Under what circumstance is it not permissible to use ultrasound for diagnostic or treatment purposes?

The use of ultrasound in a diagnostic and treatment capacity is a common practice in various healthcare settings; however, there are specific circumstances under which its use is considered unsafe or unethical. One such circumstance is the application of ultrasound on a fetus in a pregnant uterus. This is due to ethical considerations and the potential risks associated with exposing a developing fetus to ultrasound waves, particularly when there is no clear medical necessity that outweighs the risks. The use of ultrasound on a fetus is generally limited to diagnostic purposes, and even then, it is approached with caution to ensure the safety and well-being of both the mother and the unborn child.

The other scenarios present different considerations. For example, using ultrasound on patients with a skin rash may be feasible but requires careful assessment of the underlying condition and risks of exacerbating the rash. In the case of infants, while there are specific guidelines and precautions, ultrasound can be safely utilized in pediatric medicine under appropriate circumstances. Similarly, treating elderly patients with ultrasound is typically acceptable as long as their overall health and potential contraindications are evaluated.

Thus, the unique vulnerabilities of a developing fetus and the ethical implications involved make the application of ultrasound in this particular case not permissible.