Collimation and Exposure Parameter Influence Image Quality and Potential Radiation Dose to the Eye Lens of Personnel in Computed Radiography of the Canine Pelvis.

Introduction: The purpose of this study was to evaluate the effect of collimation on image quality and radiation dose to the eye lenses of the personnel involved in computed radiography of the canine pelvis. Materials and Methods: A retrospective study of canine pelvic radiographs (N = 54) was undertaken to evaluate the relationship between image quality and the degree of field the collimation used. This was followed by a prospective cadaver study (N = 18) that assessed the effects on image quality and on scattered radiation dose of different collimation field areas and exposure parameters. All radiographs were analyzed for image quality using a Visual Grading Analysis (VGA) with three observers. Finally, the potential scattered radiation dose to the eye lens of personnel restraining a dog for pelvic radiographs was measured. Results: The retrospective study showed a slightly better (statistically non-significant) VGA score for the radiographs with optimal collimation. Spatial and contrast resolution and image sharpness showed the greatest improvement in response to minimizing the collimation field. The prospective study showed slightly better VGA scores (improved image quality) with the optimal collimation. Increasing the exposure factors especially the tube current and exposure time (mAs) resulted in improved low contrast resolution and less noise in the radiographs. The potential eye lens radiation dose increased by 14, 28, and 40% [default exposures, increased the tube peak potential (kVp), increased mAs, respectively] as a result of reduced collimation (increased beam size). Conclusion: The degree of collimation has no statistically significant on image quality in canine pelvic radiology for the range of collimation used but does have an impact on potential radiation dose to personnel in the x-ray room. With regard to radiation safety, increases in kVp are associated with less potential scatter radiation exposure compared to comparable increases in mAs.

Measurement of Patellar Proximodistal Positioning with Limited Joint-Angle Sensitivity.

OBJECTIVE: Patellar luxation can be associated with abnormal proximodistal positioning of the patella. The current gold standard index (Insall-Salvati) for referencing this position is poorly suited to postoperative use, if the tibial tuberosity is moved surgically, but has the advantage of changing minimally with altered joint angles. The aim of this study was to identify an alternative index, which was simple to use, joint-angle insensitive and suitable for postoperative use. STUDY DESIGN: Candidate indices based on the angle between stifle joint landmarks were screened across a wide range of joint angles for insensitivity to joint angle changes using vulpine and canine stifle radiographs. Intraobserver and interobserver agreements were assessed for a single candidate index using canine radiographs. RESULTS: An angular index based on the caudal aspect of the femoral and tibial condyles and the apex of the patella was largely insensitive to joint angle variation. Intra- and interobserver agreements appeared suitable for clinical use, with low within-subject standard deviations (<1.3°) and coefficients of variations (<2.2%), and high intraclass correlation coefficients (>0.89). CONCLUSION: Patellar proximodistal position can be acceptably assessed at a variety of caudal joint angles using the described angular index. Further work is required to define reference intervals across a range of canine breeds.

Stifle Joint Rotational Variation in Extended Stifles in Healthy Dogs Undergoing Computed Tomography Examinations.

OBJECTIVES: The aim of this study was to evaluate stifle joint rotational stability in response to body position and repositioning in dogs undergoing computed tomography (CT). MATERIALS AND METHODS: Nine dogs (18 stifles) with no history or clinical signs of stifle injury undergoing CT examinations for other reasons were included in the study. Dogs were positioned in alternating dorsal and sternal recumbency with the pelvic limbs extended caudally and unrestrained, for a total of four examinations. Scans included the entire tibia and distal femur. Using defined landmarks on the tibia and femur, stifle joint rotational angles were measured from multiplanar reconstructions made by two independent observers, and repositioning effects and intra- and interobserver agreement evaluated. RESULTS: Repositioning produced repeatable stifle joint rotational angles (pooled within-subject standard deviations of 0.9° and 1.4°) and intraobserver repeatability was good (within-subject standard deviations 1.4°), but interobserver agreement was poor. Dorsal and sternal positioning produced equivalent results. CLINICAL SIGNIFICANCE: The results indicate that little rotation occurs in the healthy extended canine stifle joint during positioning for CT and support CT as a method for assessing limb alignment around the stifle joint, provided that the limb distal to the femorotibial joint is unrestrained. Clinically, it is likely that measured changes in rotational angles across (and distant to) the stifle joint are real, rather than being due to rotation artefact during imaging.