The document discusses several types of artifacts and noise that can appear in CT scans. It describes beam hardening as an artifact caused when lower energy x-rays are attenuated more than higher energy x-rays as the beam passes through tissue, skewing the x-ray spectrum. Motion artifacts occur if the patient moves during scanning, appearing as blurred images or double images. Partial volume averaging is an artifact caused when voxels contain mixed tissue types, resulting in an averaged CT value. The document also discusses the trade-off between spatial resolution and contrast resolution in CT imaging.