X-ray Image Intensifier Research Articles

High speed x-ray radiography diagnostic of current interruption in circuit breakers

High-speed x-ray radiography is used for the imaging of internal components of a low-voltage air circuit breaker during fast current interruption events. A continuous x-ray source was used to irradiate the circuit breaker during interruption, while a fast camera imaging system recorded the output visible light from the x-ray image intensifier up to a maximum rate of 4000 frames per second. Detailed time-resolved images were obtained of the movable contact position and tripping mechanism components of the circuit breaker during the interruption event. Experimental observations were used to validate numerical simulation results obtained using electromagnetics and dynamics/kinematics analysis software. In addition to imaging of the circuit breaker mechanism, molten metal streams and droplets ejected from the electrodes were also observed. Tracking of these metallic particles can provide valuable information about contact phenomena and gas flow fields in circuit breakers.

High-dynamic range SAXS data acquisition with an X-ray image intensifier

Data with a wide dynamic range of intensity can be collected with a pinhole high-brilliance small-angle X-ray scattering (SAXS) camera using an image-intensified charge-coupled device (CCD) detector. The point spread function (PSF) of this detector has a narrow peak with a broad low tail such that a high level of scattered intensity at small angles can cause a significant background in the detector elements at higher angles. A correction scheme for the long tail of the PSF of the detector is needed when this integrating area detector is used for measuring intensity that spans a dynamic range of four to five orders of magnitude. A procedure is described for measuring the PSF contribution by masking a small part of the detector from the scattered radiation with an absorbing material. In order to measure the PSF, it is necessary to use a high-intensity spot, which is readily achieved by using a sample that scatters strongly at small angles. Although this intensity is spread over many pixels, the sharp features in the scattering from the silica sample chosen for this study permit one to obtain simultaneously both the narrow and the broad parts of the PSF. The data are compared with the actual scattering function, which has been measured exactly with a point-geometry Bonse–Hart camera. The advantages of this procedure are discussed.

Noise aliasing in interline-video-based fluoroscopy systems.

Video-based imaging systems for continuous (nonpulsed) x-ray fluoroscopy use a variety of video formats. Conventional video-camera systems may operate in either interlaced or progressive-scan modes, and CCD systems may operate in interline- or frame-transfer modes. A theoretical model of the image noise power spectrum corresponding to these formats is described. It is shown that with respect to frame-transfer or progressive-readout modes, interline or interlaced cameras operating in a frame-integration mode will result in a spectral shift of 25% of the total image noise power from low spatial frequencies to high. In a field-integration mode, noise power is doubled with most of the increase occurring at high spatial frequencies. The differences are due primarily to the effect of noise aliasing. In interline or interlaced formats, alternate lines are obtained with each video field resulting in a vertical sampling frequency for noise that is one half of the physical sampling frequency. The extent of noise aliasing is modified by differences in the statistical correlations between video fields in the different modes. The theoretical model is validated with experiments using an x-ray image intensifier and CCD-camera system. It is shown that different video modes affect the shape of the noise-power spectrum and therefore the detective quantum efficiency. While the effect on observer performance is not addressed, it is concluded that in order to minimize image noise at the critical mid-to-high spatial frequencies for a specified x-ray exposure, fluoroscopic systems should use only frame-transfer (CCD camera) or progressive-scan (conventional video) formats.

Dynamic stereoscopic X-ray imaging

Abstract A multiple view binocular stereoscopic X-ray imaging technique developed as a part of a feasibility study for a security screening application is presented. The experimental system utilises a single X-ray source and a multiple view line-scan camera incorporating an X-ray image intensifier. This set up is used to simulate coplanar configurations of discrete linear X-ray detector arrays. A number of perspective images (typically 6–16) are produced during a single linear translation of the object under inspection. A sequential display of the images produces linear motion parallax in the display. Further work enabled motion parallax to be combined with binocular parallax [NDT&E Int 29 (1996) 27] to produce dynamic binocular stereoscopic images. The perspective images may also be used for the extraction of three-dimensional coordinate information. The results produced by an experimental system are presented together with a theoretical discussion.

Analysis of the Dose Load on Patients and Medical Personnel Exerted by the FSTs-U-01 Photoroentgenograph with an X-Ray Image Intensifier

Analysis of the Dose Load on Patients and Medical Personnel Exerted by the FSTs-U-01 Photoroentgenograph with an X-Ray Image Intensifier

Effect of sharpening filter on vessel diameter measured by quantitative coronary arteriography

At cardiac catheterization, analog images obtained using cinefilm are translated into digital images, and images appearing on the CRT are filtered by a sharpen filter. We investigated the effect of the sharpening filter on vessel diameter as measured by quantitative coronary arteriography. We acquired images of a vessel phantom filled with contrast material using an X-ray image intensifier. Vessel diameters measured by quantitative coronary arteriography were 1 mm, 1.5 mm, 2 mm, 3 mm, 4 mm, and 6 mm. Results showed that vessel diameters were decreased when the sharpening filter was used and that more intense filtering decreased the measured diameter further. When the diameter of the vessel phantom was less than 4 mm, the diameter was smaller and the ratio of decrease was larger. Vessel diameters of 2 mm, 3 mm, 4 mm, and 6 mm measured a maximum of 2.9 smaller, while those of 1 mm and 1.5 mm measured a maximum of 9.2 smaller.

Dynamic Unsharpness Optimization and Image Quality Improvement in the URI/230-Ametist Digital X-Ray Image Intensifier

Dynamic Unsharpness Optimization and Image Quality Improvement in the URI/230-Ametist Digital X-Ray Image Intensifier

Present status of high flux beamline (BL40XU) at SPring-8

High flux beamline (BL40XU) was designed to use very high X-ray flux in various experiments. The X-ray source of BL40XU is a helical undulator and the fundamental radiation can be altered from 8 to 17 keV by changing its gap. Two water-cooled mirrors are located in the optics hutch. After focusing horizontally and vertically by these two mirrors, the X-ray is introduced into the experimental hutch. At the sample position, the focused beam size is 250 μm (horizontal)×40 μm (vertical) (FWHM) and the flux is estimated to be 1×10 15 photon/s. As a detector, a fast CCD camera combined with an X-ray image intensifier with a short-decay phosphor is installed. The framing rate of the fast CCD camera is 290 frame/s (with frame size of 640×480 pixels, 10 bits) and up to 5000 frame/s is achieved by reducing the size of the frame. BL40XU was open for public use from April 2000, and various experiments that require high X-ray flux have been carried out.

Perspectives of medical X-ray imaging

While X-ray image intensifiers (XII), storage phosphor screens and film-screen systems are still the work horses of medical imaging, large flat panel solid state detectors using either scintillators and amorphous silicon photo diode arrays (FD-Si), or direct X-ray conversion in amorphous selenium are reaching maturity. The main advantage with respect to image quality and low patient dose of the XII and FD-Si systems is caused by the rise of the Detector Quantum Efficiency originating from the application of thick needle-structured phosphor X-ray absorbers. With the detectors getting closer to an optimal state, further progress in medical X-ray imaging requires an improvement of the usable source characteristics. The development of clinical monochromatic X-ray sources of high power would not only allow an improved contrast-to-dose ratio by allowing smaller average photon energies in applications but would also lead to new imaging techniques.

The practical application of signal detection theory to image qualityassessment in x-ray image intensifier-TV fluoroscopy

This paper applies a published version of signal detection theory to x-rayimage intensifier fluoroscopy data and compares the results with moreconventional subjective image quality measures. An eight-bit digitalframestore was used to acquire temporally contiguous frames of fluoroscopydata from which the modulation transfer function (MTF(u)) and noisepower spectrum were established. These parameters were then combined to givedetective quantum efficiency (DQE(u)) and used in conjunction withsignal detection theory to calculate contrast-detail performance. DQE(u) was found to lie between 0.1 and 0.5 for a range of fluoroscopysystems.Two separate image quality experiments were then performed in order to assessthe correspondence between the objective and subjective methods. First, imagequality for a given fluoroscopy system was studied as a function of doserateusing objective parameters and a standard subjective contrast-detail method.Following this, the two approaches were used to assess three differentfluoroscopy units. Agreement between objective and subjective methods wasgood; doserate changes were modelled correctly while both methods ranked thethree systems consistently.

Development of a subject-standing-type cone-beam computed tomography for chest and orthopedic imaging.

A subject-standing-type cone-beam computed tomography (CT) with high spatial resolution has been developed as a new three-dimensional imaging modality for subjects standing or sitting naturally on a turntable. A 16-in. X-ray image intensifier and charge coupled device camera acquires a 12-bit 5122-pixel projection at 60 f/s and the rotation period is 4.8 or 9.6 s for 288 or 576 projections, respectively. To reduce image noise, the system controls the X-ray pulse duration and iris-opening area through real-time analysis of the projection image. To improve CT accuracy and eliminate artifacts, the veiling glare of the image intensifier and scattered X-rays are corrected. Human chest and orthopedic studies with about 50 patients were conducted. Three-dimensional images with a spherical field of view with a diameter of 21-25 cm, 0.4- to 0.5-mm voxels and a 512(3) matrix were obtained. In coronal, sagittal and volume rendering images, the surface of arthrosis was visualized smoothly with a resolution higher than that of conventional CT. In the case of gonarthrosis, narrowing of the clearance at the surface of arthrosis was visualized clearly under body-weight burdening, which would be difficult if the subject was lying down.

Evaluation of an X-ray imaging detector based on a CMOS camera with logarithmic response

An X-ray imaging detector made of an X-ray image intensifier coupled to a non-integrating logarithmic CMOS camera is evaluated. Linearly scaled X-ray images over six decades of dynamic range are obtained after calibration of the detector response, representing a gain of more than one order of magnitude compared with state-of-the-art CCD-based X-ray detectors. The system provides images which are free of smearing or blooming at maximum exposure without mechanical shuttering. Other characteristics are a sensitive area of 123×61 mm, a pixel size of 240 μm, a noise-limited detection threshold of 25 photons/pixels/s at 18 keV. In X-ray diffraction images the effective measuring range is better than 10 4 for neighbouring diffraction spots, whereas the full 10 6 range is available for remote spots. At reduced dynamic range a frame rate of 60 images/s can be achieved. The performed evaluation demonstrates the interest of this detector concept as a possible alternative to CCD-based detectors for various applications at synchrotron sources requiring an extended dynamic range and subsecond duty cycle requirements.

X-ray image intensifier performance and patient doses for combinationsof supplemental beam filters and vascular contrast agents

We present an investigation of the fluoroscopic imaging and dosimetricperformances of iodine- and gadolinium-based vascular contrast agents incombination with K-absorption edge filters of atomic numbers between 50 (tin)and 82 (lead). These combinations were studied using a theoretical model for arange of diagnostic x-ray spectra (55 to 100 kVp) and for water phantomsrepresentative of thin and thick anatomies. Performance was characterized byradiographic contrast, a derived image quality index, the patient integral andentrance skin doses, and the x-ray tube load. For a given thickness of anatomy,an optimum combination of spectrum kVp, contrast agent and supplemental filterwas defined by maximum imaging performance for a minimum or tolerable x-raytube load and patient dose. It was possible to both improve imagingperformance and reduce dose by the use of an appropriate combination ofspectrum kVp and filter. For gadolinium-based contrast, performance wasoptimized with tungsten filtration at 90 kVp for both thin and thickanatomies. It was not possible, however, to optimize the iodinated contrastperformance with a single combination of supplemental filter and spectrum kVp.The optimal performance for iodinated contrast was achieved with gadoliniumfiltration at 60 kVp for thin anatomy and with ytterbium filtration at 80 kVpfor thick anatomy. The best performance for thin anatomy was that of thecombination of iodinated contrast/gadolinium filter at 60 kVp and the bestperformance for thick anatomy was that of the combination of gadolinium-basedcontrast/tungsten filter at 90 kVp.

Electric-field-induced structural changes measured with a CCD-coupled X-ray image intensifier

The conventional method to measure small induced changes in integrated intensity utilizes a zero-dimensional detector, which greatly limits the data collection speed. This paper shows that the use of an area detector in combination with an X-ray chopper decreases the data collection time significantly. A monochromatic diffraction setup using a charge-coupled device (CCD) detector coupled to an X-ray image intensifier was constructed and tested. The setup proved to be sufficiently stable to measure changes in integrated intensity well below 0.1%. Subsequently, a data set of a piezoelectric KD2PO4crystal in an external electric field was collected. The data were merged to yield 77 unique reflections. The induced structural changes were determined by a least-squares refinement. The results agree very well with experiments in which a zero-dimensional detector was used. The major improvement is the decrease in data collection time by one order of magnitude, without any degradation of the data quality, offering new possibilities for this type of perturbation study.

The evolution of scintillating medical detectors

The principle of scintillation detectors has been among the first realizations of radiation detectors. Despite ongoing attempts to switch to direct converting detectors, scintillators have shown great persistence in the field of medical imaging. In radiography, computer tomography and nuclear medicine, a variety of scintillating devices are the ‘workhorses’ of the clinician today. For radiography, flat X-ray detectors (FDs) with evaporated scintillation layers are at the level of product introduction. However, X-ray image intensifier tubes (XIIs) are competitive and still have features that will be hard to beat in the near future. Although XIIs have disadvantages, they have experienced a significant evolution in robust image quality and cost reduction over the decades. The so-called ‘offline’ detectors from film to storage phosphors seemed to have reached a plateau since the late 1970s. However, the distinction between on- and offline may soften in the future, because of new readout concepts. Detectors in computer tomography (CT) have evolved from scintillators to gaseous direct converters back to scintillators. Extreme timing requirements and detector modularity have ruled out designs that would rank as `high performance’ in other fields. Modern ultra-fast ceramic scintillation detectors are a prerequisite of subsecond CT and leave breathing room for future scan times even below 0.5s. The field of nuclear medicine is a good example of how difficult it is, to replace a cheap and reliable technology. Since many years, direct converters like CdTe and the likes are discussed to overthrow the regime of NaI:Tl in combination with photomultipliers (PMTs). Both components are well known since the 1950s and have shown remarkable staying power. Still the scintillator with the highest light output, NaI:Tl in combination with the basically noiseless PMT is almost unbeatable in low cost. In combination with modern digital electronics, drawbacks of analog circuitry like temperature drift and energy dependence can be made practically invisible to the user. New ultra-compact PMT designs could drive the design of the gamma camera towards more compactness, even without direct converting detectors.

Soft-Copy Quality Control of Digital Spot Images Obtained by Using X-ray Image Intensifiers

To evaluate 12 x-ray image intensifier (XRII) digital spot systems. Four objective tests were performed to assess XRII digital spots: entrance exposure, patient exposure, soft-copy gray scale, and pixel noise. Two additional tests were performed to assess high-contrast limiting resolution and threshold contrast detection. Digital spot XRII entrance exposures averaged 1 x 10(-7) C/kg (0.38 mR) for units with large fields of view (FOVs); mean entrance exposure in a medium-sized patient was 1. 25 x 10(-5) C/kg (48 mR). Luminance measurements of the table-side monitors provided a mean of 473 just-noticeable differences in gray scale with the room lights off. Mean resolution with a bar test pattern was measured as 1.5 line pairs per millimeter for systems with a 40-cm FOV. Measured pixel noise (in relative units) was 6-25. Mean threshold contrast with the lights off was 0.85%. Once input exposure is normalized for FOV and image matrix size, soft-copy assessment of limiting resolution with either low-contrast detection or, preferably, an off-line noise metric (pixel SD) provides objective measurements of digital spot image quality. With the lights on, 10 systems with room-light sensors had an 11% loss of gray scale. For systems without sensors, the loss was 33%.

The AAPM/RSNA physics tutorial for residents: X-ray image intensifiers for fluoroscopy.

The x-ray image intensifier converts the transmitted x rays into a brightened, visible light image. Within an image intensifier, the input phosphor converts the x-ray photons to light photons, which are then converted to photoelectrons within the photocathode. The electrons are accelerated and focused by a series of electrodes striking the output phosphor, which converts the accelerated electrons into light photons that may be captured by various imaging devices. Through this process, several thousand light photons are produced for each x-ray photon reaching the input phosphor. Most modern image intensifiers use cesium iodide for the input phosphor because it has a high absorption efficiency and thus decreases patient dose. Image intensifiers come in various sizes, most having more than one input image size or magnification mode. Modern image intensifiers are specified by conversion factors, which is the measure of how efficiently an image intensifier converts x rays to light. Because of design restrictions, image intensifiers are subject to inherent and induced artifacts that contribute to image degradation. Both spatial and contrast resolution gradually decrease during the lifetime of the image intensifier because the brightness gain of an image intensifier decreases with time as the phosphor ages. A well-run quality control program for the image intensifier is needed to detect the inevitable changes in settings before they appear on clinical images.

Blowing Up the Stiff Balloon: X-Ray Microtomography Reveals Decrease in Arterial Distensibility in Pulmonary Hypertension

Abstract We are developing nondestructive and non-traumatic imaging methods to quantitatively assess structural and mechanical properties of vascular trees and other complex biological systems. We are applying these methods to studies of vascular remodeling in rodent models of disease. Quantitative vascular tree morphometry has, in the past, been carried out using corrosion casting methods which supply valuable information, but are destructive and tend to be tedious, in particular with regard to associating vessel segment measurements accurately with their positions in the intact tree hierarchy. One of our goals is to refine imaging methods capable of quantifying mechanical, as well as anatomical properties, by virtue of their ability to rapidly acquire multiple image volumes of the same structure under various conditions, all in a nearphysiological state. Using the micro-CT scanner shown in Figure 1, consisting of a microfocal x-ray tube, specimen stage and image intensifier coupled to a 10242, 12-bit CCD camera, we acquire magnified (3-9X), transmitted x-ray projections of contrast enhanced, excised rat lungs or lung lobes.

Small-angle X-ray scattering station at the SPring-8 RIKEN beamline

RIKEN beamline I (BL45XU) is an undulator beamline with two branches. One is for protein crystallography (PX) and the other is for small-angle x-ray scattering (SAXS). The beam is split into the two branches by a diamond monochromator so that two experiments can be done simultaneously [Yamamoto et al. (1995) Rev. Sci. Instrum. 66, 1833-1835]. The SAXS branch was designed for studying the weak interaction of proteins or subunits of fibrous or protein solutions especially using hydrostatic pressure. The optics makes use of the good parallelism of the undulator beam in order to reduce parasitic scattering. The beamline consists of a double crystal monochromator and a K-B type focusing mirror system. In order to cope with the high flux of the beam, an x-ray image intensifier (Hamamatsu Photonics, V5445P) with a cooled CCD camera (C4880-82) was used. As a result, decreases in both collection time and sample amount were realized in standard static experiments. These improvements will greatly facilitate SAXS experiments under high pressure.

Percutaneous transpedicular biopsy of thoracic and lumbar vertebrae—method and diagnostic validity

BACKGROUND Percutaneous transpedicular needle biopsy was performed on thoracic and lumbar vertebral bodies with a thin trocar (2.0 mm outer diameter) under observation with a conventional X-ray image intensifier in order to establish a correct histopathological diagnosis. We also evaluated the clinical validity of this less invasive diagnostic method in terms of the accuracy of the pathological diagnosis. METHODS Twenty-eight thoracic or lumbar vertebrae of 26 patients with abnormalities observed on routine X-ray, CT, or MRI images underwent percutaneous transpedicular needle biopsy under local anesthesia. A threaded trocar with an outer diameter of 2.0 mm was screwed into the intra-vertebral lesion through the pedicle from the posterior side under control of X-P imaging, and a small amount of tissue or fluid was collected. RESULTS For all patients but two, where inadequate specimens were obtained, correct diagnoses were made, which were confirmed by pathological diagnoses of massive tissue obtained during subsequent reconstructive surgery. CONCLUSIONS The accuracy rate of diagnosis with this biopsy method was 92% without significant intra- or postoperative complications. Therefore, it can be concluded that this less invasive biopsy method used in conjunction with conventional X-ray apparatus has good potential to result in correct preoperative diagnosis of thoracic and lumbar lesions so that more effective treatment can be determined.