It just depends on your specific condition. With X-rays, Dr. Petkov might need to get several angles of your foot or ankle, which could require you to get multiple X-rays during a single session. Since ultrasounds are in real-time, he can continue gathering images as needed.
In many cases, it’s common to need follow-up X-ray or ultrasound imaging a couple of months after your treatment or surgery, just to ensure you’re healing properly.