Probing the microscopic environment of 23 Na ions in brain tissue by MRI: On the accuracy of different sampling schemes for the determination of rapid, biexponential T2* decay at low signal-to-noise ratio.

PURPOSE: To investigate and to reduce influences on the determination of the short and long apparent transverse relaxation times ( T2,s*, T2,l*) of 23 Na in vivo with respect to signal sampling. METHODS: The accuracy of T2* determination was analyzed in simulations for five different sampling schemes. The influence of noise in the parameter fit was investigated for three different models. A dedicated sampling scheme was developed for brain parenchyma by numerically optimizing the parameter estimation. This scheme was compared in vivo to linear sampling at 7T. RESULTS: For the considered sampling schemes, T2,s* / T2,l* exhibit an average bias of 3% / 4% with a variation of 25% / 15% based on simulations with previously published T2* values. The accuracy could be improved with the optimized sampling scheme by strongly averaging the earliest sample. A fitting model with constant noise floor can increase accuracy while additional fitting of a noise term is only beneficial in case of sampling until late echo time > 80 ms. T2* values in white matter were determined to be T2,s* = 5.1 ± 0.8 / 4.2 ± 0.4 ms and T2,l* = 35.7 ± 2.4 / 34.4 ± 1.5 ms using linear/optimized sampling. CONCLUSION: Voxel-wise T2* determination of 23 Na is feasible in vivo. However, sampling and fitting methods have to be chosen carefully to retrieve accurate results. Magn Reson Med 80:571-584, 2018. © 2018 International Society for Magnetic Resonance in Medicine.

Reproducibility of CMRO2 determination using dynamic 17 O MRI.

PURPOSE: To assess the reproducibility of 17 O MRI-based determination of the cerebral metabolic rate of oxygen consumption (CMRO2 ) in healthy volunteers. To assess the influence of image acquisition and reconstruction parameters on dynamic quantification of functional parameters such as CMRO2 . METHODS: Dynamic 17 O MRI data were simulated and used to investigate influences of temporal resolution (Δt) and partial volume correction (PVC) on the determination of CMRO2 . Three healthy volunteers were examined in two separate examinations. In vivo 17 O MRI measurements were conducted with a nominal spatial resolution of (7.5 mm)3 using a density-adapted radial sequence with golden angle acquisition scheme. In each measurement, 4.0 ± 0.1 L of 70%-enriched 17 O gas were administered using a rebreathing system. Data were corrected with a PVC algorithm, and CMRO2 was determined in gray matter (GM) and white matter (WM) compartments using a three-phase metabolic model (baseline, 17 O inhalation, decay phase). RESULTS: Comparison with the ground truth of simulations revealed improved CMRO2 determination after application of PVC and with Δt ≤ 2:00 min. Evaluation of in vivo data yields to CMRO2,GM = 2.31 ± 0.1 µmol/g/min and to CMRO2,WM = 0.69 ± 0.04 µmol/g/min with coefficients of variation (CoV) of 0.3-5.5% and 4.3-5.0% for intra-volunteer and inter-volunteer data, respectively. CONCLUSION: This in vivo 17 O inhalation study demonstrated that the proposed experimental setup enables reproducible determination of CMRO2 in healthy volunteers. Magn Reson Med 79:2923-2934, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Enhancing the quantification of tissue sodium content by MRI: time-efficient sodium B1 mapping at clinical field strengths.

Tissue sodium content (TSC) is a sensitive measure of pathological changes and can be detected non-invasively by MRI. For the absolute quantification of TSC, B1 inhomogeneities must be corrected, which is not well established beyond research applications. An in-depth analysis of B1 mapping methods which are suitable for application in TSC quantification is presented. On the basis of these results, a method for simultaneous B1 mapping and imaging is proposed in order to enhance accuracy and to reduce measurement time at clinical field strengths. The B1 mapping techniques used were phase-sensitive (PS), Bloch-Siegert shift (BSS), double-angle (DAM) and actual flip-angle imaging (AFI) methods. Experimental and theoretical comparisons demonstrated that the PS technique yields the most accurate field profiles and exhibits the highest signal-to-noise ratio (SNR). Simultaneous B1 mapping and imaging was performed for the PS method, employing both degrees of freedom of the MR signal: the B1 field is encoded into signal phase and the amplitude provides the concentration information. In comparison with the more established DAM, a 13% higher SNR was obtained and field effects could be corrected more accurately without the need for additional measurement time. The protocol developed was applied to measure TSC in the healthy human head at an isotropic resolution of 4 mm. TSC was determined to be 35 ± 1 mM in white matter and 134 ± 3 mM in vitreous humor. By employing the proposed simultaneous characterization of the B1 field and acquisition of the spin density-weighted sodium signal, the accuracy of the non-invasive measurement of TSC is enhanced and the measurement time is reduced. This should allow (23)Na MRI to be better incorporated into clinical studies and routine.

Quantitative sodium MRI of kidney.

One of the main tasks of the human kidneys is to maintain the homeostasis of the body's fluid and electrolyte balance by filtration of the plasma and excretion of the end products. Herein, the regulation of extracellular sodium in the kidney is of particular importance. Sodium MRI ((23)Na MRI) allows for the absolute quantification of the tissue sodium concentration (TSC) and thereby provides a direct link between TSC and tissue viability. Renal (23)Na MRI can provide new insights into physiological tissue function and viability thought to differ from the information obtained by standard (1)H MRI. Sodium imaging has the potential to become an independent surrogate biomarker not only for renal imaging, but also for oncology indications. However, this technique is now on the threshold of clinical implementation. Numerous, initial pre-clinical and clinical studies have already outlined the potential of this technique; however, future studies need to be extended to larger patient groups to show the diagnostic outcome. In conclusion, (23)Na MRI is seen as a powerful technique with the option to establish a non-invasive renal biomarker for tissue viability, but is still a long way from real clinical implementation.

Prevalence of musculoskeletal pain among gynecologic surgeons performing laparoscopic procedures: A systematic review and meta-analysis.

OBJECTIVE: Musculoskeletal discomfort is associated with repetitive movements and constrained body positions. The current meta-analysis was performed to determine the global prevalence of musculoskeletal symptoms among gynecologic surgeons who perform laparoscopy. METHODS: Sources included Embase, MEDLINE, PubMed, CINAHL, Web of Science Core Collection, Cochrane Central Register of Controlled Clinical Trials, and Google Scholar. Articles published between 1980 and 2022 were considered. Studies that assessed self-reported musculoskeletal symptoms were included. Relevant data were extracted and tabulated. RESULTS: Twelve studies met the inclusion criteria. In a pooled sample of 1619 surgeons, the estimated prevalence of musculoskeletal symptoms was 82% (95% confidence interval [CI], 70%-89%; I2 , 92%). Female sex was a risk factor, as identified by a pooled odds ratio of 4.64 (95% CI, 2.63-8.19; I2 , 0%) compared with male surgeons. Among surgeons who reported musculoskeletal symptoms, 30% (95% CI, 14%-52%; I2 , 95%) sought treatment and 3% (95% CI, 2%-6%; I2 , 0%) required work hour modifications. CONCLUSION: The current meta-analysis provides preliminary evidence of a high prevalence of musculoskeletal symptoms among gynecologic laparoscopic surgeons. Future research is needed to explore the underlying risk factors and interventional strategies to mitigate this risk.

Predictive Contribution of the Superficial Neck Muscles to Short-Latency Rate of Force Development of the Head and Neck.

PURPOSE: To evaluate the contribution of splenius capitis, sternocleidomastoid, and upper fibers of trapezius activation to the gains in rate of force development (RFD) of the head and neck during maximum voluntary ballistic contractions. METHODS: RFD gain was facilitated by a single-session intervention for maximum voluntary ballistic contractions in the anterior direction, oriented at 45° to the midsagittal plane, which require active restraint of axial rotation. Muscle activation for the agonist (sternocleidomastoid) and 2 antagonists (splenius capitis and upper fibers of trapezius) was evaluated. The study sample included 12 physically active men (mean age, 22.6 y). RFD (N·m·s-1; 0-100 ms) and integrated muscle activity (50 ms before and 100 ms after force onset) were measured at 10 minutes, 20 minutes, and 2 days postintervention, relative to baseline. Muscle activation predictive of RFD gains was evaluated by linear regression analysis. RFD reproducibility was evaluated using the coefficient of variation of the typical error. RESULTS: The intervention yielded a 1.95- to 2.39-fold RFD gain (P ≤ .05), with greater RFD gain for participants with a lower peak moment of force (<10.9 N·m) than those with a higher peak moment (≥10.9 N·m) at baseline (P ≤ .002). For the low group, 65% to 74% of the RFD gain was predicted by ipsilateral sternocleidomastoid activation, with ipsilateral splenius capitis activation predicting 77% to 92% of RFD gain for the high group. Absolute peak and impulse of static force were greater for the high than for the low group (P ≤ .04). RFD reproducibility was high (coefficient of variation of the typical error ≤ 14.4%). CONCLUSIONS: The agonist- and antagonist-focused synergies might reflect different functional priorities, higher RFD gain compared with higher head-neck force.

Transcranial Direct Current Stimulation Over Motor Areas Improves Reaction Time in Parkinson's Disease.

Background: Transcranial direct current stimulation (tDCS) has been shown to modulate cortical motor excitability and improve bradykinesia symptoms in Parkinson's disease. It is unclear how targeting different cortical motor areas with tDCS may differentially influence upper limb function for individuals diagnosed with PD. Objective: This study investigated whether anodal tDCS applied separately to the primary motor cortex and the supplementary motor area would improve upper limb function for individuals with Parkinson's disease. In addition, a startling acoustic stimulus was used to differentiate between the effect of stimulation on motor preparatory and initiation processes associated with upper limb movements. Methods: Eleven participants with idiopathic Parkinson's disease performed two upper limb simple reaction time tasks, involving elbow extension or a button press before and after either anodal tDCS or sham tDCS was applied over the primary motor cortex or supplementary motor area. A loud, startling stimulus was presented on a selection of trials to involuntarily trigger the prepared action. Results: Anodal tDCS led to improved premotor reaction time in both tasks, but this was moderated by reaction time in pre-tDCS testing, such that individuals with slower pre-tDCS reaction time showed the greatest reaction time improvements. Startle-trial reaction time was not modified following tDCS, suggesting that the stimulation primarily modulated response initiation processes. Conclusion: Anodal tDCS improved response initiation speed, but only in slower reacting individuals with PD. However, no differences attributable to tDCS were observed in clinical measures of bradykinesia or kinematic variables, suggesting that reaction time may represent a more sensitive measure of some components of bradykinesia.

Iterative reconstruction of radially-sampled 31P bSSFP data using prior information from 1H MRI.

The purpose of this study is to improve direct phosphorus (31P) MR imaging. Therefore, 3D density-adapted radially-sampled balanced steady-state free precession (bSSFP) sequences were developed and an iterative approach exploiting additional anatomical information from hydrogen (1H) data was evaluated. Three healthy volunteers were examined at B0=7T in order to obtain the spatial distribution of the phosphocreatine (PCr) intensities in the human calf muscle with a nominal isotropic resolution of 10mm in an acquisition time of 10min. Three different bSSFP gradient schemes were investigated. The highest signal-to-noise ratio (SNR) was obtained for a scheme with two point-reflected density-adapted gradients. Furthermore, the conventional reconstruction based on a gridding algorithm was compared to an iterative method using an 1H MRI constraint in terms of a segmented binary mask, which comprises prior knowledge. The parameters of the iterative approach were optimized and evaluated by simulations featuring 31P MRI parameters. Thereby, partial volume effects as well as Gibbs ringing artifacts could be reduced. In conclusion, the iterative reconstruction of 31P bSSFP data using an 1H MRI constraint is appropriate for investigating regions where sharp tissue boundaries occur and leads to images that represent the real PCr distributions better than conventionally reconstructed images.