A rectal ultrasound is an exam that uses high-frequency sound waves to create images of tissue layer beneath the surface of the rectum. This is a safe procedure and involves no radiation. This test provides your doctor information about rectal polyps, rectal cancer, perianal infection and sphincter muscle injuries. It’s often the next step after a finding of raised (elevated) prostate-specific antigen (PSA) during a blood test. It is also used to look at the rectum for other problems.