Redshift drift in uniformly accelerated reference frame

We construct an alternative uniformly accelerated reference frame based on a 3+1 formalism in adapted coordinates. In this frame, a time-dependent redshift drift exists between co-moving observers, which differs from that in Rindler coordinates. This phenomenon can be tested in a laboratory and improve our understanding of non-inertial frames.     

Scatter correction method for cone-beam CT based on interlacing-slit scan

Cone-beam computed tomography(CBCT) has the notable features of high efficiency and high precision, and is widely used in areas such as medical imaging and industrial non-destructive testing. However, the presence of the ray scatter reduces the quality of CT images. By referencing the slit collimation approach, a scatter correction method for CBCT based on the interlacing-slit scan is proposed. Firstly, according to the characteristics of CBCT imaging, a scatter suppression plate with interlacing slits is designed and fabricated. Then the imaging of the scatter suppression plate is analyzed, and a scatter correction calculation method for CBCT based on the image fusion is proposed, which can splice out a complete set of scatter suppression projection images according to the interlacing-slit projection images of the left and the right imaging regions in the scatter suppression plate, and simultaneously complete the scatter correction within the flat panel detector(FPD). Finally, the overall process of scatter suppression and correction is provided. The experimental results show that this method can significantly improve the clarity of the slice images and achieve a good scatter correction.     

Aberration correction for time-domain ultrasound diffraction tomography

Extensions of a time-domain diffraction tomography method, which reconstructs spatially dependent sound speed variations from far-field time-domain acoustic scattering measurements, are presented and analyzed. The resulting reconstructions are quantitative images with applications including ultrasonic mammography, and can also be considered candidate solutions to the time-domain inverse scattering problem. Here, the linearized time-domain inverse scattering problem is shown to have no general solution for finite signal bandwidth. However, an approximate solution to the linearized problem is constructed using a simple delay-and-sum method analogous to "gold standard" ultrasonic beamforming. The form of this solution suggests that the full nonlinear inverse scattering problem can be approximated by applying appropriate angle- and space-dependent time shifts to the time-domain scattering data; this analogy leads to a general approach to aberration correction. Two related methods for aberration correction are presented: one in which delays are computed from estimates of the medium using an efficient straight-ray approximation, and one in which delays are applied directly to a time-dependent linearized reconstruction. Numerical results indicate that these correction methods achieve substantial quality improvements for imaging of large scatterers. The parametric range of applicability for the time-domain diffraction tomography method is increased by about a factor of 2 by aberration correction.     

X射线CT环形伪影去除方法

为去除X射线CT图像中的环形伪影,建立了一种投影数据预处理方法。该方法通过对各角度投影数据逐一进行分段多项式拟合的方式建立异常探元的备选校正因子集合,再根据备选校正因子的概率密度分布确定最可几校正因子。介绍了方法的物理依据、原理及其实现步骤,并分析了其在复杂条件下的适应性。结果表明:该方法对稀疏环形伪影、密集环形伪影以及伴随强噪声污染的CT图像环形伪影均可去除;与中值滤波等方法相比,可以更好地保持图像的空间分辨率。该方法可用于多材质检测对象CT图像的处理。     

工业CT图像边缘伪影校正

为了去除工业CT图像中的边缘伪影,提高CT图像的识别能力和尺寸测量精度,提出一种降低串扰的系数修正法。首先分析得出边缘伪影主要是由散射射线在相邻探测通道之间的串扰所导致,并给出了探测通道串扰的数学模型;然后根据数学模型设计实验方案,通过对影响串扰率的主要因素进行实验分析,得到串扰率随入射X射线能量和被测物体厚度变化关系,再通过最小二乘拟合得出投影数据关于串扰率的函数;最后利用此函数对投影数据进行校正,降低了串扰的影响。实验结果表明,探测器间一级串扰率约为9.0%,二级串扰率约为1.2%,其中一级串扰是造成边缘伪影的主要因素,采用本文方法能够有效地抑制边缘伪影,同时较好地保留了图像细节和边缘。     

工业CT图像边缘伪影校正

为了去除工业CT图像中的边缘伪影,提高CT图像的识别能力和尺寸测量精度,提出一种降低串扰的系数修正法。首先分析得出边缘伪影主要是由散射射线在相邻探测通道之间的串扰所导致,并给出了探测通道串扰的数学模型;然后根据数学模型设计实验方案,通过对影响串扰率的主要因素进行实验分析,得到串扰率随入射X射线能量和被测物体厚度变化关系,再通过最小二乘拟合得出投影数据关于串扰率的函数;最后利用此函数对投影数据进行校正,降低了串扰的影响。实验结果表明,探测器间一级串扰率约为9.0%,二级串扰率约为1.2%,其中一级串扰是造成边缘伪影的主要因素,采用本文方法能够有效地抑制边缘伪影,同时较好地保留了图像细节和边缘。     

Attenuation correction of L-shell X-ray fluorescence computed tomography imaging

X-ray Fluorescence Computed Tomography (XFCT) is a widely-used experimental technique for investigating the spatial distribution of elements in a sample. However, image reconstruction for this technique is more difficult than for transmission tomography, one problem being self-absorption. In this work, we make use of known quantities and unknown density of elements of interest to express unknown attenuation maps. The attenuation maps are added to the contribution value of the pixel in the Maximum Likelihood Expectation Maximization (MLEM) reconstruction method. Results indicate that the relative error is less than 14.1%, which shows that this method can effectively correct L-shell XFCT.     

Automated correction of unwanted phase jumps in reference signals which corrupt MRSI spectra after eddy current correction

A commonly applied step in the postprocessing of gradient localized proton MR spectroscopy, is correction for eddy current effects using the water signal as a reference. However, this method can degrade some of the metabolite signals, in particular if applied on proton MR spectroscopic imaging data. This artifact arises from the water reference signal in the presence of a second signal which resonates close to the main water resonance. The interference of both resonances will introduce jumps in the phase of the reference time domain signal. Using this phase for eddy current correction will result in a ringing artifact in the frequency domain of the metabolite signal over the whole frequency range. We propose a moving window correction algorithm, which screens the phase of reference signals and removes phase jumps in time domain caused by interference of signals from multiple spin systems. The phase jumps may be abrupt or gradually distributed over several time data points. Because the correction algorithm only corrects time data points which contain phase jumps, the phase is minimally disrupted. Furthermore, the algorithm is automated for large datasets, correcting only those water reference signals which are corrupted. After correction of the corrupted reference signals, normal eddy current correction may be performed. The algorithm is compared with a method which uses a low-pass filter and tested on simulated data as well as on in vivo proton spectroscopic imaging data from a healthy volunteer and from patients with a brain tumor.     

Coordinate correction for parallax for gamma-ray beams detected by counters based on thin-film drift tubes

A model was put forward for finding the angle of incidence of a narrow gamma-ray beam and refining its coordinate when the beam is detected by cathode-readout counters based on thin-film drift tubes. The model can be used in solving small-angle scattering problems, which are widely met in X-ray diffraction analysis.     

Multilayered scattering reference mirror for full field optical coherence tomography with application to cell profiling

A multilayered scattering structure is proposed and demonstrated as a reference mirror for use with full field optical coherence tomography (FF-OCT) to increase contrast of tissue imaging and provide compensation. Common-path FF-OCT systems were built demonstrating high resolution cell profiling. The use of this mirror with frequency domain FF-OCT allows 3D images in real time.     

Study on scattering correction in fast neutron tomography at NECTAR facility

Fast neutron tomography has been established as an inspection and detection tool at the NECTAR facility at the FRM-II reactor.Scattered neutrons from the object become a major disturbance and bring in artifacts and deviations in reconstruction results,especially for hydrogenous material object.In this article,an iterative scattering correction method for fast neutron tomography was proposed.In each loop of iteration the scattering component of the projections will be simulated by Monte-Carlo program MCNPX based on the previous reconstruction result and then it will be subtracted from original projections.The differences between scattering components at different perspectives were quantitatively evaluated and an average scattering component image was used for all projections finally.Smooth and uniform slices with more clear edges were obtained and the new reconstructed attenuation coefficients are quite close to the real one compared to the results without scattering correction,in which case the relative error of the reconstructed attenuation coefficients is about 10%–30%.     

Scatter correction for cone-beam computed tomography using self-adaptive scatter kernel superposition

The authors propose a combined scatter reduction and correction method to improve image quality in cone beam computed tomography (CBCT). The scatter kernel superposition (SKS) method has been used occasionally in previous studies. However, this method differs in that a scatter detecting blocker (SDB) was used between the X-ray source and the tested object to model the self-adaptive scatter kernel. This study first evaluates the scatter kernel parameters using the SDB, and then isolates the scatter distribution based on the SKS. The quality of image can be improved by removing the scatter distribution. The results show that the method can effectively reduce the scatter artifacts, and increase the image quality. Our approach increases the image contrast and reduces the magnitude of cupping. The accuracy of the SKS technique can be significantly improved in our method by using a self-adaptive scatter kernel. This method is computationally efficient, easy to implement, and provides scatter correction using a single scan acquisition.     

Anisotropic total variation minimization approach in in-line phase-contrast tomography and its application to correction of ring artifacts

In-line phase-contrast computed tomography(IL-PC-CT) imaging is a new physical and biochemical imaging method.IL-PC-CT has advantages compared to absorption CT when imaging soft tissues. In practical applications, ring artifacts which will reduce the image quality are commonly encountered in IL-PC-CT, and numerous correction methods exist to either pre-process the sinogram or post-process the reconstructed image. In this study, we develop an IL-PC-CT reconstruction method based on anisotropic total variation(TV) minimization. Using this method, the ring artifacts are corrected during the reconstruction process. This method is compared with two methods: a sinogram preprocessing correction technique based on wavelet-FFT filter and a reconstruction method based on isotropic TV. The correction results show that the proposed method can reduce visible ring artifacts while preserving the liver section details for real liver section synchrotron data.     

Evaluation of dosimetry and image of very low-dose computed tomography attenuation correction for pediatric positron emission tomography/computed tomography: phantom study

In this study, phantom was used to evaluate attenuation correction computed tomography (CT) dose and image in case of pediatric positron emission tomography (PET)/CT scan. Three PET/CT scanners were used along with acryl phantom in the size for infant and ion-chamber dosimeter. The CT image acquisition conditions were changed from 10 to 20, 40, 80, 100 and 160 mA and from 80 to 100, 120 and 140 kVp, which aimed at evaluating penetrate dose and computed tomography dose index_volume (CTDI_vol) value. And NEMA PET Phantom? was used to obtain PET image under the same CT conditions in order to evaluate each attenuation-corrected PET image based on standard uptake value (SUV) value and signal-to-noise ratio (SNR). In general, the penetrate dose was reduced by around 92% under the minimum CT conditions (80 kVp and 10 mA) with the decrease in CTDI_vol value by around 88%, compared with the pediatric abdomen CT conditions (100 kVp and 100 mA). The PET image with its attenuation corrected according to each CT condition showed no change in SUV value and no influence on the SNR. In conclusion, if the minimum dose CT that is properly applied to body of pediatric patient is corrected for attenuation to ensure that the effective dose is reduced by around 90% or more compared with that for adult patient, this will be useful to reduce radiation exposure level.     

Optimization of Fizeau-based optical coherence tomography with a reference Michelson interferometer

The method of Fizeau-based optical coherence tomography with a reference Michelson interferometer has been optimized. The real-system noise and dynamic range have been estimated. The time parameters of the system are optimized according to the proposed noise model. A good correspondence between the numerical estimates and experimental data is shown.     

Scattering correction method for panel detector based cone beam computed tomography system

<正>A scattering correction method for a panel detector based cone beam computed tomography system is presented. First,the x-ray spectrum of the system is acquired by using the Monte Carlo simulation method.Secondly,scattered photon distribution is calculated and stored as correction matrixes by using the Monte Carlo simulation method according to scanned objects and computed tomography system specialties.Thirdly,scattered photons are removed from projection data by correction matrixes.A comparison of reconstruction image between before and after scattering correction demonstrates that the scattering correction method is effective for the panel detector based cone beam computed tomography system.     

Soft-breaking correction to hard supersymmetric relations QCD correction to squark decay

Supersymmetric relations between dimensionless couplings receive finite correction at one-loop when supersymmetry is broken softly. We calculate theO (α _s) correction to the squark decay width to a quark and an electroweak gaugino, which is found to be nonvanishing. Logarithmic correction appears when the gluino is heavy.     

超声反射层析成像的Fourier切片理论及对积分线弯曲影响的修正

本文针对不同接收方式推导了超声反射层析成像模型在远场条件下的Fourier切片理论,在此基础上,进一步给出了旁轴近似条件下的迭代重建公式,通过这种迭代运算,可以逐步消除投影积分线弯曲的影响,从而改善重建像的质量。     

Energy‐dependent dead‐time correction in digital pulse processors applied to silicon drift detector's X‐ray spectra

Dead‐time effects in X‐ray spectra taken with a digital pulse processor and a silicon drift detector were investigated when the number of events at the low‐energy end of the spectrum was more than half of the total, at counting rates up to 56 kHz. It was found that dead‐time losses in the spectra are energy dependent and an analytical correction for this effect, which takes into account pulse pile‐up, is proposed. This and the usual models have been applied to experimental measurements, evaluating the dead‐time fraction either from the calculations or using the value given by the detector acquisition system. The energy‐dependent dead‐time model proposed fits accurately the experimental energy spectra in the range of counting rates explored in this work. A selection chart of the simplest mathematical model able to correct the pulse‐height distribution according to counting rate and energy spectrum characteristics is included.     

Image reconstruction based on total-variation minimization and alternating direction method in linear scan computed tomography

Linear scan computed tomography (LCT) is of great benefit to online industrial scanning and security inspection due to its characteristics of straight-line source trajectory and high scanning speed. However, in practical applications of LCT, there are challenges to image reconstruction due to limited-angle and insufficient data. In this paper, a new reconstruction algorithm based on total-variation (TV) minimization is developed to reconstruct images from limited-angle and insufficient data in LCT. The main idea of our approach is to reformulate a TV problem as a linear equality constrained problem where the objective function is separable, and then minimize its augmented Lagrangian function by using alternating direction method (ADM) to solve subproblems. The proposed method is robust and efficient in the task of reconstruction by showing the convergence of ADM. The numerical simulations and real data reconstructions show that the proposed reconstruction method brings reasonable performance and outperforms some previous ones when applied to an LCT imaging problem.