OBJECTIVE To evaluate contrast agents for their ability to improve visualization of the colon wall and lumen during CT and ultrasonography.
ANIMALS 10 healthy adult Beagles.
PROCEDURES Food was withheld from dogs for 36 hours, after which dogs consumed 250 mL of polyethylene glycol solution. Dogs were then anesthetized, a contrast agent (tap water, diluted barium, or air; order randomly assigned) was administered rectally, iodine contrast medium (880 mg of I/kg) was administered IV, and CT and ultrasonography of the colon were performed. After a 1-week washout period, this process was repeated with a different contrast agent until all agents had been evaluated. Two investigators reviewed the CT and ultrasonographic images for colon wall thickness, conspicuity, artifacts, wall layering, and degree of lumen dilation at 4 sites.
RESULTS Thickness of the colon wall was greatest in CT and ultrasonographic images with water used as contrast agent, followed by barium and then air. The CT images obtained after water administration had a smooth appearance that outlined the colonic mucosa and had the highest score of the 3 contrast agents for wall conspicuity. Although no substantial artifacts related to any of the contrast agents were identified on CT images, barium- and gas-induced shadowing and reverberation artifacts hindered wall evaluation during ultrasonography. For ultrasonography, the degree of conspicuity was highest with barium in the near-field wall and with water in the far-field wall. In contrast to CT, ultrasonography could be used to distinguish wall layering, and the mucosal and muscular layers were distinct with all contrast agents.
CONCLUSIONS AND CLINICAL RELEVANCE Use of water as a contrast agent for both CT and ultrasonography of the colon in dogs compensated for each imaging modality's disadvantages and could be beneficial in the diagnosis of colon disease.
OBJECTIVE To evaluate effects of position, time in that position, and positive end-expiratory 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.
OBJECTIVE To assess by use of various diagnostic imaging modalities acute changes in livers of healthy dogs after radiofrequency ablation (RFA) and determine the capability of each imaging modality to monitor ablation lesion changes.
ANIMALS 6 healthy Beagles.
PROCEDURES 12 ablation lesions were created in the liver of the dogs (2 lesions/dog). Ablation lesions were evaluated by use of conventional ultrasonography, strain elastography, and contrast-enhanced ultrasonography immediately after (time 0), 30 to 60 minutes after, and 3 days after RFA, and by use of CT 30 minutes and 3 days after RFA. Three dogs were euthanized shortly after RFA, and the other 3 dogs were euthanized on day 3. Lesion size measured by each imaging modality was compared with necropsy findings.
RESULTS Immediately after RFA, clear margins were more visible with elastography and contrast-enhanced ultrasonography than with conventional ultrasonography, which had acoustic shadowing. On triphasic contrast CT, the ablation zone, which indicated necrosis and hemorrhage, was not enhanced and could be measured. Marked enhancement of the periablation rim was observed during the venous phase and was identified as granulation tissue. Size of the ablation area measured on enhanced CT images was strongly correlated with actual lesion size.
CONCLUSIONS AND CLINICAL RELEVANCE For dogs of this study, CT was the most reliable method for lesion size determination. Although ultrasonographic imaging measurements underestimated lesion size, all modalities could be used to provide additional real-time guidance for RFA procedures of the liver as well as for other RFA procedures.