X-rays are for bones.

Computed Tomography (CT) is noninvasive and looks at cross-sectional x-rays

A patient lies on a motorized platform while a computerized axial tomography (CAT) scanner rotates 360 degrees around the patient taking x-ray images.

Magnetic Resonance Imaging (MRI) is noninvasive form of imaging to detect cancer or malignant tissue.

Positron Emission Tomography (PET) is a medical imaging technique where patients take radiopharmaceuticals and shows multiple conditions.

Ultrasonography is an imaging technique that uses high-frequency sound waves into the body to generate an echo signal that is converted by a computer into a real-time image. It is the least invasive and is used to look at heart function and fetal growth and development.

It's most common name is an ultrasound. Ultrasounds have terrible image quality and it unable to penetrate bone and gas.