Why are lateral projections of the chest taken with the left side against the IR?

Taking lateral projections of the chest with the left side against the image receptor (IR) is primarily done to reduce magnification of the cardiac silhouette. When the left side of the chest is positioned against the IR, the heart, which is located more towards the left side of the thorax, is closer to the detector. This proximity results in less magnification compared to placing the right side against the IR. Consequently, this positioning provides a more accurate representation of the heart's size and shape, which is crucial for diagnosing cardiac conditions and assessing heart health.

Additionally, by reducing magnification, the overall quality of the lateral chest image is improved, as it enhances the delineation of the cardiac silhouette and reduces distortion that could mislead the interpretation. As a result, healthcare professionals can make more informed decisions based on clearer imaging of the heart's structure.