Final answer:
In the AP oblique projection, right posterior oblique position (RPO), the left kidney will be parallel with the plane of the IR.
Step-by-step explanation:
When performing the AP oblique projection, right posterior oblique position (RPO), the left kidney will be parallel with the plane of the IR. This is because the RPO position causes the right kidney to be slightly lower. The lower kidney is the one that will be parallel to the imaging plane. When performing the AP oblique projection, specifically the right posterior oblique (RPO) position, the anatomy of interest is oriented in a manner to better visualize the structures without overlap. In the context of imaging kidneys, the RPO position results in the left kidney being positioned parallel to the plane of the image receptor (IR). This occurs because as the patient is obliquely positioned with the right side posteriorly, the left kidney rotates anteriorly and aligns parallel to the IR, while the right kidney, which is slightly lower due to the presence of the liver, will be perpendicular to the IR plane.