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Signal encoding in magnetic particle imaging: properties of the system function
Jürgen Rahmer, Jürgen Weizenecker, Bernhard Gleich, J?rn Borgert
BMC Medical Imaging , 2009, DOI: 10.1186/1471-2342-9-4
Abstract: An analytical derivation of the 1D MPI system function exhibits its explicit dependence on encoding field parameters and tracer properties. Simulations are used to derive properties of the 2D and 3D system function.It is found that for ideal tracer particles in a harmonic excitation field and constant selection field gradient, the 1D system function can be represented by Chebyshev polynomials of the second kind. Exact 1D image reconstruction can thus be performed using the Chebyshev transform. More realistic particle magnetization curves can be treated as a convolution of the derivative of the magnetization curve with the Chebyshev functions. For 2D and 3D imaging, it is found that Lissajous excitation trajectories lead to system functions that are closely related to tensor products of Chebyshev functions.Since to date, the MPI system function has to be measured in time-consuming calibration scans, the additional information derived here can be used to reduce the amount of information to be acquired experimentally and can hence speed up system function acquisition. Furthermore, redundancies found in the system function can be removed to arrive at sparser representations that reduce memory load and allow faster image reconstruction."Magnetic Particle Imaging" (MPI) is a method for imaging distributions of magnetic nano-particles which has been introduced recently [1]. For generating a detectable particle signal, the method exploits the non-linear magnetization response of ferromagnetic particles to an externally applied oscillating magnetic drive field. The magnetization response induces a voltage in receive coils, which constitutes the MPI signal.As shown in figure 1, its spectrum contains higher harmonics of the drive frequency, which represent the fingerprint of the particles. Spatial localization is achieved by superimposing an inhomogeneous, static magnetic selection field, that limits the particle response to a small region, also called field free point (FFP).
Blind Separation Based on Particle Filtering for Chaotic Signal

Xu Mao-ge,Song Yao-liang,Liu Li-wei,

电子与信息学报 , 2007,
Abstract: A state space model for chaotic signal blind separation is first suggested,and then combined the Rao-Blackwellisaion(RB) strategy and incorporated roughening noise method,a particle filtering based online blind separation algorithm is proposed.To further decrease the residual noise in the online recovered signals,a novel delay estimation method which can effectively reduce the cross influence of source signals compared to the traditional delay-weight method is proposed.
Digital imaging of charged particle track structures with a low-pressure optical time projection chamber  [PDF]
U. Titt,V. Dangendorf,H. Schuhmacher
Physics , 2004,
Abstract: We describe first results obtained with a track structure imaging system for measuring the ionisation topology of charged particles in a low-pressure gas. The detection method is based on a time projection chamber (TPC) filled with low-pressure triethylamine (TEA). Images of ionisation tracks of electrons, protons, and heavier ions are presented and analysed.
A time projection chamber with optical readout for charged particle track structure imaging  [PDF]
U. Titt,A. Breskin,R. Chechik,V. Dangendorf,H. Schmidt-Boecking,H. Schuhmacher
Physics , 2004,
Abstract: We report about a nuclear track imaging system which is designed to study in detail the ionization topology of charged particle tracks in a low-pressure gas. The detection method is based on a time projection chamber (TPC) filled with low-pressure triethylamine (TEA). Ionization electrons produced by energetic charged particles are three-dimensionally imaged by recording light from electron avalanches with an intensified CCD system. The detector permits to inves-tigate the spatial ionization distributions of particle tracks in gas, of equivalent length and resolution in tissue of 4 mm and 40 nm (RMS), respectively. We explain the relevance of this technique for dosimetry, describe the experimental method and the basic operation parameters. First results of the chamber response to protons and alpha particles are presented.

CHEN Fei,JING Zhong,Liang,LI Jian,Xun,

红外与毫米波学报 , 2003,
Abstract: The infrared image background is obtained by morphological filtering, and the infrared images are nomalized using the estimated noise mean and variance in a local window. Composite frame is formed by normalized image dara, and target detection is performed on the composite frame. Thus, target and noise statistics in a composite frame are obtained. Considering the different distribution of noise and target intensity, the projection algorithm is further modifed to impove its signal to noise ratio. Simulations of real infrared images proved that the modified projection algorithm can successfully detect targets with SNR equaling 2.
Application of Apodization Filtering Sidelobe Suppressin Technique to Synthetic Aperture Radar

Zhang Xian-yi,Su Wei-min,Shi Ji,Gu Hong,

电子与信息学报 , 2008,
Abstract: It is known that for Linear Frequency Modulation (LFM) Synthetic Aperture Radar (SAR) echo signal, the obtained SAR image by 2-dimensional matched filtering has relatively high sidelobe level. Though such sidelobe can be depressed with amplitude weighting, the resolution of mainlobe will be accordingly reduced. To resolve this problem, in this paper, the apodization filtering technique is discussed and then applied to sidelobe suppression of SAR imaging with the detailed realization procedure presented. The theoretical analysis and simulation results show that in comparison with amplitude weighting, this technique can preserve the resolution of original SAR imaging whilst reducing the sidelobe level. The advantage of this technique has been verified with the simulation results of SAR image in multi-object case.

WANG Yi,XING Da,ZENG Ya-guang,

生物物理学报 , 2004,
Abstract: Photoacoustic imaging is a potential novel medical imaging technique to image structures in biological tissue. In the current photoacoustic imaging, the photoacoustic signals detected by a wide-band ultrasonic transducer are deconvolved by the impulse response of the transducer to compute the projection of the optical absorption of the sample, and then reconstruct the optical absorption distribution. But it's difficult to get the exact impulse response of the transducer. A relationship between the projections, detected photoacoustic signals of sample and point source are presented, and the projection can be computed with deconvolving the detected signals of the sample by the detected signal of a point source directly, which can be measured by focusing the incident laser. Experiments demonstrate that the reconstructed images agree well with the original sample. The spatial resolution of the system reaches 0.3 mm.
Image Reconstruction from Multifocal Fan-Beam Projection

中国图象图形学报 , 1998,
Abstract: Image reconstruction is one of the most exciting borderline science in the last few decades. Many applications have become known such as in diagnostic radiology, nuclear medicine, industry checking and etc. We know that fan-beam projection is a widely used scheme in these applications. One disadvantage of fan-beam projection is the truncation problem in some case which results in ring artifacts in the reconstruction. To resolve this problem, multi focal fan-beam projection is proposed in recent years to avoid the truncation problem and at the same time in the fan-beam projection' s good sensitivity especially for imaging of small organs is maintained. But the famous filering back projection method which is quick and efficient, can not be extended to such projection. In this thesis we advance a new method based on expanding fourier series and regularization technique. The method is as simple as the famous filtering back projection method and its simplified form can be applied to parallel-beam and fan-Beam cases. In implementing it, FFT is used to reduce the time of computation. Through computer simulation, it is found that the new method is noise-insensitivity and can produce accurate reconstruction almost without any visible artifacts when intensifying projection.
Revisiting the spread spectrum effect in radio interferometric imaging: a sparse variant of the w-projection algorithm  [PDF]
L. Wolz,J. D. McEwen,F. B. Abdalla,R. E. Carrillo,Y. Wiaux
Physics , 2013, DOI: 10.1093/mnras/stt1707
Abstract: Next-generation radio interferometric telescopes will exhibit non-coplanar baseline configurations and wide field-of-views, inducing a w-modulation of the sky image, which in turn induces the spread spectrum effect. We revisit the impact of this effect on imaging quality and study a new algorithmic strategy to deal with the associated operator in the image reconstruction process. In previous studies it has been shown that image recovery in the framework of compressed sensing is improved due to the spread spectrum effect, where the w-modulation can act to increase the incoherence between measurement and sparsifying signal representations. For the purpose of computational efficiency, idealised experiments were performed, where only a constant baseline component w in the pointing direction of the telescope was considered. We extend this analysis to the more realistic setting where the w-component varies for each visibility measurement. Firstly, incorporating varying w-components into imaging algorithms is a computational demanding task. We propose a variant of the w-projection algorithm for this purpose, which is based on an adaptive sparsification procedure, and incorporate it in compressed sensing imaging methods. This sparse matrix variant of the w-projection algorithm is generic and adapts to the support of each kernel. Consequently, it is applicable for all types of direction-dependent effects. Secondly, we show that for w-modulation with varying w-components, reconstruction quality is significantly improved compared to the setting where there is no w-modulation (i.e. w=0), reaching levels comparable to the quality of a constant, maximal w-component. This finding confirms that one may seek to optimise future telescope configurations to promote large w-components, thus enhancing the spread spectrum effect and consequently the fidelity of image reconstruction.
Lock-in-Amplifier Model for Analyzing the Behavior of Signal Harmonics in Magnetic Particle Imaging  [PDF]
Kenya Murase, Kazuki Shimada
Open Journal of Applied Sciences (OJAppS) , 2018, DOI: 10.4236/ojapps.2018.85014
Abstract: The purpose of this study was to present a lock-in-amplifier model for analyzing the behavior of signal harmonics in magnetic particle imaging (MPI) and some simulation results based on this model. In the lock-in-amplifier model, the signal induced by magnetic nanoparticles (MNPs) in a receiving coil was multiplied with a reference signal, and was then fed through a low-pass filter to extract the DC component of the signal (output signal). The MPI signal was defined as the mean of the absolute value of the output signal. The magnetization and particle size distribution of MNPs were assumed to obey the Langevin theory of paramagnetism and a log-normal distribution, respectively, and the strength of the selection magnetic field (SMF) in MPI was assumed to be given by the product of the gradient strength of the SMF and the distance from the field-free region (x). In addition, Gaussian noise was added to the signal induced by MNPs using normally-distributed random numbers. The relationships between the MPI signal and x were calculated for the odd- and even-numbered harmonics and were investigated for various time constants of the low-pass filter used in the lock-in amplifier and particle sizes and their distributions of MNPs. We found that the behavior of the MPI signal largely depended on the time constant of the low-pass filter and the particle size of MNPs. This lock-in-amplifier model will be useful for better understanding, optimizing, and developing MPI, and for designing MNPs appropriate for MPI.
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