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Biomedical subjects

S Rudin

Publications and source records attributed to S Rudin.

66 records · Page 4Linked to original sources
PubMedDate not supplied

Method for image equalization of ROI fluoroscopic images using mask localization, selection and subtraction.

In region of interest (ROI) fluoroscopy, a filter is used to drastically reduce the X-ray dose to the patient peripheral to an ROI, and mask subtraction is used to equalize the displayed image brightness. Methods are described for an optimized search to locate the ROI and select or construct a mask image using a descriptor look up table (DLUT) based on ROI size, relative ROI/periphery brightness and ROI shape and orientation. After mask subtraction, the brightness values of the periphery are comparable to those of the ROI providing for equalized display. This method was tested successfully on 50 actual fluoroscopic images of two anthromorphic phantoms. The methodology developed for real-time applications was successfully simulated in PC code and full real-time implementation is underway.

Calibration↗
PubMedDate not supplied

Near-field imaging of surface-enhanced second harmonic generation.

Surface-enhanced second harmonic generation from individual topographical defects of an otherwise flat gold film and from metal-coated diffraction gratings was measured using a near-field optical microscope. Experimentally measured second harmonic field distributions were compared with theoretical calculations.

Journal Article↗
PubMedDate not supplied

Assessment of patient exposure for barium enema examinations.

Methods are described for the assessment of patient exposure during clinical fluoroscopic procedures. Values of the roentgen-area-product (RAP) and their distribution throughout the examination are presented for both single-contrast and double-contrast barium enema studies. The double-contrast procedure was measured to give 50% more radiation to the patient than the single-contrast procedure when the same size optical aperture is used between the intensifier and TV pick-up tube. However, it was possible to decrease the fluoroscopic RAP value by over a factor of two for the double-contrast procedure without an adverse clinical effect by increasing the area of the aperture diaphragm.

Barium Sulfate↗
PubMedDate not supplied

Design of rotating aperture cones for radiographic scatter reduction.

A new multiple-scanning-slit or scanning-grid scatter-reduction geometry consisting of coaxial rotating aperture (RA) cones is described and compared with other RA assemblies such as the rotating aperture wheel (RAW) device. A unique feature of the new design is that the geometric and rotational axes of the conical RA surfaces coincide and are collinear with the x-ray focal spot. This arrangement of axes should provide the potential for greatly improved mechanical rigidity, higher rotational velocities, and the capability for static slit-pattern alignment. The common rotational axis of the cone assembly is angled obliquely to the central x-ray beam such that the intersections of the irradiated portion of the RA surfaces with the plane formed by the x-ray central beam and cone axes are straight lines parallel to the film plane. This geometry is compatible with the standard source-patient-image receptor radiographic relationship and allows for variable source-to-image-receptor distance.

Radiography↗
PubMedDate not supplied

Slit design considerations for rotating-aperture, scanning-beam radiography.

The rotating-aperture wheel (RAW) scanning-beam device is uniquely applicable for scatter elimination in short-time, rapid-sequence, and real-time radiographic imaging because of the continuous rotary motion of its slit pattern. This rotary motion places special restrictions on the slit pattern design. Although simple sector-shaped slits provide uniform primary transmission, they entail an unacceptable degree of slit widening on small-diameter wheels. The use of multiple slit zones with slits of different angular width has reduced the extent of this widening on a prototype RAW; however, interzone boundary artifacts caused by differential primary x-ray cutoff are apparent on some clinical images. This problem is eliminated with a unique spiral-shaped aperture pattern which consists of slits of constant width and constant spacing. Each slit is radially continuous and provides uniform primary transmission without interzone artifacts. This spiral pattern satisfies all requirements and appears to be the pattern of choice for rotating-aperture scanning-beam radiography.

Equipment Design↗
PubMedDate not supplied

Improving fluoroscopic image quality with continuously variable zoom magnification.

Coning down is commonly used during fluoroscopy to increase image contrast by reducing scatter. However, the resulting image fills only part of a video display whose resolution is limited by line rate and bandwidth. Optical or electron-optical zooming can be used to magnify the collimated image so that it fills a larger fraction of the viewable area of the video frame to make more effective use of the available video-display capacity. Modulation-transfer functions (MTFs) were measured for various zoom factors achieved using a zoom lens and the image-intensifier (II) electronic magnification mode. Significant and continuing improvement in total system MTF was observed up to zoom magnifications of greater than 3.3. For larger zoom factors, the resolution limit becomes dominated by the intrinsic resolving power of the II and by geometric unsharpness rather than by the line rate of the video system. When the MTF at infinite zoom factor, obtained by extrapolation, was divided into the measured MTFs, the resultant MTFz's were shown to scale predictably with zoom factor. Only a slight improvement in MTF was obtained using the II's electronic magnification mode compared to the same magnification using a zoom lens. It is concluded that, if improved image quality is the motivation for the use of coning down in fluoroscopy, then zooming to use fully the available video frame is warranted.

Fluoroscopy↗
PubMedDate not supplied

Accurate characterization of image intensifier distortion.

Image intensifier distortion due to photocathode curvature and electron optics is shown to be approximated by a simple two parameter odd-power polynomial. The accuracy of this fit was found to be far better than that of two other one parameter characterizations of distortion when applied to experimental data from four different model image intensifiers ranging in diameter from 9 to 14 in. The standard errors of the two parameters fits were less than 0.1 mm or 0.03% of the field of the IIs and were within the estimated measurement error.

Technology, Radiologic↗
PubMedDate not supplied

Luminance range compression for video film digitizers.

Video cameras are used in many film digitization and teleradiology systems. However, the density range of medical radiographs often exceeds the dynamic range of the camera, and all diagnostic information in the original image may not be captured. Information in both the high and low density areas of the film can be captured in a single video frame if the transmitted luminance range of the radiograph is reduced. This can be accomplished by spatially modulating the back illumination of the film such that areas of lesser density receive less illumination while areas of greater density receive greater illumination. In this work, the use of a video monitor is shown to be an effective means to provide spatially modulated light for compressing the transmitted luminance range and thereby expanding the apparent dynamic range of the video camera. A simple computer-interfaced video feedback system that determines the appropriate compression mask and a scheme for linearization of system response are described. This system provides an interactive means for control of the degree of range compression.

Analog-Digital Conversion↗
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↗
PubMedDate not supplied

Microdroplet tracking using biplane digital subtraction angiography for cerebral arteriovenous malformation blood flow path and velocity determinations.

High-speed biplane angiography is used to determine the path and velocity of microdroplets of contrast material in three dimensions. By allowing more accurate determination of detailed blood flow in feeding vessels and draining veins of cerebral arteriovenous malformations than available with standard angiography, the new method offers the potential for more accurate treatment and further study of neurovascular/cerebrovascular hemodynamics. The first study of the method is presented.

Angiography, Digital Subtraction↗
PubMedDate not supplied

Computer frame freezing of fluoroscopic images.

Simple but flexible frame freezing of fluoroscopic images can improve the utility of real-time x-ray imaging. A frame-freeze system based on a personal computer has been developed. The system is easily installed using standard hardware that is non-invasive of the fluoroscopic imaging chain. The frozen images can be used as a reference or for hard-copy documentation of real-time or videotaped procedures.

Fluoroscopy↗