ABSTRACT
To assess the background field removal method usually used in quantitative susceptibility mapping (QSM), and to analyze the cause of serious artifacts generated in the truncated -space division (TKD) method, this paper discusses a variety of background field removal methods and proposes an improved method to suppress the artifacts of susceptibility inversion. Firstly, we scanned phase images with the gradient echo sequence and then compared the quality and the speed of reconstructed images of sophisticated harmonic artifact reduction for phase data (SHARP), regularization enable of SHARP (RESHARP) and laplacian boundary value (LBV) methods. Secondly, we analyzed the reasons for reconstruction artifacts caused by the multiple truncations and discontinuity of the TKD method, and an improved TKD method was proposed by increasing threshold truncation range and improving data continuity. Finally, the result of susceptibility inversion from the improved and original TKD method was compared. The results show that the reconstruction of SHARP and RESHARP are very fast, but SHARP reconstruction artifacts are serious and the reconstruction precision is not high and implementation of RESHARP is complicated. The reconstruction speed of LBV method is slow, but the detail of the reconstructed image is prominent and the precision is high. In the QSM inversion methods, the reconstruction artifact of the original TKD method is serious, while the improved method obtains good artifact suppression image and good inversion result of artifact regions.
Subject(s)
Algorithms , Artifacts , Brain , Image Processing, Computer-Assisted , Magnetic Resonance Imaging , Phantoms, ImagingABSTRACT
Numerical simulation is a powerful technology for photoacoustic imaging (PAI) in both theory studies and practical applications. In this paper, a simulation platform for PAI was designed and implemented based on Matlab. The simulation platform utilized finite element method (FEM) and -space pseudospectral method to calculate the forward and inverse problem of PAI. And a graphical user interface (GUI) was realized. Structural design, work process and other operating details of the platform was also provided. By compared with theoretical temporal waveform of photoacoustic signal and reconstruction results of COMSOL, the validity and reliability was verified. And a reliable simulation tool was proposed for PAI.
Subject(s)
Algorithms , Computer Simulation , Finite Element Analysis , Photoacoustic Techniques , Reproducibility of ResultsABSTRACT
Abstract Objective: To study the influence that the scan percentage tool used in partial k-space acquisition has on the quality of images obtained with magnetic resonance imaging equipment. Materials and Methods: A Philips 1.5 T magnetic resonance imaging scanner was used in order to obtain phantom images for quality control tests and images of the knee of an adult male. Results: There were no significant variations in the uniformity and signal-to-noise ratios with the phantom images. However, analysis of the high-contrast spatial resolution revealed significant degradation when scan percentages of 70% and 85% were used in the acquisition of T1- and T2-weighted images, respectively. There was significant degradation when a scan percentage of 25% was used in T1- and T2-weighted in vivo images (p ≤ 0.01 for both). Conclusion: The use of tools that limit the k-space is not recommended without knowledge of their effect on image quality.
Resumo Objetivo: Estudar a influência da ferramenta scan percentage, usada para a aquisição parcial do espaço K na qualidade de imagens obtidas por ressonância magnética. Materiais e Métodos: Foi usado um equipamento de ressonância magnética Philips de 1,5 T para obter imagens de um objeto simulador e imagens in vivo do joelho de um adulto do sexo masculino. Resultados: Com o objeto simulador, não ocorreram variações significativas quanto à avaliação da uniformidade e razão sinal-ruído. Entretanto, na análise da resolução espacial de alto contraste, houve significativa degradação nas imagens quando adotada a scan percentage a 70% e 85% em T1 e T2, respectivamente. Nas imagens in vivo comprovou-se a degradação somente quando adotada a scan percentage a 25% (p ≤ 0,01) em T1 e T2. Conclusão: Não é aconselhável adotar ferramentas que limitem o espaço K sem que haja conhecimento sobre sua influência na qualidade da imagem clinicamente gerada.
ABSTRACT
Objective To compare the various partial Fourier reconstruction algorithms in MRI image processing and their advantages and disadvantages for improving algorithm .Methods Based on the conjugate symmetry in k‐space data in the partial Fourier reconstruction algorithm theory ,the 1 .5T medical magnetic resonance equipment was utilized ,the k‐space data were collect‐ed ,in reconstruction ,only 55% -80% of full data were utilized to simulate the partial collection pattern and reconstruct the images by using the several algorithms of zero filling ,conjugate synthesis ,Homodyne detection and POCS .Results The results presented that the ringing artifact was most obvious in the conjugate filling pattern and the POCS algorithm had the best effect for eliminating the ringing artifact .Conclusion The POCS algorithm repeatedly uses the weighted iteration with low frequency phase positions , which eliminates artifact ,meanwhile causes the lose of high frequency image details ,moreover the time consuming is longer ;the Ho‐modyne algorithm can keep a good balance between maintaining the image details and diminishing ringing .If the Sinc function serves as a weighting function for conducting phase unwrapping ,the image quality may be further improved .
ABSTRACT
PURPOSE: The efficacy of magnetic resonance imaging for evaluating coronary artery disease has been reported. In this study, we evaluated the usefulness of breath-hold segmented K-space cine MR imaging for evaluating the patency of coronary artery bypass grafts (CABG). MATERIALS AND METHODS: Thirty eight patients with a total of 92 CABGs (36 internal thoracic arteries and 56 saphenous vein grafts) were evaluated using segmented Kspace cardiac-gated fast gradient echo sequence (2D-FASTCARD) MR imaging. MR magnitude images were evaluated from the hard copies by two independent observers. A graft was defined as patent if it was seen as a bright small round area on at least two consecutive images throughout the cardiac cycle at a position consistent with the expected location for that graft. RESULTS: MR images were obtained successfully for 23 patients (61%). The sagittal planes were most helpful in visualizing the cross-section of sapheneous vein bypass graft to left circumflex artery branch, whereas the transverse planes were used for identification of internal mammary artery grafts to left anterior descending coronary artery or its branch and identification of saphenous vein grafts to right coronary artery. Forty five grafts were visible using this MR technique, while the grafts were not visible on seven saphenous vein grafts and two internal mammary artery grafts. In two patients showing symptoms of myocardial ischemia, one or two bypass grafts were not visible. Imaging, perpendicular plane to a CABG was important to visualize the flow inside the CABG with maximum sensitivity. CONCLUSION: Evaluation of patency of the bypass graft was clinically feasible by 2DFASTCARD MR imaging, whereas any invisible bypass grafts should be further studied by contrast-enhanced MR angiography or by conventional angiography for confirmation of abnormalities.
Subject(s)
Humans , Angiography , Arteries , Coronary Artery Bypass , Coronary Artery Disease , Coronary Vessels , Feasibility Studies , Magnetic Resonance Imaging , Mammary Arteries , Myocardial Ischemia , Saphenous Vein , Transplants , VeinsABSTRACT
The main composition of MRI system is introduced including magnet,gradient-RF system,cooling system,reconstruction system and operation system.According to the principle and functions of every component,the common troubles and the corresponding reasons of MRI system in using are analyzed,and the solutions are presented.[Chinese Medical Equipment Journal,2008,29(2):90,93]