability was assessed by sampling different segments of a single acquisition. Power calculations suggest that detecting a 15% change in GABA using a 2 min acquisition and a 27 cm3 voxel size, depending on the region, requires between 8 and 93 subjects using a within‐session design. A between‐group design typically requires more participants to detect the same difference. In brain regions with suboptimal shimming, the subject numbers can be up to 4‐fold more. Collecting data for longer than 4 min in brain regions examined in this study is deemed unnecessary, as variance in the signal did not reduce further for longer durations.

Development and prospective in-patient proof-of-concept validationof a surface photogrammetry+CT-based volumetric motion model for lung radiotherapy.

We develop and validate a motion model that uses real-time surface photogrammetry acquired concurrently with four-dimensional computed tomography (4DCT) to estimate respiration-induced changes within the entire irradiated volume, over arbitrarily many respiratory cycles. A research, couch-mounted, VisionRT (VRT) system was used to acquire optical surface data (15Hz, ROI=15×20cm2 ) from the thoraco-abdominal surface of a consented lung SBRT patient, concurrently with their standard-of-care 4DCT. The end-exhalation phase from the 4DCT was regarded as reference and for each remaining phase, deformation vector fields (DVFs) with respect to the reference phase were computed. To reduce dimensionality, the first two principal components (PCs) of the matrix of nine DVFs were calculated. In parallel, ten phase-averaged VRT surfaces were created. Surface DVFs and corresponding PCs were computed. A principal least squares regression was used to relate the PCs of surface DVF to those of volume DVFs, establishing a relationship between time-varying surface and the underlying time-varying volume. Proof-of-concept validation was performed during each treatment fraction by concurrently acquiring 30s time series of real-time surface data and "ground truth" kV fluoroscopic data (FL). A ray-tracing algorithm was used to create a digitally reconstructed fluorograph (DRF), and motion trajectories of high-contrast, soft-tissue, anatomical features in the DRF were compared with those from kV FL. For five of the six fluoroscopic acquisition sessions, the model out-performed 4DCT in predicting contour Dice coefficient with respect to fluoroscopy-derived contours. Similarly, the model exhibited a marked improvement over 4DCT for patch positions on the diaphragm. Model patch position errors varied from 5 to -15mm while 4DCT errors ranged between 5 and -22.4mm. For one fluoroscopic acquisition, a marked change in the a priori internal-external correlation resulted in model errors comparable to those of 4DCT. We described the development and a proof-of-concept validation for a volumetric motion model that uses surface photogrammetry to correlate the time-varying thoraco-abdominal surface to the time-varying internal thoraco-abdominal volume. These early results indicate that the proposed approach can result in a marked improvement over 4DCT. While limited by the duration of the fluoroscopic acquisitions as well as the resolution of the acquired images, the DRF-based proof-of-concept technique developed here is model-agnostic, and therefore, has the potential to be used as an in-patient validation tool for other volumetric motion models.

Localized B0 shimming based on 23 Na MRI at 7 T.

To validate the feasibility of localized B0 shimming based on B0 maps acquired with sodium (23 Na) MRI. A localized B0 shimming routine based on a constrained regularized algorithm in combination with 23 Na MRI data acquired with a 3D density-adapted radial readout scheme was implemented on a 7T MR system. Measurements were performed using a dual-tuned 23 Na/1 H head coil. The quality of B0 maps reconstructed from 23 Na images and the resulting shim values was examined depending on the acquisition duration between 10 minutes and 15 seconds to examine clinical applicability. The B0 shimming based on 23 Na B0 maps was performed both for phantom and human head of 6 healthy volunteers, and the resulting B0 homogeneity was compared with the vendor-provided 1 H MRI-based gradient-echo brain shimming routine. The proposed 23 Na MRI-based shimming routine showed a reduction in B0 variation comparable to the vendor-provided shim both in phantom and in vivo measurements. Within the examined multicompartment phantom, the B0 variations could be reduced by up to 77% using the 23 Na MRI-based shim. In human head, B0 variations were reduced by approximately 50% using an acquisition time of 15 seconds for the 23 Na B0 maps and only 1 iteration of B0 shimming. The 23 Na MRI-based localized B0 shimming is possible at 7 T within clinically acceptable acquisition durations (< 1 minute). It was shown that using the proposed 23 Na MRI-based shimming approach, the 23 Na image quality at ultrahigh field strength can be strongly improved.

Confucius Institute and the Completion of Chinese Cross-Border Acquisitions

As a global platform for cultural exchange, the Confucius Institute (CI) has effectively promoted sustainable development among countries and regions. However, existing literature has mostly drawn insights from the national macro-level to study the roles played by CIs, whereas the potential of CIs to influence corporate behaviors has not received extensive attention. This study expands the research on CIs from the national macro-level to the enterprise micro-level by exploring the effect of CIs on the likelihood of acquisition completion. Using data from 1695 Chinese cross-border acquisitions from 2006 to 2017, we find that establishment of CIs can significantly increase acquisition completion likelihood. Furthermore, the level of influence of CIs on acquisition completion depends on country- and firm- level factors. At the country level, the positive effect of CIs on completion likelihood intensifies when cultural distance between host countries and China is great. At the firm level, the acquirer’s past cross-border acquisition experience moderates the effects of CIs, which are more beneficial to firms with no previous successes. In addition, we have made some further analyses, and find that the presence of CIs not only helps to increase the likelihood of acquisitions completion, but also helps to shorten the acquisition durations. The role of CIs in cross-border acquisition completion likelihood do not depend on the types of Chinse enterprises, which indicates that CIs, unlike government agencies, do not offer additional help for SOEs.

Power spectrum of resting-state blood-oxygen-level-dependent signal.

Hemodynamic modeling is used to explore the origin, predict, and analyze the power spectrum of the resting-state blood-oxygen-level-dependent (BOLD) signal measured by functional magnetic resonance imaging (fMRI), which has been reported to have a power-law form, i.e., P(f)∝f^{-s}, where P(f) is the power, f is the frequency, and s>0 is the power-law exponent. However, current fMRI experimental paradigms have limited acquisition durations, affecting the spectral resolution of fMRI data at the low-frequency regime. Here, the claimed power-law spectrum is investigated by using a recent hemodynamic model to analytically derive the BOLD power spectrum, with parameters that are related to neurophysiology. The theoretical results show that, for all realistic parameter combinations, the BOLD power spectrum is flat at f≲0.01Hz, has a weak resonance originating from intrinsic oscillations of vasodilatory response, and becomes a power law for high frequencies, all of which is in agreement with an empirical data set that describes the spectrum of one subject and brain region. However, the results are contrary to studies reporting a pure power-law spectrum at f≲0.2Hz. The discrepancy is attributed largely to data averaging employed by current approaches that averages together important properties of the BOLD power spectrum, such as its resonance, that biases the spectrum to only show a power law. Data averaging also reduces the high-frequency power-law exponent relative to individual cases. Overall, this work demonstrates how the model can reproduce BOLD dynamics and further analyze its low-frequency behavior. Moreover, it also uses the model to explain the impact of procedures, such as data averaging, on the reported features of the BOLD power spectrum.

Education for Sustainability: Lessons from Living Systems Governance

Abstract To survive that is to eat and not to be eaten. Whatever its spatial and temporal level of organisation, every living system owns 7 invariant capacities (the gauge invariance paradigm). Emerging by embedments and juxtapositions of previous systems, every living system-of-systems is both dependent and independent from its new global level of organisation and past and present local situations of emergence. Mass growth governs growth phase duration. Local actors, modules of past, present and new modules of modules become mutually integrated (percolation process) into a new Whole through their merging into an ARMSADA (Association for the Reciprocal and Mutual Sharing of Advantages and DisAdvantages). Reversely (systemic constructal law) the global Whole is integrating the local parceners. Whatever the organisation level, the living systems obey the same principle of evolution and emergence, the volume and time of generation of the adult system obey a correlation: The mass controlled duration of acquisition of the reproductive capacity and the volume at its acquisition are linked by a 3/2 exponent power law. This dynamic fractal law is invariant, between and within le- vels of organisation. Brownian motion is the basic phenomenon of growth control: Matter and energy are exchanged at a constant flow rate. A Pareto-like relationship governs limits and limitations: Mutual survival depends on reciprocal limitations, through interactive feedbacks, for the best and for the worst. To survive that is to transform disadvantages into advantages and to avoid advantages turn to disadvantages.

Microcavity enhancement of low‐frequency Raman scattering from a CsPbI3 thin film

AbstractLow‐frequency Raman (LFR) spectroscopy is a powerful, nondestructive method used for chemical and structural characterization of materials. Typically, the signal intensity of LFR is relatively low, resulting significantly longer signal acquisition duration. Here, we show a photonic structure based on a planar optical microcavity consists of two distributed Bragg reflectors that is capable of enhancing the LFR signal of the material placed in between the mirrors. CsPbI3 forms smooth and uniform thin films and has distinct LFR signatures; thus, we chose to use it for investigating the microcavity enhancement capabilities. By compromising the quality factor of the cavity, we achieved a broader transmission peak and essentially earned enhancement from the double‐resonance effect. Measurements on a CsPbI3 thin film inside a cavity compared with a bare film spin coated on glass demonstrated two orders of magnitude enhancement. In addition, we fabricated the microcavity with a gradient in the resonance wavelength, in order to study the tuning effect on spectral features and on the enhancement factor. Our results show that microcavity is a promising device for enhancing LFR scattering signal and for sensitive characterization of nanomaterials.

Investigation of the influence of B0 drift on the performance of the PLANET method and an algorithm for drift correction

PurposeThe PLANET method was designed to simultaneously reconstruct maps of T1 and T2, the off‐resonance, the RF phase, and the banding free signal magnitude. The method requires a stationary B0 field over the course of a phase‐cycled balanced SSFP acquisition. In this work we investigated the influence of B0 drift on the performance of the PLANET method for single‐component and two‐component signal models, and we propose a strategy for drift correction.MethodsThe complex phase‐cycled balanced SSFP signal was modeled with and without frequency drift. The behavior of the signal influenced by drift was mathematically interpreted as a sum of drift‐dependent displacement of the data points along an ellipse and drift‐dependent rotation around the origin. The influence of drift on parameter estimates was investigated experimentally on a phantom and on the brain of healthy volunteers and was verified by numerical simulations. A drift correction algorithm was proposed and tested on a phantom and in vivo.ResultsDrift can be assumed to be linear over the typical duration of a PLANET acquisition. In a phantom (a single‐component signal model), drift induced errors of 4% and 8% in the estimated T1 and T2 values. In the brain, where multiple components are present, drift only had a minor effect. For both single‐component and two‐component signal models, drift‐induced errors were successfully corrected by applying the proposed drift correction algorithm.ConclusionWe have demonstrated theoretically and experimentally the sensitivity of the PLANET method to B0 drift and have proposed a drift correction method.

Transition to LPG for cooking: A case study from two states of India

This study uses 810 households data collected from two states of India-Raipur district in Chhattisgarh State and Ranchi in Jharkhand- to analyse the LPG cooking transition. Most of the available studies for the South Asia region and particularly for India had mainly focused on the access aspect of clean cooking in terms of fuel or stove. In this study, we particularly focus on the household transition to clean cooking fuel (LPG) in terms of its usage. Using the Tobit regression model for censored data the study highlights the socioeconomic and other factors that may influence LPG transition. The study finds that there could be common as well as location specific factors driving LPG transition. Income linkages with LPG usage may be weak in regions with high prevalence of home produced or collected solid fuel consumption. Duration of LPG acquisition, considered in the study as a factor of behavioural aspect, has emerged as an important variable promoting LPG transition over time. The analysis suggests that LPG capital subsidy scheme, PMUY, has provided a trigger for LPG transition among beneficiary households. Increasing the share of LPG in monthly cooking fuel may require good LPG services such as doorstep delivery.

On-call transthoracic echocardiographic interpretation by first year cardiology fellows: comparison with attending cardiologists

BackgroundTransthoracic echocardiograms (TTE) performed and interpreted by cardiology fellows during off-duty hours are critical to patient care, however limited data exist on their interpretive accuracy. Our aims were to determine the discordance rate between TTEs performed and interpreted by cardiology fellows and National Board of Echocardiography certified attending cardiologists and to identify factors associated with discordance.MethodsConsecutive on-call TTEs acquired and interpreted by 1st year cardiology fellows over 4.6 years at an academic center were prospectively evaluated by attending cardiologists. Fellow interpretations were classified as concordant or discordant with the attending interpretation. We assessed the association of patient, imaging and fellow characteristics with discordance.ResultsA total of 777 TTE interpretations (730 patients) were performed/interpreted by 40 first year fellows and overread by 13 attendings. The most common indications were assessment of left ventricular function (40.9%) and pericardial effusion (37.3%). There was a major or minor discordance in 4.1 and 17.4% of studies, respectively with 42.1% of disagreements occurring in assessment of left ventricular size and function. The indication to assess left ventricular function [OR 2.19, 95% CI (1.32, 3.62), P = 0.002 vs. pericardial effusion] and greater duration of echocardiographic image acquisition (OR 1.02, 95% CI 1.01, 1.03, P = 0.004) were independently associated with overall discordance.ConclusionsIn this large prospective study we found that attending cardiologists disagreed with 1 in 5 fellow TTE interpretations. Standardized tools for evaluation of echocardiograms performed by fellows are needed to ensure quality of training and patient safety.

ECG Signal as Robust and Reliable Biometric Marker: Datasets and Algorithms Comparison.

In this paper, the possibility of using the ECG signal as an unequivocal biometric marker for authentication and identification purposes has been presented. Furthermore, since the ECG signal was acquired from 4 sources using different measurement equipment, electrodes positioning and number of patients as well as the duration of the ECG record acquisition, we have additionally provided an estimation of the extent of information available in the ECG record. To provide a more objective assessment of the credibility of the identification method, some selected machine learning algorithms were used in two combinations: with and without compression. The results that we have obtained confirm that the ECG signal can be acclaimed as a valid biometric marker that is very robust to hardware variations, noise and artifacts presence, that is stable over time and that is scalable across quite a solid (~100) number of users. Our experiments indicate that the most promising algorithms for ECG identification are LDA, KNN and MLP algorithms. Moreover, our results show that PCA compression, used as part of data preprocessing, does not only bring any noticeable benefits but in some cases might even reduce accuracy.

An 8-channel receive array for improved 31 P MRSI of the whole brain at 3T.

PurposeTo demonstrate a 1H/31P whole human brain volume coil configuration for 3 Tesla with separate 31P transmit and receive components that maintains 1H MRS performance and delivers optimal 31P MRSI with 1H decoupling.MethodsWe developed an 8‐channel 31P receive array coil covering the head to be used as an insert for a commercial double‐tuned 1H/31P birdcage transmit‐receive coil. This retains the possibility of using low‐power rectangular pulses for 1H‐decoupled 3D 31P MRSI (nominal resolution 17.6 cm3; acquisition duration 13 min) but increases the SNR with the receive sensitivity of 31P surface coils. The performance of the combined coil setup was evaluated by measuring 1H and 31P SNR with and without the 31P receive array and by assessing the effect of the receive array on the transmit efficiencies of the birdcage coil.ResultsCompared to the birdcage coil alone, the 31P insert in combination with the birdcage achieved an average 31P SNR gain of 1.4 ± 0.4 in a center partition of the brain. The insert did not cause losses in 1H MRS performance and transmit efficiency, whereas for 31P approximately 20% more power was needed to achieve the same γB1.ConclusionThe new coil configuration allows 1H MRSI and optimal 1H‐decoupled 3D 31P MRSI, with increased SNR of the human brain without patient repositioning, for clinical and research purposes at 3 Tesla.

Steady-State Visually Evoked Potentials Elicited by Multifrequency Pattern-Reversal Stimulation.

PurposeIt has been shown that multifrequency stimulation with multifocal electroretinography can reduce recording time without a loss in signal-to-noise ratio. Here, we studied the applicability of multifrequency stimulations for steady-state visually evoked potential (VEP) recordings.MethodsMultifrequency VEPs were recorded monocularly from 10 healthy subjects using pattern-reversal stimuli. The reversal frequency varied between 5 and 30 Hz. Pattern-reversal checkerboard stimuli were generated using four square arrays, each containing 100 light-emitting diodes (LEDs), positioned in four quadrants. Each array had a temporal frequency that differed slightly from the nominal frequency. The long duration of the data acquisition ensured that the slightly different stimulus frequencies in the four LED arrays can be resolved and that the responses to the stimulus in each array can be distinguished (e.g., with a frequency resolution: 0.011 Hz at 12 Hz). The best response from the four recording electrode configuration, defined as the recording with the maximal signal-to-noise ratio, was used for further analysis. Algorithmic latencies were calculated from the ratio of phase data and frequencies in a range of 4 and 20 Hz.ResultsQuadrant-VEPs with simultaneous pattern-reversal stimulation yielded a significant dependency on temporal frequency and stimulus location. The frequency range leading to the maximal response amplitude was between 10 and 12 Hz. Response phases decreased approximately linearly, with increasing temporal frequency suggesting a mean algorithmic latency between 112 and 126 ms.ConclusionsMultifrequency stimulation using LED arrays is an efficient method for recording pattern-reversal VEPs while all stimuli are presented at the same time.Translational RelevanceSimultaneously recorded VEPs as performed by the multi-frequency method can be used for objective measurements of visual field defects.

Energy dispersive X‐ray fluorescence determination of Fe in solid powder samples: A quality improvement perspective

The various factors affecting energy dispersive X‐ray fluorescence determination of iron in solid powder samples were evaluated, to improve the quality of these measurements. Influence of samples/standards preparation and instrumental parameters such as applied voltage to the X‐ray tube, tube output current, and duration of acquisition were assessed, and the optimized instrumental parameters were 12 kV, 200 μA, and 200 s, respectively. Linear dynamic range of the spectrometer was found to be 0.0052 to 5.042 g kg−1. Detection limits of iron in various organic/inorganic samples were found to be 2.5 to 21.9 mg kg−1. The values obtained during the present method were evaluated with neutron activation analysis.

Tissue sodium concentration and sodium T1 mapping of the human brain at 3 T using a Variable Flip Angle method

PurposeThe state-of-the-art method to quantify sodium concentrations in vivo consists in a fully relaxed 3D spin-density (SD) weighted acquisition. Nevertheless, most sodium MRI clinical studies use short-TR SD acquisitions to reduce acquisition durations. We present a clinically viable implementation of the Variable Flip Angle (VFA) method for robust and clinically viable quantification of total sodium concentration (TSC) and longitudinal relaxation rates in vivo in human brain at 3 T. MethodsTwo non-Cartesian steady-state spoiled ultrashort echo time (UTE) scans, performed at optimized flip angles, repetition time and pulse length determined under specific absorption rate constraints, are used to simultaneously compute T1 and total sodium concentration (TSC) maps using the VFA method. Images are reconstructed using the non-uniform Fast Fourier Transform algorithm and TSC maps are corrected for possible inhomogeneity of coil transmission and reception profiles. Fractioned acquisitions are used to correct for potential patient motion. TSC quantifications obtained using the VFA method are validated at first in comparison with a fully-relaxed SD acquisition in a calibration phantom. The robustness of similar VFA acquisitions are compared to the short-TR SD approach in vivo on seven healthy volunteers. ResultsThe VFA method resulted in consistent TSC and T1 estimates across our cohort of healthy subjects, with mean TSC of 38.1 ± 5.0 mmol/L and T1 of 39.2 ± 4.4 ms. These results are in agreement with previously reported values in literature TSC estimations and with the predictions of a 2-compartment model. However, the short-TR SD acquisition systematically underestimated the sodium concentration with a mean TSC of 31 ± 4.5 mmol/L. ConclusionThe VFA method can be applied successfully to image sodium at 3 T in about 20 min and provides robust and intrinsically T1-corrected TSC maps.