Thoracic radiograph

Thoracic radiographs are one of the most frequently obtained sets of images in small animal veterinary practice. They consist of a standard set of views providing orthogonal projections to view the three-dimensional anatomy within the thorax.

Indications

Thoracic radiographs are used for diagnostic and screening purposes. Some examples of indications for thoracic radiographs include

• respiratory disease
• cardiac disease
• screening for metastatic neoplasia
• esophageal disease
• pleural disease
• placement of nasogastric tubes, endotracheal tubes, etc.
• follow up of known thoracic disease to assess progress

Standard projections

At least two orthogonal projections, lateral and either dorsoventral or ventrodorsal should be obtained. Ideally, both the left and right lateral recumbent projections are used in a standard 3-view radiographic study. The use of two lateral projections maximizes the inflation of the uppermost lung and increased conspicuity of lung lesions.

Lateral projection

• performed in left lateral or right lateral recumbency
• provides maximum view of the thoracic structures
• used to assess heart size, pulmonary pathology, vasculature, mediastinum, pleural space
• the diaphragmatic crus nearest to the table will be positioned cranially
• the fundus of the stomach is under the left crus, and the caudal vena cava enters the right crus

Dorsoventral projection

• performed in sternal recumbency with thoracic limbs extended
• provides orthogonal view of the cardiac silhouette and laterality of lung lesions
• conspicuity of the heart is decreased with pleural effusion
• most comfortable position for the animal while restrained, best if respiratory difficulty present

Ventrodorsal projection

• performed in dorsal recumbency with thoracic limbs extended
• provides orthogonal view of the cardiac silhouette and laterality of lung lesions
• may be more challenging to position straight and needs animal's compliance

Additional projections

To obtain the maximum amount of information, all 4 views may be obtained. A ventrodorsal projection is particularly useful in cases with pleural effusion, as it pools the fluid away from the heart. 

Pitfalls

• rotation of the thorax in any projection alters the opacity and symmetry of structures
• superimposition of thoracic limbs, positioning aids may obscure lesions
• the heart appears different in size between the ventrodorsal and dorsoventral projections
• the diaphragmatic silhouette is more pronounced on the ventrodorsal projection
• skin folds and cutaneous masses may cause artifacts of superimposition
• chemical restraint will cause increase in heart size due to increased cardiac filling and low heart rate

Animal preparation

• remove collars and harnesses
• use adequate physical and chemical restraint to obtain optimal positioning without requiring personnel to restrain the animal

Imaging techniques