Artifacts can be divided into two categories, namely, those related to patient and those related to technique. Most of these artifacts are usually easy to identify, prevent, or correct.

The size and shape of breasts vary individually. They become pendulous with advancing age and pregnancy (Rosse and Gaddum-Rose 1997) (Fig. 12.18). Generally, a normal female adult breast shadow is seen as a soft tissue opacity with an incomplete border overlying the lower thorax. The inferolateral border of the breast is well-defined and sharp due to its free edge being surrounded by air, while the superior portion fades out (Fig. 12.18). The breast tissues generate an ill-defined shadow over the lower lung zones (Fig. 12.18c). As both breasts are usually not quite equal, asymmetric ill-defined opacities from breast shadows may produce confusion during image interpretation. It may sometimes be difficult to distinguish among normal breast shadows, normal lung, and either breast or lung pathology (Fig. 12.18a). Lateral views may be helpful to exclude underlying lung pathology. After breast removal for breast cancer surgery, the ipsilateral hemithorax is typically more lucent than the other hemithorax; mimicking lung emphysema or pulmonary oligemia (Fig. 12.19). Recently, new radiographic imaging tools have been added that help to separate lung tissue from the overlying bony thorax, such as dual-energy subtraction (Fig. 12.19) or digital tomosynthesis (Fig. 12.20), which enables pulmonary pathology, calcification, or bony portions to be more easily detected.

Each nipple is usually noticeable on the chest radiograph as a 0.5–1 cm well-defined oval nodular density over the lower thorax (Fig. 12.21). In some cases, only one nipple is identified to be projected over the lungs. In such cases, differentiation from an intrapulmonary lesion may be difficult. For small and flat breasts, the standard solution is to repeat a chest radiograph using radio-opaque markers placed round the nipples. In the past, augmentation mammoplasty was performed by direct injection of liquid silicone and paraffin. It has now been replaced by newer procedures, due to resultant complications, such as fibrous mass, foreign body granuloma, calcification within the breast, or migration throughout the body (Erguvan-Dogan and Yang 2006; Yi et al. 2008; Yang and Muradali 2011), and serious complications, e.g., acute lung injury or pulmonary embolism, after subcutaneous silicone injection (Parikh et al. 2008). Chest radiographs show a mass or heterogeneous opacity over the lower thorax, which could be misinterpreted as a pulmonary lesion. Recent breast implants involve placing an artificial implant under the breast glandular tissue or under the pectoralis muscle. Silicone bags and its fluid component are seen as a large well-circumscribed mass at the lower chest, resulting in increased opacity projecting over the lung on chest radiographs (Fig. 12.22).

A skin tag, mole, or wart can produce a nodular density similar to the nipple, resulting in a pseudonodule (Fig. 12.23).

The pectoralis major and minor muscles appear as a triangular soft tissue density around each shoulder that is contiguous with the breast on the chest radiograph. The trapezius is a large triangle-shaped muscle covering the shoulder posterosuperiorly and is seen as a soft tissue density extending from its superior portion in the neck to the shoulder area on chest radiographs. The serratus anterior is a large fan-shaped muscle sheet consisting of eight thick-set digitations, which form the medial wall of the axilla. On a frontal chest radiograph of a muscular man, its shadow can be partly superimposed on the lateral margin of the lung, seen as a companion shadow with a pleural line at the first three ribs or at the middle third of thorax, or “bowling pin”-like or curtain-like shadow at the costophrenic angle (Fig. 12.11c).