Effect of position and time held in that position on ground-glass opacity in computed tomography images of dogs

OBJECTIVE To evaluate effects of position, time in that position, and positive endexpiratory pressure on ground-glass opacity caused by physiologic atelectasis on lung CT images and to determine effects of recumbency position before CT. ANIMALS 6 healthy Beagles. PROCEDURES In a crossover study, dogs were placed in 4 positions (sternal, dorsal, right lateral, and left lateral recumbency) for 2 holding times (30 and 60 minutes). Dogs were then repositioned in sternal recumbency, and CT was performed at 2 positive end-expiratory pressures (0 and 15 mm Hg). Location, distribution, and degree of ground-glass opacities were evaluated on lung CT images. Volume and mean density of the lungs and ground-glass opacities as well as maximum density of ground-glass opacities were evaluated. RESULTS Ground-glass opacities were mainly observed in parts of the lungs that were dependent during the various positions before CT, except for sternal recumbency. Opacities were reversible and decreased or disappeared after lung inflation. Ground-glass opacities were observed most frequently and had greatest severity when dogs were positioned in left lateral recumbency before CT. Ground-glass opacities were negligible for dogs positioned in sternal recumbency before CT. CONCLUSIONS AND CLINICAL RELEVANCE Location and reversibility of ground-glass opacities may help clinicians distinguish whether they are attributable to atelectasis or a result of pathological changes. Dogs should be positioned in sternal recumbency to minimize the occurrence of ground-glass opacities, particularly when several procedures are performed before CT, which increases the time that a dog will remain in the same position.