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Basics of thoracic computed tomography

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Abstract

Computed tomography (CT) should be used in dogs and cats with suspected thoracic disease where other diagnostic imaging modalities, such as radiography and ultrasonography, fail to identify the cause and extent of the disease. CT is also indicated if the abnormalities cannot be clearly attributed to specific thoracic organs. The chapter discusses the following topics: Indications; Restraint and patient preparation; Technique.

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Figures

Image of 3.1
3.1 Contrast-enhanced CT image of the cranial thorax of an 8-year-old Domestic Longhair cat with a mineralized sarcoma arising from the palmaroproximal aspect of the left scapula. This image is set with a narrow window (level 65 HU, width 187 HU) to emphasize the peripheral contrast enhancement of the mass at the expense of increased visibility of image noise and streak artefacts. The lungs cannot be appropriately assessed with this window.
Image of 3.2
3.2 Contrast-enhanced CT image of the cranial mediastinum in a 6-year-old Labrador Retriever with an extraskeletal osteosarcoma. The image is set with a narrow window (level 70 HU, width 220 HU). The mass extended from the midcervical region to the cranial mediastinum where it deviated and compressed contrast-enhanced vessels, the trachea (T) and oesophagus (O). There is also compression of the cranial lung lobes.
Image of 3.3
3.3 High-resolution CT image (1 mm slice width, 1 second rotation time, high spatial algorithm) of the caudal thorax of a 10-year-old Miniature Poodle with a salivary adenocarcinoma. The image is set with a centre in the negative HU range and a wide window (level −744 HU, width 2456 HU). There is a single small lung nodule (arrowhead) in the dorsal aspect of the accessory lung lobe (AL) assessed as a potential metastasis. This lesion was not seen on survey radiographs. A post-chemotherapy treatment follow-up CT examination four weeks later revealed no growth of the nodule. A = Aorta; C = Caudal vena cava; O = Oesophagus with oesophageal stethoscope.
Image of 3.4
3.4 An anaesthetized Boston Terrier in ventral recumbency and ‘head first’ position on the CT table. Note the anaesthetic tubing and pulse oximetry cable crossing the gantry, which can create significant artefacts. The dog now in a ‘tail first’ position. When the thorax is scanned, the anaesthetic equipment will not cross the gantry and artefacts are avoided. Note the extended forelegs to move them out the scanning area. ECG clips (not seen here) should be placed well cranial or caudal to the scanning area.
Image of 3.5
3.5 The canine muffin sign. Occasionally CT offers completely unexpected new vistas. This 4-year-old St Bernard dog was positioned for a thoracic CT scan in the largest trough available. The CT image of the caudal thorax reveals a muffin-shaped cross-sectional anatomy of the dog, indicating that the trough was not big enough and was potentially restricting respiration.
Image of 3.6
3.6 Dorsal plane CT image of an 11-year-old Domestic Shorthair cat with a cavitated tumour in its left caudal lung lobe (arrowhead). The image was reconstructed from a helical CT series with 1 mm slice thickness and a pitch of 1, resulting in an image resolution close to the axial plane images. The main advantages of this plane are the better alignment of the lesion with the bronchial and vascular tree and the increased viewing area.
Image of 3.7
3.7 Mid-thoracic CT image of a 3-year-old crossbred dog with perihilar lymphadenopathy, demonstrating the set-up for a CT-assisted transpulmonary fine-needle lymph node aspiration. The needle is supported by a box, aligned with the image plane and advanced subcutaneously (left side of image). A black streak artefact emanates from the needle tip. From this image, the depth and angle of needle advancement can be planned and the aspirate then pursued accordingly. Recheck CT scan. There is a small area of pulmonary haemorrhage along the previous needle track (arrowhead) and a small pneumothorax (small amount of free gas dorsal aspect right hemithorax). The dog recovered uneventfully from anaesthesia and a granulomatous lymphadenopathy was diagnosed.

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