Local reconstruction algorithm has been proposed to reduce the reconstructing time in the single photon emission computer tomography (SPECT).To improve the image quality,it is necessary to de-noise the projection image before reconstruction.Revised biva-shrinkage de-nosing based on wavelet transformation,which has a property of reserving detail information,is used to pre-treat the image.The mean square error (MSE)is adopted to evaluate the de-noising image of local reconstruction.The results show that wavelet based de-noising method is effective in local reconstruction algorithm.

SPECT is one of the nuclear medicine imaging techniques. It can reconstruct the functional image of the organ of interest, and has great help for early diagnosis of diseases. Cone-beam SPECT reconstruction can improve the photon density and spatial resolution of the reconstructed image, but it is time consuming. In clinic, doctors usually just care about the region of interest (ROI), such as heart, not the whole body. Local reconstruction can reduce the reconstruction time. In this paper, we build a framework for local cone-beam SPECT reconstruction with non-uniform attenuation. Firstly, we rebin the cone-beam projection to a fan-beam projection using SSRB method, and then perform a data extrapolation in each slice. Finally, after rebinning from fan-beam projection to parallel-beam projection, the reconstructed images of ROI could be obtained by using Novikov's analytical SPECT reconstruction algorithm. In computer simulation, clear local reconstruction images are obtained, which are almost the same as the ROI images of phantom. Computer simulation results show that our reconstruction framework is feasible.

In the conventional single photon emission computed tomography (SPECT), reconstruction algorithm requires full projection data to reconstruct the images, which will be time-consuming. While in clinic, doctors usually just care about the region of interest (ROI), such as heart, not whole body, in this case, a local SPECT reconstruction algorithm is needed to reconstruct the ROI by only using the projection data from the ROI. In SPECT, the non-stationary Possion noise in the projection data (sinogram) is a major cause to compromise the quality of the reconstructed images. To improve the reconstruction quality, we must remove the Possion noise in the sinogram before reconstruction. However, the conventional space or frequency domain de-noising methods possibly remove the edge information, which is very important for the accurate reconstruction, especially for the local SPECT reconstruction with non-uniform attenuation. Wavelet transform, due to its excellent localization property, has rapidly become an indispensable image processing tool for de-noising. In this paper, we tried to find out the properties of wavelet based de-noising methods for local SPECT reconstruction with non-uniform attenuation. From the de-noising results, we can see that wavelet based de-noising methods have good performance for local SPECT reconstruction.

Single photon emission computed tomography (SPECT) is one of the nuclear medical imaging techniques and widely used in the clinical applications. Cone-beam SPECT reconstruction can improve the photo density and spatial resolution of the reconstructed image. In this paper, based on our analytical fan-beam SPECT reconstruction formula with nonuniform attenuation and Feldkamp method, we present an analytical cone-beam SPECT reconstruction algorithm for the non-uniform attenuated Radon transform. The computer simulation experiments had demonstrated its accuracy and robustness.

Single photon emission computed tomography (SPECT) could achieve the functional image of the organ of interest, so the diseases can be found much earlier. Cone-beam SPECT reconstruction can improve the photo density and spatial resolution of the reconstructed image. A simple method for cone beam reconstruction is to rebin the cone-beam projection data into 2D sinograms and use 2D reconstruction method to obtain the 3D reconstructed images. In this paper, we proposed two rebinning methods for cone-beam SPECT reconstruction with non-uniform attenuation, these two algorithms both can obtain good reconstruction results, especially when reconstructed slice is close to the mid-plane.

A novel and precise micron-scale nanosecond laser spot measurement based on film-scanning method is presented. The method can be used to measure the spot size, beam profile, and intensity distribution of the pulse. The central spot radius of the pulsed Bessel beams with pulse width of 25 ns is measured to be 94.86+-5 micron in our experiment through the analysis of the digital image by film scanning, and the result is consistent with the theoretical value of 92.33 micron. Compared with charge-coupled device/complementary metal oxide semiconductor (CCD/CMOS) laser beam profilers, the film-scanning method shows higher measurement accuracy, single shot ultrashort pulse measurable, larger measurable size, and wider measurable wavelength range.

A simple concept is applied to the construction of a Bessel-Gauss resonator based on an axicon with a plane output mirror.Fox-Li algorithm and numerical integral are applied respectively to describe the radical amplitude at output mirror and the three-dimensional field distribution of output beam.Analysis reveals that the dominant mode of the resonator has similar features as zero-order Bessel-Gauss beams do.Effect of varying the cavity length on the output transverse profile of the dominant mode of the cavity is discussed.Simulation results show that the features of the dominant mode of the resonator remain unchanged when the cavity length change is small.The resonator scheme based on Nd: YAG laser was implemented in an experiment to confirm the possibility of generating zero-order Bessel-Gauss beams.The output transverse intensity distributions captured by beam analyzer roughly agree with the theoretical expectations.

Based on the generalized Huygens-Fresnel diffraction integral theory and the stationary phase method,within the maximum non-diffraction distance behind an axicon,the optical field distribution of a nanosecond Gaussian beam pulse passing through axicons with the ideal manufacture quality and with the elliptical manufacture error were investigated.According to the derived field expression,the three-dimensional intensity distributions and corresponding beam patterns were simulated numerically.It is shown that the different elliptical manufacture error,the propagation distance and the beam wavelength had an effect on the propagation of the nanosecond Bessel beam pulse in the presence of an elliptical manufacture error in the axcion.The film-scan method was adopted to record the nanosecond beam patterns in the transverse plane which perpendicular to the propagation axis.The experimental results fit the theoretical simulations well.

In a simple picture,a Bessel beam can be decomposed into a pair of conical waves,one slanting inwards towards the axis and the other expanding away from it,and the end mirrors are considered as being used to conjugate the radial phase of the field that oscillate in a resonator.In this paper,we discuss the design of a Bessel resonator based on an axicon,we find that the field oscillating inside the resonator is a conical waves modulated by a bell-shaped function. The modes of the cavity have similar features to Bessel-Gauss beams.The conclusions consist with the result simulated with the rigorous Fox-Li algorithm.

Based on the theory of diffraction integral,the optical field distribution of plane wave passing through an axicon is given,and he intensity distribution in cross-section of Bessel beam is simulated.In the experiment,using a Nd:YAG Q-switched laser with the plane-ARR critical resonator and a axicon,a high stability nanosecond Bessel beam is obtained.Based on the film-scanning and the 3-D visualization of the energy distribution in laser spot,the 2D and 3D energy distribution in cross-section of nanosecond Bessel beam are shown.There is a good agreement between experimental observation and theoretical simulation,moreover by comparing with the laser beam analyzer of TaperCamD-UCM-20-15 made by DataRay Corporation,a higher image resolution can be obtained.Furthermore,it will be an effective way to record the spatial energy distribution of picosecond ultrashort pulse,even of femtosecond.

Relative parameters of nanosecond diffraction-free Bessel laser pulse were theoretically analyzed and measured in experiments.The expressions of the optical intensity distribution behind an axicon illuminated by a plane wave,maximum diffraction-free distance,minimum central spot radius were given based on the generalized Huygens-Fresnel diffraction integral theory.Relative parameters were also theoretically simulated and calculated.In the experiment,high stability nanosecond Bessel laser pulses were generated by using a Q-switched Nd∶YAG laser with a plane-antiresonant ring(ARR) resonator and an axicon system.The pulse duration,maximum diffraction-free distance,optical intensity in the cross-section and minimum central spot radius were measured.Experimental results were consistent with the theoretical analysis.The fine structure of the optical intensity in the laser beam cross-section was presented by film-scanning,and the resolution of the beam pattern is much higher than that in a laser parameter analyzer.

Based on an axicon-based Bessel-Gauss resonator,a nanosecond high power non-diffracting pulsed Bessel-Gauss beam was generated directly from a flashlamp pumped Q switched Nd:YAG laser for the first time.The experimental results were analyzed using the Bessel-Gauss model deduced from the diffraction integral theory and they were consistent with the numerical simulation.On the other hand,by a high stability nanosecond Gaussian pulse generated from a Q switched Nd:YAG laser with an anti-resonant ring and pulse shaping passing through an axicon,a nanosecond non-diffracting zero order Bessel beam was obtained using the passive method.A film-scanning was used to record the fine structure of the intensity profile,and a beam analyzer to measure the pulse characteristics. The measured results show that the central spot size is about 90 μm and the peak power density of the central spot reaches to 2.3×109 W/cm2.Finally,the active and passive schemes for generating the nanosecond non-diffracting beam were compared and analyzed.

We present what we believe to be a novel, simple, and compact axicon-based resonator Nd:YAG laser in which a nanosecond pulsed Bessel-Gauss beam is generated directly for the first time. Using the theory of the Bessel-Gauss beam, theoretical analysis and numerical simulation are consistent with the experimental results.