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At least 793 records · Page 44Linked to original sources
PubMed2003

On the use of C-arm fluoroscopy for treatment planning in high dose rate brachytherapy.

Treatment planning for brachytherapy requires the acquisition of geometrical information of the implant applicator and the patient anatomy. This is typically done using a simulator or a computed tomography scanner. In this study, we present a different method by which orthogonal images from a C-arm fluoroscopic machine is used for high dose rate brachytherapy treatment planning. A typical C-arm is not isocentric, and it does not have the mechanical accuracy of a simulator. One solution is to place a reconstruction box with fiducial markers around the patient. However, with the limited clearance of the C-arm this method is very cumbersome to use, and is not suitable for all patients and implant sites. A different approach is adopted in our study. First, the C-arm movements are limited to three directions only between the two orthogonal images: the C-orbital rotation, the vertical column, and the horizontal arm directions. The amounts of the two linear movements and the geometric parameters of the C-arm orbit are used to calculate the location of the crossing point of the two beams and thus the magnification factors of the two images. Second, the fluoroscopic images from the C-arm workstation are transferred in DICOM format to the planning computer through a local area network. Distortions in the fluoroscopic images, with its major component the "pincushion" effect, are numerically removed using a software program developed in house, which employs a seven-parameter polynomial filter. The overall reconstruction accuracy using this method is found to be 2 mm. This filmless process reduces the overall time needed for treatment planning, and greatly improves the workflow for high dose rate brachytherapy procedures. Since its commissioning nearly three years ago, this system has been used extensively at our institution for endobronchial, intracavitary, and interstitial brachytherapy planning with satisfactory results.

Artifacts↗
PubMed2004

How should low-contrast detail detectability be measured in fluoroscopy?

The relationship and precision of four methods for measuring the low-contrast detail detectability in fluoroscopic imaging were studied. These included the physical measurement of the accumulation rate of the square of the signal-to-noise ratio (SNR(rate)2), two-alternative forced-choice (2-AFC) experiments, sixteen-alternative forced-choice (16-AFC) experiments and subjective determination of the threshold contrast. The precision and sensitivity of the threshold contrast measurement were seen to be modest in the constancy testing of fluoroscopic equipment: only large changes in system performance could be reliably detected by that method. The measurement of the SNR(rate)2 is suggested instead. The relationship between the results of the various methods were studied, and it was found that human performance can be related to SNR(rate)2 by introducing the concept of the effective image information integration time (t(eff)). When measured for an unlimited observation time, it depicts the saturation of human performance in detecting a static low-contrast detail in dynamic image noise. Here, t(eff) was found to be about 0.6 s in 2-AFC tests and 0.3 s in 16-AFC tests.

Algorithms↗
PubMed2005

Performance of a static-anode/flat-panel x-ray fluoroscopy system in a diagnostic strength magnetic field: a truly hybrid x-ray/MR imaging system.

Minimally invasive procedures are increasing in variety and frequency, facilitated by advances in imaging technology. Our hybrid imaging system (GE Apollo flat panel, custom Brand x-ray static anode x-ray tube, GE Lunar high-frequency power supply and 0.5 T Signa SP) provides both x-ray and MR imaging capability to guide complex procedures without requiring motion of the patient between two distant gantries. The performance of the x-ray tube in this closely integrated system was evaluated by modeling and measuring both the response of the filament to an externally applied field and the behavior of the electron beam for field strengths and geometries of interest. The performance of the detector was assessed by measuring the slanted-edge modulation transfer function (MTF) and when placed at zero field and at 0.5 T. Measured resonant frequencies of filaments can be approximated using a modified vibrating beam model, and were at frequencies well below the 25 kHz frequency of our generator for our filament geometry. The amplitude of vibration was not sufficient to cause shorting of the filament during operation within the magnetic field. A simple model of electrons in uniform electric and magnetic fields can be used to estimate the deflection of the electron beam on the anode for the fields of interest between 0.2 and 0.5 T. The MTF measured at the detector and the DQE showed no significant difference inside and outside of the magnetic field. With the proper modifications, an x-ray system can be fully integrated with a MR system, with minimal loss of image quality. Any x-ray tube can be assessed for compatibility when placed at a particular location within the field using the models. We have also concluded that a-Si electronics are robust against magnetic fields. Detailed knowledge of the x-ray system installation is required to provide estimates of system operation.

Electromagnetic Fields↗
PubMedDate not supplied

Absorption-edge fluoroscopy using a three-spectrum technique.

We have recently reported on a 1-kVp, two-filter image subtraction method for visualizing low concentrations of elements like iodine which have K-shell absorption edges in the diagnostic x-ray energy range. However, in the application of this technique to human thyroid imaging, superimposed images due to variations in tissue and bone thickness presented serious difficulties. In this paper, a technique is described for implementing a 3-kVp, three-filter approach. Using carefully chosen spectra and logarithmic image processing, images are produced which are compatible with our previously described two-stage storage-tube subtraction device. Proper manipulation of the resulting difference images results in a final absorption-edge image in which only the element of interest is visualized, with unwanted background images suppressed. Computer calculations are presented to illustrate the relative sizes of difference signals arising from the element of interest and from tissue and bone backgrounds. Phantom studies using iodine concentrations as small as 1 mg/cm2, with variations of 10 cm of tissue and 2 g/cm2 of bone, suggest that the theory is sound and that, with straightforward apparatus modifications, images of good quality should be possible.

Fluoroscopy↗
PubMedDate not supplied

Characterization of aberrations in image-intensified fluoroscopy.

A procedure is developed for characterizing and measuring the distortion and intensity variations which are present in x-ray image-intensifier systems. These effects often seriously limit the usefulness of such systems, and the results here make possible an evaluation and comparison of competing intensifier instruments.

Fluoroscopy↗
PubMedDate not supplied

Characterization of the veiling glare PSF in x-ray image intensified fluoroscopy.

A theoretical derivation for the point spread function (PSF) which describes the veiling glare in x-ray image intensifiers (II) is presented. The PSF is dependent on two parameters which can be determined experimentally for a given II. An experimental investigation of the linearity of veiling glare phenomenon is undertaken. The experimental results indicate that veiling glare could be described as a linear process to a high degree of accuracy.

Fluoroscopy↗
PubMedDate not supplied

Scatter-glare corrections in quantitative dual-energy fluoroscopy.

Previous attempts to use time subtraction intravenous digital subtraction angiography for ventricular imaging have been hampered by artifacts due to cardiac and respiratory motion. We have previously reported a motion-immune dual-energy technique in which kVp is switched between 60 and 120, at 300-500 mA, 30 times/s. In order to quantitate parameters such as ejection fraction and left ventricular volume, it is necessary to correct for scatter and veiling glare (SVG), which are the major sources of nonlinearities in videodensitometric digital subtraction angiography (DSA). In this report, a convolution filtering method has been investigated to estimate SVG in DSA images. In the first step, a grey level transformation of the detected image is utilized to get an estimated SVG image. In the second step this image is convolved to produce an image with appropriate spatial frequency content. Estimates of SVG in several Humanoid chest phantom images were obtained using Gaussian convolution kernels with a full width at half-maximum (FWHM) of 51-125 pixels. The root-mean-square (rms) percentage error of these estimates was obtained by comparison with direct SVG measurement. A convolution kernel with a FWHM of 75 pixels in each dimension applied to 16 Humanoid phantom images with various projections, thicknesses, and beam energies resulted in an average rms percentage error of 9.7% in the SVG estimate, for the 16 cases studied. The SVG estimation consisting of grey scale-to-SVG fraction lookup table (LUT) is made based on previous measurements. The x-ray settings required for each patient are utilized to alter the LUT in order to account for patient thickness variations.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiocardiography↗
PubMedDate not supplied

Region of interest fluoroscopy.

In some medical imaging applications, it is necessary to visualize only the center of the field of view with optimal quality. For example, often in interventional radiographic procedures only the region directly adjacent to the catheter tip must be well seen. A new imaging approach which reduces the number of photons exposing the patient outside a region of interest (ROI), while allowing the photon fluence to be maintained or increased in the ROI, may make more optimal use of the total integral radiation dose to the patient as well as enable increased contrast and reduced artifacts in the ROI. A demonstration is given with an angiographic phantom, for an ROI which is less than 10% of the total field of view and where the periphery receives 6% of the ROI exposure. Contrast is improved about 30% in the ROI, and yet the images are adequate in the periphery for visualizing high contrast reference features while there is a reduction in total integral patient dose. Details of the technique are discussed along with requirements for clinical implementation.

Fluoroscopy↗
PubMed2005

Treatment of 10 dogs with discospondylitis by fluoroscopy-guided percutaneous discectomy.

Ten dogs suffering from discospondylitis were treated by percutaneous discectomy and local and systemic antibiotic therapy. With fluoroscopic guidance, a cylinder 5 mm in diameter was removed from the centre of the intervertebral space, yielding a fenestration and decompressing the disc without producing any spinal instability. The causative bacteria were identified in nine of the 10 biopsy specimens, but in only three urine cultures and four blood cultures. In two cases, the antibiotics used initially had to be changed owing to the organisms' antibiotic resistance. The clinical signs of the dogs improved markedly after two to nine days (mean 4.2 days) and had resolved completely after five to 14 days (mean 9.1 days). In all the cases the disease could be classified histologically as either acute or chronic, and the disease was classified as chronic in one dog. No side effects were observed.

Animals↗