Stability of phase-contrast tomography

Phase-contrast tomography (PCT) allows three-dimensional imaging of objects that display insufficient contrast for conventional absorption-based tomography. We prove that PCT is stable with respect to high-frequency noise in experimental phase-contrast data, unlike conventional tomography, which is known to be mildly unstable. We use known properties of the three-dimensional x-ray transform and transport-of-intensity equation to construct a matrix representation of the forward PCT operator. We then invert this formula to show that, under natural boundary conditions, the PCT reconstruction operator exists and leads to a unique solution. We show that the singular values s(n) of the reconstruction operator have asymptotic behavior s(n)=O(n(-3/2)), guaranteeing the mathematical stability of the reconstruction process.     

Evaluation of cortical bone by peripheral quantitative computed tomography in continuous ambulatory peritoneal dialysis patients

Several studies have suggested an increased prevalence of osteopenia in dialysis. Peripheral quantitative computed tomography (pQCT) is a new technique that allows the noninvasive evaluation of trabecular and cortical bone separately. The aim of the study was: (1) to evaluate cortical bone by pQCT in continuous ambulatory peritoneal dialysis (CAPD) patients and compare the data with that obtained in healthy controls; and (2) to correlate cortical bone parameters with bone mineral density (BMD) of the lumbar spine and femoral neck and total bone mineral content (TBMC). Cortical bone parameters were obtained in 22 CAPD patients and 27 healthy individuals at the distal radius using a Stratec XCT 960 pQCT machine. In the dialysis patients, we also determined BMD and TBMC by bone densitometry. Dialysis patients, compared with controls, showed a significant reduction in volumetric cortical BMD (VcBMD) (p = 0.04) and cortical thickness (cThk) (p < 0.0001) with a significant increase in radial total cross-sectional area (TA) (p = 0.006), endosteal circumference (p < 0.0001), and buckling ratio (p < 0.0001). In CAPD patients, total time on dialysis correlated negatively with radial total BMD (p < 0.01) and VcBMD (p < 0.01). Age correlated positively with TA (p < 0.01), endosteal (p < 0.01), and periosteal circumferences (p < 0.01). Serum intact parathyroid hormone (PTH) levels correlated positively with endosteal (p = 0.04) and periosteal perimeter (p = 0.01). Total alkaline phosphatase correlated negatively with VcBMD (p < 0.01), and positively with endosteal perimeter (p = 0.02). Total bone mineral content correlated significantly with radial cortical content (p < 0.001), cross-sectional cortical area (cA; p < 0.001), and cThk (p < 0.01) but not with total radial BMD, VcBMD, or buckling ratio. No correlations were found between radial cortical parameters and BMD measured at the lumbar spine or femoral neck. We conclude that dialysis patients show cortical osteopenia with marked cortical thinning partially mediated by PTH action on bone. Total bone mineral content correlated with various radial cortical parameters (content, area, and thickness) but not with others. No correlations were found between cortical bone parameters measured at the peripheral skeleton with areal bone density measured at the axial skeleton. These findings suggest that pQCT may be a new tool in the assessment of bone fragility in dialysis patients.     

High-resolution 3D imaging of microvascular architecture in human glioma tissues using X-ray phase-contrast computed tomography as a potential adjunct to histopathology

Gliomas are rich in blood vessels, and the generation of tumor-associated vessels plays an important role in glioma growth and transfer. Histology can directly depict microvascular architecture in the tumor, but it just provides two-dimensional (2D) images obtained by destroying three-dimensional (3D) tissue specimens. There is a lack of high-resolution 3D imaging methods for observing the microvasculature throughout the entire specimens. X-ray phase-contrast computed tomography (PCCT) which is an emerging imaging method has demonstrated its outstanding potential in imaging soft tissues. Thus, this study aims to evaluate the potential of PCCT as an adjunct to histopathology in nondestructive and 3D visualization of the microvascular architecture in human glioma tissues. In this study, seven resected glioma tissues were scanned via PCCT and then processed histologically. The obtained PCCT data was analyzed and compared with corresponding histological results. Significant anatomical structures of the glioma such as microvessels, thrombi inside the microvessels, and areas of vascular proliferation could be clearly presented via PCCT, confirmed by the histological findings. Moreover, PCCT data also provided additional 3D information such as morphological alterations of the microvasculature, 3D distribution of the thrombi and stenosis severity of the vessels in glioma tissues, which cannot be fully analyzed in 2D histological slices. In conclusion, this study demonstrated that PCCT can offer excellent images at a near-histological level and additional valuable information in screening gliomas, without impeding further histological investigations. Thus, this technique could be potentially used as an adjunct to conventional histopathology in 3D nondestructive characterization of glioma vasculature.     

Relation between computed tomography and diffraction tomography

The relationship between computed tomography (CAT) and diffraction tomography (DT) is investigated. A simple condition with a clear physical meaning is derived for the applicability of CAT. Corrections due to scattering are incorporated into CAT, and it is shown that the effect of scattering may be characterized by a two-dimensional fractional Fourier transform. The implications of these results for the three-dimensional imaging of weakly scattering objects are also discussed.     

Diffuse optical tomography guided quantitative fluorescence molecular tomography

We describe a method that combines fluorescence molecular tomography (FMT) with diffuse optical tomography (DOT), which allows us to study the impact of heterogeneous optical property distribution on FMT, an issue that has not been systemically studied. Both numerical simulations and phantom experiments were performed based on our finite-element reconstruction algorithms. The experiments were conducted using a noncontact optical fiber free, multiangle transmission system. In both the simulations and experiments, a fluorescent target was embedded in an optically heterogeneous background medium. The simulation results clearly suggest the necessity of considering the absorption coefficient (mu(a)) and reduced scattering coefficient (mu'(s)) distributions for quantitatively accurate FMT, especially in terms of the accuracy of reconstructed fluorophore absorption coefficient (mu(a(x-->m))). Subsequent phantom experiments with an indocyanine green (ICG)-containing target confirm the simulation findings. In addition, we performed a series of phantom experiments with low ICG concentration (0.1, 0.2, 0.4, 0.6 and 1.0 microM) in the target to systematically evaluate the quantitative accuracy of our FMT approach. The results indicate that, with the knowledge of optical property distribution, the accuracy of the recovered fluorophore concentration is improved significantly over that without such a priori information. In particular absolute value of mu(a(x-->m) ) from our DOT guided FMT are quantitatively consistent with that obtained using spectroscopic methods.     

Comparison of computed tomography dose reporting software

Computed tomography (CT) dose reporting software facilitates the estimation of doses to patients undergoing CT examinations. In this study, comparison of three software packages, i.e. CT-Expo (version 1.5, Medizinische Hochschule, Hannover, Germany), ImPACT CT Patients Dosimetry Calculator (version 0.99×, Imaging Performance Assessment on Computed Tomography, www.impactscan.org) and WinDose (version 2.1a, Wellhofer Dosimetry, Schwarzenbruck, Germany), has been made in terms of their calculation algorithm and the results of calculated doses. Estimations were performed for head, chest, abdominal and pelvic examinations based on the protocols recommended by European guidelines using single-slice CT (SSCT) (Siemens Somatom Plus 4, Erlangen, Germany) and multi-slice CT (MSCT) (Siemens Sensation 16, Erlangen, Germany) for software-based female and male phantoms. The results showed that there are some differences in final dose reporting provided by these software packages. There are deviations of effective doses produced by these software packages. Percentages of coefficient of variance range from 3.3 to 23.4 % in SSCT and from 10.6 to 43.8 % in MSCT. It is important that researchers state the name of the software that is used to estimate the various CT dose quantities. Users must also understand the equivalent terminologies between the information obtained from the CT console and the software packages in order to use the software correctly.     

Industrial computed tomography image size measurement

As one of the most useful modern detection technologies, Industrial Computed Tomography (ICT) image size measurement can correctly non-destructively measure the size of workpieces’ inner construction, and it is considered as the standard for quality assurance and reverse engineering. In view of the advantages and disadvantages compared to conventional methods, this paper improves the precision of image size measurement with a new algorithm that uses an approximate function to describe edge degradation. First, this algorithm constructs the approximate function and determines the optimal point of edge detection, based on image intensity and inflexions. Then, in order to accurately extract the image edge, this algorithm is used to revise the primary image, completing construction of the CT image.Excellent results are obtained from simulations and experiments. The experimental results indicate that the relative error is 2% for the CT image when the step evolution of the image edge is pooled. The relative error of this method is decreased by as much as 1.5% compared to wavelet transformation and ridgelet transformation. Therefore, this new algorithm demonstrates increased effectiveness in extracting an accurate measurement of the CT image edge.     

Lamb波CT成像的实验研究

根据Ｘ射线ＣＴ成像原理和方法，利用Ｌａｍｂ波对薄层铝板的人工伤进行了ＣＴ成像的实验研究，得到较好的成像结果。     

医用CT剂量指数测量结果的不确定度评定

为了使医用诊断计算机断层摄影装置（CT）X射线辐射源在模体中的剂量指数测量结果的不确定度评定合理。基于用带有100mm长杆电离室的积分剂量仪测量CT剂量指数的数学模型,对其测量不确定度来源进行分析,列出了方差、灵敏系数及标准不确定度的计算公式,从而给出了CT剂量指数测量的合成标准不确定度和扩展不确定度。     

Survey of practice in paediatric computed tomography

The purpose of this study was to explore the frequency of paediatric computed tomography (CT) examinations in several hospitals in Bulgaria and to assess the current practice. The standard forms provided by the International Atomic Emergency Agency for survey of the paediatric CT practice were used. Six hospitals provided data on frequency of paediatric CT examinations performed in 2009. Large variations in dose, up to a factor of 4, were found among the centres within the same age group for a given procedure, and in one of the hospitals the paediatric dose was twice higher than the adult dose. Seven departments use dedicated CT protocols for children. Only 4 in 12 departments keep records of patient dose. Dose information for previous examinations is not required by the radiologists. The collected detailed data provided preliminary information how the patient doses in paediatric CT can be reduced. Recommendations were given based on the findings.     

Theory of total-internal-reflection tomography

A method is presented to reconstruct three-dimensional tomographic images of weakly scattering objects with subwavelength resolution. The method may be applied to data available in phase-sensitive, total-internal-reflection microscopy. The results follow from an analysis of the near-field inverse scattering problem with evanescent waves.     

A quantitative analysis of computed hypervelocity debris clouds

This paper presents quantitative analyses of computed hypervelocity debris clouds due to aluminum spheres, rods and disks impacting aluminum bumper plates. The computations were performed using an algorithm to convert distorted Lagrangian finite elements to meshfree particles. The analyses were performed using a new postprocessing algorithm. The combination of this computational approach and this postprocessing algorithm is also used to characterize behind-armor debris due to tungsten rods impacting steel plates at ballistic velocities, and the results are compared to test data. The quantitative analyses are an extension of previous qualitative comparisons to radiographs of hypervelocity debris clouds.