What type of CR angle is required for the AP semi-axial projection of the lung apices?

In the AP semi-axial projection of the lung apices, a CR angle of 15 to 20 degrees cephalad is used to effectively visualize the lung apices and to project the clavicles above them. This angle helps to reduce superimposition and allows for better definition of the lung structures.

The cephalad direction of the angle is essential as it directs the central ray away from the clavicles and towards the chest structures, providing a clearer view of the lung apices. This positioning maximizes the visibility of any pathologies that may be present in that region, such as tumors or infections.

In contrast, other angles outside the recommended range may either not provide sufficient separation of the anatomical structures or may lead to distortion of the image, ultimately hindering proper diagnosis. Thus, employing the 15 to 20 degrees cephalad angle is key for optimal imaging of the lung apices in this projection.