Microfocus X-ray Tube Research Articles

Toward quantifying the composition of soft tissues by spectral CT with Medipix3

To determine the potential of spectral computed tomography (CT) with Medipix3 for quantifying fat, calcium, and iron in soft tissues within small animal models and surgical specimens of diseases such as fatty liver (metabolic syndrome) and unstable atherosclerosis. The spectroscopic method was applied to tomographic data acquired using a micro-CT system incorporating a Medipix3 detector array with silicon sensor layer and microfocus x-ray tube operating at 50 kVp. A 10 mm diameter perspex phantom containing a fat surrogate (sunflower oil) and aqueous solutions of ferric nitrate, calcium chloride, and iodine was imaged with multiple energy bins. The authors used the spectroscopic characteristics of the CT number to establish a basis for the decomposition of soft tissue components. The potential of the method of constrained least squares for quantifying different sets of materials was evaluated in terms of information entropy and degrees of freedom, with and without the use of a volume conservation constraint. The measurement performance was evaluated quantitatively using atheroma and mouse equivalent phantoms. Finally the decomposition method was assessed qualitatively using a euthanized mouse and an excised human atherosclerotic plaque. Spectral CT measurements of a phantom containing tissue surrogates confirmed the ability to distinguish these materials by the spectroscopic characteristics of their CT number. The assessment of performance potential in terms of information entropy and degrees of freedom indicated that certain sets of up to three materials could be decomposed by the method of constrained least squares. However, there was insufficient information within the data set to distinguish calcium from iron within soft tissues. The quantification of calcium concentration and fat mass fraction within atheroma and mouse equivalent phantoms by spectral CT correlated well with the nominal values (R(2) = 0.990 and R(2) = 0.985, respectively). In the euthanized mouse and excised human atherosclerotic plaque, regions of calcium and fat were appropriately decomposed according to their spectroscopic characteristics. Spectral CT, using the Medipix3 detector and silicon sensor layer, can quantify certain sets of up to three materials using the proposed method of constrained least squares. The system has some ability to independently distinguish calcium, fat, and water, and these have been quantified within phantom equivalents of fatty liver and atheroma. In this configuration, spectral CT cannot distinguish iron from calcium within soft tissues.

Construction and test of an X-ray CT setup for material resolved 3D imaging with Medipix based detectors

A prototype computerized tomography (CT) setup has been recently built at Nikhef in order to exploit the material resolved capabilities of Medipix based detectors in X-ray imaging. The CT scanner contains a Hamamatsu 90 kVp microfocus X-ray tube and an entirely remotely controllable sample alignment system. The complete setup is fully integrated with the detector operation software. Moreover the 120 frames/s RelaxD readout system [1] allows real time X-ray imaging of fast moving samples.In this work, the description of the setup is given and the firstresults obtained with Medipix2 [2] andTimepix [3] detectors are presented. They concerndetector calibration with fluorescence lines, CT reconstruction ofsmall biological and non-biological samples and material resolved 3Dmicro-imaging [4].

A reconstruction method for cone-beam differential x-ray phase-contrast computed tomography

Most existing differential phase-contrast computed tomography (DPC-CT) approaches are based on three kinds of scanning geometries, described by parallel-beam, fan-beam and cone-beam. Due to the potential of compact imaging systems with magnified spatial resolution, cone-beam DPC-CT has attracted significant interest. In this paper, we report a reconstruction method based on a back-projection filtration (BPF) algorithm for cone-beam DPC-CT. Due to the differential nature of phase contrast projections, the algorithm restrains from differentiation of the projection data prior to back-projection, unlike BPF algorithms commonly used for absorption-based CT data. This work comprises a numerical study of the algorithm and its experimental verification using a dataset measured with a three-grating interferometer and a micro-focus x-ray tube source. Moreover, the numerical simulation and experimental results demonstrate that the proposed method can deal with several classes of truncated cone-beam datasets. We believe that this feature is of particular interest for future medical cone-beam phase-contrast CT imaging applications.

Spectral CT of carotid atherosclerotic plaque: comparison with histology

To distinguish components of vulnerable atherosclerotic plaque by imaging their energy response using spectral CT and comparing images with histology. After spectroscopic calibration using phantoms of plaque surrogates, excised human carotid atherosclerotic plaques were imaged using MARS CT using a photon-processing detector with a silicon sensor layer and microfocus X-ray tube (50 kVp, 0.5 mA) at 38-μm voxel size. The plaques were imaged, sectioned and re-imaged using four threshold energies: 10, 16, 22 and 28 keV; then sequentially stained with modified Von Kossa, Perl's Prussian blue and Oil-Red O, and photographed. Relative Hounsfield units across the energies were entered into a linear algebraic material decomposition model to identify the unknown plaque components. Lipid, calcium, iron and water-like components of plaque have distinguishable energy responses to X-ray, visible on spectral CT images. CT images of the plaque surface correlated very well with histological photographs. Calcium deposits (>1,000 μm) in plaque are larger than iron deposits (<100 μm), but could not be distinguished from each other within the same voxel using the energy range available. Spectral CT displays energy information in image form at high spatial resolution, enhancing the intrinsic contrast of lipid, calcium and iron within atheroma. Spectral computed tomography offers new insights into tissue characterisation. Components of vulnerable atherosclerotic plaque are spectrally distinct with intrinsic contrast. Spectral CT of excised atherosclerotic plaques can display iron, calcium and lipid. Calcium deposits are larger than iron deposits in atheroma. Spectral CT may help in the non-invasive detection of vulnerable plaques.

SU-E-I-99: An Ultra-High Resolution Small Field-Of-View Solid State X-Ray Imaging Detector Based on an Electron Multiplying CCD.

To demonstrate the ultra-high resolution capability of a small field-of-view (FOV) solid state x-ray imaging detector based on an EMCCD sensor. A micro-solid state x-ray image intensifier (micro-SSXII) was developed to serve as an ultra-high resolution region-of-interest (ROI) imaging detector. It is based on an 8 micron, 1004 by 1002 pixel electron multiplying CCD (EMCCD) optically coupled to a 100 micron thick CsI(Tl) phosphor through a fiber optic window resulting in a FOV of 8 mm. The modulation transfer function (MTF) of the micro-SSXII was measured by the slanted edge method. A cast of a rat kidney (made by mixing resin and iodine for contrast) and a mammography line pair test object were imaged at 50 kVp to demonstrate the detector's ultra-high resolution capability visually. The MTF was determined and was 5% at 20 cycles/mm. This is consistent with the clear visualization of the maximum 20 lp/mm group in the image of the mammography test object. Also, iodine bubbles with diameters as small as 25 microns, which are formed by the non-uniform mixing of the iodine in the resin cast, can be clearly identified in the rat kidney vessels. The ultra-high resolution capability (>20 lp/mm) but small FOV (8 mm) of the micro-SSXII in combination with a low-energy x-ray source may have application for investigations of vascular specimen details and other fine structures where optical or other surface imagers would be unsuited for evaluating features below the surface. Contact radiography with this imager combined with a large higher-load focal spot x-ray tube may be a promising substitute for magnification radiography which is limited by the use of specialized low output microfocus x-ray tubes and geometric un-sharpness for large magnifications. Supported in part by: NIH Grants R01-EB008425, R01-EB002873 and an equipment grant from Toshiba Medical Systems Corp.

미소초점엑스선원 개발을 위한 전산모사

MFX tube를 개발하기 위하여, MFX tube 내에서 전계방출음극으로부터 방출된 전자의 궤적을 SIMION 프로그램을 이용하여 전산모사하였다. 전자의 출발위치와 상관없이 emitter에서 방출된 전자빔을 한곳에 집중시킬 수 있는 optimum extractor voltage Ve가 존재한다는 것을 알아내었다. Extractor voltage Ve는 source voltage Vs에 따라 변하지만, 두 전압의 비율(Ve/Vs)는 항상 일정하고, 그 값은 99.4%였다. Source와 extractor에 인가된 전압의 비율(Ve/Vs)이 99.4%일 때, 교차점에서의 빔 직경은 <TEX>$1.2{\mu}m$</TEX>였다. MFXG의 초점 크기는 교차점에서의 beam diameter보다 작을 수 없기 때문에, 교차점에서의 beam diameter을 작게 할 수 있는 조건을 찾는 것은 중요하다. 따라서 위의 두 결과는 MFX tube의 개발에 있어서 매우 중요한 결과로 판단된다. To develop the MFX (Micro-Focus X-ray) tube, the trajectories of electrons emitted from the field emission cathode was simulated using SIMION program. Regardless of starting position of the electron in emitter, we found out the fact that there is the optimum extractor voltage Ve, which can focus the electron beam on one place. Extractor voltage Ve varies depending on the source voltage Vs, but the ratio of two voltages (Ve/Vs) is always constant, its value was 99.4%. When the ratio of two voltages (Ve/Vs) was 99.4%, the beam diameter in the cross-over point was <TEX>$1.2{\mu}m$</TEX>. Because the focal spot size in MFXG (Micro-Focus X-ray Generator) can not be less than the cross-over diameter within MFX tube, it is important to find out the conditions that can make a smaller beam diameter. Therefore, the above results is considered to be a very important ones in the development of the MFXG.

Evaluation of a YAG:Ce scintillation crystal based CCD X-ray imaging detector with the Medipix2 detector

Over the last decades the traditional photographic films used in radiology are being replaced by digital X-ray imaging sensors in many applications. The main advantages of these systems are their detection efficiency of image acquisition and the ability to directly digitally transfer and enhance obtained images. In this paper we characterize and evaluate the X-ray imaging performance of a YAG:Ce single crystal scintillator. The scintillator converts X-rays into visible light that is collected by an optical camera. The camera uses a CCD sensor with the size of 36x24 mm2 and with 4050 x 2630 pixels of 9x9 μm2 pitch, and is equipped with a macro objective. The semiconductor pixel detector Medipix2 was used for the evaluation of the imaging capabilities of this imaging system. The imaging capability is evaluated in terms of several basic characteristics: spatial resolution, edge response function, signal to noise ratio and contrast to noise ratio. A microfocus X-ray tube was used for high spatial resolution measurements in order to minimize the influence of the X-ray tube spot size. Measurements were done using an edge phantom, step wedge phantom and low contrast fibres. The corresponding measurements for all phantoms were done under identical conditions in order to assure comparability. The results measured by the CCD camera demonstrate the possibilities of sensitive X-ray radiography imaging with high spatial resolution.

Secondary radiation in transmission-type X-ray tubes: Simulation, practical issues and solution in the context of X-ray microtomography

Abstract In laboratory-based X-ray radiography and computed tomography, the X-rays are assumed to originate from one single focal spot with a finite spot size, which is generated by focussing accelerated electrons on the target material. However, apart from this focal spot, X-rays can also be produced elsewhere in the tube system. A major contribution of this parasitic radiation originates from electrons that are backscattered from the target material, into the X-ray tube system, where they can produce so-called off-focus or secondary X-rays. This phenomenon has been widely studied for rotating anode X-ray tubes in medical imaging systems, but not for transmission-type microfocus X-ray tubes. This paper presents a study on the origin of secondary radiation in this kind of X-ray tubes, which is performed by Monte Carlo simulations and by experimental measurements. The impact of this phenomenon on the imaging process is studied, and two correction methods are proposed, both on the hardware and on the software levels.

Compact x-ray microradiograph for in situ imaging of solidification processes: Bringing in situ x-ray micro-imaging from the synchrotron to the laboratory

A laboratory based high resolution x-ray radiograph was developed for the investigation of solidification dynamics in alloys. It is based on a low-power microfocus x-ray tube and is potentially appropriate for x-ray diagnostics in space. The x-ray microscope offers a high spatial resolution down to approximately 5 μm. Dynamic processes can be resolved with a frequency of up to 6 Hz. In reference experiments, the setup was optimized to yield a high contrast for AlCu-alloys. With samples of about 150 μm thickness, high quality image sequences of the solidification process were obtained with high resolution in time and space.

Noise in x‐ray grating‐based phase‐contrast imaging

Grating-based x-ray phase-contrast imaging is a fast developing new modality not only for medical imaging, but as well for other fields such as material sciences. While these many possible applications arise, the knowledge of the noise behavior is essential. In this work, the authors used a least squares fitting algorithm to calculate the noise behavior of the three quantities absorption, differential phase, and dark-field image. Further, the calculated error formula of the differential phase image was verified by measurements. Therefore, a Talbot interferometer was setup, using a microfocus x-ray tube as source and a Timepix detector for photon counting. Additionally, simulations regarding this topic were performed. It turned out that the variance of the reconstructed phase is only dependent of the total number of photons used to generate the phase image and the visibility of the experimental setup. These results could be evaluated in measurements as well as in simulations. Furthermore, the correlation between absorption and dark-field image was calculated. These results provide the understanding of the noise characteristics of grating-based phase-contrast imaging and will help to improve image quality.

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Model of the 3D X-ray television system

Flat-panel volume computed tomography (VCT) systems enables imaging of entire organs in one axial acquisition. Higher spatial resolution in such systems can be obtained because of moving patient closer to the digital receptor. It can be used not microfocus X-ray tubes, that is shown at the optical transfer function. Stands for such CT system become simpler. As flat panels reliable, comparatively not expensive CCD sensor array structure with good spatial resolution can be used. 3D image can be formed in radiologist’s mind when revolving object is shown on the monitor’s screen. Enumerated factors make it possible to construct new generation of inexpensive fluoroscopic systems with 3D and CT modes.

Compact pnCCD-Based X-ray Camera with High Spatial and Energy Resolution: A Color X-ray Camera

For many applications there is a requirement for nondestructive analytical investigation of the elemental distribution in a sample. With the improvement of X-ray optics and spectroscopic X-ray imagers, full field X-ray fluorescence (FF-XRF) methods are feasible. A new device for high-resolution X-ray imaging, an energy and spatial resolving X-ray camera, is presented. The basic idea behind this so-called "color X-ray camera" (CXC) is to combine an energy dispersive array detector for X-rays, in this case a pnCCD, with polycapillary optics. Imaging is achieved using multiframe recording of the energy and the point of impact of single photons. The camera was tested using a laboratory 30 μm microfocus X-ray tube and synchrotron radiation from BESSY II at the BAMline facility. These experiments demonstrate the suitability of the camera for X-ray fluorescence analytics. The camera simultaneously records 69,696 spectra with an energy resolution of 152 eV for manganese K(α) with a spatial resolution of 50 μm over an imaging area of 12.7 × 12.7 mm(2). It is sensitive to photons in the energy region between 3 and 40 keV, limited by a 50 μm beryllium window, and the sensitive thickness of 450 μm of the chip. Online preview of the sample is possible as the software updates the sums of the counts for certain energy channel ranges during the measurement and displays 2-D false-color maps as well as spectra of selected regions. The complete data cube of 264 × 264 spectra is saved for further qualitative and quantitative processing.

放射線技師教育用コーンビームＣＴシステムの開発

For radiological technologists, it is very important to understand the principle of computed tomography (CT) and CT artifacts derived from mechanical and electrical failure. In this study, a CT system for educating radiological technologists was developed. The system consisted of a cone-beam CT scanner and educational software. The cone-beam CT scanner has a simple structure, using a micro-focus X-ray tube and an indirect-conversion flat panel detector. For the educational software, we developed various educational functions of image reconstruction and reconstruction parameters as well as CT artifacts. In the experiments, the capabilities of the system were evaluated using an acrylic phantom. We verified that the system produced the expected results.

Evaluation of strain field in microstructures using micro-CT and digital volume correlation

X-ray digital micro-tomography was employed for precise strain measurement which is essential for evaluation of the experiments with small samples of trabecular bone. X-ray Digital Volumetric Correlation (DVC) method was used to identify the three-dimensional strain field in loaded complex microstructure. DVC relies on tracking selected sample points within the three-dimensional image data throughout the sequence of captured projections. In this study an improved DVC method is applied for evaluation of the strain field in trabecular bone sample subjected to compressive loading. The deformed sample was tomographically scanned using micro-focus X-ray tube and the single-photon counting silicon pixel detector Medipix2.

Measurements and simulations analysing the noise behaviour of grating-based X-ray phase-contrast imaging

In the last decades, phase-contrast imaging using a Talbot–Lau grating interferometer is possible even with a low-brilliance X-ray source. With the potential of increasing the soft-tissue contrast, this method is on its way into medical imaging. For this purpose, the knowledge of the underlying physics of this technique is necessary. With this paper, we would like to contribute to the understanding of grating-based phase-contrast imaging by presenting results on measurements and simulations regarding the noise behaviour of the differential phases. These measurements were done using a microfocus X-ray tube with a hybrid, photon-counting, semiconductor Medipix2 detector. The additional simulations were performed by our in-house developed phase-contrast simulation tool “SPHINX”, combining both wave and particle contributions of the simulated photons. The results obtained by both of these methods show the same behaviour. Increasing the number of photons leads to a linear decrease of the standard deviation of the phase. The number of used phase steps has no influence on the standard deviation, if the total number of photons is held constant. Furthermore, the probability density function (pdf) of the reconstructed differential phases was analysed. It turned out that the so-called von Mises distribution is the physically correct pdf, which was also confirmed by measurements. This information advances the understanding of grating-based phase-contrast imaging and can be used to improve image quality.

Phase contrast imaging: Effect of increased object–detector distances at X-ray diagnostic and megavoltage energies

Abstract The effect of varying object to detector separation at constant and varying magnification has been investigated at an accelerating potential of 30 kVp. Edge-contrast enhancement provided by phase effects was investigated for a drinking straw and found to provide up to 2.52±0.02× the contrast for a PVC Heaviside step function. An optimum magnification of 1.5× was found to apply for the microfocus X-ray tube setup used. Imaging at nominal megavoltage energies was investigated using a Rapiscan Systems Eagle M4500 series scanner. For a fixed source–detector separation, increased magnification improved edge contrast and spatial resolution.

Strain analysis of trabecular bone using time-resolved X-ray microtomography

A micro-radiographic system composed of microfocus X-ray tube and a large flat panel detector has been adapted for imaging complicated internal microstructure of trabecular bone under applied deformation. To capture the deforming microstructure a load was applied in small increments while the sample was tomographically scanned. Reconstruction of the internal structure is provided using backprojection algorithm for equiangular cone-beam projection data. From the reconstructed cross-sections a finite element (FE) model of the microstructure was developed and loaded according to the experiment. Deformation behavior of the FE model was compared to the experimentally determined response of the sample.

The scope of detector Medipix2 in micro-radiography of biological samples

We present our experimental setup devoted to high resolution X-ray micro-radiography that is suitable for imaging of small biological samples. The photon source is a FeinFocus micro-focus X-ray tube. The single photon counting pixel device Medipix2 serves as imaging area. Recently used imaging detectors as radiography films or scintillator detectors, cannot visualize required information about inner structure of scanned sample. Detectors Medipix2 do not suffer from so-called dark current noise and work in unlimited dynamic range. These features of detectors confer high quality and high contrast of final images. The radiographic imaging with detectors Medipix2 represents non-invasive and non-destructive method of investigation. Hereby, we demonstrate results of micro-radiographic study of internal structures of tiny biological samples. In addition to morphological and anatomical studies, we would like to present preliminary study of dynamic processes inside of organisms using micro-radiographic video-capturing.

Combined system of fluorescence diffuse optical tomography and microcomputed tomography for small animal imaging

We developed a dual-modality system that combines fluorescence diffuse optical tomography (fDOT) and flat panel detector-based microcomputed tomography (micro-CT) to simultaneously reveal molecular and structural information in small animals. In fDOT, a 748 nm diode laser was used as an excitation source, while a cooled charge coupled device camera was adopted to collect transmission fluorescence. In micro-CT, a flat panel detector based on amorphous silicon, with active area of 13 x 13 cm(2), and a microfocus x-ray tube were used. The fDOT system was mounted orthogonally to the micro-CT and the projection images were acquired without rotation of the sample, which is different from the method used for micro-CT alone. Both the finite element method and the algebraic reconstruction technique were used to reconstruct images from the fDOT. Phantom data showed that the resolution of the fDOT system was about 3 mm at an imaging depth of 7 mm. Quantitative error was no more than 5% and imaging sensitivity for 1,1(')-dioctadecyl-3,3,3('),3(')-etramethylindotricarbocyanine iodide bis-oleate (DiR-BOA) was estimated to be higher than 100 nM at a depth of 7 mm. Calculations of the phantom's center of mass showed that the location accuracy of fDOT was about 0.7 mm. We applied a Feldkamp algorithm to reconstruct the micro-CT image. By measuring the presampled modulation transfer function with a 30 microm tungsten thread, we estimated that the micro-CT has a resolution of 5 mm(-1) when the field of view was 6.5 cm. Our results indicate the uniformity of the transaxial micro-CT image and the contrast-to-noise ratio was measured as 1.95 for a radiation dose of 1 cGy. A non-image-based method was employed for merging images from the two imaging modalities. A nude mouse with DiR-BOA, imaged ex vivo, was used to validate the feasibility of the dual-modality system.