Basics of thoracic radiography and radiology

Ian Porter

doi:10.22233/9781910443941.1

British Small Animal Veterinary Association , 1 (2024); https://doi.org/10.22233/9781910443941.1

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Basics of thoracic radiography and radiology

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Author: Ian Porter
From: BSAVA Manual of Canine and Feline Thoracic Imaging
Item: Chapter 1, pp 1 - 21
DOI: 10.22233/9781910443941.1
Copyright: © 2024 British Small Animal Veterinary Association
Publication Date: January 2024

Thoracic radiography is a cost-effective, non-invasive, readily available diagnostic and screening tool for thoracic and systemic disease in small animals. The procedure is relatively easy to perform but requires careful attention to technique. In contrast to the ease of image acquisition, thoracic radiographic interpretation is challenging. This chapter provides an overview of anatomical variations seen in thoracic imaging and contains example radiographs from healthy animals for use as reference images. From discussing basic principles and equipment to techniques for positioning and restraint, this chapter aims to enhance the understanding and application of thoracic radiography.

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Figures

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1.1

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1.1 Computed radiography system including (a) a cassette reader and (b) digital workstation.

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1.3

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1.3 Commonly used aids or physical restraint.

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1.4

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1.4 A sedated cat positioned for thoracic radiography using non-manual restraint devices (sandbags, tape and a cloth muzzle that covers the eyes).

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1.5

Two people restraining a dog for thoracic radiography. Using two people allows each person to remain as far from the primary beam and patient as possible. Manual restraint should only be performed when chemical and non-manual physical restraint are not possible or are ineffective. © 2024 British Small Animal Veterinary Association

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1.5 Two people restraining a dog for thoracic radiography. Using two people allows each person to remain as far from the primary beam and patient as possible. Manual restraint should only be performed when chemical and non-manual physical restraint are not possible or are ineffective.

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1.7

Radiographs of a human hand-and-wrist phantom. (a) The phantom is placed inside a 0.5 mm lead equivalent glove and exposed to the primary X-ray beam; the bones of the phantom are easily identified with the primary beam penetrating the lead glove and reaching the detector. (b) The phantom is placed beside a patient, over the detector but outside of the primary beam. Note the degree of exposure of the phantom due to scatter radiation. © 2024 British Small Animal Veterinary Association

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1.7 Radiographs of a human hand-and-wrist phantom. (a) The phantom is placed inside a 0.5 mm lead equivalent glove and exposed to the primary X-ray beam; the bones of the phantom are easily identified with the primary beam penetrating the lead glove and reaching the detector. (b) The phantom is placed beside a patient, over the detector but outside of the primary beam. Note the degree of exposure of the phantom due to scatter radiation.

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1.8

Lateral thoracic radiographs of a cat acquired with (a) a stationary grid and (b) tabletop (without the use of a grid). In the magnified inserts, notice the prominent parallel grid lines displayed across the image in (a). © 2024 British Small Animal Veterinary Association

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1.8 Lateral thoracic radiographs of a cat acquired with (a) a stationary grid and (b) tabletop (without the use of a grid). In the magnified inserts, notice the prominent parallel grid lines displayed across the image in (a).

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1.9

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1.9 Right lateral thoracic radiograph of a cat demonstrating patient motion artefact.

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1.10

Magnification and penumbra. The objects on the left and right are equal in size. The object on the right is farther away from the detector than the object on the left; the resulting image of the object on the right is magnified and has penumbra (unsharpness) around its margin. © 2024 British Small Animal Veterinary Association

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1.10 Magnification and penumbra. The objects on the left and right are equal in size. The object on the right is farther away from the detector than the object on the left; the resulting image of the object on the right is magnified and has penumbra (unsharpness) around its margin.

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1.12

(a) DV and (b) VD thoracic radiographs of a dog with pleural fluid. Notice the redistribution of fluid between views with border effacement of the cardiac silhouette on the DV radiograph and the retraction of the dorsal aspect of the lungs from the lateral thoracic body walls with wide interlobar fissures (arrowed) on the VD view. © 2024 British Small Animal Veterinary Association

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1.12 (a) DV and (b) VD thoracic radiographs of a dog with pleural fluid. Notice the redistribution of fluid between views with border effacement of the cardiac silhouette on the DV radiograph and the retraction of the dorsal aspect of the lungs from the lateral thoracic body walls with wide interlobar fissures (arrowed) on the VD view.

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1.13

Patient positioning for a right lateral thoracic radiograph. (a) In some patients, foam wedges may be needed to comfortably level the patient both dorsally and ventrally. (b) The patient is positioned and restrained in right lateral recumbency using sandbags for physical restraint and a foam wedge to level the sternum and vertebral column. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2024 British Small Animal Veterinary Association

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1.13 Patient positioning for a right lateral thoracic radiograph. (a) In some patients, foam wedges may be needed to comfortably level the patient both dorsally and ventrally. (b) The patient is positioned and restrained in right lateral recumbency using sandbags for physical restraint and a foam wedge to level the sternum and vertebral column. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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1.14

Optimal collimation for a lateral thoracic radiograph, including centring of the X-ray beam. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2024 British Small Animal Veterinary Association

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1.14 Optimal collimation for a lateral thoracic radiograph, including centring of the X-ray beam. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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1.15

Patient positioning for a DV thoracic radiograph using (a) foam wedges and (b) a trough. These positioning aids help maintain the proper position while keeping the patient comfortable. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2024 British Small Animal Veterinary Association

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1.15 Patient positioning for a DV thoracic radiograph using (a) foam wedges and (b) a trough. These positioning aids help maintain the proper position while keeping the patient comfortable. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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1.16

(a, b) Patient positioning for a VD thoracic radiograph using a trough and sandbags. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2024 British Small Animal Veterinary Association

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1.16 (a, b) Patient positioning for a VD thoracic radiograph using a trough and sandbags. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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1.17

(a) Patient positioning for a VD (right decubitus/horizontal) thoracic radiograph. Note that collimation is insufficient; the X-ray beam should be collimated to only include the required region of anatomy and never extend beyond the margins of the detector. (b) DV thoracic radiograph of a dog with idiopathic pneumothorax that was drained. It is difficult to ascertain whether residual pleural gas is present or not. (c) VD (left decubitus/horizontal) thoracic radiograph of the same dog as in (b) demonstrating the presence of a large volume of right-sided pleural gas. © 2024 British Small Animal Veterinary Association

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1.17 (a) Patient positioning for a VD (right decubitus/horizontal) thoracic radiograph. Note that collimation is insufficient; the X-ray beam should be collimated to only include the required region of anatomy and never extend beyond the margins of the detector. (b) DV thoracic radiograph of a dog with idiopathic pneumothorax that was drained. It is difficult to ascertain whether residual pleural gas is present or not. (c) VD (left decubitus/horizontal) thoracic radiograph of the same dog as in (b) demonstrating the presence of a large volume of right-sided pleural gas.

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1.18

(a) Left–right lateral thoracic radiograph and (b) left–right lateral (standing/horizontal) thoracic radiograph of a 5-year-old German Shepherd Dog with megaoesophagus. Compare the distribution of air and fluid within the oesophageal lumen between the views. A distinct gas–fluid interface is only detected on the horizontal beam view. © 2024 British Small Animal Veterinary Association

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1.18 (a) Left–right lateral thoracic radiograph and (b) left–right lateral (standing/horizontal) thoracic radiograph of a 5-year-old German Shepherd Dog with megaoesophagus. Compare the distribution of air and fluid within the oesophageal lumen between the views. A distinct gas–fluid interface is only detected on the horizontal beam view.

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1.19

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1.19 Patient positioning for a left–right lateral (standing/horizontal) thoracic radiograph.

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1.20

(a) VD and (b) lesion-oriented oblique VD thoracic radiographs of a dog with a mass arising from the left fourth rib. Notice how the oblique VD radiograph highlights the osseous portion of the mass. © 2024 British Small Animal Veterinary Association

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1.20 (a) VD and (b) lesion-oriented oblique VD thoracic radiographs of a dog with a mass arising from the left fourth rib. Notice how the oblique VD radiograph highlights the osseous portion of the mass.

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1.21

Patient positioning for (a) an oblique DV thoracic radiograph and (b) an oblique VD thoracic radiograph. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2024 British Small Animal Veterinary Association

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1.21 Patient positioning for (a) an oblique DV thoracic radiograph and (b) an oblique VD thoracic radiograph. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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1.22

(a) Patient positioning for the ‘humanoid’ view. (b) The resulting radiograph demonstrating the displacement of the scapulae from the cranial aspect of the thorax. © 2024 British Small Animal Veterinary Association

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1.22 (a) Patient positioning for the ‘humanoid’ view. (b) The resulting radiograph demonstrating the displacement of the scapulae from the cranial aspect of the thorax.

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1.23

Normal DV thoracic radiographs of (a) an 8-year-old neutered Greyhound bitch with a deep narrow-chested conformation and (b) a 7-year-old male Bulldog with a wide shallow-chested conformation, breed-related vertebral abnormalities, and a wide cranial mediastinum due to fat accumulation. © 2024 British Small Animal Veterinary Association

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1.23 Normal DV thoracic radiographs of (a) an 8-year-old neutered Greyhound bitch with a deep narrow-chested conformation and (b) a 7-year-old male Bulldog with a wide shallow-chested conformation, breed-related vertebral abnormalities, and a wide cranial mediastinum due to fat accumulation.

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1.24

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1.24 DV thoracic radiograph of a 4-month-old German Shepherd Dog bitch with a visible thymus (arrowheads).

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1.25

(a–c) Three orthogonal thoracic radiographs of a 15-year-old Domestic Shorthaired cat. Note the aorta is tortuous and appears elongated. The long axis of the heart is more parallel to the sternum with increased sternal contact. These findings are common age-related changes of minor consequence. (b) On the VD view, the tortuous aorta (arrowed) should not be mistaken for a mass. L = left; R = right. © 2024 British Small Animal Veterinary Association

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1.25 (a–c) Three orthogonal thoracic radiographs of a 15-year-old Domestic Shorthaired cat. Note the aorta is tortuous and appears elongated. The long axis of the heart is more parallel to the sternum with increased sternal contact. These findings are common age-related changes of minor consequence. (b) On the VD view, the tortuous aorta (arrowed) should not be mistaken for a mass. L = left; R = right.

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1.26

Right lateral thoracic radiograph of a 4-year-old male German Shepherd Dog with minimal fat accumulation in the cranial mediastinum and increased visibility of the left subclavian artery (LeS), cranial vena cava (CrVC) and internal thoracic arteries/veins (InT). CdVC = caudal vena cava. © 2024 British Small Animal Veterinary Association

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1.26 Right lateral thoracic radiograph of a 4-year-old male German Shepherd Dog with minimal fat accumulation in the cranial mediastinum and increased visibility of the left subclavian artery (LeS), cranial vena cava (CrVC) and internal thoracic arteries/veins (InT). CdVC = caudal vena cava.

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1.28

Normal (a, b) VD and (c, d) right lateral thoracic radiographs of a 6-year-old Border Collie bitch acquired during (a, c) expiration and (b, d) inspiration. © 2024 British Small Animal Veterinary Association

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1.28 Normal (a, b) VD and (c, d) right lateral thoracic radiographs of a 6-year-old Border Collie bitch acquired during (a, c) expiration and (b, d) inspiration.

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1.29

Sequential VD thoracic radiographs of a 14-year-old English Setter acquired during (a) diastole and (b) systole. Compare the size and shape of the cardiac silhouette. © 2024 British Small Animal Veterinary Association

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1.29 Sequential VD thoracic radiographs of a 14-year-old English Setter acquired during (a) diastole and (b) systole. Compare the size and shape of the cardiac silhouette.

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1.31

Normal (a) right lateral and (b) left lateral canine thoracic radiographs. Notice the difference in appearance of the diaphragmatic crura. Black line = left crus; black dotted line = diaphragmatic cupula; D = duodenum; GF = gastric fundus; PA = pyloric antrum; white line = right crus; white dotted line = caudal vena cava. © 2024 British Small Animal Veterinary Association

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1.31 Normal (a) right lateral and (b) left lateral canine thoracic radiographs. Notice the difference in appearance of the diaphragmatic crura. Black line = left crus; black dotted line = diaphragmatic cupula; D = duodenum; GF = gastric fundus; PA = pyloric antrum; white line = right crus; white dotted line = caudal vena cava.

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1.33

Normal (a) VD and (b) DV canine thoracic radiographs. Notice the difference in cardiac size and shape due to magnification and view, and the appearance of the diaphragmatic crura. (b) The pulmonary blood vessels in the caudodorsal lung field extend caudal to the dotted diaphragmatic line and form a positive summation shadow with the liver. Black line = left crus; black dotted line = diapragmatic cupula; white line = right crus; white dotted line = caudal vena cava. © 2024 British Small Animal Veterinary Association

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1.33 Normal (a) VD and (b) DV canine thoracic radiographs. Notice the difference in cardiac size and shape due to magnification and view, and the appearance of the diaphragmatic crura. (b) The pulmonary blood vessels in the caudodorsal lung field extend caudal to the dotted diaphragmatic line and form a positive summation shadow with the liver. Black line = left crus; black dotted line = diapragmatic cupula; white line = right crus; white dotted line = caudal vena cava.

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1.34

Lateral thoracic radiographs of a dog acquired on a DR system demonstrating (a) correct exposure, (b) overexposure, and (c) underexposure. (b) Arrows indicate regions of the thoracic body wall where saturation artefacts have occurred (in saturation, information is lost or ‘clipped’ from an image when an exposure exceeds the dynamic range of the image-processing algorithm and/or the image detector); * indicates regions where overexposure has occurred to a degree where the calibration mask of the system is visible (seen as linear ‘plank-like’ lines, sometimes referred to a planking artefact). (c) The image is ‘grainy’ or ‘has noise’ due to insufficient radiation reaching the detector (quantum mottle). © 2024 British Small Animal Veterinary Association

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1.34 Lateral thoracic radiographs of a dog acquired on a DR system demonstrating (a) correct exposure, (b) overexposure, and (c) underexposure. (b) Arrows indicate regions of the thoracic body wall where saturation artefacts have occurred (in saturation, information is lost or ‘clipped’ from an image when an exposure exceeds the dynamic range of the image-processing algorithm and/or the image detector); * indicates regions where overexposure has occurred to a degree where the calibration mask of the system is visible (seen as linear ‘plank-like’ lines, sometimes referred to a planking artefact). (c) The image is ‘grainy’ or ‘has noise’ due to insufficient radiation reaching the detector (quantum mottle).

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1.35

(a) Lateral and (b) VD thoracic radiographs of a dog obtained using a CR system. (a) The radiograph was obtained with the CR detector cassette upside down. Notice the circles and radiating lines summating with the thorax. (b) The radiograph demostrates a double exposure. Notice the double images of the cardiac silhouette (arrowed), diaphragm (arrowheads), and ribs (* = duplicate images of the same rib). © 2024 British Small Animal Veterinary Association

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1.35 (a) Lateral and (b) VD thoracic radiographs of a dog obtained using a CR system. (a) The radiograph was obtained with the CR detector cassette upside down. Notice the circles and radiating lines summating with the thorax. (b) The radiograph demostrates a double exposure. Notice the double images of the cardiac silhouette (arrowed), diaphragm (arrowheads), and ribs (* = duplicate images of the same rib).

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1.36

(a) Left lateral and (b) VD thoracic radiographs of an 11-year-old male Flat Coated Retriever. Radiography was performed to test for thoracic metastasis. (a) There is concern for a pulmonary nodule versus a positive summation shadow (arrowed). (b) On the orthogonal view, the nodule is confirmed to be a superficial nodule on the body wall (arrowed), not a lung nodule. © 2024 British Small Animal Veterinary Association

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1.36 (a) Left lateral and (b) VD thoracic radiographs of an 11-year-old male Flat Coated Retriever. Radiography was performed to test for thoracic metastasis. (a) There is concern for a pulmonary nodule versus a positive summation shadow (arrowed). (b) On the orthogonal view, the nodule is confirmed to be a superficial nodule on the body wall (arrowed), not a lung nodule.

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1.37

Right lateral thoracic radiographs of an obese Boston Terrier under general anaesthesia. (a) Image acquired after a period of lateral recumbency. The findings are highly concerning for cranioventral lung consolidation due to a disease such as aspiration pneumonia. (b) Image obtained approximately 10 minutes later after temporarily repositioning the patient and improving ventilation. Resolution of pulmonary opacification and improved lung expansion confirmed the finding was due to atelectasis. © 2024 British Small Animal Veterinary Association

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1.37 Right lateral thoracic radiographs of an obese Boston Terrier under general anaesthesia. (a) Image acquired after a period of lateral recumbency. The findings are highly concerning for cranioventral lung consolidation due to a disease such as aspiration pneumonia. (b) Image obtained approximately 10 minutes later after temporarily repositioning the patient and improving ventilation. Resolution of pulmonary opacification and improved lung expansion confirmed the finding was due to atelectasis.

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1.38

VD thoracic radiograph of a dog. The skin folds create positive summation shadows with the lungs (arrowed). The less opaque regions lateral to the skin folds should not be confused with a pneumothorax. An easy way to identify skin folds is that they often extend across the body wall or beyond the margin of the thorax (pneumothorax does not). © 2024 British Small Animal Veterinary Association

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1.38 VD thoracic radiograph of a dog. The skin folds create positive summation shadows with the lungs (arrowed). The less opaque regions lateral to the skin folds should not be confused with a pneumothorax. An easy way to identify skin folds is that they often extend across the body wall or beyond the margin of the thorax (pneumothorax does not).

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1.39

Lateral thoracic radiographs of a 10-year-old Staffordshire Bull Terrier bitch diagnosed with mammary carcinoma. Radiography was performed to test for thoracic metastasis. (a) On the initial radiograph, a soft tissue nodule was observed (arrowed) that might be a pulmonary nodule, body wall nodule or nipple. No body wall nodule was palpated. (b) After application of barium paste topically to the nipples, the nodule (arrowed) is distinct from the nipples (arrowheads), supporting a diagnosis of a pulmonary nodule. © 2024 British Small Animal Veterinary Association

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1.39 Lateral thoracic radiographs of a 10-year-old Staffordshire Bull Terrier bitch diagnosed with mammary carcinoma. Radiography was performed to test for thoracic metastasis. (a) On the initial radiograph, a soft tissue nodule was observed (arrowed) that might be a pulmonary nodule, body wall nodule or nipple. No body wall nodule was palpated. (b) After application of barium paste topically to the nipples, the nodule (arrowed) is distinct from the nipples (arrowheads), supporting a diagnosis of a pulmonary nodule.