[DR image denoising based on Laplace-Impact mixture model].

A novel DR image denoising algorithm based on Laplace-Impact mixture model in dual-tree complex wavelet domain is proposed in this paper. It uses local variance to build probability density function of Laplace-Impact model fitted to the distribution of high-frequency subband coefficients well. Within Laplace-Impact framework, this paper describes a novel method for image denoising based on designing minimum mean squared error (MMSE) estimators, which relies on strong correlation between amplitudes of nearby coefficients. The experimental results show that the algorithm proposed in this paper outperforms several state-of-art denoising methods such as Bayes least squared Gaussian scale mixture and Laplace prior.

[The design method of gradient coils in permanent MRI].

According to the features of the open permanent MRI system, this paper designs the gradient magnetic field, in which the designed parameters are optimized. The simulation experiments demonstrate the effectiveness of the algorithm.

[An adaptive scaling hybrid algorithm for reduction of CT artifacts caused by metal objects].

A new adaptively hybrid filtering algorithm is proposed to reduce the artifacts caused by metal in CT image. Firstly, the method is used to preprocess the projection data of metal region and is reconstruct by filtered back projection (FBP) method. Then the expectation maximization algorithm (EM) is performed on the iterative original metal project data. Finally, a compensating procedure is applied to the reconstructed metal region. The simulation result has demonstrated that the proposed algorithm can remove the metal artifacts and keep the structure information of metal object effectively. It ensures that the tissues around the metal will not be distorted. The method is also computational efficient and effective for the CT images which contains several metal objects.

[Algorithm of digital demodulation and filtering in MRI spectrometers].

In the design of RF receiver of the digital MRI spectrometer console, a digital demodulation and filtering algorithm is presented in this thesis. The MR signals are firstly converted to digital signals by the A/D converter, and then quadrature-demodulated from high frequency carrier wave. The CIC filter, half-band filter and linear phase FIR filter are designed to process the cascaded filtering and decimation of the demodulated signals. This method achieves a satisfying processing speed and filtering effect, and also reduces the data size obviously. The experiment based on the permanent magnetism resonance imaging system proves its effectiveness and practicability.

[An algorithm of nodule detection based on high resolution CT images].

Combining the speed of two-dimensional detection with the precision of three-dimensional detection, an automatic algorithm based on high resolution CT images is proposed to identify nodules in this paper. Nodule candidates are extracted by a two-dimensional convergence index (CI) filter, then a three-dimensional Hessian matrix detection filter is introduced to reduce false positive lung nodules, Experiments show that the algorithm is effective with a sensitivity of 90% and the false positive lung nodules per slice is 0.33.

[Design of a digital spectrometer for the MRI system].

A spectrometer is one of the most important parts in a Magnetic Resonance Imaging (MRI) system. This paper describes the design of a digital MRI spectrometer. It is constructed on a PXI platform with several data acquisition boards and a high-resolution timing board. All functions of a MRI spectrometer are realized by the specially- designed software. The software architecture and its implementing details are discussed and experimental results are introduced.

[Finite element method-based optimal design of MRI permanent magnet].

This paper presents a simulation method to study and improve the technology of designing magnets. With the finite element method, it analyzes the magnetic field distribution of the magnet model constructed by CAD software. Based on the distribution characteristics of magnetic field, the redundancy parts of the magnet configuration are removed accurately. The experiment results show that this method can significantly lighten the magnet.

[Design of the image browser for PACS image workstation].

The design of PACS image workstation based on DICOM3.0 is introduced in the paper, then the designing method of the PACS image browser based on the control system theory is presented,focusing on two main units:DICOM analyzer and the information mapping transformer.

[Research on designing MRI permanent magnet].

Based on the theory of magnet circuits, the paper introduces the process of designing MRI (Magnetic Resonance Imaging) permanent magnet. The measurement of magnet properties is improved by simulation technology. In order to increase the magnetic field homogeneity. We have designed a shim-loop and a trapeziform shim-board to optimize the magnetic field distribution. The results of both simulation analysis and experiments show that the innovative design improves magnetic field properties significantly and the magnet structure accords with the technology requirements.

[Controlling of the high-voltage generator in a direct radiography system].

A proposal is presented to improve the original complicated control of the exposure parameters in the direct radiography system (DR). The interface circuitry of the high-voltage generator is redesigned using RS-232 serial COM port. The data and signals are transmitted between the personal computer and the high-voltage generator in the serial mode. A program package is designed to realize the control of the exposure parameters of the high-voltage generator in DR on the PC machine. Experiment results have shown that the proposed console operates steadily and it is capable of providing a more convenient operation console for the direct radiography system.

[Wavelet threshold denoising algorithm for CR images].

A wavelet threshold denoising algorithm for CR images is put forward here . A noised CR image is decomposed into wavelet coefficients, which are processed by the algorithm, and the denoised CR image is reconstructed based on the processed coefficients. Examples are too presented to demonstrate the efficiency of the algorithm on denoising and, maintaining the detail of the CR images.

[An automatic color correction algorithm for digital human body sections].

OBJECTIVE: To find a new approach to improve the uniformity of color parameters for images data of the serial sections of the human body. METHOD: An auto-color correction algorithm in the RGB color space based on a standard CMYK color chart was proposed. The gray part of the color chart was auto-segmented from every original image, and fifteen gray values were attained. The transformation function between the measured gray value and the standard gray value of the color chart and the lookup table were obtained. In RGB color space, the colors of images were corrected according to the lookup table. RESULT: The color of original Chinese Digital Human Girl No. 1 (CDH-G1) database was corrected by using the algorithm with Matlab 6.5, and it took 13.475 s to deal with one picture on a personal computer. CONCLUSION: Using the algorithm, the color of the original database is corrected automatically and quickly. The uniformity of color parameters for corrected dataset is improved.

[A rapid method of eddy current compensation in magnetic resonance imaging systems].

Imaging objects are spatially encoded by gradient magnetic fields in magnetic resonance imaging systems. The eddy current caused by rapid switches of gradient fields will result in artifacts in the images. A method of eddy current compensation based on pre-emphasis of gradient current is presented in this thesis. The compensation parameters are acquired rapidly utilizing Faraday's induction theorem and data fitting method. The experiments prove that the method is efficient for reduction of the debugging time and for the improvement of the image quality.

Volume rendering based on sorted volumetric data.

OBJECTIVE: To describe a spatial data structure called sorted volumetric data structure which speeds up the volume rendering and will not affect image quality. METHOD: Before volume rendering we transfer each slice of volume into an array indexed by the value of voxels, element in which stores the position of each voxel. According to the opacity transfer function, we can affirm the value ranges of voxels that are non-transparent. Therefore we translate, resample and composite only the voxels in the value ranges. By marching through the sorted arrays, we locate the non-transparent voxels rapidly and skip all voxels that are transparent. The sorted data structures need not recompute whenever the opacity transfer function changes and are not restricted on the opacity transfer function. RESULT: The method presented in this paper has been implemented in a standard personal computer. The rendering time for CT head volume data is less than 1 s that is satisfied with the diagnostic purpose. CONCLUSION: The concept of proposed algorithm is simple, easy to realize and it is not recomputed whenever the opacity transfer function changes. By using the sorted volumetric data structure, we speed up the volume rendering without affecting image quality.

[Fast 3D surface rendering for CT or MR image on a personal computer].

Objective. To design a 3D surface reconstruction algorithm capable of reconstructing 3D shapes of the organs, bones and tissues rapidly from CT or MR image on a personal computer. Method. By transforming and decomposing the projection of the discrete 3D data field into shear transformation and warp transformation, a Shear-Warp algorithm realizing the 3D reconstruction was established. The algorithm reduce the amount of computation obviously. The 3D surface was reconstructed by using the principle of the parallel projection, basing on the Shear-Warp algorithm. Shear transformation was performed on the volume data at first. Then the warped 3D surface was obtained by making a threshold in the sheared space. The brightness of the 3D surface was calculated using Phong brightness model, and the final image was generated through the Warp transformation. Result. A direct 3D surface reconstruction algorithm was established basing on a principle of projection from the Shear-Warp algorithm, which was able to display 3D surface on a personal computer rapidly. Conclusion. Compared with other surface reconstruction algorithms, the proposed algorithm has the advantages of no preprocessing, no intermediate data are generated in the reconstruction. With this new algorithm, it is possible to realize fast 3D surface rendering for medical images on a personal computer without the support of any hardware accelerator.

[Design of print out function for a multi-parameter patient monitor].

This paper describes the design of the printing output function for a multi-parameter patient monitor by using the graphic plot function of a Laser Printer. The ECG data are preprocessed with a notch filter and interpolation algorithm. A logical page is constructed in the extended memory for virtual page printing. This monitor is able to output a satisfied printing with ECG waveforms of high quality.