x-rays basically only see bone air and areas of calcification. an ultrasound can see "soft tissue" like cysts. having clinical information from both tests is often very helpful when your medical provider is trying to get an accurate diagnosis.
why is an ultrasound needed after an x-ray? . i went home after an abd x-ray for abd pain. got a call from the facility to call back and schedule an u/s. why would they need an u/s after the x-ray?