This study is about using a special ultrasound test called **FAST** (Focused Assessment with Sonography for Trauma) to help doctors decide if a child with a belly injury needs a **CT scan** (a type of X-ray that uses radiation to take detailed pictures inside the body). **Blunt torso trauma** means the child got hurt by something hitting or squeezing them, but nothing sharp went into their body. CT scans can be dangerous because they have radiation, which can sometimes cause cancer. The FAST test can be done quickly and safely without any radiation. This study will check if using the FAST test can help doctors care for injured children better by reducing the number of CT scans. Children younger than 18 years old with certain types of serious belly injuries can take part in this study, but not if they have very low blood pressure, have been stabbed or shot, or if they had certain tests or injuries before coming to the hospital.

• This study takes place in six different hospitals and involves 3,194 children.
• The FAST test only takes 3-5 minutes and is done at the child's bedside.
• There is no exposure to radiation with the FAST test, unlike CT scans.