Computed tomography of cats without general anesthesia: feasibility, protocol development and assessment of cats with thoracic disease

This study consisted of three phases. On phase one, the VetMouseTrapTM, a novel device that allows computed tomography (CT) of awake cats and provides a clinically supportive environment, was designed. Ten normal cats were used to test the device for safety parameters, including ambient internal oxygen, carbon dioxide levels and temperature. The final design of the VetMouseTrapTM was a transparent acrylic tube with easy access for oxygen administration at therapeutic levels with ports on both ends of the device and easy access for intravenous lines. The device is safe and met the clinical needs of cats. In phase two, CT protocols were developed and tested in awake normal cats using the VetMouseTrapTM. Twenty two awake normal cats were imaged using a 16 multi-slice helical CT unit to evaluate dose equivalent protocols. Two different x-ray tube potentials (kV???s), 80 and 120, and 2 different helical pitches, 0.562 and 1.75, were evaluated. The signal intensity of the pulmonary parenchyma (SIlung), signal intensity of background (SIbackgr.), contrast, noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were calculated. Three evaluators ranked the images for quality parameters including sharpness of liver margins, motion artifact, helical artifact and windmill artifact. The CT examinations were successfully completed in 90.9%of (20/22) normal cats. No artifacts directly related to the device were detected and 94% (75/80) of examinations were judged to have an absence of or minimal motion artifact. A statistically significant difference was found for SNR (P = 0.001) and CNR (P = 0.001) between all protocols. The higher pitch protocols had significantly lower noise and higher SNR and CNR, lower motion artifact, but greater helical artifacts. The findings of the study suggest that a protocol using 80 kV, 130 mA, 0.5 s, and 0.562 pitch with a 1.25 mm slice thickness, and 0.625 mm slice reconstruction interval is recommended. On phase three, thoracic CT was performed in 54 cats and thoracic radiography in 50 cats, and these imaging modalities were compared for imaging awake cats with signs of thoracic disease. The final diagnosis was obtained with cytology, histopathology, necropsy, or response to therapy. Cats were imaged in the VetMouseTrapTM using a 16 multi-slice helical CT system. The cats used in phase two served as control for imaging evaluation. The images were anonymized, randomized, and evaluated in consensus by two radiologists. The most common final diagnoses were lung neoplasia, lower airway disease, and cardiomyopathy (9 each). Other disease groups included mediastinal mass (8), infection (7), trauma (4) and hernia (3). CT provided additional correct diagnoses in 28% (14/50) and additional information in 76% (38/50) of the cats. Additional correct diagnoses achieved only with CT were most common for cats with trauma (n=3) and lower airway disease (n=4). The most common additional findings were lung hyperlucency (n=10), lung nodules (n=4), lung masses (n=4), bronchiectasis (n=4), and mediastinal lymphadenopathy (n=3), and the majority of these were found in cats with lower airway disease (n=8), pulmonary neoplasia (8) and mediastinal mass (6). Survey CT clinically changed the diagnosis or prognosis in 20 of the 50 cats that underwent both modalities. Contrast CT was performed without complications and most commonly in cats with lung neoplasia (n=6), mediastinal mass (n=4), and infectious (n=3) diseases, providing additional correct diagnosis in 2 cats not achieved with survey CT. Based on the results, survey and contrast thoracic CT using the VetMouseTrapTM in diseased cats is safe and clinically useful