The Analysis For Quantifying Morphological Changes Of Pulmonary Artery Tree And Whole Lung Perfusion From Multi-slice CT

BackgroundThe traditional approach to lung imaging, contribute to the analysis for progress and property of disease, is increasingly replaced by novel methods.The introduction of multi-slice row CT (MSCT) has enabled coronal, sagital, and oblique reformatting at greater spatial resolution than before, while contrast-enhanced CT methods now allow assessment of vasculature and lung perfusion. It is expected that HRCT will become antiquated in the not too distant future as CT evolves from mere static assessment of morphology into a dynamic and quantifiable tool for assessment of the lung.There is a significance to the morphometry of pulmonary artery using MDCT. Over the past thirty years, many other efforts have been made to establish reliable and reproducible diagnostic imaging methods for assessment of pulmonary artery (PA) pressure using CT. Earlier results with computer tomography (CT) have shown that the increase in the main pulmonary artery diameter is a reliable indicator of PH, and greater than28.6mm was100%specific for PH. The ratio of the PA to ascending aorta (AA) size and the segmental PA compared to that of the homologous segmental bronchus were also investigated. However, most studies identify PA dilatation by measuring partial PA dimensions and segmental vessels in the axial plane and do not reflect the feature of pulmonary arterial tree which is available by image post-processing.Fractal dimension (FD) analysis is a mathematical technique that provides an excellent explanation of the ruggedness of natural surfaces, and many other natural phenomena. In the field of medicine, fractal analysis has been applied to pathology, anatomy, medical imaging etc. researcheres deployed the FD analysis to assess the increased pulmonary blood flow on chest radiography. Previous research reported quantifications of pulmonary emphysema in CT imaging by FD analysis. For FD analysis of pulmonary artery tree, some authors deployed postmortem human or animal pulmonary arteries which were prepared by the silicone elastomer casting technique for assessment of morphological property. These studies may obtain the accurate and detailed information of PA, but in vitro. FD analysis potentially offers a way of investigating and quantifying the morphous of entire pulmonary artery from CT.Pulmonary perfusion imaging is an important clinical investigation, and the detection of changes in regional perfusion may be helpful in clinical diagnosis or in the evaluation of pulmonary function. The perfusion of the pulmonary parenchyma may provide visualization and assessment of the reduction in pulmonary blood flow that results from a pulmonary embolism (PE) or emphysema. Nuclear medicine scintigraphy has been considered the gold standard for assessment of pulmonary perfusion, but it has substantial limitations with respect to spatial and temporal resolution. Magnetic resonance imaging (MRI) is a more promising technique owing to its high spatial resolution and the ability to detect lobar and segmental abnormalities of perfusion. MR could not provide the accurate assessment of pulmonary parenchyma, which remain based on high-resolution computed tomography (CT). Therefore, the comparison of the morphological changes within the lung with areas of impaired pulmonary perfusion requires an additional technique.In recent years, increasing attention has been focused on CT pulmonary perfusion. With dual-energy CT (DECT) systems that can acquire two spiral CT datasets with different photon spectra simultaneously, DECT has the potential to map iodine distribution patterns as lung perfusion images. A new CT subtraction technique for perfusion imaging is used to evaluate the morphological and functional changes in the resulting color-coded images subtracting the plain CT data from the enhanced CT data. However, none of these techniques offer real measurement of perfusion from dynamic CT images, as they provide only an image of pulmonary perfusion rather than a quantitative study. Because of the limited coverage of the current designs of CT detector, lung perfusion based on dynamic scanning can only provide quantitative studies in regional pulmonary parenchyma. With the rapid development of CT techniques, volume perfusion CT (VPCT) of a total organ has now become available.The introduction of a new128-slice scanner technique allows for dynamic perfusion imaging with its inherent possibility of adaptive spiral scanning. This is implemented by bidirectional table movements and broad detector range, resulting in coverage of organs and tumors up to the coverage of27cm. It is now possible to provide a comprehensive assessment of the perfusion of the total pulmonary parenchyma.The aim of our study was the analysis for quantifying morphological changes of pulmonary artery tree and whole lung perfusion from multi-detector CT in two sections. In the first section, our aimwas to using FD analysis for quantifying morphological changes of pulmonary artery tree in pulmonary hypertension from MDCT. We tried to evaluate the difference of the FD between with PH patients and without PH patients. In the second section, our aim wasto evaluate the feasibility of dynamic volume perfusion CT (VPCT) of the whole lung using a128-slice CT for the quantitative assessment and visualization of pulmonary perfusion. We tried to evaluate the difference of perfusionparameter in the gravitational and isogravitational directions in the normal lung group. We evaluated the differences of VPCT between the normal and abnormal lungs.Section one:Fractal dimension analysis for quantifying morphological changes of pulmonary artery tree in pulmonary hypertension from MSCTPurpose:The aim was to using fractal dimension (FD) analysis for quantifying morphological changes of pulmonary artery tree in pulmonary hypertension (PH) from multi-slice computed tomography (MSCT).Materials and methods:14patients with PH and17patients without PH as controls were studied. All of the patients were underwent contrast helical CT and transthoracic echocardiography respectively. Pulmonary artery trees were generated using post-processing software, the FD and projected image area of pulmonary artery trees were determined with ImageJ software in personal computer. FD, projected image area, and pulmonary artery pressure (PAP) were statistically evaluated in two groups.Results:The FD, projected image area and PAP of patients with PH were higher than patients without PH (p<0.05, t-test). There was a high correlation of FD with PAP (r0.82, p<0.05, partial correlation analysis). There was a moderate correlation of FD with projected image area (r=0.49, p<0.05, partial correlation analysis). There was a correlation of PAP with projected image area (r=0.65, p<0.05, Pearson correlation analysis).Conclusions:FD of pulmonary arteries in PH patients exhibited significantly higher than controls. There was a high correlation of FD with PAP. Section two:An evaluation of the feasibility of assessment of volume perfusion for the whole lung by128-slice spiral CTPurpose:The aim of this study was to evaluate the feasibility of dynamic volume perfusion CT (VPCT) of the whole lung using a128-slice CT for the quantitative assessment and visualization of pulmonary perfusion.Material and methods:Imaging was performed in a control group of17subjects who had no signs of disturbance of pulmonary function or diffuse lung disease, and15patients (5patients with acute pulmonary embolism and10with emphysema) who constituted the abnormal lung group. Dynamic VPCT was performed in all subjects, with calculation of pulmonary blood flow (PBF), pulmonary blood volume (PBV), and mean transit time (MTT) generated from dynamic contrast images with a coverage of20.7cm. Regional and volumetric PBF, PBV, and MTT were statistically evaluated and comparison made between the normal and abnormal lung groups.Results:Regional PBF, PBV, and MTT demonstrated significant differences in the gravitational and isogravitational directions in the normal lung group. The PBF and PBV by dynamic VPCT showed significant differences between the normal and abnormal lungs, notwithstanding a few lungs in big size beyond the coverage of20.7cm.Conclusion:Dynamic VPCT of the whole lung is feasible for the quantitative assessment of pulmonary perfusion by128-slice CT, and may in future permit the evaluation of both morphological and functional features of the whole lung in a single examination.