Final answer:
The appropriate depth for ultrasound imaging of the breast is about 0.11 m (110 mm) using a frequency of 7 MHz, balancing the need for detail with penetration depth.
Step-by-step explanation:
The appropriate depth to image the breast on ultrasound can vary, but a good rule of thumb is to aim for a penetration depth of approximately 0.11 m (110 mm) with a frequency of 7 MHz. This general guideline stems from the penetration capabilities of ultrasound frequencies and their corresponding wavelengths in human tissue, which relate to the level of detail that can be seen. The resolution or detail attainable is partly determined by the ultrasound probe's frequency, with higher frequencies providing more detail but penetrating less deeply.
For example, a 7 MHz ultrasound can effectively scan to a depth of about 500 times its wavelength in tissue; since the wavelength for 7 MHz is 0.22 mm, this results in an effective depth of 0.11 m. However, when imaging structures requiring very fine detail, such as the eye, higher frequencies might be employed, although they have a reduced penetration depth.