What do composite filters consist of in terms of materials?

Composite filters are designed to enhance image quality while minimizing patient exposure during fluoroscopic procedures. They consist of multiple materials, where the material with the lowest atomic number is positioned closest to the patient. This arrangement is critical because it helps to effectively attenuate low-energy photons that contribute to patient dose without significantly impacting the quality of the diagnostic image.

The lowest atomic number material acts as a "shutter" for softer x-rays, which are more likely to be absorbed by the patient and contribute to unnecessary radiation exposure. By using a combination of materials in the filter, it achieves a balanced attenuation, where higher atomic number materials can absorb higher energy x-rays, while lower atomic number materials reduce the softer, less penetrating radiation. This layered approach optimizes both patient safety and imaging performance.

In contrast, options suggesting a single material or homogeneous blending would not provide the same level of optimization for radiation dose management and image clarity, as they lack the ability to selectively filter different energy levels of x-rays. Similarly, filters made only of aluminum would not capture the benefits of a composite design, which leverages multiple materials for effective filtration and patient care.