Rotating Aperture Wheel Research Articles

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.

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.

Scatter Reduction In Conventional Radiographic Tomography Using Rotating Apertures

Since images in conventional radiographic tomography are in-herently low in subject contrast, it is essential that scattered radiation be prevented from reaching the image receptor. Scanning beam or slit radiographic techniques are known to be the most efficient scatter elimination methods, yet have been inapplicable to this area of radiography. In this work it is shown that the scanning beam method using rotating aperture wheel (RAW) devices can be used in conventional tomography. One coder wheel between the x-ray tube and patient and two scatter discriminator wheels between the patient and image recep-tor form sections of the RAW "projection cone" with the lines of radia-tion from the x-ray source forming the "flux pyramid." As long as the projection cone follows the motion of the x-ray flux pyramid (with the ratios of the distances between the x-ray source, RAWs, patient, and image receptor kept constant throughout the motion) any RAW pattern may be used. Simple relations are given which describe the geometric constraints for various tomographic motions. As in any application of scanning slit techniques, it is possible to use the excellent scatter elimination capabilities of a RAW device either to improve image contrast or to reduce patient dose.

Improved Contrast in Special Procedures Using a Rotating Aperture Wheel (RAW) Device

Improved Contrast in Special Procedures Using a Rotating Aperture Wheel (RAW) Device

Improved contrast in special procedures using a rotating aperture wheel (RAW) device.

A new scatter control technology consisting of multiple rotating aperture wheels (RAWs) is being developed to provide improved radiographic contrast and/or reduced patient dose in both single frame and dynamic procedures. The unique geometry of this system allows the conventional source-patient-image receptor geometric relationship to remain unchanged so that the device can be added to existing radiographic, fluoroscopic, and conventional tomographic installations. A prototype RAW device has been used with a rapid film changer for simulated abdominal angiography. The resulting images show improved contrast over those obtained with a standard 12:1 fixed grid.

Editorial, Forum and Book Reviews

Stephen Rudin's article [Optical Engineering 19(1), 132 (1980)] on a Rotating Aperture Wheel Device for Improving Radiographic Contrast presents an interesting development that may eventually have wide acceptance and wide application in diagnostic radiography. Unfortunately, there is a most misleading error of nomenclature perpetuated in the summary, in the text, and in Figure 2.

Rotating Aperture Wheel (RAW) Device For Improving Radiographic Contrast

A Rotating Aperture Wheel (RAW) technology is under development which involves replacing a grid for scatter elimination with an assembly of one fore and two aft lead aperture wheels which are rotated to maintain the alignment between the slit or aperture pattern of each. Such a design has the unique feature that its motion can be made independent of the x-ray exposure time and duration allowing for the first time the practical use of a moving slit anti-scatter technique in rapid sequence and dynamic radiographic procedures. The technology is flexible as to lend itself toward use with varying source-to-image receptor distances (SIDs) such as are involved in fluoroscopy.

An airborne polarimeter for atmospheric radiation studies

A new polarimeter, to measure the Stokes parameters of linearly polarized atmospheric visible radiation in four narrow spectral regions, is described. The instrument was developed for airborne application to measure polarization of reflected solar radiation from various land, sea and cloud surfaces. It consists essentially of a polarizing prism assembly of four Glan Thompson prisms oriented so as to transmit light vibrations at 0°, 45°, 90° and 135° with respect to a chosen direction. A rotating aperture wheel allows the light beams transmitted by the polarizers to reach the cathode of a photomultiplier tube in sequence. The signals from the photomultiplier tube are separated and identified with gate circuits triggered by pulses from magnetic transducers fixed near the polarizing prisms. From simple relations between the output signals the desired Stokes parameters are obtained. The transducer pulses are also passed through delay circuits to give delayed pulses to gate housekeeping data such as spectral region, optical gain, scan angle, etc. The method of measurement and some results obtained during a recent meteorological expedition are presented.