What is the correct order from least-to-most radiodense (darkest-to-whitest) on a film?

The correct order from least-to-most radiodense on a film is indeed gas, fat, soft tissue and fluid, bone, and metal. This sequence reflects the varying degrees of radiopacity that different tissues and materials exhibit in imaging, with gas being the least radiodense, allowing the most X-rays to pass through, and appearing the darkest on a radiographic image.

Gas has a low density, resulting in minimal attenuation of X-rays, which creates darker areas on the film. In contrast, fat is denser than gas but still relatively low in radiodensity, appearing darker than soft tissues which include muscles and organs that have a higher density. Soft tissue and fluid have similar densities that allow them to appear lighter than fat but darker than bone.

Bone is significantly denser than all the aforementioned materials, reflecting more X-rays and appearing whiter on the film due to its high calcium content. Finally, metal, with the highest density among typical substances encountered in radiography, reflects an extensive amount of X-rays, resulting in the brightest areas on imaging.

This order is crucial for understanding how various tissues will appear on radiographs and is foundational knowledge in fields like radiography and medical imaging diagnostics.