Final answer:
The left lateral chest position is used when the patient's left side is against the image receptor and the X-ray goes from right to left; it is beneficial for detecting left-sided chest issues and correctly viewing devices like pacemakers in relation to the heart's position in the thoracic cavity.
Step-by-step explanation:
The specific position performed when a patient is erect with the left side of his chest placed against the image receptor, and the central ray enters the right side of the upper chest and exits the left, is the left lateral chest position. In this position, the X-ray beams pass horizontally from the right to the left side of the thorax, making it ideal for evaluating problems on the left side of the chest, such as detecting conditions like pneumonia, which can appear as a lung infiltrate on an X-ray image, or for proper placement of devices like an artificial pacemaker. It is crucial to be aware of the heart's location within the thoracic cavity, particularly the position of the apex and base when interpreting chest X-rays.