You are imaging a tissue using a system operating a 1 MHz. If you double the ultrasonic frequency, what happens to the power of the returning scattered signal?

For most of the tissues, the attenuation or loss is proportional to the frequency.

Explanation:

So, If double the frequency, attenuation or loss also increases. So, the returning scattered signal power will decrease with increase in frequency. The amount by which it will decrease depends on the specific tissue.