Feasibility of using signal strength indicator data to estimate soil moisture based on GNSS interference signal analysis

The use of multipath signals to estimate soil moisture is an important application of Global Navigation Satellite System (GNSS) reflectometry. In most studies the data used to estimate the soil moisture are raw signal to noise ratio (SNR) data. However, the SNR data are only regarded as auxiliary data used to determine the quality of signal in most of the widely distributed Continuous Operational Reference System (CORS) receivers. So SNR data are generally ignored and unavailable. Fortunately, the GNSS receivers output the standard data format as Rinex, where the Signal Strength Indicator (SSI) is recorded as alternative data to SNR. This study aims to investigate the feasibility of soil moisture estimation based on SSI data. An experiment was conducted to estimate SSI phase and record the in situ soil moisture data for comparison. Then the relationship between the phase and soil moisture is determined by 44 days SSI data processing. Finally, the relationship is used to further estimate soil moisture with 36 days data. Experimental results show the correlation coefficient between the SSI phase and in situ soil moisture is approximately 0.7, and that the root mean square estimation error of soil moisture is lower than 9.9%. Results demonstrate the feasibility of using SSI data to estimate soil moisture.     

Multi-shell diffusion signal recovery from sparse measurements

For accurate estimation of the ensemble average diffusion propagator (EAP), traditional multi-shell diffusion imaging (MSDI) approaches require acquisition of diffusion signals for a range of b-values. However, this makes the acquisition time too long for several types of patients, making it difficult to use in a clinical setting. In this work, we propose a new method for the reconstruction of diffusion signals in the entire q-space from highly undersampled sets of MSDI data, thus reducing the scan time significantly. In particular, to sparsely represent the diffusion signal over multiple q-shells, we propose a novel extension to the framework of spherical ridgelets by accurately modeling the monotonically decreasing radial component of the diffusion signal. Further, we enforce the reconstructed signal to have smooth spatial regularity in the brain, by minimizing the total variation (TV) norm. We combine these requirements into a novel cost function and derive an optimal solution using the Alternating Directions Method of Multipliers (ADMM) algorithm. We use a physical phantom data set with known fiber crossing angle of 45° to determine the optimal number of measurements (gradient directions and b-values) needed for accurate signal recovery. We compare our technique with a state-of-the-art sparse reconstruction method (i.e., the SHORE method of Cheng et al. (2010)) in terms of angular error in estimating the crossing angle, incorrect number of peaks detected, normalized mean squared error in signal recovery as well as error in estimating the return-to-origin probability (RTOP). Finally, we also demonstrate the behavior of the proposed technique on human in vivo data sets. Based on these experiments, we conclude that using the proposed algorithm, at least 60 measurements (spread over three b-value shells) are needed for proper recovery of MSDI data in the entire q-space.     

对MRI设备层间射频信号干扰进行检测的实践

目的 对3台MRI设备的层间射频信号干扰情况进行检测,以加深对层间射频信号干扰现象的认识。方法 通过3台MRI设备（设备1：GE 1.5T HDi,装机时间：2012年;设备2：GE 3.0T HD,装机时间：2006年;设备3：GE 3.0T 750W,装机时间：2016年）采用轴位T1WI序列扫描ACR模体,记录层间距为5.0、1.0、0.5和0 mm时的SNR,绘制SNR变化百分比与层间距百分比的函数图。处置标准：当层间距从5 mm减小到0时,由层间射频信号干扰作用所导致的SNR的下降不超过20%。结果 当层间距由5 mm减小到0时,设备1的SNR下降幅度为18.16%,设备2的SNR下降幅度为23.57%,设备3的SNR下降幅度为10.75%;设备1和设备3的层间射频信号干扰检测结果达到处置标准,设备2（使用时间超过10年）的检测结果未达标。结论 3台MRI设备都存在不同程度的层间射频信号干扰现象,其中使用时间最久的设备检测结果不达标。层间射频信号干扰检测应该在临床质量控制工作中受到重视。     

MRI信号强度预测子宫肌瘤微波消融能量的可行性

目的 探讨根据MR T2WI信号强度预测微波消融子宫肌瘤所需能量的可行性。方法 于超声引导对143例子宫肌瘤患者(共197个病灶)行经皮微波消融治疗,对其中42例(49个病灶)于微波消融术前、术后进行盆腔平扫+MR增强扫描。微波消融功率为50 W,微波天线型号均为T11a。术前根据MR T2WI中子宫肌层信号强度为标准,将子宫肌瘤分为高、等、低信号3组;消融后测量增强MRI中无灌注区体积作为消融体积,对子宫肌瘤微波消融能效因子进行统计学分析。结果 低、等、高信号组子宫肌瘤微波消融平均能效因子分别为(685.01±206.27)J/cm³、(702.70±254.25)J/cm³和(945.12±321.83)J/cm³,高信号组与低信号组比较差异有统计学意义(P=0.015)。结论 根据MR T2WI中子宫肌瘤的信号强度可初步预测微波消融所需能量;微波消融中,T2WI呈高信号的子宫肌瘤所需能量高于呈低信号者。     

Using reflected signal power from the BeiDou geostationary satellites to estimate soil moisture

Satellites-based microwave sensors are sensitive to soil moisture at the surface of the Earth, but their performance is limited by their continuously varying footprints due to the repeat cycle of satellites. In recent years, Global Navigation Satellite System (GNSS) microwave signals have been used to estimate soil moisture and the BeiDou system (BDS) provides new signal sources. Unlike Global Positioning System, BDS includes five geostationary earth orbit (GEO) satellites. Because their orbits are geosynchronous, the footprints of the GEO satellites remain nearly unchanged for fixed receivers; this property is beneficial for continuous long-term observation of reflection studies in the fixed area. We conducted a ground-based field experiment and collected data that included signals from GEO satellites and in situ soil moisture observations during this experiment to investigate the soil moisture estimation using the power of the reflected BDS signals. In this letter, we first designed a filter to separate the effect of GEO slight motion on raw signal. We then calculated and calibrated reflection coefficient. Finally, we estimate the continuous soil moisture in the fixed area per half hour using the reflection coefficient. The results show that the estimated soil moisture changes are largely consistent with the in situ soil moisture data except rainy days in which soil moisture changes rapidly and the mean absolute error of the estimation is less than 2.37%. This experiment demonstrates that the BDS GEO satellites represent an important source of data for use in GNSS reflectometry.     

低管电压结合迭代重建技术配合不同对比剂注射方案在冠状动脉CTA成像中的可行性研究

目的 探讨迭代重建技术（IDose⁴）在降低管电压配合不同对比剂碘流率注射方案下行冠状动脉CT血管成像（CCTA）的可行性。方法 对10只实验猪分别重复9次CCTA扫描[管电压分别为120 kV（A₁）、100 kV（A₂）、80 kV（A₃）,对比剂碘流率分别约为1300 mgI/s（B₁）、1000 mgI/s（B₂）及750 mgI/s（B₃）,两两组合成9组方案];对原始图像分别采用滤波反投影法（FBP）及IDose⁴重建,将A₁B₁+FBP重建设为对照组。比较各组图像的主、客观指标。结果 在相同条件下,IDose⁴重建较FBP重建显著降低图像噪声、提高SNR及CNR（P均<0.001）。随管电压及碘流率的降低,图像噪声增大,SNR、CNR降低。采用IDose⁴重建,除A₃B₁、A₃B₂、A₃B₃组噪声仍明显增加外（P均<0.05）,其余各组噪声、SNR、CNR均与对照组无统计学差异（P均>0.05）。采用FBP重建,A₃B₁、A₃B₂、A₃B₃组及A₂B₃组冠状动脉远段可诊断率较对照组明显减低（P均<0.05）,而经IDose⁴重建后,除A₃B₃组冠状动脉远段可诊断率仍明显低于对照组（P=0.015）外,余各组均明显改善,与对照组无统计学差异（P均>0.05）。结论 采用IDose⁴重建结合低管电压及低碘流率行CCTA是可行的。     

MRI评价壁虎活性成分对兔VX2肝移植瘤的疗效

目的 探讨MRI评价壁虎活性成分对兔VX2肝移植瘤疗效的价值.方法 用中药无蹼壁虎提取分离得到抗肿瘤活性成分,制作成卵磷脂脂质体.建立兔VX2肝移植瘤模型,12天后肿瘤生长至0.5～1.5 cm.将16只荷瘤兔随机分为活性成分组和生理盐水组,分别经耳缘静脉注射壁虎活性成分0.3 mg/kg和0.9%生理盐水10 ml/kg,每天1次,持续用药12天.于用药前1天及用药后第3、7、12天行MR检查,测量肿瘤体积并观察T1WI、T2WI的信号特征,用药第12天后行病理学检查.结果 活性成分组于用药第3天肿瘤组织内信号开始不均匀,出现片状长T1长T2信号;而生理盐水组肿瘤组织信号尚均匀,无明显长T1长T2信号.用药第7天,生理盐水组肿瘤内部也可见长T1长T2信号.用药第7、12天MRI测量肿瘤体积,活性成分组与生理盐水组比较差异有统计学意义(P<0.05).用药12天MRI和病理测量的肿瘤体积分别为(4.74±1.67)cm3和(5.48±1.09)cm3,差异无统计学意义,但具有较高相关性 (r=0.87,P=0.0222).结论 MRI能准确、无创性反映壁虎活性成分对兔VX2移植瘤的抑制作用.     

Weighted spectral reconstruction method for discrimination of bacterial species with low signal-to-noise ratio Raman measurements

Raman spectroscopy is a label-free and non-destructive spectroscopic technique that has been explored for bacterial identification. However, noise often interferes with the interesting Raman peaks because the Raman signal is inherently weak, especially for bacterial samples. Although this problem can be solved by increasing the exposure time or the power of the excitation laser, a longer acquisition time is required or the risk of sample damage is increased. In contrast, short exposure time and low laser power often lead to inadequate acquisition of Raman scattering, in which the Raman spectra with low signal-to-noise ratio (SNR) is difficult to be further analyzed. In order to quickly and accurately characterize biological samples by using low SNR Raman measurements, a weighted spectral reconstruction based method was developed and tested on Raman spectra with low SNR from 20 bacterial samples of two species. Principal component analysis followed by support vector machine was applied on the reference Raman spectra and the spectra recovered from the low SNR Raman measurements by the proposed method, the traditional spectral reconstruction method, and four other commonly used de-noising methods for the discrimination of bacterial species. The results showed that a classification accuracy of 90% was achieved based on our method, which was comparable to that of the reference Raman spectra and showed significant advantages over other spectral recovery methods. Therefore, the weighted spectral reconstruction method can preserve the most biochemical information for the bacterial species'' identification while removing the noise from the low SNR Raman spectra, in which the advantages of lesser sample damage and shorter acquisition time would promote wider biomedical applications of Raman spectroscopy.

Raman spectra recovered from low SNR Raman measurements by weighted spectral reconstruction method show excellent preservation of information about bacterial identification.     

超低剂量下不同迭代重建技术在肺动脉成像中的优化

目的 探讨不同迭代重建技术在超低剂量肺动脉成像中的应用价值。方法 对30例临床疑似肺动脉栓塞患者行CT肺动脉成像,扫描采用80 kV管电压并开启自动管电流调制技术,分别采用滤波反投影法(FBP)、iDOSE⁴、迭代模型重建(IMR)重建图像。采用5分制评价肺动脉主干及其分支的图像质量,测量计算图像噪声值、SNR、CNR,记录CT容积剂量指数(CTDIvol)、剂量长度乘积(DLP)、计算有效剂量(ED)。比较不同重建技术图像噪声、SNR、CNR及主观图像质量。结果 30例患者的平均体质量指数(BMI)为(25.12±2.48)kg/m²;平均CTDIvol为(0.78±0.28)mGy;平均DLP为(30.46±11.34)mGy·cm,平均ED为(0.43±0.16)mSv。IMR、iDOSE⁴、FBP图像噪声依次增高(P<0.05),SNR、CNR依次降低(P<0.05),CT值差异无统计学意义(P>0.05)。IMR、iDOSE⁴图像的主观评分显著高于FBP(P<0.05);IMR、iDOSE⁴图像可诊断率高于FBP(P<0.05),IMR图像优良率高于iDOSE⁴(P<0.05)。结论 采用80 kV联合IMR可保证肺动脉成像较高的图像质量,同时大大降低患者辐射剂量。     

Estimation of volumetric surface soil moisture content using microwave-calibrated soil evaporative efficiency information

ABSTRACT

Soil moisture (SM) is a critical variable in energy and water partitioning at the interface between the land surface and atmosphere. In this study, we provided a robust method to retrieve soil moisture using optimal remotely sensed soil evaporative efficiency (SEE) information. Specifically, SEE was deduced from the triangle space constituted by remotely sensed land surface temperature (LST) and fractional vegetation cover (Fc). Theoretical solutions of the dry and wet boundaries were derived by annual-scale optimization and microwave SM calibration. The two limits of SM were obtained by linear fit function between SEE and microwave-based SM. The proposed method was validated at the Liaoning Province of China in the year 2011 by using MODerate Resolution Imaging Spectroradiometer (MODIS) and Soil Moisture and Ocean Salinity (SMOS) satellite images as input. Results indicated that the new method has not only bypassed the complex parametric scheme in the calculation of boundaries within the LST-Fc feature space but also performed superior in the estimation of soil moisture status at all-sky days. Besides, the optimal method has reproduced the spatial and temporal patterns of soil moisture reasonably well, with a root mean square error of 0.07 m³ m^?3. Therefore, the proposed method can be regarded as a suitable tool to provide accurate and continuous monitoring of soil moisture.     

调整空气距离与骨距离参数减少足部双能量CT痛风石成像指甲伪影

目的 探讨通过调整空气距离与骨距离参数减少足部双能量CT(DECT)痛风石成像指甲伪影的可行性。方法 收集20例痛风患者进行足部DECT扫描,分别采用标准空气距离与骨距离参数、调整后空气距离与骨距离参数对图像进行重建,应用自动体积计算软件测量痛风石体积及指甲伪影体积,并进行统计学分析。结果 20例患者均存在痛风石及指甲伪影。采用标准参数检测到66个痛风石,63个指甲伪影。调整参数后共检测到66个痛风石,31个指甲伪影。调整参数后痛风石体积[0.07(0.03~0.12)cm³]与标准参数下[0.07(0.03~0.16)cm³]的差异无统计学意义(Z=-0.2,P=0.84),指甲伪影体积[(0.02±0.02)cm³]较标准参数下[(0.07±0.06)cm³]明显减小(t=4.56,P<0.01)。结论 通过调整空气距离与骨距离参数可以明显减少DECT痛风石成像中的指甲伪影,且不影响痛风石的观察。     

人脑血氧水平依赖信号有源仿真和成像

目的 对人脑血氧水平依赖（BOLD）信号进行仿真并成像，以之作为金标准和标准信号，基于信号成像灰度幅值变化评价脑功能磁共振成像（fMRI）质量和检出率。方法 设计一种能有源模拟人脑BOLD的激发电路，实现不同电流幅值、不同频率、不同占空比的稳定矩形波输出，在时间域内仿真人脑BOLD信号。结果 3台不同型号、不同场强MR皆有稳定的矩形波输入，且检出率一致。结论 同一设备对同一刺激模式检出率相近，可作为已知且确定信号的参考标准，定量分析MR系统对BOLD信号的检出率和一致性。     

A KBr-impregnated paper substrate as a sample probe for the enhanced ATR-FTIR signal strength of anionic and non-ionic surfactants in an aqueous medium

Herein, we report a KBr-impregnated paper substrate as a sample probe to enhance the attenuated total reflection-Fourier transform infrared (ATR-FTIR) signal strength of anionic surfactants (AS) and non-ionic surfactants (NS) in an aqueous solution. The mechanism for the sensing of AS and NS is based on the strong interaction of surfactants with the silicate groups (SiO₄⁴⁻) of the KBr-impregnated paper substrate. The role of SiO₄⁴⁻ on the surface of the paper is to enhance the adsorption of AS and NS, resulting in improved IR signal intensities for the target analytes. The improved signal intensity at 1253 cm⁻¹ (SO₄²⁻, symmetric stretching) for AS and 1114 cm⁻¹ (C–O–C, stretching vibration) for NS were selected for quantification. SEM-EDX was employed to determine the elemental compositions of pre- and post-adsorbed AS and NS on glass fibre filter paper (GFF). The linear range for the determination of AS and NS was 10–100 μg L⁻¹ with a method detection limit (MDL) of 4 μg L⁻¹ and method quantification limit (MQL) of 12 μg L⁻¹. The good relative recovery of 71.4–109.7% and the interference studies showed the selectivity of the method for the determination of AS and NS in environmental water and commodity samples. The advantages of this method include its cost-effectiveness, enhanced sensitivity, disposability and accessibility of the paper substrate.

Flow diagram of the procedures for the analysis of surfactants using modified GFF paper substrate.     

Qualitative and Quantitative Seed Characteristics Diversity from Girnar Reserve Forest,Gujarat, India

Seeds of 97 plant species were studied for morphological characteristics after collection during botanical field visits from Girnar Reserve Forest, Gujarat, India. There was a significant variation in quantitative characters of seeds, while qualitative traits also exhibited great diversity. Seeds of trees showed highest values for all quantitative features measured as volume, length, width, thickness and weight among all other botanical group such as climbers, herbs, undershrubs and shrubs during the study. The range of seed volume varied from 0.01 to 21.48 cm³ for 63 trees, 0.23 to 1.42 cm³ for 12 herbs, 0.31 to 0.72 cm³ for 10 undershrubs, 0.35 to 0.93 cm³ for 9 shrubs, and 0.37 to 1.77 cm³ for 3 climbers. Fruiting time varied for species within groups, but mostly for all plants seed collection time was during dry season after fruit ripening. In the principal component multivariate analysis, only one principal component had an Eigen value above one and hence found significant, which explained 73 % morphological variation in the whole data set. The separation of 97 species using PCA and cluster analysis was mostly in agreement with their group specific taxonomical identification of each plant. This study not only provided information related to seed morphology and taxonomy, but can be used effectively in diversity study as well as social forestry programmes.     

Diffusion MRI signal reconstruction with continuity constraint and optimal regularization

In diffusion MRI, the reconstruction of the full Ensemble Average Propagator (EAP) provides new insights in the diffusion process and the underlying microstructure. The reconstruction of the signal in the whole Q-space is still extremely challenging however. It requires very long acquisition protocols, and robust reconstruction to cope with the very low SNR at large b-values. Several reconstruction methods were proposed recently, among which the Spherical Polar Fourier (SPF) expansion, a promising basis for signal reconstruction. Yet the reconstruction in SPF is still subject to noise and discontinuity of the reconstruction. In this work, we present a method for the reconstruction of the diffusion attenuation in the whole Q-space, with a special focus on continuity and optimal regularization. We derive a modified Spherical Polar Fourier (mSPF) basis, orthonormal and compatible with SPF, for the reconstruction of a signal with continuity constraint. We also derive the expression of a Laplace regularization operator in the basis, together with a method based on generalized cross validation for the optimal choice of the parameter. Our method results in a noticeable dimension reduction as compared with SPF. Tested on synthetic and real data, the reconstruction with this method is more robust to noise and better preserves fiber directions and crossings.     

自适应统计迭代重建算法在儿童头部CT扫描中的应用

目的 探讨自适应统计迭代重建(ASiR)算法在儿童头部CT扫描中的应用价值。方法 对1个水模进行CT扫描,管电压100 kV,管电流分别为200、180、160、140、120和100 mA,ASiR比例分别设置为0、10%、20%、30%、40%、50%,采用FBP和ASiR迭代重建两种重建算法进行图像重建,比较不同条件下图像CNR、SNR和图像噪声。将80例接受头部CT扫描的患儿分为对照组(n=40)和试验组(n=40)。对照组采用管电压100 kV、管电流200 mA,FBP重建算法进行图像重建;试验组采用管电压100 kV、管电流140 mA,分别采用FBP和ASiR两种重建法进行图像重建;将重建后的图像分别记为试验FBP亚组和试验ASiR亚组;对两组中图像的CNR、SNR、图像噪声、CTDIvol、DLP、ED进行比较。结果 水模研究中,采用ASiR(30%)、管电流140 mA、ASiR算法重建图像的SNR、CNR及空气噪声值与管电流 200 mA、FBP重建图像最为接近。对照组与试验ASiR亚组图像的图像噪声、灰白质CNR和灰质SNR值差异均无统计学意义(P均>0.05);对照组和试验ASiR亚组图像的噪声、灰质SNR、灰白质CNR均优于试验FBP亚组,且差异均有统计学意义(P均<0.001)。结论 采用ASiR重建算法的头部CT扫描,既可降低患儿接受的辐射剂量,又保证了图像质量,具有较高的临床应用价值。     

基于心电门控技术的体素内不相干运动成像评价正常肝脏图像质量

目的 探讨体素内不相干运动（IVIM）DWI条件下心电门控技术对肝脏图像质量和参数测量的影响。方法 前瞻性收集20名志愿者行IVIM DWI,采用自由呼吸和心电门控扫描,并对所得图像进行主观评分,测量肝左、右叶SNR、ADC值及IVIM各参数值[真扩散系数（D）、假扩散系数（D^*）、灌注分数（f）]。采用Wilcoxon符号秩和检验比较肝脏图像主观质量评分,以配对t检验比较SNR、ADC值及IVIM各参数值,以Bland-Altman方法评价各参数值的一致性。结果 采用心电门控技术所得图像质量主观评分明显高于自由呼吸（P均<0.01）;不同b值时采用心电门控技术测得肝左叶SNR均高于自由呼吸图像（P<0.01）,肝左叶ADC、f值均低于自由呼吸图像（P均<0.05）,而D值则高于自由呼吸图像（P<0.05）。采用心电门控技术肝左叶D、D^*和f值的一致性好于自由呼吸图像。结论 心电门控IVIM DWI可获得较好的图像质量,有效克服心脏搏动对肝左叶各参数值数据测量的影响。     

正弦图确定迭代重建在评价冠状动脉支架中的应用

目的 与传统滤波反投影(FBP)重建比较,评价Flash双源CT基于原始数据的正弦图确定迭代重建(SAFIRE)在冠状动脉支架中的应用价值。 方法 对54例患者冠状动脉支架术后行DSCT冠状动脉成像,比较FBP、SAFIRE(1~5)重建6组图像的平均CT值、SNR、支架内CT值净增比(SAIR)、图像质量主观评分、支架显示情况等。 结果 主动脉根部、支架内、支架上方冠状动脉的平均CT值差异均无统计学意义(P均>0.05)。SAIR、SNR差异有统计学意义(P均<0.05),FBP重建SAIR值最大,SAFIRE 3重建SAIR值最小;SAFIRE 3的SNR值最大。FBP与SAFIRE重建图像质量主观评分差异有统计学意义(P<0.05),SAFIRE 3主观评分最高[(3.24±0.57)分]。FBP与SAFIRE重建对于病灶的显示情况基本一致。 结论 与传统的FBP重建比较,SAFIRE重建可明显降低冠状动脉支架图像噪声,改善图像质量,更清晰显示支架内斑块。SAFIRE强度采用机器默认的重建强度3图像质量最佳。     

新双源CT冠状动脉CTA不同扫描参数与重建算法获得图像质量的体模研究

目的 探讨基于原始数据域的迭代重建(SAFIRE)算法与滤波反投影(FBP)算法冠状动脉CT血管造影(CCTA)图像质量的差异。方法 对置入模拟左、右冠状动脉的仿真体模,采用两组管电压(100 kV、120 kV)行双源CT检查,对冠状动脉原始图像在工作站上分别进行FBP及SAFIRE两种算法的图像重建,对不同管电压及不同管电流组内图像质量指标SNR、CNR、CT值标准差进行t检验;相同管电压不同重建算法,不同管电压相同管电流SAFIRE重建方式的两组SNR、CNR、CT值标准差及CT值采用配对t检验。结果 两组管电压扫描后经SAFIRE重建的冠状动脉图像质量均明显优于FBP重建;两组管电压两种重建算法图像,随着管电流的增加,200~360 mA图像质量呈改善趋势,管电流340 mA及以上图像质量指标趋于稳定;不同管电压相同管电流SAFIRE重建算法成像其图像质量比较,CNR、SNR、CT值标准差差异均有统计学意义(t=5.36、2.49、21.82,P均<0.05)。结论 随着扫描参数(管电流与管电压)的增加,图像质量随之上升,但到达一定值后图像质量趋于稳定;采用SAFIRE在相同扫描条件下可以明显提高图像质量。     

Compressed sensing to accelerate magnetic resonance spectroscopic imaging: evaluation and application to 23Na-imaging of mouse hearts

Background

Magnetic Resonance Spectroscopic Imaging (MRSI) has wide applicability for non-invasive biochemical assessment in clinical and pre-clinical applications but suffers from long scan times. Compressed sensing (CS) has been successfully applied to clinical ¹H MRSI, however a detailed evaluation of CS for conventional chemical shift imaging is lacking. Here we evaluate the performance of CS accelerated MRSI, and specifically apply it to accelerate ²³Na-MRSI on mouse hearts in vivo at 9.4 T.

Methods

Synthetic phantom data representing a simplified section across a mouse thorax were used to evaluate the fidelity of the CS reconstruction for varying levels of under-sampling, resolution and signal-to-noise ratios (SNR). The amplitude of signals arising from within a compartment, and signal contamination arising from outside the compartment relative to noise-free Fourier-transformed (FT) data were determined. Simulation results were subsequently verified experimentally in phantoms and in three mouse hearts in vivo.

Results

CS reconstructed MRSI data are scaled linearly relative to absolute signal intensities from the fully-sampled FT reconstructed case (R² > 0.8, p-value < 0.001). Higher acceleration factors resulted in a denoising of the reconstructed spectra, but also in an increased blurring of compartment boundaries, particularly at lower spatial resolutions. Increasing resolution and SNR decreased cross-compartment contamination and yielded signal amplitudes closer to the FT data. Proof-of-concept high-resolution, 3-fold accelerated ²³Na-amplitude maps of murine myocardium could be obtained within ~23 mins.

Conclusions

Relative signal amplitudes (i.e. metabolite ratios) and absolute quantification of metabolite concentrations can be accurately determined with up to 5-fold under-sampled, CS-reconstructed MRSI. Although this work focused on murine cardiac ²³Na-MRSI, the results are equally applicable to other nuclei and tissues (e.g. ¹H MRSI in brain). Significant reduction in MRSI scan time will reduce the burden on the subject, increase scanner throughput, and may open new avenues for (pre-) clinical metabolic studies.