According to the cosine law, the maximal therapeutic effect occurs when energy rays strike the body at what angle relative to the tissue surface?

According to the cosine law, the maximal therapeutic effect occurs when energy rays strike the body at what angle relative to the tissue surface?

• A. 90 degrees.
• B. 0 degrees.
• C. 45 degrees.
• D. 60 degrees.

Answer: (A)

When energy meets tissue, how much actually enters the tissue is greatest when the rays strike the surface perpendicularly. At this perpendicular incidence, the full energy component enters along the tissue normal and there is minimal reflection at the boundary. As the angle becomes more oblique relative to the surface, more energy is reflected and less penetrates, reducing the therapeutic effect. So the maximal effect occurs when energy rays strike the tissue at a right angle to the surface (perpendicular).

When energy meets tissue, how much actually enters the tissue is greatest when the rays strike the surface perpendicularly. At this perpendicular incidence, the full energy component enters along the tissue normal and there is minimal reflection at the boundary. As the angle becomes more oblique relative to the surface, more energy is reflected and less penetrates, reducing the therapeutic effect. So the maximal effect occurs when energy rays strike the tissue at a right angle to the surface (perpendicular).