Approximation of the Field Components of TE and TM Modes in Waveguides and Cavities with General Cross Section
This paper shows that the field components of TE and TM modes of waveguides and cavities with general cross section can be approximated by a power series consisting of a separeble solution and nonseparable solutions of Helmholtz wave equation corresponding to the rectangular waveguide.
Non-separable solutions of Helmholtz' equation revisited
Even if the idea is already very old (proposed first by Moseley in 1965), it offers analytical solutions of Helmholtz equations for curved waveguides. One of the key elements in their successful use is the computation of recursion formulas to find a numerical solution to the problem of analysis of generally shaped waveguides. They will be derived in this paper. Even if the original theory includes a generalisation to 3 dimensional cavities we will limit ourselves to 2 dimensional waveguide cases.
The effect of collimation on image quality and radiation safety in digital radiography of small animals
Collimating the primary x-ray beam to the specific area of anatomic interest has traditionally been strongly recommended to produce high quality radiographic images, even though some small animal patients can fit their entire torso on a single radiographic casette or detector. However, modern digital radiography may allow for whole-body projections for these patients at similar quality to specific collimated projections. Lateral and ventrodorsal projections of 31 small dogs were obtained to evaluate the effect of collimation on the quality of the resulting digital radiograph. Each projection was performed using both a collimated and whole-body technique. Scatter radiation was detected during each exposure as well to determine the effect of collimation on radiation safety for veterinary personnel. The resulting images were cropped to portray only the thorax, and were evaluated by five radiologists blinded to the procedure used for each image. Visual grading characteristics analysis was performed. An overall trend towards higher image quality was found in the collimated approach compared to the whole-body, but in most cases this change was not significant. Overall image quality for the ventrodorsal images was found to be significantly better in the collimated approach compared to the whole-body. Evaluation of image histograms suggests that the application of digital processing and the look-up table differs between them, and this may account for a large portion of any quality difference. Over twice as much scatter radiation was detected during the whole-body images as during the collimated images. Overall image quality was rated as adequate to high for almost all images with both approaches. Adequate collimation remains recommended to provide the highest quality images with the lowest exposure to veterinary personnel.