Jianbao Gui

Geometric Calibration of a Micro-CT System and Performance for Insect Imaging

Micro-CT with a high spatial resolution in combination with computer-based-reconstruction techniques is considered a powerful tool for morphological study of insects. The quality of CT images crucially depends on the precise knowledge of the scan geometry of the micro-CT system. In this paper, we have proposed a method to calculate the deviation of rotating axis for compensating deficiency of existing methods. A practical application of this geometric calibration method of the micro-CT system for insect imaging is presented. We have performed the computer-simulation study and experimental study with our prototype micro-CT system. The results demonstrate that the proposed technique is accurate and robust. In addition, we have evaluated the imaging characteristics of the detector in terms of modulation-transfer function (MTF). Finally, insect imaging performance and image reconstruction from data acquired with different energies are presented.

A Novel Interactive Image Processing Approach for DICOM Medical Image Data

The development of more flexible and accurate medical image processing technique and platform is important requirement for clinical diagnosis and treatment. A new interactive image processing method is proposed in this work. Using this method, image smoothing, sharpening, histogram processing, pseudo-color processing, segmentation, reading, local amplification and measurement for medical image in DICOM format can be realized. Application of the method for processing human CT image data demonstrated the method is a convenient and flexible approach for medical image processing. This user-friendly image processing technique could be clinically useful to assist image analysis and diagnosis. Keywords-DICOM; medical image; image processing; local amplification

Investigation of BPF algorithm in cone-beam CT with 2D general trajectories

A mathematical derivation was conducted to illustrate that exact 3D image reconstruction could be achieved for z-homogeneous phantoms from data acquired with 2D general trajectories using the back projection filtration (BPF) algorithm. The conclusion was verified by computer simulation and experimental result with a circular scanning trajectory. Furthermore, the effect of the non-uniform degree along z-axis of the phantoms on the accuracy of the 3D reconstruction by BPF algorithm was investigated by numerical simulation with a gradual-phantom and a disk-phantom. The preliminary result showed that the performance of BPF algorithm improved with the z-axis homogeneity of the scanned object.

Geant4-Based Monte Carlo Simulator for Fan-and Cone-Beam X-ray CT

An X-ray computed tomography (CT) simulator based on Geant4 toolkit was developed for simulation of both fan- and cone-beam CT scanners. There major components X-ray tube, phantom and detector are simulated. Different to analytical simulation, this simulation is accordance with imaging physics by adopting the Geant4 toolkit. Compared with ordinary statistical simulation, acceleration investigation and parameters optimization are considered. Also,experiments on beam-hardening and scatter are simulated. As expected, this simulator is not only a tool for acquiring scanning data, but also a tool for evaluating dose, the effect of physical, geometrical and potential artifacts and corresponding correction schemes in CT system.

The Study of Reconstruction Image Quality Resulting from Geometric Error in Micro-CT System

The reconstruction images often suffer from artifacts caused by misaligned geometry of flat detector in micro-CT. This paper mainly simulates the causality between the reconstruction image quality and the flat detector geometry by the eight-spheres phantom. The simulation results show that the most influential parameter is β (the rotation angle of the detector plane along the center point O) among the five detector parameters, next is a, b, θ and α degressively. We should control β under 7° and a, b offset lower than 8 pixels, when adjusting micro-CT systems. We also show that the relevant correction is efficient to improve the reconstruction image quality affected by the tiny geometric error.

Geometric Calibration Method Based Micro-CT System for Small-Animal Imaging

Small-animal imaging technology has been rapidly developed for longitudinal screening of laboratory animals raised with disease developments or genetic manipulations. Micro-CT is a noninvasive imaging modality used to assess morphology and function in small-animal imaging. Geometric calibration involves the estimation of a set of parameters that describes the geometry of such systems, and is essential for accurate image reconstruction. Noo F et al (2000) have proposed a new analytic method for calibration of x-ray cone-beam scanners that use a circular path for the cone vertex. In this paper, we use this analytic calibration method for the estimation of the geometric parameters of a practical small-animal imaging micro-CT system. We improve calibration phantom of this method in order to make it more suitable for micro-CT system. The overall performance of the micro-CT system is demonstrated in some results of small-animal imaging. The projection images demonstrated that the adopt method is robust and easy to implement with high precision.

Real-Time Visualization and Interaction of Three- dimensional Human CT Images

Three-dimensional medical image visualization becomes an essential part for medical field, including computer-aided diagnosis, surgery planning and simulation, artificial limb surgery, radiotherapy planning, and teaching etc. In this paper, marching cubes algorithm is adopted to reconstruct the 3-D images for the CT image sequence in DICOM format under the VC++6.0 and the visual package VTK platform. The relatively simple interactive operations such as rotation and transfer can be realized on the platform. Moreover, the normal vector and interior point are calculated to form the virtual clipping plane, which is then used to incise the 3-D object. Information of the virtual slice can be obtained, in the mean while the virtual slice images are displayed on the screen. The technique can realize the real time interaction extraction of virtual slice on 3-D CT image. The cuboids structured can be zoomed, moved and circumrotated by operating mouse to incise the 3-D reconstruction object. Real time interaction can be realized by clipping the reconstruction object. The coordinates can be acquired by the mouse clicking in the 3D space, to realize the point mouse pick-up as well angle and distance interactive measurement. We can get quantitative information about 3-D images through measurement.

Teeth segmentation using dental CT data

Cone-beam dental computerized tomography has been introduced as a system geared towards maxillofacial imaging, which is gradually becoming a common tool within the dental industry. Segmentation of teeth from dental CT data is vital for a variety of computer-aided procedures such as dental implants, orthodontic planning and cosmetic surgeries. Teeth segmentations near soft tissue structures can help clinicians to assess the quality of a patients teeth more easily. Moreover, the ability to identify particular regions surrounding teeth can help to provide better image results generated using 3D surface/volume rendering techniques. This paper, presents an experimental study for teeth segmentation employing two different thresholding techniques. The performances of these techniques are compared with each other. The experimental results show that there is a noticeable difference in segmentation quality between the two methods presented in this paper.

Phase-contrast Imaging Simulation Based on a Micro-CT System

Propagation-based phase-contrast imaging was simulated based on paraxial Fresnel-Kirchoff diffraction integral and spherical wave illumination. Under a developed micro-CT system parameters, the effects of focal-spot size and imaging geometry on phase-contrast imaging have been investigated using a 2 mm thickness polystyrene edge phantom. An equivalent mono-energy was used to substitute the polychromatic spectrum of the micro-focus x-ray source. To consider effects of focal-spot size and detector resolution, the obtained phase-contrast image with an ideal point source was convolved with source intensity distribution and point spread function of detector. Simulations show reasonable influences of the two parameters and are in good agreement with experimental results.

Iterative reconstruction method for irregular object

Conventional CT reconstruction algorithm, filtered-backprojection (FBP), requires the projection data acquired within the angular range from 0 to 2pi. However, for an irregular object, the data acquired at some projection views may be not available due to the detector saturation. In this work, we proposed a method to optimize the current patterns for obtaining two sets of complementary attenuation data and to employ an iterative method based on equation and inequality to improve the reconstruction quality. The simulation results obtained from the projection data, which are generated by use of the GEANT toolkit, show that the uses of optimal current scanning method and the corresponding iterative reconstruction method can yield the accuracy images with lower noise level.