A routine posteroanterior (PA) chest radiograph is usually obtained with a source-to-image receptor distance (SID) of:

A routine posteroanterior (PA) chest radiograph is typically performed with a source-to-image receptor distance (SID) of 72 inches. This distance is chosen because it helps to minimize magnification and distortion of the heart and lungs, which are critical structures in a chest radiograph. A longer SID reduces the impact of scatter radiation and produces clearer images, which is particularly important for accurately assessing structures in the thoracic cavity.

In practice, a 72-inch SID is standard for chest imaging, as it provides the right balance between image quality and patient positioning comfort. While shorter distances such as 60 inches are sometimes used for specific purposes or in certain settings, they do not provide the same level of detail or accuracy for routine assessments as the longer SID does. On the other hand, excessively long SIDs like 80 or 100 inches, while they could theoretically provide better image quality, are not practical for routine PA chest radiography due to difficulties in positioning the patient and the equipment, as well as increased exposure times.