Synchrotron Radiation Computed Tomography Research Articles

Imaging of lung function using synchrotron radiation computed tomography: What's new?

There is a growing interest in imaging techniques as non-invasive means of quantitatively measuring regional lung structure and function. Abnormalities in lung ventilation due to alterations in airway function such as those observed in asthma and COPD are highly heterogeneous, and experimental methods to study this heterogeneity are crucial for better understanding of disease mechanisms and drug targeting strategies. In severe obstructive diseases requiring mechanical ventilation, the optimal ventilatory strategy to achieve recruitment of poorly ventilated lung zones remains a matter of considerable debate. We have used synchrotron radiation computed tomography (SRCT) for the in vivo study of regional lung ventilation and airway function. This imaging technique allows direct quantification of stable Xenon (Xe) gas used as an inhaled contrast agent using K-edge subtraction imaging. Dynamics of Xe wash-in can be used to calculate quantitative maps of regional specific lung ventilation. More recently, the development of Spiral-CT has allowed the acquisition of 3D images of the pulmonary bronchial tree and airspaces. This technique gives access to quantitative measurements of regional lung volume, ventilation, and mechanical properties. Examples of application in an experimental model of allergic asthma and in imaging lung recruitment as a function of mechanical ventilation parameters will be presented. The future orientations of this tecnique will be discussed.

High-density three-dimensional mapping of internal strain by tracking microstructural features

The three-dimensional (3-D) strain map is useful to elucidate the relationships between microstructures and locally caused deformation and fracture. However, a robust tracking method, which enables error-free tracking in synchrotron radiation computed tomography (SR-CT) images with >10 000 microstructural features, is not currently available. In this study, a model sample was subjected to a tensile test and scanned by the SR-CT technique in order to develop a new tracking method. The developed tracking methods indicated a high tracking ratio and tracking success ratio of nearly 100% in a wide strain range, which included the assumed strain in a practical experiment. It was confirmed that tracking errors produce an incorrect strain distribution in 3-D strain mapping. This study verified the validity of the developed tracking method. The application of this method to high-resolution SR-CT images will make measurement and visualization of the strain distribution possible in three dimensions in bulk materials.

Myocardial Ischemia Diagnosed by Dual-Energy Computed Tomography

For decades, dual-energy imaging has been used for tissue differentiation with several x-ray–based imaging modalities, exploiting the fact that the tissues in the human body show different absorption characteristics when penetrated with different x-ray spectra, spectra that are typically generated by different kV settings of the x-ray tube. Recently, dual-source computed tomography (CT) with 2 x-ray tubes and 2 detector arrays mounted in the same gantry has become available.1 After experience with earlier experimental prototypes, this dual-source CT for the first time enables the clinical acquisition of dual-energy CT studies simultaneously with a single scan. We used a dual-source CT scanner (Definition, Siemens, Forchheim, Germany) in dual-energy mode for performing coronary CT angiography in a 74-year–old woman with suspected coronary artery disease and prior abnormal nuclear rest/stress single-photon emission CT (SPECT). The CT scan was acquired with retrospective ECG-gating and the following scan parameters: 330-ms gantry rotation, pitch 0.2, and 32×2×0.6-mm …

Simultaneous in vivo synchrotron radiation computed tomography of regional ventilation and blood volume in rabbit lung using combined K-edge and temporal subtraction

In K-edge subtraction (KES) imaging with synchrotron radiation computed tomography (SRCT), two images are taken simultaneously using energies above and below the K-absorption edge of a contrast agent. A logarithmic difference image reveals the contrast agent concentration with good accuracy. Similarly, in temporal subtraction imaging (TSI) the reference image is taken before the introduction of the contrast agent. Quantitative comparisons of in vivo images of rabbit lung indicated that similar results for concentrations of iodine in blood vessels and xenon in airways are obtained by KES and TSI, but the level of noise and artifacts was higher in the latter. A linear fit showed that in the lung parenchyma ρTSI = (0.97 ± 0.03)ρKES + (0.00 ± 0.05) for xenon and ρTSI = (1.21 ± 0.15)ρKES + (0.0 ± 0.1) for iodine. For xenon the calculation of time constant of ventilation gave compatible values for both of the methods. The two methods are combined for the simultaneous determination of the xenon concentration (by KES) and the iodine concentration (by TSI) in lung imaging, which will allow simultaneous in vivo determination of ventilation and perfusion.

Three-Dimensional Measurement of Local Strain Distribution by Tracking Microstructural Features in High-Resolution SR-CT Image

The local elastic and plastic strain during deformation are very complicated and different form the macroscopic strain, because most materials have inhomogeneous microstructure. In this study, local strain distribution in three dimensions has been measured using the new developed method based on image analysis in high-resolution synchrotron radiation computed tomography (SR-CT). Model and practical specimens, which made of cupper alloy and aluminum alloy, respectively, were prepared for a development procedure and application of local strain measurements. Gauging intervals of microstructural features before and after deformation gave us information of inhomogeneous local strain distribution in three dimensions. High strain was observed in a necking region appeared after tensile deformation in the model sample. A combination of non-destructive measurements by SR-CT and three-dimensional analysis revealed inhomogeneous strain distributions in practical aluminum samples.

3-D High-Density Strain Mapping Procedure Based on High-Resolution CT

A tracking procedure for the high-resolution X-ray computed tomography (CT) has been developed in order to measure 3-D local strain within a deforming material in high-density. A dispersion-strengthened copper alloy model sample with alumina particles, which contains micropores, was visualized by the synchrotron radiation CT. The pores observed in reconstructed CT volumes were used as tracking markers. The developed tracking method using a set of matching parameters, which classifies matched, pended and rejected markers, exhibited high ratio of success tracking. Furthermore, the ratio was improved by applying the spring model method, which is one of the particle image velocity (PIV) methods utilized in the field of the fluid mechanics, to the pended markers. The method based on the image analysis of CT imaging volumes provides us 3-D high-density strain mapping.

高分解能 X 線 CT イメージ解析と特徴点追跡法による三次元ひずみ計測

Measurement of interior strain distribution has been developed based on the synchrotron radiation computed tomography (SR-CT). In metal deformation, local strain distribution differs from macroscopic strain due to microstructural factors such as grains, grain boundaries, particles, pores, voids, and cracks. A model sample, which was made from a copper alloy strengthened with alumina, was prepared containing artificial pores. Tensile loading was applied to the sample step by step. High-resolution tomographic experiment was performed at the third-generation synchrotron radiation facility (SPring-8) in Japan. Gravity center position, volume and surface area in the pores, which were regarded as markers in a tracking procedure, were measured by 3-D digital image analysis in the SR-CT images. The markers before and after the deformation were provided for registration and macroscopic strain correction before the tracking procedure. The marker tracking was carried out by means of matching parameter that was described as functions of distance, volume and surface at markers. The ratio of success tracking was evaluated in order to clarify whether the tracking method developed in this study was reliable. The 3-D strain distribution was represented successfully by the tracking results. A combination of high-resolution SR-CT and tracking of microstructural features is effective to visualize interior strain distribution in materials in 3-D.

OS3-1-2 Measurement of 3-D strain distribution based on tracking of microstructural features in high-resolution SR-CT image

A tracking procedure for the high-resolution X-ray computed tomography has been developed in order to measure 3-D local strain within a deforming material in high-density. A model sample, which made of a dispersion-strengthened copper with alumina particles and contains artificial micro-pores, was visualized by the synchrotron radiation computed tomography (SR-CT) with in-situ test rig. Tensile loading was applied to the sample step by step. High-resolution tomographic experiment was performed at the third-generation synchrotron radiation facility (SPring-8) in Japan. Gravity center position, volume and surface area in the pores, which were regarded as markers in a tracking procedure, were measured by 3-D digital image analysis. The markers before and after the deformation were provided for registration and macroscopic strain correction before the tracking procedure. The marker tracking was carried out by means of matching parameter that was described as functions of distance, volume and surface at markers. The developed tracking method indicated high tracking ratio and tracking success ratio, which was approximately 100%, up to the macroscopic strain level that exceed in the strain range of practical tracking experiment. The 3-D strain distribution was represented successfully by the tracking results. A combination of high-resolution SR-CT and tracking of microstructural features is effective to visualize interior strain distribution in materials in 3-D.

Utilization of nPAG dosimeter for synchrotron radiotherapy: first results

The specificity of synchrotron stereotactic radiotherapy requires new developments in dose calculation and appropriate experimental procedures. The medical beamline of the European Synchrotron Radiation Facility allows quantitative synchrotron radiation CT (SRCT) images to be obtained from a monochromatic x-ray beam. This paper investigates initial experimental dosimetry with normoxic polyacrylamide gel dosimeters. MRI and SRCT readouts are compared.

Small airway changes in healthy and ovalbumin-treated mice during quasi-static lung inflation

Previously, we developed a synchrotron radiation CT system to evaluate the morphometric changes (length and diameter, D) and small airway compliance (sC(aw)) of euthanized mice under quasi-static inflation [Sera, T., Uesugi, K., Yagi, N., 2005. Localized morphometric deformations of small airways and alveoli in intact mouse lungs under quasi-static inflation. Respir. Physiol. Neurobiol. 147, 51-63). Using this system, this study compared normal and asthmatic small airways. Ovalbumin-treated mice were used as an asthma model. Compared with the values at functional residual capacity, D of normal and asthmatic small airways (D<200microm) increased by 48% and 36% at the end of tidal inspiration. For larger airways (D>500microm), the increases were 23% and 20%, respectively. The ratio of the sC(aw) of asthmatic small airways to that of healthy small airways was 0.57, and the ratio was 0.70 for larger airways. The morphometric changes and sC(aw) in asthma model mice were significantly lower than those of healthy mice. The differences in sC(aw) between healthy and asthma model mice were greater for smaller airways.

Differences in the time course of proximal and distal airway response to inhaled histamine studied by synchrotron radiation CT

We studied the kinetics of proximal and distal bronchial response to histamine aerosol in healthy anesthetized and mechanically ventilated rabbits up to 60 min after histamine administration using a novel xenon-enhanced synchrotron radiation computed tomography imaging technique. Individual proximal airway constriction was assessed by measuring the luminal cross-sectional area. Distal airway obstruction was estimated by measuring the ventilated alveolar area after inhaled xenon administration. Respiratory system conductance was assessed continuously. Proximal airway cross-sectional area decreased by 57% of the baseline value by 20 min and recovered gradually but incompletely within 60 min. The ventilated alveolar area decreased immediately after histamine inhalation by 55% of baseline value and recovered rapidly thereafter. The results indicate that the airway reaction to inhaled histamine and the subsequent recovery are significantly slower in proximal than in distal bronchi in healthy rabbit. The findings suggest that physiological reaction mechanisms to inhaled histamine in the airway walls of large and small bronchi are not similar.

Fine Structural Analysis of Cortical Bone by Synchrotron Radiation CT

Fine Structural Analysis of Cortical Bone by Synchrotron Radiation CT

Can bone quality be assessed non-invasively?--Imaging--

Properties of "bone quality" contain "structural property" and "material property" . Most components of "material properties" cannot be visualized by current technology. Mineralization, one of material properties, can be evaluated using synchrotron radiation CT or contact microradiography with high spatial and density resolution, but they are invasive examinations. On the other hand, "structural property" can be radiographically delineated, even though only a few methods are available non-invasively. Assessments of macrostructure of bone by radiograms or CT, and trabecular microstructure by high resolution CT or MR can be done non-invasively, and provide valuable results in clinical studies. Bone scintigram provides limited but useful information of bone turnover.

Plasma Volume and Permeability Coefficient measurements in the C6 glioma model using Synchrotron Radiation CT coupled to injection of P743, Xenetix and Iomeron

Plasma Volume and Permeability Coefficient measurements in the C6 glioma model using Synchrotron Radiation CT coupled to injection of P743, Xenetix and Iomeron

Localized morphometric deformations of small airways and alveoli in intact mouse lungs under quasi-static inflation

Localized morphometric deformations of small airways and alveoli during respiration have several biomechanical and physiological implications. We developed fast synchrotron radiation CT system to visualize the small airways and alveoli of an intact mouse lung without fixation and dehydration, and analyzed their localized morphometric deformations between functional residual capacity (FRC) and total lung capacity (TLC). The maximum resolution of 32.6lp/mm at the 5% modulation transfer function level can be achieved with 11.8-microm voxels and 7-min scanning. Compared with the values at FRC, the diameter and length for smaller airways (diameter at FRC <200 microm) increased by 68.8% and 29.5% (averaged value), and those for larger airways (diameter at FRC >400 microm) increased by 45.2 and 22.9% (averaged value), at TLC. Moreover we defined the volume behavior as the percentage of airway volume at FRC for TLC. The volume behavior for the small airways was not similar to that of the lung volume. These results indicated that all airways did not behave homogenously.

High-Resolution Blood–Brain Barrier Permeability and Blood Volume Imaging Using Quantitative Synchrotron Radiation Computed Tomography: Study on an F98 Rat Brain Glioma

The authors previously provided evidence of synchrotron radiation computed tomography (SRCT) efficacy for quantitative in vivo brain perfusion measurements using monochromatic X-ray beams. However, this technique was limited for small-animal studies by partial volume effects. In this paper, high-resolution absolute cerebral blood volume and blood-brain barrier permeability coefficient measurements were obtained on a rat glioma model using SRCT and a CCD camera (47x47 microm2 pixel size). This is the first report of in vivo high-resolution brain vasculature parameter assessment. The work gives interesting perspectives to quantify brain hemodynamic changes accurately in healthy and pathological small animals.

高分解能シンクロトロン放射光CTによる粒界3次元ネットワーク構造の可視化

高分解能シンクロトロン放射光CTによる粒界3次元ネットワーク構造の可視化

Morphometric Deformations of Small Airways and Alveoli under Quasi-static Inflation Process

Localized morphometric deformations of small airways and alveoli during respiration have many biomedical and physiological implications. We developed fast synchrotron radiation CT system to visualize the small airways and alveoli of an intact mouse lung without fixation and dehydration, and analyzed their localized morphometric deformations between functional residual capacity (FRC) and total lung capacity (TLC). In the diameter behavior, the averaged and range values were significantly larger for smaller airways (68.8%, range: 0.36-0.89) than larger airways (45.2%, range: 0.40-0.57). These results indicated that the airway did not deformed in same manner and that these morphological differences characterized the heterogeneous lung function.

Assessment of cortical bone microstructure and material properties using high resolution scanning acoustic microscopy

Combined evaluation of bone microstructural and mechanical information remains a challenging task which is required for bone phenotyping or accurate finite element modeling. Our objective was to assess the value of quantitative scanning acoustic microscopy (SAM) for bone characterization in comparison to synchrotron radiation computed tomography (SR-CT). Ten specimens of human cortical bone (radius) were investigated using SR-CT and SAM (200 MHz) with spatial resolution of 10 and 8 μm, respectively. An image fusion and analysis software was developed to derive site-matched estimates of (1) microstructural parameters, e.g., haversian cavity density and mean diameter and porosity, and (2) tissue properties such as mineral density (MD, SR-CT) and acoustic impedance (Z, SAM) for distinct anatomical regions of interest (osteons, interstitial tissue). Local stiffness c33 was derived from the combination of MD and Z. An almost perfect correlation was found for all microstructural indices derived by both techniques. Impedance was correlated to the square of MD (R2=0.39, p&amp;lt;1e−4). The derived stiffness c33 (35.9±12.8) was highly correlated with Z (R2=0.99, p&amp;lt;1e−4). These findings suggest that SAM fulfills the requirement for a simultaneous evaluation of cortical bone microstructure and material properties at the tissue level.

Structural and elastic determinants of axial transmission ultrasonic velocity in the human radius

Accurate clinical interpretation of the sound velocity derived from axial transmission devices requires a detailed understanding of the propa-gation phenomena involved and of the bone factors that have an impact on measurements. In the low-megahertz range, ultrasonic propagation in cortical bone depends on anisotropic elastic tissue properties, porosity, and the spatial dimensions, e.g., cortical thickness. A subset of ten human radius samples from a previous biaxial transmission investigation was inspected using 50-MHz scanning acoustic microscopy (SAM) and synchrotron radiation computed tomography (SR-CT). Low-frequency axial transmission sound speed at 1 and 2 MHz was related to structural properties (cortical thickness C.Th, porosity POR, Haversian cavity density CDH) and tissue parameters (acoustic impedance Z, mineral density MD) on site-matched cross sections. Significant linear multivariate regression models (1 MHz: R=0.84, p&amp;lt;1E−4, 2 MHz: R=0.65, p&amp;lt;1E−4) were found for the combination of C.Th with POR and Z (measured in the external cortical quarter). A modified model accounting for the nonlinear dispersion relation with C.Th was also highly significant (R=0.75, p&amp;lt;1E−4, rmse=49.22 m/s) and explained (after adjustment for dispersion) 55.6% of the variance of the sound velocity by variations of porosity (15.6%) and impedance (40%).