Why do you use hard X-ray photography in chest X-ray photography?

Only soft x-rays, ordinary x-rays, high kilovolt x-rays, but I didn't listen to hard x-rays. For your question, it is mainly considered that there are ribs in the chest, which will absorb more X-rays, so soft X-rays may not be absorbed through the chest, and the IP board will not receive rays. Secondly, the front and back meridians of the chest are large, and scattering will make X-ray imaging blurred and more obvious.