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D R Bednarek

Publications and source records attributed to D R Bednarek.

At least 19 recordsLinked to original sources
PubMed2001

Computer-aided bootstrap generation of characteristic curves for radiographic imaging systems.

Determination of the characteristic curve is essential for quantitative evaluation of digital as well as screen-film radiographic imaging systems. When it is not practical to generate the entire curve through variation of a single exposure parameter, bootstrap methods can be used. For the bootstrap method used here, curve segments are generated by varying one exposure parameter and multiple segments are produced at different exposure levels by varying a second parameter. The segments then are joined to form a single composite characteristic curve. If the second parameter is one for which the sensitivity of the receptor is not constant (such as x-ray tube potential or beam filtration), the shift of each segment along the log relative-exposure axis needed to join the overlapping curve sections is not known and some form of segment matching must be employed. A spline interpolation method and a polynomial fit integral method were developed for automatic segment matching and compared. For both methods, the shifts between successive segment pairs which result in optimal overlap are determined and the cumulative shifts to obtain the complete composite curve are calculated for all segments. The two methods are evaluated for several image receptors and with a known curve generated from an analytic function. Both methods closely agreed in the shifts determined for the image receptors and provided a good visual matching of the curve segments. The spline interpolation method more accurately determined the appropriate shifts for the mathematically generated curve segments. The bootstrap methods can provide complete, accurate characteristic curves, and the segment joining program makes the process fast and precise.

Diagnostic Imaging↗
PubMed2000

Comparison of two dose-area-product ionization chambers with different conductive surface coating for over-table and under-table tube configurations.

A custom-built graphite-coated transmission ionization chamber is compared to the VacuDAP 2001 (VacuTec, Dresden, Germany), which has transparent conductive electrodes. A study was made of the dependence of response on x-ray tube potential for both types of chamber under identical conditions of exposure using over-table and under-table x-ray tubes. Since the calibration factor is the dose-area product of the radiation incident on the patient per chamber reading, it depends on the intrinsic response of the chamber as well as the effect of material in the beam between the x-ray tube and patient. Differences of about 20% were measured between the intrinsic and the over-table calibration factors and between the over-table and the under-table calibration factors for both chambers. The VacuDAP display is specifically calibrated for the over-table condition and would overstate the actual DAP in the under-table case. The intrinsic response of the graphite chamber is nearly independent of tube potential. Although the variation of response with tube potential of the graphite chamber is increased when it is used as an over-table and an under-table patient monitor, it shows less overall variation of response than the VacuDAP. The average deviation of each calibration factor from the mean is less than 5% over the range of 40 to 140 kVp for both chambers.

Equipment Design↗
PubMed1999

Real-time equalization of region-of-interest fluoroscopic images using binary masks.

In region-of-interest (ROI) radiologic imaging, the x-ray beam is attenuated peripherally to the region of interest to reduce patient exposure. This attenuation reduces the peripheral image brightness which may cause contrast in the periphery to also be reduced due to video chain nonlinearity. For optimal viewing, it is necessary that the image brightness and contrast in the periphery be brought back to the levels in the ROI. Previously, digital subtraction angiography roadmapping equipment has been used for this equalization; however, the procedure is not independent of patient and gantry motion. A new motion independent method to achieve this equalization involves dividing the real-time video signal into two digital streams one of which is brightness and contrast enhanced. A pre-acquired binary mask image is created by thresholding the image of a uniform object obtained with the ROI filter in place. This binary mask is used to control the recombination of the two image streams in a digital pipeline processor in order to select the ROI from the unprocessed stream and the periphery from the enhanced stream. This system provides image equalization at 30 frame/s for real-time ROI imaging display. Images from this method demonstrate excellent image quality even for peripheral exposure reduction factors exceeding 10.

Equipment Design↗
PubMed1999

Super-global distortion correction for a rotational C-arm x-ray image intensifier.

Image intensifier (II) distortion changes as a function of C-arm rotation angle because of changes in the orientation of the II with the earth's or other stray magnetic fields. For cone-beam computed tomography (CT), distortion correction for all angles is essential. The new super-global distortion correction consists of a model to continuously correct II distortion not only at each location in the image but for every rotational angle of the C arm. Calibration bead images were acquired with a standard C arm in 9 in. II mode. The super-global (SG) model is obtained from the single-plane global correction of the selected calibration images with given sampling angle interval. The fifth-order single-plane global corrections yielded a residual rms error of 0.20 pixels, while the SG model yielded a rms error of 0.21 pixels, a negligibly small difference. We evaluated the accuracy dependence of the SG model on various factors, such as the single-plane global fitting order, SG order, and angular sampling interval. We found that a good SG model can be obtained using a sixth-order SG polynomial fit based on the fifth-order single-plane global correction, and that a 10 degrees sampling interval was sufficient. Thus, the SG model saves processing resources and storage space. The residual errors from the mechanical errors of the x-ray system were also investigated, and found comparable with the SG residual error. Additionally, a single-plane global correction was done in the cylindrical coordinate system, and physical information about pincushion distortion and S distortion were observed and analyzed; however, this method is not recommended due to a lack of calculational efficiency. In conclusion, the SG model provides an accurate, fast, and simple correction for rotational C-arm images, which may be used for cone-beam CT.

Biophysical Phenomena↗
PubMed1998

Filter material selection for region of interest radiologic imaging.

Region of interest (ROI) fluoroscopic techniques have the potential for improving image quality and greatly reducing radiation dose. The utility of ROI imaging depends on the material used for the filter. Various materials for x-ray beam shaping ROI filters are evaluated using a computer simulation to determine their transmission and effect on radiographic image quality as a function of kVp. Selected measurements were also performed to verify the results of the simulation. Rare earth materials such as gadolinium (Gd) showed distinct advantages over conventional filter materials such as copper (Cu). The effects of Gd and Cu filters on transmission, contrast, and contrast to noise ratio using a CsI image receptor were investigated for beams of 40 to 100 kVp for a broad range of thicknesses of iodine, barium, bone, fat, and for a range of phantom thicknesses. The results were the following: (1) Gd generally increases image contrast while Cu substantially decreases contrast for all materials at all kVp's; (2) Gd has much less variation in transmission with kVp than Cu; and (3) for the same signal in the ROI and with thicknesses of filters which provides the same entrance phantom kerma, Gd provides higher contrast to noise ratio than Cu for lower kVp values while Cu provides higher contrast to noise ratio at higher kVp values. Analytical results of transmission and contrast improvement as a function of iodine concentration, filter thickness, and kVp compared favorably with experimental values. In conclusion, Gd appears to be the filter material of choice when it is important to maintain a higher level of image contrast in the periphery, such as during angiography, since image contrast is not degraded with Gd while it is degraded substantially with Cu. Although contrast is degraded with Cu, Cu may be the preferred filter material for higher kVp procedures such as GI exams since the detected signal in the periphery would be substantially higher permitting either greater reduction in patient dose or a decrease in image noise for the same dose reduction.

Adipose Tissue↗
PubMed1997

Automatic system for measuring dose-area product (DAP) in ROI fluoroscopy.

A computerized system for monitoring dose-area product (DAP) has been developed for region of interest (ROI) fluoroscopy in which patient exposure is reduced using an x-ray attenuating filter with an aperture. The system includes an IBM compatible computer which is connected through an IEEE-488 interface to an electrometer which measures the charge from a DAP ionization chamber. A digital input/output board connects the computer to the filter placement device to determine whether the filter is in or out of the beam, and to the x-ray generator to determine when the exposure is due to spot filming. The computer logs the DAP from conventional fluoroscopy, ROI fluoroscopy and spot filming separately, applying the appropriate calibration factor for each. Measured DAPs, fluoroscopic DAP rates and exposure times are displayed in real-time. The system has been installed in a GI fluoroscopic room so that the dose-reduction potential of ROI imaging can be evaluated.

Automation↗
PubMed1997

Primary beam exposure outside the fluoroscopic field of view.

Fluoroscopic units can irradiate an area outside the displayed field of view (FOV) which provides no additional information to the fluoroscopist and may significantly increase the integral dose to the patient. This unnecessary exposure can be reduced using region of interest (ROI) filtration techniques to attenuate the x rays peripheral to the ROI as well as outside the displayed FOV [Granger et al., Med. Phys. 23, 1059 (1996)]. A survey was conducted to quantitatively determine the deviation between the total exposed area and the displayed FOV on 18 fluoroscopic x-ray units which have different shaped collimation. A film was taken in fluoroscopic mode and the area of the FOV was determined from the image of markers placed at the edge of the displayed FOV. For each unit, a measurement was made for each magnification mode at various source to image distances. The measured difference between the total exposed area and the area of the displayed FOV ranged between 5% and 32% for units meeting federal compliance standards and between 22% and 48% for units which were found to be out of compliance. The results of the survey and the application of ROI imaging techniques as a possible method to reduce dose due to inexact fluoroscopic collimation are presented.

Evaluation Studies as Topic↗
PubMed1996

Clinical application of region-of-interest techniques to radiologic imaging.

In region-of-interest (ROI) imaging, a filter with a central aperture is used to substantially reduce patient dose outside of an ROI while maintaining or improving image quality within the ROI. The benefits of ROI imaging can be realized by using standard imaging equipment. ROI imaging has been clinically applied to gastrointestinal radiology and interventional procedures. In gastrointestinal procedures, ROI fluoroscopy without image processing can be used without adversely affecting the procedure or interfering with spot radiography. ROI fluoroscopy can reduce the dose-area product by a factor of 1.7 for gastrointestinal procedures. In interventional neuroradiologic procedures, equalized display brightness is achieved with road mapping during fluoroscopy and with standard digital subtraction techniques during angiography. In interventional radiology, ROI filters can generally reduce the patient skin dose to levels below the threshold for skin effects, thus eliminating these effects across more than 85% of the field of view.

Central Nervous System↗
PubMed1996

Application of region-of-interest imaging techniques to neurointerventional radiology.

To reduce radiation exposure to patients and staff during neurointerventional procedures, region-of-interest (ROI) techniques were used with fluoroscopy, road mapping, and digital subtraction angiography in 19 patients. ROI filters, made of multiple layers of gadolinium, were attached to the collimators. Patient skin exposure was reduced by a factor of 3.3-10.0 across 85% of the field of view, and exposures were reduced to below thresholds for skin effects.

Angiography, Digital Subtraction↗
PubMed1996

Increasing the utility of the mammographic phantom image.

To increase the utility of the monthly accreditation mammographic phantom image, the authors added a light sensitometric strip on the same film. The optical densities of the steps on the sensitometric strip with values nearest those of the phantom background and disk were measured, and these optical densities and the density difference were recorded and plotted on a control chart. The ability was increased to determine if changes in the contrast or optical density on an image were due to film and associated processing or to the x-ray source.

Mammography↗
PubMed1995

Implementation of region-of-interest fluoroscopy by using the road mapping mode of a real-time digital radiographic unit.

In region-of-interest (ROI) fluoroscopy, a filter is used to greatly attenuate the x-ray beam outside the ROI and digital image processing is used to equalize the displayed brightness. The method is applicable to real-time imaging procedures such as vascular interventions for which a high-quality image is essential only over an ROI (eg, near the catheter tip), whereas the noise-degraded periphery may be acceptable for visualizing landmarks. Use of ROI fluoroscopy can greatly reduce radiation exposure to the patient and to staff while image quality in the ROI is maintained or improved. Exposure reduction factors greater than 5 were demonstrated for coil placement in a canine aneurysm model by using standard digital angiographic equipment operating in the road mapping mode. Potential applications for which future work will determine the clinical acceptability of ROI fluoroscopy include many of the highest-dose interventional procedures, in addition to general gastrointestinal fluoroscopy.

Animals↗
PubMed1992

Minimizing radiation dose to patient and staff during fluoroscopic, nasoenteral tube insertions.

It is possible to reduce greatly fluoroscopic radiation dose if some image degradation is acceptable. Since the fluoroscopic image during nasoenteral tube placements is used for guidance and not for diagnosis, a lower contrast image with increased quantum mottle can be easily tolerated. The three methods to reduce the radiation dose rate that were investigated consisted of removing the antiscatter grid, increasing the diameter of the optical aperture controlling the percentage of light reaching the television camera from the image intensifier output phosphor, and setting the fluoroscopic mA to the minimum value so that the kVp could be maximized. Fluoroscopic frozen video frames of a clinical tube insertion comparing the images with and without the dose-saving techniques are presented. Measurements of the radiation dose rates using a Plexiglas phantom show that the dose for patient and staff during fluoroscopic-guided nasoenteral tube placements can be reduced by over a factor of 10 without significantly adversely affecting the actual placement procedure.

Adult↗
PubMed1991

Blurred-mask density compression for improved reproduction of radiographs.

A film-based, blurred-mask subtraction technique can be used to reduce the apparent density range of medical radiographs so that a wider range of actual densities can be captured with video digitizers or reproduced on photographic paper for publication. The density compression and the edge enhancement resulting from this process is examined. A good balance between compression and enhancement for small structures was obtained with a 6-mm gap between the subtraction film and the original when producing the mask. As an example, a photographic print of a compressed chest film showed significant condensation of image information within the restricted reflection density scale of the print paper; detail was well demonstrated in the mediastinal, retrocardiac, and subdiaphragmatic regions that was not shown in the noncompressed print.

Humans↗
PubMed1991

Dose reduction during fluoroscopic placement of feeding tubes.

By both increasing the optical iris of the video camera and removing the grid in fluoroscopic procedures involved in placement of a Dubbhoff feeding tube, the radiation dose to patients and staff was reduced by five to seven times. An average expected dose to a patient of about 300 mGy per procedure was reduced by two to three times when the grid was removed and by an additional three times when an iris of increased diameter was used. Because Dobbhoff procedures do not involve obtaining a diagnosis, the image degradation was acceptable and did not affect the total exposure times or ability to conduct the procedure. With the grid out, the difference between the mean exposure times of 5.1 minutes in 96 patient studies done with a normal iris opening and 4.0 minutes in 52 studies done with an enlarged iris was not statistically significant. The importance of reducing patient dose is reinforced by the finding that one-third of the patients underwent repeated procedures, accounting for almost 60% of the total.

Environmental Exposure↗
PubMed1983

Artifacts produced by moving grids.

Anti-scatter grids reduce the amount of secondary radiation contributing to the image and improve the signal-to-noise ratio. However, they may also lead to the creation of linear artifacts representing the shadows of the radiopaque septa. Grid motion perpendicular to the septa during the exposure can cause blurring of the artifacts; however, the wider septa of recently proposed grids increase the difficulty of suppressing the artifacts entirely. Physical characteristics which affect perceptibility of grid-line artifacts and the conditions needed for their elimination are analyzed. Sufficient grid movement can eliminate overlap artifacts, while synchronization of linear grid motion with exposure time can suppress artifacts for relatively small grid movements.

Technology, Radiologic↗
PubMed1983

Reduction of fluoroscopic exposure for the air-contrast barium enema.

In a fluoroscopic imaging system, image quality and patient dose are both affected by the optical system linking the image intensifier with the video camera. The effect on patient exposure of increasing the optical iris aperture size over that required for other procedures performed on the same imaging system was investigated for the air-contrast barium enema examination. Using a large-area transmission ionisation chamber to monitor the Roentgen-area-product of entrance exposure, a decrease in fluoroscopic radiation of greater than 50% was clinically documented for a fluoroscopic system utilising kVp and mA variable automatic brightness control. For this iris change, the video image was of acceptable quality for positioning and monitoring the patient, and no deleterious effect was detected in the conduct of the air-contrast exam. The availability of a variable-sized operator-selectable iris diaphragm would permit this dose-reduction approach to be extended to other fluoroscopic procedures.

Air↗