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Results for “FLUOROSCOPY”

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At least 487 records · Page 27Linked to original sources

PubMed2001

Half-scan cone-beam CT fluoroscopy with multiple x-ray sources.

To develop volumetric micro-CT fluoroscopy for small animal imaging, we have proposed a cone-beam system with multiple x-ray sources. In this paper, we extend Parker's single-source half-scan weighting scheme to the case of an odd number of x-ray sources that are equiangularly distributed, and apply it for half-scan Feldkamp-type reconstruction in this unique geometry. In the numerical simulation with the Shepp-Logan phantom, representative images indicate that the proposed half-scan Feldkamp-type algorithm produces temporal resolution significantly superior to that with a single x-ray source cone-beam system.

Algorithms↗

PubMed2002

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.

Fluoroscopy↗

PubMed2002

A filtering method for signal equalization in region-of-interest fluoroscopy.

A method to significantly reduce the exposure area product in fluoroscopy using a pre-patient region-of-interest (ROI) attenuator is presented. The attenuator has a thin central region and a gradually increasing thickness away from the center. It is shown that the unwanted brightening artifact caused by the attenuator can be eliminated by attenuating the low spatial frequencies in the detected image using digital image processing techniques. An investigation of the best image processing method to correct for the presence of the attenuator is undertaken. The correction procedure selected is suitable for use with real-time image processors and the ROI attenuator can be permitted to move during image acquisition. Images of an anthropomorphic chest phantom acquired in the presence of the ROI attenuator using an x-ray image intensifier/video chain are corrected to illustrate the clinical feasibility of our approach.

Biophysical Phenomena↗

PubMed2004

Evaluation of the imaging properties of an amorphous selenium-based flat panel detector for digital fluoroscopy.

The imaging performance of an amorphous selenium (a-Se) flat-panel detector for digital fluoroscopy was experimentally evaluated using the spatial frequency dependent modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE). These parameters were investigated at beam qualities and exposures within the range typical of gastrointestinal fluoroscopic imaging (approximately 0.1 - 10 microR, 75 kV). The investigation does not take into consideration the detector cover, which in clinical use will lower the DQE measured here by its percent attenuation. The MTF was found to be less than the expected aperture response and the NPS was not white which together indicate presampling blurring. The cause of this blurring was attributed to charge trapping at the interface between two different layers of the a-Se. The effect on the DQE was also consistent with presampling blur, which reduces the aliasing in the NPS and thereby reduces the spatial frequency dependence of the DQE. (The DQE was independent of spatial frequency from 0.12 to 0.73 mm(-1) due to antialiasing of the NPS.) Moreover, the first zero of the measured MTF and the aperture response appeared at the same spatial frequency (6.66 mm(-1) for a pixel of 150 microm). Hence, the geometric fill factor (77%) was increased to an effective fill factor of 99 +/- 1%. A large scale ( approximately 32 pixels) correlation in the noise due to the configuration of the readout electronics caused increased noise power in the gate line NPS at low spatial frequency (< 0.1 mm(-1)). The DQE (f = 0) was exposure independent over a large range of exposures but became exposure dependent at low exposures due to the electronic noise.

Equipment Design↗

PubMed2004

Automatic measurements of image geometry for online calibration of C-arm fluoroscopy.

Calibrated C-arm fluoroscopy is used for a variety of surgical procedures where surgical tools and anatomical structures need to be located in space. Calibration can be performed online by combining measurements of the geometry of the image (center and radius) with measurements of a grid of fiducial markers. This article focuses on the first aspect--image geometry--and describes a method to perform the geometry measurements automatically. The accuracy, robustness, and speed of the method are validated on 100 images obtained from several hospitals with different C-arm scanners. All 100 images were successfully measured with an average error of 0.8 mm for the center and 0.8 mm for the radius. The execution time is less than one second per image.

Algorithms↗

PubMed2005

Automatic detection of fiducial markers in fluoroscopy images for on-line calibration.

Calibrated C-arm fluoroscopy is used for a variety of medical procedures where objects and anatomical structures need to be located in space. Calibration is often based on imaging a grid of fiducial markers and using the C-arm image's geometrical measurements (radius and center) together with the positions of the markers. An on-line technique is developed to automatically locate the fiducial markers and validated on 97 images. The success rate of the detection algorithm is 96.28% with an average error of 0.46 mm and a standard deviation of 0.32 mm.

Algorithms↗

PubMed2006

Optimization of detector pixel size for stent visualization in x-ray fluoroscopy.

Pixel size is of great interest in the flat-panel detector design because of its potential impact on image quality. In the particular case of angiographic x-ray fluoroscopy, small pixels are required in order to adequately visualize interventional devices such as guidewires and stents which have wire diameters as small as 200 and 50 microm, respectively. We used quantitative experimental and modeling techniques to investigate the optimal pixel size for imaging stents. Image quality was evaluated by the ability of subjects to perform two tasks: detect the presence of a stent and discriminate a partially deployed stent from a fully deployed one in synthetic images. With measurements at 50, 100, 200, and 300 microm, the 100 microm pixel size gave the maximum contrast sensitivity for the detection experiment with the idealized direct detector. For an idealized indirect detector with a scintillating layer, an optimal pixel size was obtained at 200 microm pixel size. A channelized human observer model predicted a peak at 150 and 170 microm, for the idealized direct and indirect detectors, respectively. With regard to the stent deployment task for both detector types, smaller pixel sizes are favored and there is a steep drop in performance with larger pixels. In general, with the increasing exposures, the model and measurements give the enhanced contrast sensitivities and a smaller optimal pixel size. The effects of electronic noise and fill factor were investigated using the model. We believe that the experimental results and human observer model predications can help guide the flat-panel detector design. In addition, the human observer model should work on the similar images and be applicable to the future model and actual flat-panel implementations.

Algorithms↗

PubMedDate not supplied

Spectral considerations for absorption-edge fluoroscopy.

In our previous reports on absorption-edge fluoroscopy, it was not possible to relate fully the subtleties involved in the selection of spectral parameters. This paper is intended as an overview of this important aspect of the technique. It is shown that, by using the 1-kVp, 2-filter technique, it is possible to image certain elements (e.g., iodine and xenon) in the presence of tissue variations of +/-2 cm about the thickness at which perfect tissue cancellation takes place. Use of logarithmic signal processing extends this range, but bone thickness variations may not be accomodated because only two x-ray energies are involved in the imaging process. Use of a 3-kVp, 3-filter technique with logarithmic signal processing is shown to solve this problem. Computer simulations show that 1-mg/cm2 iodine may be imaged in the presence of 10 cm or more tissue variations and 2000-mg/cm2 bone variations.

Bone and Bones↗

PubMedDate not supplied

The optimization of signal detectability in digital fluoroscopy.

An optimization analysis of digital fluoroscopy has been carried out using (signal/noise)2/dose as a figure of merit. Three signal detection tasks have been considered: (i) small iodine-containing blood vessels; (ii) regions of fat; and (iii) microcalcifications. The effects of x-ray beam filtration and kilovoltage on the figure of merit have been parameterized and the associated x-ray tube power loadings have been defined. Results are presented in a fashion that facilitates the choice of parameters (amount of aluminum filtration, kilovoltage, and x-ray tube power loading) such that an acceptable balance can be achieved between signal detection sensitivity, patient dose, and x-ray tube power loading.

Adipose Tissue↗

PubMedDate not supplied

Quantification of coronary arterial calcium by dual energy digital subtraction fluoroscopy.

Clinical studies of the heart with fluoroscopy have shown that fluoroscopic visualization of calcium in the coronary arteries is strongly associated with coronary artery disease. However, fluoroscopic detection is limited by its low sensitivity, which is partly due to the interfering background tissue structures and image quantum noise. Moreover, quantification of the absolute amount of calcium in an arterial segment has not been possible. A real-time dual-energy subtraction technique has been investigated as a possible solution to the above problem. In this energy subtraction technique, the kVp and filtration are switched at 30 Hz. In order to assess the potential utility of this videodensitometric technique to quantitate coronary artery calcium, arterial phantoms and excised segments of diseased human arteries were imaged. The low- and high-energy images were corrected for scatter and veiling glare before subtraction. Calcium measurements were made using the tissue-suppressed energy-subtracted images. The estimated calcium phosphate and ashed weights of the calcified arterial segments (N = 20) were highly correlated (slope = 1.04, Intercept = -0.33 mg, r = 0.92).

Calcium↗

PubMedDate not supplied

Dynamic pulmonary imaging: performance properties of a digital fluoroscopy system.

The physical characteristics of dynamic pulmonary imaging with digital fluoroscopy, which differ from those in DSA equipment, have been determined. The spectral distributions and mean energies were calculated and corresponding exposures with varying high voltage and copper filtration (60-100 kVp, 0-2.83 mm Cu) were measured. The utilization of 90-100 kVp with a filter consisting of 1.39 mm Cu and 3 mm Al minimized disturbing skeletal artifacts and reduced the radiation exposure by a factor of approximately 5 in comparison with imaging at 60 kVp without copper filtration. Simultaneously, the measured signal decreased by about 25%. The mean energy of this spectrum exceeded that of 140 kVp chest imaging. The dynamic pulmonary imaging method produces logarithmically transformed x-ray transmittance values linearly related (r = -0.999) to water thickness between 7-10.5 cm, which is equivalent to the normal range of the chest in pediatric patients. A good linear correlation (r = 0.933,N = 92) was obtained when the change in transmitted radiation was compared with tidal volume measured in a rabbit model using a pneumotachometer. The results indicate that the method is applicable for quantitative measurements of pulmonary ventilation. Changes in tidal ventilation can be measured with this noninvasive x-ray imaging technique.

Animals↗

PubMed1994

Comparison of beam-hardening and K-edge filters for imaging barium and iodine during fluoroscopy.

This study investigated the dose reduction performance of several beam-hardening and K-edge filter materials for the imaging of barium or iodine during fluoroscopy. A computer model was developed to simulate the effect of added filtration on entrance exposure rate (Xp), integral dose rate (Di), contrast (C), signal to noise ratio (SNR), imaging performance per dose (SNR2/Di), and tube load. The model incorporated the response characteristics, in both manual and automatic control modes of operation, of fluoroscopic systems to increasing or decreasing x-ray intensity at the input of the image intensifier. Input parameters to the computer model included choice of filter material and thickness, a barium or iodine test object, tube potential, phantom thickness, a CsI input phosphor, and a set of algorithms for controlling the fluoroscopic system. In all cases, the performance of systems with added filtration was judged with respect to a reference system operating under comparable conditions. In general, either beam-hardening or K-edge filters provided a significant reduction in entrance exposure and integral dose rates, but with an attendant increase in tube load. For a fluoroscopic system constrained to follow a representative automatic brightness control algorithm, added filtration provided a reduction in entrance exposure and integral dose rates for all phantom or uniformly distributed barium thickness. However, the imaging performance per dose, in some cases, decreased rapidly and was less than that of the reference system at large thicknesses. Only as change in the algorithm controlling the kVcp and mA operating points on the fluoroscopic system provided an imaging performance per dose greater than the reference system's at large thicknesses. The practical implementation of adding filtration to fluoroscopic systems is most simply accomplished with beam-hardening filters rather than K-edge filters. However, the systems with K-edge added filtration can provide slightly better performance when used over a limited range of phantom thicknesses such as the range normally associated with pediatric patients.

Algorithms↗

PubMed1994

The x-ray fovea, a device for reducing x-ray dose in fluoroscopy.

The x-ray fovea (U.S. patents pending) is a device for reducing x-ray dose to patients and operations during x-ray fluoroscopy. It consists of a semitransparent collimator with an open, circular, central hole. The fovea collimator is placed at the exit of the x-ray tube, and the attenuation of the peripheral x-ray beam reduces x-ray exposure to patients and operators. The shadow caused by the x-ray fovea can be compensated using real-time image processing hardware. Accurate compensation is demonstrated for both linearly and logarithmically acquired images using a model that accounts for beam hardening in the fovea collimator. The central fovea region has improved image quality due to reduced scatter and veiling glare from the periphery. From beam-stop measurements, a 40% reduction in scatter plus veiling glare is measured using the fovea. A contrast improvement ratio of 1.5 is measured throughout the central region. In the compensated periphery, noise is increased by a factor of 1.66 because fewer photons are detected, but a small amount of temporal filtering compensates this degradation. The Roentgen area product (RAP) exposure to patients is reduced by approximately 70%, while scattered exposure to operators is reduced by approximately 60%.

Equipment Safety↗

PubMed1997

Effect of patient support pads on image quality and dose in fluoroscopy.

An investigation was performed of the changes in image quality and patient dose as a result of increasing filtration for fluoroscopy performed under automatic brightness control. Filtration was added either at the x-ray tube housing (i.e., scatter-free geometry) or adjacent to a tissue equivalent phantom simulating the patient (i.e., with-scatter geometry). Patient doses were expressed in terms of the total energy imparted to patients simulated by either a 10 cm (i.e., pediatric) or 20 cm (i.e., adult) acrylic phantoms. Changes in image quality were determined by measuring the relative visibility of circular disks in a Leeds Test Object 10 contrast-detail phantom. In the scatter-free geometry, the addition of 4 mm Al filtration reduced the energy imparted by 27% (10 cm phantom) and 20% (20 cm phantom). In the with-scatter geometry, the corresponding reductions in energy imparted were 17% and 9% for the 10 and 20 cm phantoms, respectively. The visibility of low contrast disks generally decreased as the thickness of the added aluminum increased but the location of the added Al (i.e., with-scatter or scatter-free geometry) had no significant effect on the resultant image quality. These results demonstrate that the use of patient support pads with a thickness of approximately 4 mm Al will generally have an adverse impact on fluoroscopic image quality and result in modest reductions (approximately 10%) of adult patient doses.

Adult↗

PubMed1997

Feasibility of a large area x-ray sensitive vidicon for medical fluoroscopy: signal and noise factors.

A large area x-ray sensitive vidicon is being investigated as an alternative to the x-ray image intensifier and television camera combination for medical fluoroscopy. Signal generation in an x-ray vidicon involves an x-ray photoconductive layer whose surface is scanned by an electron beam. The single x-ray to electron conversion stage of the x-ray vidicon offers a greatly improved modulation transfer function (MTF) over the x-ray image intensifier. This superior MTF allows signal and x-ray quantum noise at high spatial frequencies to be passed to the preamplifier with less attenuation. In cardiac cine applications this would allow quantum noise limited operation at higher spatial frequencies than is possible with the x-ray image intensifier system.

Electrons↗

PubMed1997

Analysis of the temporal response of computed tomography fluoroscopy.

Computed tomography fluoroscopy (CTF) has found many applications in interventional procedures. The advantage of CTF is its ability to remove overlapping structures in the human anatomy and, thereby, provide accurate spatial information. Another advantage is its ability to reconstruct images in a short period of time so that "real-time" information can be provided. In this paper, we perform theoretical analysis and computer simulations to evaluate the temporal response of the CTF. We investigate the impact of various reconstruction algorithms on CTF and demonstrate the inherent limitations of the CTF in terms of the time lag and delay. The analysis provides a useful guidance to the CTF operators to avoid potential pitfalls.

Algorithms↗

PubMed1997

Feasibility of a large area x-ray sensitive vidicon for medical fluoroscopy: resolution and lag factors.

A large area x-ray-sensitive vidicon utilizing amorphous selenium (a-Se) is being investigated as an alternative to the x-ray image intensifier and television camera combination (XRII/TV) for medical fluoroscopy. The x-ray vidicon is, to a first approximation, a scaled up version of the 1" (2.54 cm) light-sensitive vidicon. The modulation transfer function (MTF) of an x-ray vidicon is mainly determined by the number of lines used, the beam spot profile, and the electronic bandwidth. The x-ray vidicon is expected to have roughly the same MTF as the 1" vidicon from a XRII/TV system referenced to the x-ray input and as such will be superior to the MTF of the complete XRII/TV system especially in high resolution applications such as cardiac cine. Beam discharge lag is expected to be approximately the same as in the 1" vidicon since they have comparable photoconductor layer capacitance. Photoconductive lag is also expected to be low since a-Se is known to have a low trap density.

Electrons↗

PubMed1981

Video funduscopy and fluoroscopy.

A system of television ophthalmoscopy has been developed using commercially available colour television cameras and a specially designed high-sensitivity monochrome television camera. Funduscopy and fluoroscopy can be performed at low light levels and recorded on standard video tape for clinical evaluation and also as a teaching aid. A computerised television stereo ophthalmoscope image processor is being developed for real-time volumetric recording the volume of the optic disc cup in glaucoma.

Fluorescein Angiography↗