X-ray Tube Current Research Articles

Fundamentals of multichannel CT.

Multichannel computed tomography (MCCT) has created a technical revolution in CT scanning. Following the introduction of single-channel helical scanning in 1989, 4-channel systems were introduced in 1998 and 16-channel systems in 2002. The core of this new technique is the X-ray detector array design, which allows for multiple simultaneous registration of slice information during gantry rotation. This design allows for faster scanning and acquisition of thinner slice widths. The high-speed scanning also minimizes motion artifacts. The ability to scan with very thin slice thickness creates a scanned volume with isotropic voxels. This allows for two- and three-dimensional reconstructions with similar resolution as the source images. MCCT also allows for higher X-ray tube currents, which create better penetration of metallic orthopedic fixation devices. Musculoskeletal imaging benefits from MCCT because large anatomic areas may be covered with thin slices. When needed, high tube currents can be applied for scanning areas of interest in the presence of metal. Thin slice acquisition allows isotropic viewing, which we use routinely.

Use of Microfocus X-ray Computer Tomography for 3D-image Construction and Quantitative Morphoanalysis

Microfocus X-ray computed tomography (μCT) is becoming widely used in various research fields relevant to the oral sciences. This technology, in conjunction with computer-assisted 3D reconstruction and quantitative structural analysis, is most suitable for investigating hard tissues in a non-invasive way. Despite this recognition, it still remains a concern whether the data acquisition process is conducted properly and accurately in order to ensure the reproducibility of 3D imaging and the determination of structural parameters such as bone volume (BV) and surface area (BS). In this report, we aim to provide an overview of the experimental procedures and conditions that are necessary for optimizing the acquisition of gray-scale CT images and their conversion into digital images (TIFF or JPEG) prior to 3D reconstruction and measurements. Towards these objectives, we collected μCT images of a 4-week-old mouse temporomandibular joint using a μCT apparatus (Nittetsu ELEX Co., ELE-SCAN model). Data proceedings and measurements were conducted using software (RATOC System Engineering Co., TRI-BON and TRI-SRF2). Special care was taken in optimizing experimental conditions and variables, e.g., X-ray tube voltage and current, selection of an adequate shiftvalue to compensate the mismatching between the specimen-rotating center and incident X-ray beam, and window level and width for contrast adjustment. The results of our empirical approach showed that careful selection of the experimental conditions and computation variables ensures the high quality of the 3D images and the accuracy and reproducibility of the quantitative measurements. The magnitude of errors associated with each of the determined structural parameters was confirmed to be within 3% of the determinations. Further knowledge and refinement of μCT technology and data acquisition will help to improve our understanding of the architecture and dynamic modeling of hard tissues.

Characteristics of specifications of transportable inverter-type X-ray equipment

Our X-ray systems study group measured and examined the characteristics of four transportable inverter-type X-ray equipments. X-ray tube voltage and X-ray tube current were measured with the X-ray tube voltage and the X-ray tube current measurement terminals provided with the equipment. X-ray tube voltage, irradiation time, and dose were measured with a non-invasive X-ray tube voltage-measuring device, and X-ray output was measured by fluorescence meter. The items investigated were the reproducibility and linearity of X-ray output, error of pre-set X-ray tube voltage and X-ray tube current, and X-ray tube voltage ripple percentage. The waveforms of X-ray tube voltage, the X-ray tube current, and fluorescence intensity draw were analyzed using the oscilloscope gram and a personal computer. All of the equipment had a preset error of X-ray tube voltage and X-ray tube current that met JIS standards. The X-ray tube voltage ripple percentage of each equipment conformed to the tendency to decrease when X-ray tube voltage increased. Although the X-ray output reproducibility of system A exceeded the JIS standard, the other systems were within the JIS standard. Equipment A required 40 ms for X-ray tube current to reach the target value, and there was some X-ray output loss because of a trough in X-ray tube current. Owing to the influence of the ripple in X-ray tube current, the strength of the fluorescence waveform rippled in equipments B and C. Waveform analysis could not be done by aliasing of the recording device in equipment D. The maximum X-ray tube current of transportable inverter-type X-ray equipment is as low as 10-20 mA, and the irradiation time of chest X-ray photography exceeds 0.1 sec. However, improvement of the radiophotographic technique is required for patients who cannot move their bodies or halt respiration. It is necessary to make the irradiation time of the equipments shorter for remote medical treatment.

Optimization of multidetector array CT acquisition parameters for CT colonography.

Multidetector array computed tomography technology has increased the number of acquisition parameters that a user must select. This article examines the criteria by which detector collimation, reconstructed scan width, reconstruction scan interval, pitch, image noise, and patient dose can be optimized. A water phantom containing tissue-equivalent polyps in an air-filled tube was scanned using multiple acquisition parameter combinations. X-ray tube current was changed to independently match dose and noise to a single-detector array technique. Images were assessed in axial and three-dimensional formats. All polyps were visible in axial and three-dimensional images for all scans. Helical artifacts were noted at higher table speed values. The 5-mm-wide scans spaced at 3-mm intervals allowed visualization of the smallest polyps: 5 x 5 or 7 x 3 (diameter x height; mm). Our results indicate that thin-scan and low-noise techniques need not be used to visualize polyps of clinically relevant sizes.

Image quality and dose in film-screen magnification mammography.

Extended exposure times in magnification mammography are a result of the reduced X-ray tube currents required for a small focal spot. The consequences of this are the potential for reduced image quality through motion blur during exposure as well as the onset of film reciprocity law failure. Previous investigators have suggested increasing the X-ray tube potential as a practical mechanism for reducing exposure times in magnification mammography and have demonstrated negligible image quality degradation at least up to 32 kVp. This paper describes a film-screen magnification mammography study that expands upon this previous work to investigate the magnitude of the reduction of breast mean glandular dose and exposure time and the changes in subjective image quality (visibility of low contrast details in an RMI 152 phantom) with increases in tube potential between 28 kVp and 35 kVp. Measures of changes in the radiographic contrast and in the scatter-to-primary ratio (SPR) in magnification geometry as a function of tube potential were also obtained. Evidence for reciprocity law failure was also assessed. For a constant film optical density, increasing the X-ray tube potential from 28 kVp to 35 kVp reduced the mean glandular dose from 3.9 mGy to 2.7 mGy and reduced the exposure time from 3.2 s to 1.0 s. Over this range, the detection rate of fibrils and microcalcification-mimicking specks did not vary with tube potential at the 0.05 level of significance. It was found that only the low contrast mass detail detection rate at 35 kVp was significantly less than that at 28 kVp. The measured radiographic contrast decreased with tube potential and the SPR increased with tube potential. However, both changes were weak, and linear regressions determined that the 95% confidence intervals of the slopes relating both contrast and SPR with tube potential encompassed zero. It is concluded that magnification mammography performed at 34 kVp yields significant reductions in exposure time and mean glandular dose, with a detail detection capability similar to that at 28 kVp.

Optimal technique factors for magnification mammography.

Use of small focal spots with low x-ray tube currents may result in very long exposure times and thus result in motion blur in magnification mammography. The authors investigated the reduction in exposure time with increasing x-ray tube kVp and the corresponding decrease in perceived visibility of low-contrast objects in phantom images. Exposure times required to radiograph an RMI 156 phantom in a magnification geometry were measured as a function of x-ray tube kVp when operated under automatic exposure control. Magnification images of the RMI 156 phantom were obtained at x-ray tube voltages ranging from 28 to 34 kVp. Five radiology residents ranked the visibility of two borderline fibers and six borderline microcalcification specks using a 5-point scale ranging from excellent to barely visible. Between 28 and 34 kVp, the density of the RMI phantom images was nearly constant with a mean value of 1.32 +/- 0.04. Increasing the x-ray tube voltage from 28 kVp to 34 kVp reduced the exposure time from 1.27 seconds to 0.66 seconds. Image quality at 30 and 32 kVp was not significantly worse than that achieved at 28 kVp. Increasing the x-ray tube voltage to 34 kVp, however, resulted in a statistically significant (P < 0.001) deterioration in the relative visibility of fibers and microcalcification specks. Magnification mammography performed at 32 kVp will decrease exposure times significantly and result in a microcalcification and fiber visibility that is similar to that achieved at 28 kVp.

Growth and characterisation of CVD diamond wires for X-ray detection

Abstract In order to gain insight into the mechanism of diamond growth on metallic wires (50–500 μm diameter), we have investigated the deposition process in a hot filament chemical vapour deposition (HFCVD) reactor. A two-dimensional model of our HFCVD reactor was developed in order to interpret the experimental data which indicate an evident influence of the substrate wire diameter on the gas species concentration and on the diamond growth rate. The theoretical model indicates a reduction of the growth rate as the substrate diameter increases due to the reduction of hydrogen and the active radicals concentrations at the substrate as its growth area increases. In view of a possible application of such samples as X-ray detectors, we investigated their electrical properties by analysing the current/voltage characteristic in a metal/diamond/metal geometry at different temperatures. The activation energy of the conductivity is found to be dependent on the applied electric field. The experimental data support a Poole-Frenkel conduction with overlapping centres. Finally the response of our diamond wires to X-ray radiation flux was investigated. A sensitivity of about 5 × 10 −6 A s Gy −1 was measured under a 100 keV Bremsstrahlung X-ray flux and the photocurrent is almost linear with respect to X-ray tube current.

Cone-beam X-ray microtomography of small specimens

Microtomography is a technique for creating three-dimensional images of the internal structure of objects with high spatial resolution. This can potentially allow inspection of the architecture of breast lumpectomy specimens and visualisation of tumours in small animals and also has an application as a tool for nondestructive testing. An efficient method to perform microtomography is to use an area detector and cone-beam reconstruction techniques. Here the authors report on the development of an instrument for microtomography and show example images. The equipment consists of a microfocal X-ray tube (energies and currents up to 30 kVp, 0.2 mA, focal spot size <5 mu m), a rotating specimen stage and a high-resolution X-ray image intensifier optically coupled to a CCD video camera. Data acquisition and 3D image reconstruction are performed by a desktop computer. The well-known Feldkamp cone-beam reconstruction algorithm is used to produce tomographic images from the recorded X-ray projections. The instrument can image samples with diameters of 5-50 mm and create tomographic images with spatial resolution of the order 10-100 mu m and signal-to-noise ratio of better than 5:1. This work is a continuation and improvement of an earlier instrument with a low-energy X-ray source and detector.

小児 X 線撮影実態調査

In 1991, the inquiry was conducted among 114 institutes who belong to the society for pediatric radiological technology. The reply rate of the inquiry was 68.4%. The examinations included; chest, upper airway, abdomen, hip, skull, knee. The inquiry items consisted of irradiation conditions for; 6 month-olds, 3 year-olds, 7 year-olds, type of X-ray generator, model of automatic processor, FCR usage; for a total of 28 items in all. Single phase X-ray generator was almost never used. Most of the institutes used mid-high voltage as the irradiation condition for the chest examinations. The X-ray tube currents have peak to 200mA and 400mA. The irradiation times, the 50 ms full is the half above-mentioned. The automatic processor's developer temperatures were set lower than the recommented set point. The standard contrast films are used about 90%.

XPS determination of band bending in defective semiconducting oxide surfaces

X-ray photoelectron spectroscopic studies of polycrystalline, p-type semiconducting nickel oxides and manganese oxides, with different defect levels, have revealed dependence of the surface potential, V ch , on X-ray power, bulk oxide defect concentrations, electron donor and acceptor adsorption and temperature. Mechanisms for the development of surface potential during X-irradiation are described and their dependence on these factors is examined. At low X-ray power (below 200 W) V ch is shown to be linearly dependent on X-ray tube current. At high X-ray power, V ch is given by: V ch = [ (K 1−K 3) B(σ 0) ]exp( eV s kT ) where K 1 and K 3 are constants; B( σ 0) represents a functional dependence on bulk conductivity of the sample and V s is the band bending at the surface. From linear experimental plots of In V ch versus 1 T , values of V s between 0.24 and 0.63 V were determined for four oxide samples. More defective oxides, after evacuation at 400°C, have larger V s values and the expected larger values of B( σ 0). From related studies of these surfaces, the higher concentration of surface defects can be shown to produce higher concentrations of electron-accepting hydroxyl groups which, when partially removed (with some surface oxygen as CO) by high temperature evacuation, cause free hole annihilation and increased band bending.

An Integrated, Stabilized Power Supply forX-Ray Tubes

A solid-state power-supply unit incorporating all the three regulated and adjustable supplies, required for the operation of an X-ray tube, is designed, built and tested. The three supplies include 40 kV/0.5 mA HT supply, 600 V/1 mA grid-bias supply and 12 V/8 A filament supply. In particular, the HT supply has very low ripple (≃10−2%) and stability of better than 0.1% for minimum of eight hours after 15 minutes warm-up time. All the supplies have excellent temperature stability from about 18° to 40°C. The filament supply has a control voltage that is proportional to the difference between a reference voltage and a dc voltage proportional to the X-ray tube current supplied by the HT supply. This stabilizes the X-ray tube current. The whole system of power supplies is tested for performance and is discussed.

Image noise reduction on the EMI 7070 CT scanner by the reduction of the noise resident in the CT wedge profiles.

On the EMI 7070 CT scanner the data contained in the wedge files has been averaged resulting in a 6% reduction in the noise content of images. This noise reduction can either be used to improve image quality or can be offset by reducing the x-ray tube current by 12%. The averaging method will be outlined and its rationale discussed.

CT Scannerにおける被曝線量の低減 : 管電流・付加フィルタによる変化

Recently computed tomography (CT) scanners have become popular among hospitals, and they are in the process of changing from the first generation to the third or fourth generation. Exposure has been increased due to an increase in the matrics by which to obtain better image quality. We have researched how to decrease patient dose by changing X-ray tube current (mA) and adding additional filters and by combining these two methods with better quality due to less deterioration. As a result of the experiment, we discovered that it was possible to decrease about 10% of patient dose with less deterioration in image quality by reducing mA up to 29 mA and by adding 1mm thick Al to 33 mA.

An investigation and explanation of the fall-off of X-ray tube current during an exposure

It was observed that the radiation output of X-ray tubes falls off exponentially during an exposure with a time constant of about 120 ms. The equilibrium value is approximately 15% lower than that at the beginning of the exposure. The clinically noticeable consequences are discrepancies in X-ray generator calibration, the loss of the strict mA s (tube current*exposure time) linearity, and, in scanning devices, the possibility of artefact generation. A systematic investigation of the phenomenon revealed that it is caused by the cooling of the cathode due to evaporation of electrons. Theoretical expressions for the magnitude and time constant of the fall-off derived from basic thermodynamics are in good agreement with the observations. A simple mA stabilisation circuit which prevents the fall-off is described.

A portable instrument for the measurement of single-phase radiographic X-ray tube currents

The problems inherent in the usual method of measurement, that is, inserting a meter into the circuit, are avoided by using a device which relies on an induction method. It enables tube current to be measured accurately on a single pulse (0.01s). It addition, the instrument is independent of the shape of the current waveforms found in practice and permits their form to be studied if desired. It is safe, flexible and easy to operate in a hospital environment.

Rare-Earth Analyses by X-Ray-Excited Optical Fluorescence

AbstractX-ray excitation causes rare-earth impurities in yttrium oxide and gadolinium oxide to emit intense and highly characteristic optical line fluorescence, which enables their analyses at low concentrations. The limits of detection for praseodymium, ncodymium, samarium, europium, gadolinium, terbium, dysprosium. holmium, erbium, thulium, and ytterbium in these two oxides range from 1 to 100 parts per billion (ppb). In other rare-earth oxides which have been investigated. the fluorescent intensities arc greatly reduced. Successful analyses can be made only by dilution in high-purity Y2O3. This dilution raises the detection limits for rare earths in these other oxides to the part per million range. X-rays from the chromium target of a cual-target X-ray tube are about two times more efficient in exciting rareeaith optical fluorescence than are the tungsten-target X-rays, even though the total energy output of the chromium target is only about one-third that of the tungsten target. With either target material, the rare-earth intensities vary linearly with the X-ray tube current, but a plot of intensity versus the square of the accelerating potential is not linear; it drops off at higher voltages.

Experimental Considerations for Polaroid Film X-Ray Photographs

Polaroid type 57 sheet film (ASA 3000) has been evaluated as a means for recording x-ray Laue and pinhole diffraction photographs; both transmission and back reflection geometries have been employed. Consideration has been given to the effect of x-ray tube target material, tube voltage and current, exposure and processing times, collimator size, and specimen-to-film distance on resultant pattern quality. Examples are given which illustrate the the ability to obtain high quality Polaroid film patterns in considerably less (5 to 20%) time than is required for comparable wet process films.

Analysis of high voltage waveforms in X-ray units: II abnormal voltages

Under adverse exposure factors, abnormal voltage appears at the instant of primary circuit closing of a high-voltage transformer, and also at the cut-of instant of grid-controlled X-ray tube current. These properties core analysed. The equations and graphs for estimating the abnormal voltage peaks are shown. Preventive procedures are also explained.

Experiments with Fluorescent X Rays in the 10- to 50-Å Wavelength Region

Apparatus for the production, dispersion, and detection of soft fluorescent x-rays (10 to 50 Å) is described. The apparatus includes a new type of gaseous discharge x-ray tube capable of operating at 3000 v and 200 ma, a servo-type vacuum controller for maintaining constant x-ray tube current, and built-up films of heavy-metal soaps for use as analyzing crystals. Photographs are included of fluorescent spectral lines of carbon from graphite (Kα, λ=44.5 Å) and of copper (Lα, λ=13.3 Å) obtained, respectively, in 2 and in 4½ hr.

Some results obtained in developing a recording Geiger-counter x-ray intensity monitor

A single-beam monitor is described which samples the general background radiation scattered from an x-ray beam by a thin foil, and its behaviour compared to that of the main spectrometer counter receiving the K component from the same beam. Equal fractional changes of counting rate for monitor and main counter are observed when x-ray beam fluctuations are caused by changes in the x-ray tube current. No such simple relationship holds between monitor and main counter for changes in x-ray tube voltage. The response required of a counter for monitoring purposes is discussed briefly and the suitability of an end-window argon-filled Geiger counter established experimentally.