Towards an operational method for land surface temperature retrieval from Landsat 8 data

Land surface temperature (LST) is a key parameter in the physics of land surfaces through the processes of energy and water exchange with the atmosphere. For Landsat data with only one thermal infrared channel (Landsat 4 to Landsat 7), LST cannot actually be retrieved, and external data sources, such as meteorological observations or Moderate Resolution Imaging Spectroradiometer (MODIS) data, are needed to obtain the water vapour content parameter (an important input parameter for the LST retrieval algorithm); this results in limitations on deriving LST. However, the band designations of the Landsat 8 sensors enable the derivation of LST from the Landsat 8 data. This article demonstrates an LST retrieval methodology that makes use of only Landsat 8 image data. In this methodology, the split-window covariance-variance ratio (SWCVR) technique is introduced to derive water vapour content from Landsat 8. A comparison between the retrieved LST and the in situ LST measurements shows good accuracy, with a root mean squared error (RMSE) of 0.83 K. The fact that the proposed LST estimation method utilizing solely Landsat 8 image data does not rely on any external data is a significant advantage for the development of an operational Landsat 8 LST product generating system.     

Latent heat flux estimation using trapezoidal relationship between MODIS land surface temperature and fraction of vegetation – application and validation in a humid tropical region

The present study was taken up with the objective of developing a methodology for estimation of actual evapotranspiration (AET) using only satellite data. Accordingly, an algorithm based on the popular Priestley–Taylor method was developed. While previous studies have assumed a triangular relationship between land surface temperature (LST) and fraction of vegetation (FV) to calculate the Priestley–Taylor parameter (φ), a trapezoidal relationship was adopted in the present study to enable applications in forested regions in the humid tropics. The developed algorithm was applied to the humid tropical Mae Klong region, Thailand, and latent heat flux (λ_ET) estimates were validated with measurements made at a flux tower located at the centre of the region. Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing satellite data products corresponding to the study area were used to derive various inputs required by the algorithm. Comparison of estimated and measured fluxes on five cloud-free days in 2003 yielded root mean square error (RMSE) of 64.73 W m^?2 which reduced to 18.65 W m^?2 when one day was treated as an outlier. The methodology developed in this study derived inputs only from satellite imagery and provided reasonably accurate estimates of latent heat flux at a humid tropical location.     

How can the variability in ultrasound measurement of intima-media thickness be reduced? Studies of interobserver variability in carotid and femoral arteries

A critical component in scientific studies of most biological variables is the variation or error in measurements which leads to non-identical results of repeated measurements from the same subject. The aim of this study was to investigate whether the interobserver error (s) in measurement of intima-media thickness (IMT) in carotid and femoral arteries could be decreased if the mean value obtained using two ultrasound images from each of the right and left arteries was used in the analyses instead of the mean value obtained using images from only the right artery. In addition, we wished to evaluate two different reading procedures, one based on manual tracing of echo interfaces and the other on automated edge detection. In a methodological study, 50 subjects were examined with ultrasound twice in the same day by two independent laboratory technologists. The ultrasound images were analysed in two ways: using a computerized manual tracing analysing system and an automated analysing system. When both right and left carotid arteries were examined (manual reading), the interobserver error was smaller than that determined for the examination of only the right artery, for IMT_mean in both the common carotid artery (P = 0·06) and the carotid artery bulb (P<0·05). The interobserver error was also significantly smaller for double-sided vs. one-sided examination with automated reading of IMT_mean in the common carotid artery (P<0·01) and in the carotid artery bulb (P<0·01). The coefficient of variation (CV) for measurement in the common carotid artery decreased from 8·6% (one-sided, manual reading) to 5·3% (double-sided, automated reading). The interobserver error in measurement of IMT in the common femoral artery did not improve by examination of both right and left arteries. The results from this study show that the interobserver errors in measurement of IMT can be decreased by using ultrasound images from both the right and the left carotid arteries, and that the use of an automated analysing system greatly simplifies the reading of ultrasound images with sustained low variability.     

Analysis of Landsat-8 OLI imagery for land surface water mapping

The normalized difference water indices (NDWIs) were successfully used in map land surface water mapping (LSWM) from Landsat series multispectral images. This paper evaluates the potential of the recent Landsat satellite (Landsat-8) Operational Land Imager (OLI) multispectral images for LSWM using three NDWI models. We tested the accuracy and robustness of the three OLI NDWI models in the Yangtze River Basin and the Huaihe River Basin in China. The results demonstrate that the three OLI NDWI models achieve an overall accuracy of more than 95%, a kappa coefficient of 0.89 and a producer’s accuracy of 95% for LSWM. The results also demonstrate that the NDWI model using the green band (Band 3) and the SWIR1 band (Band 6) (referred to as NDWI_O6,3) of the OLI sensor has a higher LSWM accuracy than the other two NDWI models.     

Comparison of surface reflectance derived by relative radiometric normalization versus atmospheric correction for generating large-scale Landsat mosaics

Generating large-scale Landsat mosaics of surface reflectance is challenging because of the tediousness arising from atmospheric correction for a large number of scenes. To find out an alternative approach, we conducted an empirical investigation to compare the surface reflectance derived by relative radiometric normalization versus atmospheric correction using four pairs of adjoining Landsat Thematic Mapper/Enhanced Thematic Mapper Plus scenes in northern Canada. Each image was first atmospherically corrected to convert top-of-atmosphere radiance to surface reflectance. One of the converted images in each pair was then respectively used as a reference to radiometrically normalize the other original one for deriving surface reflectance. Comparison of the surface reflectance derived by these two different approaches indicates that they can match reasonably well for different landscapes, atmospheric conditions, and sensors, and the difference measured by root mean square error is no more than 0.0098 for the visible band (Band 3), 0.0271 for the near-infrared band (Band 4), and 0.022 for the middle-infrared band (Band 5). Given such a small difference, we would expect that relative radiometric normalization may be used as an alternative approach for reliable and fast retrieval of surface reflectance from Landsat data for generating mosaics of surface reflectance over large areas, overcoming the tediousness arising from atmospheric correction for a large number of scenes.     

适应性统计迭代重建技术降低胸部低剂量CT图像噪声的效果

目的 探讨适应性统计迭代重建(ASIR)技术降低胸部低剂量CT图像噪声的效果。方法 选取180例接受胸部CT检查的患者随机分为3组,采用自动毫安调节技术行胸部CT扫描。3组预设噪声指数(NI)分别为20、30及40,对每组图像均行ASIR为0、30%、50%及80%重建成4种图像。记录3组的CT剂量指数(CTDI_vol)、剂量长度乘积(DLP)并估算有效剂量(ED)。由2名医师对图像质量采用5分制进行评估,并用Kappa检验评价观察者间的一致性。结果 3组图像的质量均满足临床诊断要求,观察者间的评估具有一致性(Kappa值为0.485)。第一组的CTDI_vol为(3.41±1.28)mGy,第二组为(1.40±0.58)mGy,第三组为(0.76±0.46)mGy。第三组的ED降至(0.35±0.20)mSv。第二组ASIR₅₀的图像噪声和第三组的ASIR₈₀比较差异无统计学意义。结论 ASIR技术有助于降低胸部低剂量图像的噪声,在保证诊断图像质量的前提下,ED可降至0.35 mSv。     

Determining meaningful changes in hip abductor muscle strength obtained by handheld dynamometry

This study quantified the minimal detectable change (MDC), defined as the smallest change that falls outside the expected range of error, for isometric hip abductor muscle strength in healthy persons obtained with a handheld dynamometer (HHD). Ninety volunteers (45 males and 45 females) between the ages of 22 and 70 years participated in the study. Bilateral measurements of isometric hip abductor muscle force were obtained with a digital HHD using a “make” test with the subject in supine. All measurements were obtained by one female examiner. The muscle force measurements were normalized to a volunteer's body weight (BW). Intratester reliability of hip abductor muscle force was estimated by using an intraclass correlation coefficient (ICC_3,1) and calculated to be 0.96. The standard error of measurement (SEM) was 2 Newtons. The MDC was calculated by using an appropriate formula that included a 95% level of confidence. The MDC₉₅ was 5.4% BW for males and 5.3% BW for females. If a person's isometric hip abductor muscle force production changes less than the MDC₉₅ value between measurements, then the muscle force production is within measurement error, and it can be determined there has been no change in the strength of hip abductor muscles.     

An open-source method of constructing cloud-free composites of forest understory temperature using MODIS

Surface air temperature (T_air) is a critical driver of ecosystem processes and phenological dynamics, and can be estimated in near-real time with satellite remote sensing. However, persistent cloud cover often creates large spatial and temporal gaps in our observation records. Previous studies have successfully mapped T_air; however, the challenges of mapping forest understory temperatures (T_ust) are relatively unexplored. This study describes a methodology for constructing cloud-free composites of T_ust at 250 m spatial resolution. We used generalized linear models to correlate daily average T_ust with ground-surveyed forest structural characteristics and land surface temperature (LST) obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS). Models were applied to all four daily MODIS overpasses and combined in to a single image to maximize cloud-free spatial coverage. Pixel temperatures within the remaining cloud gaps were estimated using a temporal averaging algorithm that incorporated a novel approach for factoring the relative cloudiness between days. Models predicted T_ust to within 1.5°C (R² ~ 0.87), with an overall final map accuracy having a mean absolute error of 2.2°C. Maps were produced for two growing seasons using in situ observation data from forested sites throughout the Rocky Mountains of Alberta, Canada. By avoiding complex physical models, our procedure is computationally efficient and capable of processing large volumes of data using open-source programming languages and desktop computers.     

Deep Learning Estimation of Median Nerve Volume Using Ultrasound Imaging in a Human Cadaver Model

Median nerve swelling is one of the features of carpal tunnel syndrome (CTS), and ultrasound measurement of maximum median nerve cross-sectional area is commonly used to diagnose CTS. We hypothesized that volume might be a more sensitive measure than cross-sectional area for CTS diagnosis. We therefore assessed the accuracy and reliability of 3-D volume measurements of the median nerve in human cadavers, comparing direct measurements with ultrasound images interpreted using deep learning algorithms. Ultrasound images of a 10-cm segment of the median nerve were used to train the U-Net model, which achieved an average volume similarity of 0.89 and area under the curve of 0.90 from the threefold cross-validation. Correlation coefficients were calculated using the areas measured by each method. The intraclass correlation coefficient was 0.86. Pearson's correlation coefficient R between the estimated volume from the manually measured cross-sectional area and the estimated volume of deep learning was 0.85. In this study using deep learning to segment the median nerve longitudinally, estimated volume had high reliability. We plan to assess its clinical usefulness in future clinical studies. The volume of the median nerve may provide useful additional information on disease severity, beyond maximum cross-sectional area.     

The compensation for asynchronous cardiac quiescence in coronary wall MR imaging

The aim of the present study was to assess the incremental benefit of compensating asynchronous cardiac quiescence in coronary wall MR imaging. With the approval of IRB, black-blood coronary wall MR imaging was performed on 30 older subjects (90 coronary wall segments). For round 1 coronary wall MR imaging, acquisition windows were traditionally set within rest period_4-chamber. Totally 51 of 90 images were ranked as “good” images and resulted in an interpretability rate of 57 %. Then, an additional cine-MR was centered at coronary segments to obtain rest period_{cross-sectional}. The rest period_overlap (the intersection between rest period_4-chamber and rest period_{cross-sectional}) was measured for each coronary segment. The “good” images had a longer rest period_overlap and higher acquisition coincidence rate (the percentage of acquisition window covered by the rest period_overlap) than “poor” images. Coronary wall rescans (round 2) were completed at 39 coronary segments that were judged as having “poor” images in round 1 scans. The acquisition window was set within the rest period_overlap. For the round 2 images, 17 of 39 (44 %) coronary segments were ranked as “good” images. The overall interpretability rate (68 of 90, 76 %) was significantly higher than that of the round 1 images alone. Our data demonstrated that asynchronous cardiac quiescence adversely affects the performance of coronary wall MR imaging. Individualizing acquisition windows based on multi-plane cine-MR helps to compensate for this motion discrepancy and to improve image quality.     

SPECT/CT图像配准测试方法

目的 提出SPECT/CT一体机中SPECT和CT图像配准精度的测试方法。方法 试验模体由立方体构形的8个点源构成,点源由放射性同位素和碘对比剂制备,在SPECT和CT上均可清晰成像,模体构形和尺寸可代表典型的临床应用条件。首先选用具有临床代表性的实验条件和参数,对模体分别行SPECT和CT成像。对图像分别进行分析,得到点源空间坐标,计算配准精度;以点源最大值像素点为中心,得到3个坐标方向的一维分布,分别计算分布重心作为对应方向的坐标值。结果 本文提出的方法在GE和Philips的主流SPECT/CT产品上进行验证,点源都可在SPECT和CT图像中完整成像,测试和分析方法的精度达0.1 mm以上。结论 该实验方法可为SPECT/CT产品性能评估和质量控制提供方法基础。     

Assessment of boreal forest height from WorldView-2 satellite stereo images

WorldView-2 (WV2) satellite stereo images were used to derive a digital surface model, which together with a high-resolution digital terrain model from airborne laser scanning (ALS) were used to estimate forest height. Lorey’s mean height (H_L) could be estimated with a root mean square error of 1.5 m (8.3%) and 1.4 m (10.4%), using linear regression, at the two Swedish test sites Remningstorp (Lat. 58°30?N, Long. 13°40?E) and Krycklan (Lat. 64°16?N, Long. 19°46?E), which contain hemi-boreal and boreal forest. The correlation coefficients were r = 0.94 and r = 0.91, respectively. The 10 m sample plots were 175 in Remningstorp and 282 in Krycklan. It was furthermore found that WV2 data are sometimes unstable for canopy top height estimations (ALS height percentile 100, p100) and that the reconstructed heights are generally located below the actual top height. The WV2 p60 was found to correlate best with ALS p70 in Remningstorp, while WV2 p95 was found to correlate best with ALS p70 in Krycklan, and it moreover reached the highest correlation for all other estimated variables, at both test sites. It was concluded that WV2 p95 height data overall represent approximately the forest height ALS p70. The overall high correlation coefficients above 0.90 at both test sites, with different forest conditions, indicate that stereo matching of WV2 satellite images is suitable for forest height mapping.     

Use of Ferric Chloride to Identify Salicylate-Containing Poisons

Objective: Ferric chloride (FeCl₃) is used to qualitatively test the urine of patients with presumed salicylate exposure. FeCl₃ testing of an unidentified poison might provide evidence of salicylate exposure in situations where FeCl₃ urine testing cannot be used. Such situations include the absence of a urine sample, immediately after ingestion before urine contains a detectable quantity of salicylate, or for patients chronically using salicylates for which FeCl₃ testing is unhelpful. This study seeks to determine if FeCl₃ can be used to identify salicylate-containing products. Methods: We assessed the reactivity of FeCl₃ with commercially available salicylate-containing products. We applied 0.1 mL of 10% FeCl₃ solution to each of 15 various salicylate-containing products including: regular and buffered acetylsalicylic acid, bismuth subsalicylate, methylsalicylate, physostigmine salicylate, salicylic acid, trolamine salicylate, and herbal tablets with salicin-containing white willow bark (Salix sp.). These products tested were: regular and enteric-coated pills (n=4), powder (n=1), topical creams (n=5), topical liquids (n=4), and intravenous solution (n=1). FeCl₃ was applied to crushed tablets and added directly to liquids and creams. Fifteen salicylate-free controls including liquids, pills, and creams similar in appearance to experimental samples were also tested. Three blinded physicians familiar with FeCl₃ testing independently observed the addition of FeCl₃ to each sample and rated a positive or negative result. Results: All salicylate-containing products were interpreted to be clearly FeCl₃ positive and all control samples were interpreted to be clearly FeCl₃ negative. Conclusion: Salicylate-containing products may be identified using FeCl₃. When using FeCl₃ testing as described herein, only a positive test result should be applied; any negative result should be considered inconclusive.     

Robust non-contact peripheral oxygenation saturation measurement using smartphone-enabled imaging photoplethysmography

We propose a robust non-contact method to accurately estimate peripheral oxygen saturation (SpO₂) using a smartphone-based imaging photoplethysmography. The method utilizes the built-in color camera as a remote sensor and the built-in flashlight as illumination to estimate the SpO₂. Following the ratio of ratios between green and red channels, we introduce a multiple linear regression algorithm to improve the SpO₂ estimation. The algorithm considers the ratio of ratios and the reflectance images recorded at the RGB channels during a calibration process to obtain a set of weighting coefficients to weigh each contributor to the final determination of SpO₂. We demonstrate the proposed smartphone-based method of estimating the SpO₂ on five healthy volunteers whose arms are conditioned by a manual pressure cuff to manipulate the SpO₂ between 90∼100% as detected simultaneously by a medical-grade pulse oximeter. Experimental results indicate that the overall estimated error between the smartphone and the reference pulse oximeter is 0.029 ± 1.141%, leading to a 43% improvement over the conventional ratio of ratios method (0.008 ± 2.008%). In addition, the data sampling time in the current method is 2 seconds, similar to the sampling cycle used in the commercial medical-grade pulse oximeters.     

The twitch interpolation technique for the estimation of true quadricepsmuscle strength

The aim of this study was to examine the reliability of the twitchinterpolation technique when used to estimate the true isometric knee extensor muscle strength.This included an examination of whether submaximal activation causes any bias in the estimationof the true muscle strength and an examination of the precision of the method. Twenty healthysubjects completed three contraction series, in which the sub-jects were told to perform as if theirvoluntary strength was 60%, 80% or 100% of that determined by a maximalvoluntary contraction (MVC). Electrical muscle stimulations were given at each of five differentcontraction levels in each series. At torque levels above 25% of MVC the relationshipbetween torque and twitch size could be approximated to be linear. The true muscle strength(TMS) could therefore be estimated using linear regression of the twitch–torquerelationship to the torque point of no twitch in each of the three series, termed TMS₆₀, TMS₈₀ and TMS₁₀₀. The TMS₈₀ was slightly lower (P<0·01), median 94% (IQ range 87–101%) of the TMS₁₀₀. The TMS₆₀ was median 99% (IQ range 83–125%)(NS) of TMS₁₀₀, but a few severe outliers were ob-served. In conclusion, we foundthe reliability of the method acceptable for many research purposes, if series with estimated centralactivation of below 40–50% were excluded. The only moderate precision and theslightly lower estimations in subjects applying submaximal does, however, limit its usefulness.     

Estimating the CDOM absorption coefficient in tropical inland waters using OLI/Landsat-8 images

Coloured dissolved organic matter (CDOM) is the most abundant dissolved organic matter (DOM) in many natural waters and can affect the water quality, such as the light penetration and the thermal properties of water system. So the objective of this letter was to estimate the CDOM absorption coefficient at 440 nm, a_CDOM(440), in Barra Bonita Reservoir (São Paulo State, Brazil) using operational land imager (OLI)/Landsat-8 images. For this two field campaigns were conducted in May and October 2014. During the field campaigns remote sensing reflectance (R_rs) were measured using a TriOS hyperspectral radiometer. Water samples were collected and analysed to obtain the a_CDOM(440). To predict the a_CDOM(440) from R_rs at two key wavelengths (650 and 480 nm) were regressed against laboratory-derived a_CDOM(440) values. The validation using in situ data of a_CDOM(440) algorithm indicated a goodness of fit, R² = 0.70, with a root mean square error (RMSE) of 10.65%. The developed algorithm was applied to the OLI/Lansat-8 images. Distribution maps were created with OLI/Landsat-8 images based on the adjusted algorithm.     

Accuracy of expiratory carbon dioxide measurements using the coaxial and circle breathing circuits in small subjects

Mass spcctrometry is widely used to measure the end-tidal concentrations of inhalation anesthetics and other gases during surgery in order to estimate their arterial concentrations. When certain breathing circuits are used in newborns, however, fresh gas or ambient air may contaminate the expired sample, introducing a systematic error in the measurement of any end-tidal gas concentration. We estimated this error in newborn piglets using carbon dioxide as an indicator substance of expired gas. The capnograms and the difference between arterial carbon dioxide tension (PaCO₂) and peakexpired carbon dioxide tension (PeCO₂) were compared when either a coaxial (Bain) or circle breathing circuit was used. Gas was sampled from the proximal airway and distal trachea. No combination of circuit and sampling site produced a flat alveolar phase until the circle circuit was modified with diversion valves to reduce gas mixing. The mean PaCO₂-PeCO₂ gradients using the coaxial/proximal sampling, coaxial/distal sampling, and modified circle/proximal sampling circuits were 12.4, 9.2, and 8.8 mm Hg, respectively. The mean PeCO₂ in each of these combinations was significantly different from the corresponding mean PaCO₂ (p<0.05). Using the modified circle circuit with distal sampling, mean PeCO₂ was not significantly different from mean PaCO₂: the mean PaCO₂-PcCO₂ gradient was 2.2 ± 0.2 mm Hg (SEM), range, 0 to 6 mm Hg, with 95% confidence limits ⩽ 8 mm Hg. When a coaxial breathing circuit is used in small subjects, PaCO₂ may be significantly underestimated regardless of sampling site, although the circle breathing circuit with distal tracheal sampling yields accurate results. Supported in part by BRS Grant SO RR05507-20 from the Biomedical Research Support Grant Program, Division of Research Resources, National Institutes of Health, and by the American Heart Association, Lancaster, PA Chapter. The authors thank Robert Hirsch, PhD, for his statistical advice, and Greg Harris and Perkin-Elmer, Inc for loaning the mass spectrometer.     

基于多级串联深度卷积神经网络配准大形变图像

目的 采用无监督方式基于多级串联深度卷积神经网络(CNN)建立大形变图像配准网络(LDIRnet)模型,评估其配准脑部MRI及肺部CT图像的性能.方法 串联多个结构相同而参数不同的深度CNN,以端到端方式学习待配准图像之间的多个小形变场;再通过叠加小形变场计算待配准图像之间的大形变场,实现大形变图像配准.结果 配准3D...     

Elastic Image Registration to Quantify 3-D Regional Myocardial Deformation from Volumetric Ultrasound: Experimental Validation in an Animal Model

Although real-time 3-D echocardiography has the potential to allow more accurate assessment of global and regional ventricular dynamics compared with more traditional 2-D ultrasound examinations, it still requires rigorous testing and validation should it break through as a standard examination in routine clinical practice. However, only a limited number of studies have validated 3-D strain algorithms in an in vivo experimental setting. The aim of the present study, therefore, was to validate a registration-based strain estimation methodology in an animal model. Volumetric images were acquired in 14 open-chest sheep instrumented with ultrasonic microcrystals. Radial strain (?_RR), longitudinal strain (?_LL) and circumferential strain (?_CC) were estimated during different stages: at rest, during reduced and increased cardiac inotropy induced by esmolol and dobutamine infusion, respectively, and during acute ischemia. Agreement between image-based and microcrystal-based strain estimates was evaluated by their linear correlation, indicating that all strain components could be estimated with acceptable accuracy (r = 0.69 for ?_RR, r = 0.64 for ?_LL and r = 0.62 for ?_CC). These findings are comparable to the performance of the current state-of-the-art commercial 3-D speckle tracking methods. Furthermore, shape of the strain curves, timing of peak values and location of dysfunctional regions were identified well. Whether 3-D elastic registration performs better than 3-D block matching-based methodologies still remains to be proven.     

Deformable mapping using biomechanical models to relate corresponding lesions in digital breast tomosynthesis and automated breast ultrasound images

This work investigates the application of a deformable localization/mapping method to register lesions between the digital breast tomosynthesis (DBT) craniocaudal (CC) and mediolateral oblique (MLO) views and automated breast ultrasound (ABUS) images. This method was initially validated using compressible breast phantoms. This methodology was applied to 7 patient data sets containing 9 lesions. The automated deformable mapping algorithm uses finite element modeling and analysis to determine corresponding lesions based on the distance between their centers of mass (d_COM) in the deformed DBT model and the reference ABUS model. This technique shows that location information based on external fiducial markers is helpful in the improvement of registration results. However, use of external markers are not required for deformable registration results described by this methodology. For DBT (CC view) mapped to ABUS, the mean d_COM was 14.9 ± 6.8 mm based on 9 lesions using 6 markers in deformable analysis. For DBT (MLO view) mapped to ABUS, the mean d_COM was 13.7 ± 6.8 mm based on 8 lesions using 6 markers in analysis. Both DBT views registered to ABUS lesions showed statistically significant improvements (p ≤ 0.05) in registration using the deformable technique in comparison to a rigid registration. Application of this methodology could help improve a radiologist's characterization and accuracy in relating corresponding lesions between DBT and ABUS image datasets, especially for cases of high breast densities and multiple masses.