PDF《The CARESTREAM Tube and Grid》

White Paper | CARESTREAM DRX-Revolution Mobile X-ray System The CARESTREAM Tube and Grid Alignment System provides better image quality and consistent techniques for portable diagnostic radiography Anti-Scatter Grids Improve Image Quality Scattered radiation is a major contributor to reduced image quality in diagnostic radiography.

Anti-scatter grids, when properly aligned, provide an effective means for reducing scatter [1-6]. The preferential transmission of primary versus scattered X-rays improves the contrast-to-noise ratio (CNR). Figure

1 shows a pair of portable chest images captured of an ICU patient with and without grids and under the same exposure conditions. Comparing the two images, the contrast improvement with grids is significant. Figure

1 -- Comparison of portable chest images captured of an ICU patient without (left) and with (right) anti-scatter grid Grid Benefits Can be Realized with Less Exposure Increments in Digital Radiography The Bucky factor is the reciprocal of the total X-ray penetration through an anti-scatter grid. The analog screen- film system has a fixed sensitometry response. When a grid is used, a Bucky factor technique increment was necessary to ensure sufficient exposure to produce a film image with proper density and contrast for diagnosis. The benefits of anti-scatter grids can be realized in digital radiography (DR) with less exposure technique increments than would be indicated by traditional Bucky factors [7]. This is because DR does not have a fixed sensitomety response;

the global contrast and brightness of a DR image can be arbitrarily modified by digital image processing. DR systems are fundamentally noise limited C within a broad range of exposure levels to the patient, the image quality is determined by the anatomy CNR in the captured image. Anti-scatter grids can improve the image CNR at a minor expense of reduced primary X-ray transmission. This suggests some exposure technique increase may be required to compensate for primary X-ray attenuation, but usually at a lower level than the Bucky factor. White Paper | CARESTREAM DRX-Revolution Mobile X-ray System

2 Challenges in Using Grids for Portable Radiography Grid usage in portable radiography is often sporadic and inconsistent. This causes greater variability in image quality, and a greater number of radiographs of poorer quality than those captured in the radiology department being delivered for interpretation. From the perspective of the radiographic technologist, using grids for portable exams involves a variety of time-consuming workflow implications. These include attaching and detaching the add-on grids to the X-ray cassettes;

the stringent requirements to properly position and align the X-ray source relative to the cassette behind the patient to avoid grid cutoff;

the increased probability that repeated exposures will be required due to grid-cutoff artifact;

and more. In addition, there is the misperception that grids are not required in digital radiography because increasing the exposure can overcome the scatter-noise level, and that image processing adjustments, such as window and level manipulations, can sufficiently compensate for the quality losses that are introduced by scattered radiation. With all of these considerations in mind, there would seem to be little motivation for the technologists to use grids in portable digital radiography. DRX-Revolution Tube and Grid Alignment System The CARESTREAM Tube and Grid Alignment System (TGA) for the CARESTREAM DRX-Revolution Mobile X-ray System provides guidance to the radiographic technologist for proper alignment of the X-ray source relative to the grid/detector. This optional feature integrates seamlessly with the DRX-Revolution System C no additional operational steps are required in the normal workflow (Figure 2). Two transmitters mounted under the collimator Eight receivers inside the grid holder frame Figure