Comparison of radiographic and computed tomographic images of the lungs in healthy neonatal foals

OBJECTIVE: To compare CT and radiographic images of the lungs in sedated healthy foals positioned in sternal recumbency and to investigate whether a relationship exists between CT-derived measurements of lung attenuation and PaCO2 and PaO2.

ANIMALS: 6 healthy Standardbred foals < 14 days of age.

PROCEDURES: Thoracic CT images were acquired followed by radiographic views with each foal sedated and positioned in sternal recumbency. For each foal, both CT and radiographic images were evaluated for severity and extent of changes by lung regions on the basis of a subjective scoring system by 3 investigators. Quantitative analysis of CT images was also performed. Assessments of PaO2 and PaCO2 were performed before sedation, following sedation prior to CT, and after CT prior to radiography.

RESULTS: Interobserver agreement for CT and radiographic image scoring was strong (0.73) and fair (0.65), respectively; intraobserver agreement was near perfect for CT (0.97) and radiographic (0.94) image scoring. Increased CT attenuation and radiographic changes were identified for all foals and were preferentially distributed in the caudoventral portion of the lungs. Radiographic scores were significantly lower than CT image scores. A positive correlation (r = 0.872) between lung attenuation and CT image score was identified. A significant increase in PaCO2 was not considered clinically relevant. Significant changes in PaO2 were not observed.

CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that interpretation of CT images may be less subjective, compared with interpretation of radiographic images. These findings may aid in the evaluation of CT and radiographic images of neonatal foals with respiratory tract disease.