CT理论与应用研究

Investigation of Image Reconstruction Algorithms for In-line X-ray Phase Contrast Tomography

LI Cheng-quan, LI Zheng, LI Chen, YU Ai-min

2007, 16(2): 1-7.

Abstract(2027) PDF(20)

Abstract:
We dicuss a fundamental theorem of phase contrast tomography,which plays a similar role as the Fourier slice theorem does for absorption-based CT.The theorem leads to develop a combined phase retrieval-reconstruction algorithm.With experimental results of In-line phase contrast CT from the Beijing Synchrotron Radiation Facility,we used the algorithm to reconstruct the three dimensional refractive distribution of the specimens,and compare the reconstruction quality for the conventional FBP algorithm.Some influencing factors of the algorithm has be dicussed.

Development of Image Reconstruction Algorithms for Synchrotron Radiation

ZHANG Shu-ming, HU Yu-guang, SHI Yuan-ding, CHEN Zhi-cheng, LIU Li

2007, 16(2): 8-13.

Abstract(945) PDF(1)

Abstract:
Our purpose was to evaluate two different reconstruction algorithms applied in micro-radiological imaging using synchrotron radiation.In our experiment,a bird feather was imaged by the synchrotron radiation and projections were acquired by high resolution X-ray camera.All equipments are supported by the Synchrotron Radiation Research Center located in scientific park in Hsinchu,Taiwan.In this work,filtered back-projection (FBP) and gradient-based maximum-likelihood algorithms (ML algorithm) were applied to reconstruct synchrotron tomographic images for comparison.An edge blurring is shown in results of the ML reconstructed image.Ring artifacts are more obvious in the image reconstructed by the FBP as compared to that of the ML algorithm.The FBP can do fast reconstruction,but the ML algorithm can reduce noise and artifacts.Thus,the two algorithms show very different characteristics.

Studies of the Relaxation Parameter Selection of the Block-iterative Algorithm for Image Reconstruction

SUN Jie, QU Gang-rong

2007, 16(2): 14-19.

Abstract(1126) PDF(3)

Abstract:
Landweber's iterative algorithm is an important method in the image reconstruction.In this article we study the relaxation parameter's selection in the Landweber's block-iterative algorithms.We select the special relaxation parameter and put the projection matrix into many blocks according to the projection angles in the reconstruction procedure.We select the product ofλand one ratio the maximal eigenvalues of the multiples of the block-matrixes (specified later) and their conjugate transpose matrixes as the special relaxation parameters.By performing numerical experiment,we conclude that ifλapproach to 1/6-1/7,we will get the best result when we can obtain the complete datum.;Otherwise,that we select the special relaxation parameter and put the projection matrix into many blocks according to the projection angles is available to the limited angle problem.

Symmetric Mesh-Iterative Algorithms for Image Reconstruction

QIU Jun, WANG Liang

2007, 16(2): 20-30.

Abstract(870) PDF(2)

Abstract:
This paper provides the improved iterative algorithms as commonly applied in Industrial Computerized Tomography (ICT).The symmetric mesh-iterative reconstruction technique (SM-IRT) is introduced based on the existing symmetric structure of projection lines so as to better solve the image reconstruction problems.This method proposes simplified computation of projection matrix and effectively adjusts the successive line iterative sequences.The experimental image reconstruction utilizing both simulated data and ICT experimental data is undertaken.The results show that the image reconstruction adopting the presented algorithms is much faster and takes on better precision than other conventional algorithms.

Conjugate Gradient Applied to Image Reconstruction

LI Hua-xin

2007, 16(2): 31-35.

Abstract(1016) PDF(3)

Abstract:
Image reconstruction is often converted to the nonrestraint extremum of the nonlinear equations.We have deduced a conjugate gradient algorithm from the extremum of norm.The experimental results of reconstruction from simulated projections and real tomography projections have successfully shown that conjugate gradient guarantees the fitness to original image,speeds the iteration time,and can be specially used for reconstruction for incomplete projections.

Tomographic image of Rayleigh Surface Wave in Eurasia and western Pacific marginal seas

GU Qin-ping, ZHU Jie-shou, WU Lian, CHEN Lei

2007, 16(2): 36-41.

Abstract(683) PDF(0)

Abstract:
More than 1 800 seismic events(which occurred from 1982 to 2006,distributed in the range of 40°W~180°E,40°S -80°N,with magnitudes in 5.0~7.0 and focal depths shallower than 100 km)are selected from nearly 10,000 events recorded by 114 digital seismic stations in Asia,Europe and west Pacific networks.Totally 10450 accurate Rayleigh surface dispersion curves are employed for dispersion inversion,and the distribution map of Reyleigh wave group velocity in 28 periods from 8 S to 200 S for Eurasia continent and marginal seas of west Pacific are obtained.The great circle routes of surface waves cover Eurasia and the west Pacific Ocean.This paper preprocesses the original datum to determine surface dispersion curves at first, including the steps as following:intercepting Rayleigh surface wave,analyzing in time domain,to obtain the actual datum of dispersion.Then it lattice partitions the researched zone,and calculates the group velocity in theory,which means getting the datum of pure-path dispersion by inversion method of dispersion curve of latticing pure-path.At last,it inversed the pure-path dispersion to get the velocity distribution of S wave along with the depth of every unit by making use of datum for each unit as observed datum and by generalized inversion method like LSQR,SVD and so on.

Test Equipment Problems on Studying Concrete Using X-Ray CT

DING Wei-hua, ZHANG Jian-jun, CHEN Hou-qun, LIU Shao-cong

2007, 16(2): 42-47.

Abstract(909) PDF(0)

Abstract:
The purpose of studying concrete using X-ray CT is to analyze concrete meso-crack evolution process and explain concrete macroscopic strength and strain character based on concrete CT images.The problem of concrete CT is that the functions of loading system and CT machine can not be carried out simultaneously.Based on current medical CT machine and special loading equipment,the real-time detecting can be realized on meso-crack evolution process ofⅠ,Ⅱgrade concrete under dynamic loading.The far demand is to make new CT machine to raise scanning velocity,make new special loading equipment to conduct the damage test toⅡgrade concrete under dynamic compression load.

X-ray Detection of Tyre with Digital Image Processing

YUAN Pei-xin, ZHANG Xiao-hui

2007, 16(2): 48-51.

Abstract(645) PDF(0)

Abstract:
Based on the theory of digital image processing and X-ray detecting,the match algorithm of tyre meridian image and pattern plate image is studied,the search strategy of“first scanning globally then locally”is presented.

Low-dose CT Cardiac Imaging

Jiang Hsieh, John Londt, Melissa Vass, Xiangyang Tang, Jay Li, Darin Okerlund

2007, 16(2): 52-59,65.

Abstract(742) PDF(1)

Abstract:
Cardiac imaging with computed tomography （CT） is one of the most recent advancements in CT clinical applications.Because of the low helical pitch employed in the cardiac acquisition protocols,radiation dose to patient is high.In this paper,we present a different data acquisition and image reconstruction technique that reduces dose to patient by 50%～89%.The key enabler for such technique is the large volume coverage （40 mm） of the 64-slice scanner.Compared to an average heart size of 120 mm to 140 mm the new VCT scanner is capable of covering the entire organ in 3 to 4 steps. In conjunction with the new acquisition,we present a complimentary reconstruction algorithm that overcomes incomplete projection samples.We conducted extensive phantom and clinical experiments to demonstrate the efficacy of the proposed approach.

Technique Advancements of Light Speed VCT and Its Clinical Applications

LI Jian-ying

2007, 16(2): 60-65.

Abstract(809) PDF(0)

Abstract:
In this paper we introduced some of the technique advancements of GE Light Speed VCT in hardware, software and reconstruction algorithm areas,and how these advancements improved image quality and brought many advanced clinical applications into reality including 5-beat cardiac,emergency chest pain Triple Rule Out^TM and total stroke work-up.We also discussed the need to balance image quality and X ray dose and what GE was doing to achieve the goal of getting diagnostic CT images at the lowest possible dose.

Study of MRCP on Obstruction of Internal and External Bile Duct

OUYANG Chao-wen, CHEN Hua-ping

2007, 16(2): 66-70.

Abstract(609) PDF(0)

Abstract:
Objective: To evaluate the diagnostic value of MR cholangio-pancreatography (MRCP) on the obstruction of internal and external bile duct.Method: Weight T₂W I MRCP combining routine MRI of GE 1.5T MRI scanner was used in diagnosing 49 cases.Results: The accuracy rating of positioning and qualitation in diagnosing the obstruction of bile duct was 100% and 91.8% respectively.Conclusion: MRCP combining routine MRI can display the process of internal and external bile duct accurately.

Application Value of 3-D reconstruction with Spiral CT in Lumbar Trauma

LI Zhi-hong, GUO Jian-guo

2007, 16(2): 71-74.

Abstract(789) PDF(0)

Abstract:
Objective To investigate the application value of 3D reconstruction with spiral CT in lumbar trauma. Methods: 76 cases with Lumbar trauma were examined by CT axial scan,the images of each were done by 3D reconstruction (SSD,MPR) and then compared with routine 2DCT.Result: The location and types of Lumbar fracture,Lumbar three columns structure,narrowing of Lumbar canal,the nerve roots and spinal cord to be compressed were revealed accurately and stereoscopically by 3D imaging.Conclusion: 3D reconstruction of spiral CT is an important complement of trans-axial images.It is helpful to select reasonable treatment plan and judge curative effect.It can help to show vertebra trauma and display intervertebral disk trauma intuitionistically.

Guidance of Multislice Helical Computed-tomography Angiography of Abdomen in Interventional Operation of Liver Tumors

GAO Yun, HU Dao-yu, LI Zhen, MENG Ling-shan, ZHANG Wei-min

2007, 16(2): 75-79.

Abstract(742) PDF(0)

Abstract:
Objective: Investigate the value of the multislice helical computed-tomography angiography used before the interventional operation of the fiver tumors.Materials and Methods: 37 cases liver tumors were made angiographies by MSCT before they were interventional operated.The angiographies pictures could display the position of abdomen blood vessel,the branch of blood vessel,and the relation of vessel and tumor.And these could guide the interventional operation. Results: 16 cases of the norm coeliac trunk artery were displayed by MSCTA.9 cases of the coeliac trunk artery location were misregistration.4 cases superior mesenteric artery,debounch from celiac trunk.2 cases coelical trunk artery were imperforation.32 cases clear displayed the coelical trunk artery,common hepatic artery,proper hepatic artery and left and right hepatic artery.29 cases displayed tumor feeding artery,2 cases display mutation feeding artery.Conclusion: With the guidance of MSCT angiography,the time of interventional operation decreased and it got easy to intubate.MSCT angiography of abdomen was valuable to guide the liver tumor interventional operation.

Hyaline Cartilage Imaging with Improved FS-3D-TrueFISP Sequence:Comparison with Conventional Sequences

YUE Yun-long, HAN Hong-bin

2007, 16(2): 80-85.

Abstract(645) PDF(0)

Abstract:
Objective: To explore the feasibility of improved fat-saturated three-dimensional true fast imaging with steady-state precession (FS-3D-TrueFISP) sequence for imaging hyaline cartilage of the knee.Methods: Single knee of 10 volunteers was scanned with two FS-3D-TrueFISP sequences after improved and conventional hyaline cartilage defects sequences.Measured the signal intensity of the hyaline cartilage of patellar facets,synovial fluid and background noise respectively.The signal to noise ratio (SNR) of hyaline cartilage,contrast to noise ratio (CNR) of hyaline cartilage to synovial fluid and CNR efficiency (CNReff) was calculated for each of the five sequences.Statistically significant differences in SNR,CNR and CNReff were determined.Results: On improved sequence hyaline cartilage showed moderate intensity,4 cases on FS-3D-TrueFISP showed three layers structure same as FS-3D-FLASH.The SNR,CNR and CNReff of the five sequences had statistically significant differences (P<0.05),the CNR and CNReff of FS-3D-TrueFISP,in which the number of acquisition is 2,was best.Conclusion: The improved TrueFISP sequence can image cartilage with excellent CNR in shorter scan time,this improved sequence can be used to image the hyaline cartilage in the knee.

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2007 Vol. 16, No. 2