The medical test that captures live imags from inside the body, using high-frequency sound waves, is called an ultrasound scan. The ultrasound waves, once passed through the abdomen, reflect echoes that are captured by transducers (probe), and post processed to create images of parts inside the body.

There are superficial and deep probe transducers.
They are cheap and portable.
Their use in medical & surgical conditions, ante-natal scans, etc., is vital.

X-rays are projected at various levels, multiple times, as is necessary. The image data is thus captured in specialized detectors, which is then processed. The post processed image is printed in a CT film.
The hi-speed spiral CT scan has high resolution than conventional x-rays. It can also produce HRCT (High Resolution CT) for lungs.