ECG-gated <Superscript>23</Superscript>Na-MRI of the human heart using a 3D-radial projection technique with ultra-short echo times

Pathological changes in tissue often manifest themselves in an altered sodium gradient between intra- and extracellular space due to a malfunctioning Na⁺–K⁺ pump, resulting in an increase in total sodium concentration in ischaemic regions. Therefore, ²³Na-MRI has the potential to non-invasively differentiate viable from non-viable tissue by detecting concentration changes of intra- and extracellular sodium. As the in vivo sodium signal shows a bi-exponential T₂ decay, with a short component of less than 1 ms, the accurate quantification of the total sodium content requires imaging techniques with ultra-short echo times (TE) below 0.5 ms. A 3D-radial projection technique has been developed which allows the acquisition of ECG-triggered sodium images of the human heart with a TE of 0.4 ms. With this pulse sequence ²³Na-MRI volunteer measurements of the head or the heart were performed in less than 18 min on a 1.5-T clinical scanner with an isotropic resolution of 10 mm³. The signal to noise ratio of the radial projection technique is twofold higher than that of a Cartesian gradient echo pulse sequence (TE = 3.2 ms). Radial ²³Na-MRI provides a tool for clinical studies, aiming at the differentiation of viable and non-viable tissue.     

Accelerated time-resolved 3D contrast-enhanced MR angiography at 3T: clinical experience in 31 patients

Purpose: To evaluate whether time-resolved 3D MR-angiography at 3T with a net acceleration factor of eight is applicable in clinical routine and to evaluate whether good image quality and a low artifact level can be achieved with a temporal update rate that allows for additional information on pathologies. Materials and methods: Thirty-one consecutive patients underwent time-resolved 3D contrast-enhanced MR-angiography on a 3T system. Imaging consisted of accelerated 3D gradient echo sequences combining parallel imaging with an acceleration factor of four, partial Fourier acquisition along phase and slice encoding direction, and twofold temporal acceleration using view sharing. Data volumes representing the arterial and venous contrast phases were independently evaluated by two experienced radiologists by grading of image quality and artifact level on a 0–3 scale. Results: Time-resolved MR-angiography was successfully performed in all subjects without the need for contrast agent bolus timing. Excellent arterial (average score = 2.65 ± 0.32) and good venous (average score = 2.56 ± 0.28) diagnostic image quality and little image degrading due to artifacts (average score = 2.20 ± 0.16) were confirmed by both independent readers (agreement in 65.2% of all evaluations). In 14 patients vascular pathologies were identified in the arterial phases. In eight examinations temporal resolution and depiction of contrast agent dynamics provided additional information about pathology. Discussion: Without the necessity for additional bolus timing, time-resolved 3D contrast-enhanced MR-angiography with imaging acceleration along both the spatial encoding direction and temporal domain revealed excellent diagnostic image quality in neurovascular and thoracic imaging. Despite the limited spatial resolution as compared to high-resolution imaging of the carotid artery bifurcation, the results demonstrate the applicability of contrast-enhanced MR-angiography in thoracic and abdominal MRA as well as cervical imaging with a temporal update rate allowing for additional information on pathologies. Future studies may include an evaluation of optimal trade-offs between spatial and temporal resolution, different acceleration factors and a comparison to the gold-standard for accuracy.     

Correction to: 3D APT and NOE CEST-MRI of healthy volunteers and patients with non-enhancing glioma at 3 T

Magnetic Resonance Materials in Physics, Biology and Medicine -     

大型电站锅炉T23钢焊缝开裂失效分析

从诸多电厂应用T23钢的结果来看,出现了许多问题,且多出现在焊缝及其热影响区.此次通过多种理化试验,对某大型电站超超临界锅炉高温再热器T23钢焊缝开裂的原因进行了失效分析,并根据T23钢的特性,指出了其在实际运用中的应注意工艺要求,以确保电厂安全运行.     

塔式炉T23水冷壁泄漏分析及措施

通过分析宁海电厂5、6号锅炉T23水冷壁泄漏情况,提出了在基建调试期间采取的各项应对措施,并在锅炉水冷壁刚性附件结构设计、制造及T23水冷壁安装工艺等方面提出建议,为同类型锅炉提供借鉴。     

超超临界塔式炉T23水冷壁早期失效分析

对国内多台超超临界塔式炉T23水冷壁早期失效案例进行了统计,对典型失效管样进行宏观和微观分析,测试接头的力学性能,在此基础上分析失效机理及主要影响因素。研究结果表明,失效是由于焊缝产生横向裂纹,裂纹沿晶界扩展。初步判断裂纹性质为楔形蠕变裂纹。合金过饱和固溶使焊缝处于高硬度水平是产生楔形蠕变裂纹的内因,水冷壁密集焊缝结构使接头部位的拉伸应力增大,它与内压应力叠加提供了裂纹形成和扩展的力学条件。降低焊缝硬度和细化晶粒有利于避免失效。     

Quantitative in vivo 23Na MR imaging of the healthy human kidney: determination of physiological ranges at 3.0T with comparison to DWI and BOLD

Objectives

The purpose of this prospective study was to assess the normal physiologic ranges of the renal corticomedullary ²³Na-concentration ([²³Na]) gradient at 3.0T in healthy volunteers. The corticomedullary [²³Na] gradient was correlated with other functional MR imaging parameters—blood oxygenation level dependent (BOLD) and diffusion-weighted imaging (DWI)—and to individual and physiologic parameters—age, gender, estimated glomerular filtration rate (eGFR), body mass index (BMI), and blood serum sodium concentration ([²³Na]_serum).

Methods and materials

50 healthy volunteers (30 m, 20 w; mean age: 29.2 years) were included in this IRB-approved study, without a specific a priori preparation in regard to water or food intake. For ²³Na-imaging a 3D density adapted, radial gradient echo (GRE)-sequence (spatial resolution = 5 × 5 × 5 mm³) was used in combination with a dedicated ²³Na-coil and ²³Na-reference phantoms. [²³Na] values of the corticomedullary [²³Na] gradient were measured by placement of a linear region of interest (20 × 1 mm²) from the renal cortex in the direction of the renal medulla. By using external standard reference phantoms, [²³Na] was calculated in mmol/L of wet tissue volume (mmol/l WTV). Axial diffusion-weighted images (spatial resolution = 1.7 × 1.7 × 5.0 mm³) and 2D GRE BOLD images (spatial resolution = 1.2 × 1.2 × 4.0 mm³) were acquired. Mean values ± standard deviations for [²³Na], apparent diffusion coefficient (ADC) values, and R2* values were computed for each volunteer. The corticomedullary ²³Na-concentration gradient (in mmol/l/mm) was calculated along the area of linear concentration increase from the cortex in the direction of the medulla. Correlations between the [²³Na] and DWI, BOLD, and the physiologic parameters were assessed with Pearson correlation coefficients.

Results

The mean corticomedullary [²³Na] for all healthy volunteers increased from the renal cortex (58 ± 17 mmol/l WTV) in the direction of the medulla (99 ± 18 mmol/l WTV). The inter-individual differences ranged from respective cortical and medullary values of 27 and 63 mmol/L WTV to 126 and 187 mmol/L WTV. No statistically significant differences in renal [²³Na] were found based on differences in individual or physiologic parameters (age, gender, [²³Na]_serum, BMI, GFR). No ADC or R2* gradients were identified, and [²³Na] did not correlate with these parameters.

Conclusion

Renal corticomedullary [²³Na] values increase from the cortex in the direction of the medullary pyramid, demonstrating wide inter-individual ranges and no significant correlations with age, gender, [²³Na]_serum, BMI, GFR, ADC, or R2* values. For future clinical evaluations, an approach relying on renal stimulation (e.g. pharmacologically induced diuresis) may be applicable to account for wide inter-individual ranges of normal [²³Na].     

Clinical application of single-shot echo-planar diffusion-weighted imaging with compressed SENSE in prostate MRI at 3T: preliminary experience

Magnetic Resonance Materials in Physics, Biology and Medicine - Image quality (IQ) of diffusion-weighted imaging (DWI) with single-shot echo-planar imaging (ssEPI) suffers from low signal-to-noise...     

Mapping tumour heterogeneity with pulsed 3D CEST MRI in non-enhancing glioma at 3 T

Objective

Amide proton transfer (APT) weighted chemical exchange saturation transfer (CEST) imaging is increasingly used to investigate high-grade, enhancing brain tumours. Non-enhancing glioma is currently less studied, but shows heterogeneous pathophysiology with subtypes having equally poor prognosis as enhancing glioma. Here, we investigate the use of CEST MRI to best differentiate non-enhancing glioma from healthy tissue and image tumour heterogeneity.

Materials & Methods

A 3D pulsed CEST sequence was applied at 3 Tesla with whole tumour coverage and 31 off-resonance frequencies (+6 to -6 ppm) in 18 patients with non-enhancing glioma. Magnetisation transfer ratio asymmetry (MTRasym) and Lorentzian difference (LD) maps at 3.5 ppm were compared for differentiation of tumour versus normal appearing white matter. Heterogeneity was mapped by calculating volume percentages of the tumour showing hyperintense APT-weighted signal.

Results

LDamide gave greater effect sizes than MTRasym to differentiate non-enhancing glioma from normal appearing white matter. On average, 17.9 % ± 13.3 % (min–max: 2.4 %–54.5 %) of the tumour volume showed hyperintense LDamide in non-enhancing glioma.

Conclusion

This works illustrates the need for whole tumour coverage to investigate heterogeneity in increased APT-weighted CEST signal in non-enhancing glioma. Future work should investigate whether targeting hyperintense LDamide regions for biopsies improves diagnosis of non-enhancing glioma.

     

高温再热器T23/12Cr1MoV异种钢焊缝失效机理

通过裂纹宏观形貌、硬度试验、裂纹微观形态等分析,研究了1 900 t/h锅炉高温再热器T23/12Cr1MoV异种钢安装焊缝运行8 000 h断裂失效机理。结果表明:取消焊前预热及焊后热处理,将造成焊缝及热影响区产生淬硬马氏体组织,粗晶区晶粒严重粗化,晶界弱化;在高温运行温度下,焊接残余应力及管内蒸汽运行压力下,在焊缝与粗晶区界面处产生应力集中,随着外加应力塑性增加,在焊缝与粗晶区界面粗晶界产生裂纹。再热裂纹是造成高温再热器T23/12Cr1MoV异种钢焊缝断裂失效的主要原因。     

Correction to: 3D SASHA myocardial T1 mapping with high accuracy and improved precision

Purpose

To improve the precision of a free-breathing 3D saturation-recovery-based myocardial T1 mapping sequence using a post-processing 3D denoising technique.

Methods

A T1 phantom and 15 healthy subjects were scanned on a 1.5 T MRI scanner using 3D saturation-recovery single-shot acquisition (SASHA) for myocardial T1 mapping. A 3D denoising technique was applied to the native T1-weighted images before pixel-wise T1 fitting. The denoising technique imposes edge-preserving regularity and exploits the co-occurrence of 3D spatial gradients in the native T1-weighted images by incorporating a multi-contrast Beltrami regularization. Additionally, 2D modified Look-Locker inversion recovery (MOLLI) acquisitions were performed for comparison purposes. Accuracy and precision were measured in the myocardial septum of 2D MOLLI and 3D SASHA T1 maps and then compared. Furthermore, the accuracy and precision of the proposed approach were evaluated in a standardized phantom in comparison to an inversion-recovery spin-echo sequence (IRSE).

Results

For the phantom study, Bland–Altman plots showed good agreement in terms of accuracy between IRSE and 3D SASHA, both on non-denoised and denoised T1 maps (mean difference −1.4 ± 18.9 ms and −4.4 ± 21.2 ms, respectively), while 2D MOLLI generally underestimated the T1 values (69.4 ± 48.4 ms). For the in vivo study, there was a statistical difference between the precision measured on 2D MOLLI and on non-denoised 3D SASHA T1 maps (P = 0.005), while there was no statistical difference after denoising (P = 0.95).

Conclusion

The precision of 3D SASHA myocardial T1 mapping was substantially improved using a 3D Beltrami regularization based denoising technique and was similar to that of 2D MOLLI T1 mapping, while preserving the higher accuracy and whole-heart coverage of 3D SASHA.

     

Association of white matter deficits with clinical symptoms in antipsychotic-naive first-episode schizophrenia: an optimized VBM study using 3T

Object

To examine the whole brain white matter morphology in antipsychotic-naive patients with first-episode schizophrenia (FES) and its correlations with symptom severity.

Materials and methods

High-resolution T1-weighted images of 64 drug-naive FES patients and 64 matched healthy controls were acquired using a 3 T MR imaging system. Then, optimized voxel-based morphometry was performed to compare the group differences. Finally, correlation analyses were conducted between the white matter volume (WMV) changes and clinical symptoms.

Results

The FES showed significantly decreased WMV in the bilateral posterior limb of the internal capsule (PLIC) and right subgyral frontal white matter. The volume of the bilateral PLIC was negatively correlated with the Positive and Negative Syndrome Scale positive scores. Positive correlations were observed between all of the changed WMV measures and the Global Assessment of Functioning scores.

Conclusion

The current findings provide further evidence to support internal capsule and subgyral frontal white matter deficits at the early stage of schizophrenia that are potentially related to the core pathophysiology of the disease. Furthermore, these anatomical alterations were related to the clinical symptoms but not the untreated illness duration, suggesting that these deficits are related to aberrations in the neurodevelopmental process and may be relatively stable during the early course of schizophrenia.     

屏式过热器T23/12Cr1MoV异种钢接头失效分析

对某1 000 MW超超临界发电机组屏式过热器管屏进口段T23/12Cr1 MoV异种钢焊接接头的失效进行了试验分析.宏观与微观检查表明,裂纹沿管子焊缝周向分布,开裂起始于12Cr 1MoV管内壁粗晶粒热影响区,扩展至1/3厚度处进入焊缝,在焊缝中继续扩展至管子外壁.通过力学性能试验得出失效的主要原因是热影响区及焊缝的硬度高而塑韧性低,建议进行焊后热处理,以改善接头塑韧性和消除焊接残余应力.     

Effects of functional electrical stimulation in denervated thigh muscles of paraplegic patients mapped with T 2 imaging

OBJECT: Functional electrical stimulation (FES) for paraplegic patients, with the long-term goal of ultimately restoring muscle function, is associated with several positive effects: improvement of blood circulation, skin condition, peripheral trophism and metabolism, prophylaxis against decubitus ulcer and better physical fitness. Since fibres of denervated muscles (lacking a supplying nerve) need to be activated directly, the fraction of elicited muscle tissue follows the geometric distribution of the electrical field, which can be simulated using electrophysiological computer models. Experimental validation of these results, however, has not yet been established. MATERIALS AND METHODS: We acquired T (2) parameter images using a multislice multi-spin-echo MR sequence before and immediately after FES in nine denervated paraplegic patients and three healthy subjects in order to visualise the geometric distribution of activation by electrically induced muscle stimulation in denervated versus innervated (healthy) thigh muscle. RESULTS AND CONCLUSION: After realigning and normalisation, maps of relative T (2) increase were calculated. The results demonstrate that the spatial distribution of short-term effects of FES of denervated muscle tissue of paraplegic patients who regularly perform FES can be visualised by T (2) parameter images. This may be used to refine models of the electrical field of FES in muscle and fibre activation in the future.     

GLINT: GlucoCEST in neoplastic tumors at 3 T—clinical results of GlucoCEST in gliomas

Objective

Clinical relevance of dynamic glucose enhanced (DGE) chemical exchange saturation transfer (CEST) imaging has mostly been demonstrated at ultra-high field (UHF) due to low effect size. Results of a cohort study at clinical field strength are shown herein.

Materials and methods

Motion and field inhomogeneity corrected T1ρ‐based DGE (DGE⍴) images were acquired before, during and after a d-glucose injection with 6.3 s temporal resolution to detect accumulation in the brain. Six glioma patients with clear blood–brain barrier (BBB) leakage, two glioma patients with suspected BBB leakage, and three glioma patients without BBB leakage were scanned at 3 T.

Results

In high-grade gliomas with BBB leakage, d-glucose uptake could be detected in the gadolinium (Gd) enhancing region as well as in the tumor necrosis with a maximum increase of ∆DGE⍴ around 0.25%, whereas unaffected white matter did not show any significant DGE⍴ increase. Glioma patients without Gd enhancement showed no detectable DGE⍴ effect within the tumor.

Conclusion

First application of DGE⍴ in a patient cohort shows an association between BBB leakage and DGE signal irrespective of the tumor grade. This indicates that glucoCEST corresponds more to the disruptions of BBB with Gd uptake than to the molecular tumor profile or tumor grading.

     

国产T23钢在台山电厂2×1000 MW塔式锅炉水冷壁上的运用现状

以台山电厂2×1000MW超超临界压力直流锅炉为例,在学习SA-213-T23钢产生再热裂纹原因的基础上,根据锅炉的设计特点,制定与之相适应的焊接与安装工艺,减少或避免T23钢因焊接产生再热裂纹而发生水冷壁管的泄漏事故。     

考虑剪切变形效果的薄壁结构三维动力计算

为了分析考虑剪切变形效果的薄壁结构三维振动响应,本文推导剪切变形梁柱单元动力刚度矩阵,首先列出一般形式下薄壁梁柱的势能方程,得到位移与力之间的转换方程;接着,推导力与变形的关系,并采用变分原理,从势能方程中得到动力方程;然后,构造14个位移参数的变量来对高阶的动力方程进行降阶与求解,从而得到精确的位移函数表达式及动力刚度矩阵。数值算例的检验结果表明,这套程序计算所得到的结果与NASTRAN计算结果相一致,说明这一结果具有较好的通用性,它提供给薄壁结构振动计算一个较为实用的工具。