Theoretical considerations predicted the feasibility of K-edge x-ray computed tomography (CT) imaging using energy discriminating detectors with more than two energy bins. This technique enables material-specific imaging in CT, which in combination with high-Z element based contrast agents, opens up possibilities for new medical applications. In this paper, we present a CT system with energy detection capabilities, which was used to demonstrate the feasibility of quantitative K-edge CT imaging experimentally. A phantom was imaged containing PMMA, calcium-hydroxyapatite, water and two contrast agents based on iodine and gadolinium, respectively. Separate images of the attenuation by photoelectric absorption and Compton scattering were reconstructed from energy-resolved projection data using maximum-likelihood basis-component decomposition. The data analysis further enabled the display of images of the individual contrast agents and their concentrations, separated from the anatomical background. Measured concentrations of iodine and gadolinium were in good agreement with the actual concentrations. Prior to the tomographic measurements, the detector response functions for monochromatic illumination using synchrotron radiation were determined in the energy range 25 keV-60 keV. These data were used to calibrate the detector and derive a phenomenological model for the detector response and the energy bin sensitivities.

Purpose:To investigate the potential of spectral computed tomography (CT) (popularly referred to as multicolor CT), used in combination with a gold high-density lipoprotein nanoparticle contrast agent (Au-HDL), for characterization of macrophage burden, calcifi cation, and stenosis of atherosclerotic plaques. Materials and Methods:The local animal care committee approved all animal experiments. A preclinical spectral CT system in which incident x-rays are divided into six different energy bins was used for multicolor imaging. Au-HDL, an iodine-based contrast agent, and calcium phosphate were imaged in a variety of phantoms. Apolipoprotein E knockout (apo E-KO) mice were used as the model for atherosclerosis. Gold nanoparticles targeted to atherosclerosis (Au-HDL) were intravenously injected at a dose of 500 mg per kilogram of body weight. Iodine-based contrast material was injected 24 hours later, after which the mice were imaged. Wild-type mice were used as controls. Macrophage targeting by Au-HDL was further evaluated by using transmission electron microscopy and confocal microscopy of aorta sections. Results:Multicolor CT enabled differentiation of Au-HDL, iodinebased contrast material, and calcium phosphate in the phantoms. Accumulations of Au-HDL were detected in the aortas of the apo E-KO mice, while the iodine-based contrast agent and the calcium-rich tissue could also be detected and thus facilitated visualization of the vasculature and bones (skeleton), respectively, during a single scanning examination. Microscopy revealed Au-HDL to be primarily localized in the macrophages on the aorta sections; hence, the multicolor CT images provided information about the macrophage burden. Conclusion:Spectral CT used with carefully chosen contrast agents may yield valuable information about atherosclerotic plaque composition.q RSNA, 2010Supplemental material: http://radiology.rsna.org/lookup /suppl

The purpose of this study was to investigate whether spectral computed tomography (CT) has the potential to improve luminal depiction by differentiating among intravascular gadolinium-based contrast agent, calcified plaque, and stent material by using the characteristic k edge of gadolinium. A preclinical spectral CT scanner with a photon-counting detector and six energy threshold levels was used to scan a phantom vessel. A partially occluded stent was simulated by using a calcified plaque isoattenuated to a surrounding gadolinium chelate solution. The reconstructed images showed an effective isolation of the gadolinium with subsequent clear depiction of the perfused vessel lumen. The calcified plaque and the stent material are suppressed.

In this paper it is shown that diffuse-scattering experiments within the region of total external reAection can be explained quantitatively using the distorted-wave Born approximation for layer systems. Three Si/Ge samples with different degrees of complexity were investigated. The simultaneous analysis of the specular rejected intensity and the diffuse scattering leads to one consistent set of interface and layer parameters, which is able to fit both the shapes and the locations of all dynamic peaks in the off-specular scans and the characteristics of the rejected intensity. Therefore the distorted-wave Born approximation seems to give a correct and complete description of the diffuse scattering in the region of total external reflection.

Multicolored imaging: A new class of molecular imaging agent has been developed based on low‐molecular‐weight organically soluble bismuth to detect and quantify intraluminal fibrin presented by ruptured plaque in the context of computed tomography angiograms without calcium interference.

The feasibility of K-edge imaging using energy-resolved, photon-counting transmission measurements in X-ray computed tomography (CT) has been demonstrated by simulations and experiments. The method is based on probing the discontinuities of the attenuation coefficient of heavy elements above and below the K-edge energy by using energy-sensitive, photon counting X-ray detectors. In this paper, we investigate the dependence of the sensitivity of K-edge imaging on the atomic number Z of the contrast material, on the object diameter D , on the spectral response of the X-ray detector and on the X-ray tube voltage. We assume a photon-counting detector equipped with six adjustable energy thresholds. Physical effects leading to a degradation of the energy resolution of the detector are taken into account using the concept of a spectral response function R(E,U) for which we assume four different models. As a validation of our analytical considerations and in order to investigate the influence of elliptically shaped phantoms, we provide CT simulations of an anthropomorphic Forbild-Abdomen phantom containing a gold-contrast agent. The dependence on the values of the energy thresholds is taken into account by optimizing the achievable signal-to-noise ratios (SNR) with respect to the threshold values. We find that for a given X-ray spectrum and object size the SNR in the heavy element's basis material image peaks for a certain atomic number Z. The dependence of the SNR in the high- Z basis-material image on the object diameter is the natural, exponential decrease with particularly deteriorating effects in the case where the attenuation from the object itself causes a total signal loss below the K-edge. The influence of the energy-response of the detector is very important. We observed that the optimal SNR values obtained with an ideal detector and with a CdTe pixel detector whose response, showing significant tailing, has been determined at a synchrotron differ by factors of about two to three. The potentially very important impact of scattered X-ray radiation and pulse pile-up occurring at high photon rates on the sensitivity of the technique is qualitatively discussed.

The surfaces of liquid thin perfluorohexane, cyclohexane, decane, and ethanol films adsorbed on silicon wafers have been investigated by means of x-ray reflectivity, diffuse scattering, and grazing incidence diffraction. The measurements prove that the surface structure of the wetting films can be described by a universal height-height correlation function derived from a capillary wave model with the surface tension and particular cutoffs as parameters. The data favor a reduced capillary wave surface tension as predicted by exact theories, over an enhanced capillary wave surface tension, as suggested by simple mode-coupling models. PACS numbers: 68.15. + e, 61.41. + e, 68.45.Gd While liquid thin films have been in the center of theoretical work (see, e.g., [1][2][3][4][5][6][7] and references therein) for several years, there is a considerable lack of experimental studies of their surface structure [8,9]. This is largely caused by experimental demands. One major challenge in the investigation of liquid films is to control their thickness with high accuracy. A stability of about one angstrom during many hours is required. Furthermore, liquid surfaces possess long-range correlations (capillary waves, see below). Hence, high resolution in reciprocal space is required making x-ray experiments at synchrotron sources mandatory. In fact, to our knowledge, the study of Tidswell et al. [10] is the only quantitative x-ray scattering experiment centering on the structure of the interfaces of liquid thin films on solid substrates. In this Letter, we show for the first time (i) that distinct capillary wave features-they will be specified beloware common for a large variety of liquids and film thicknesses; and (ii) that the surface tension which has to be used within the capillary wave model for thin films may be considerably lower than the macroscopic value.The usual approach to describe a liquid/vapor interface is based on the presence of an "intrinsic interface" of width s 0 and a surface tension g 0 . The surface structure of semi-infinite liquids possessing thermally excited capillary waves superimposed on the intrinsic profile was calculated by Buff et al. [11,12]. It turns out that the wave spectrum depends solely on g 0 and a shortwavelength cutoff q max which is commonly assumed to be q max ϳ 2p͞k, where k is on the order of the molecular diameter of the liquid. In the past, this simple capillary wave model has been successfully tested for various bulk liquids [13][14][15]. However, the precise magnitude and physical origin of the short-wavelength cutoff are still discussed controversially [16]. Meunier's mode-coupling approach [17,18] leads to a wave number dependent surface tension g͑q͒. To simplify the further discussion only the respective average g cw ͗g͑q͒͘ over all modes is considered with the resultfor the surface tension which has to be used in the capillary wave model. More recently, another approach based on the exact form of the van der Waals interactions was published by Napiórkowski, Dietrich, and Mec...

Mehrfarbige Bildgebung: Eine neue Klasse von molekularen Bildgebungsmitteln basierend auf niedermolekularem, organisch löslichem Bismut wurde entwickelt. Damit gelingen mittels computertomographischer Angiogramme der Nachweis und die Quantifizierung von intraluminalem Fibrin in Plaquerupturen ohne Calciuminterferenz.