CAMRT Radiography Practice Exam

For AP knee imaging, 19 - 24 cm ASIS to table top measurement requires which degree of angulation?

1. 3 - 5 degrees caudad

2. Perpendicular

3. 3 - 5 degrees cephalad

4. 15 - 20 degrees cephalad

The correct answer is: Perpendicular

In AP knee imaging, when the measurement from the ASIS (anterior superior iliac spine) to the table top falls within the range of 19 to 24 cm, the central ray is oriented perpendicular to the film or receptor. This approach is based on the average anatomy and the positioning of the knee joint relative to the radiographic plate, ensuring a proper alignment that minimizes distortion and provides optimal visualization of the knee structures. Using a perpendicular angle allows for an accurate representation of the knee anatomy without introducing additional magnification or distortion that might occur with angulation. The knee is inherently a hinge joint with a center of rotation that is consistent across various body types, and positioning the central ray straight on provides a consistent method for imaging. Other given angle options involve cephalad or caudad angulation, which would be relevant for different measurement ranges or specific anatomical considerations. However, for the indicated measurement range of 19 to 24 cm, a perpendicular angle is the standard practice to ensure the best imaging results.