Final answer:
In quality assurance checks for CT simulators, water is used to check CT number accuracy because of its stable X-ray attenuation properties, ensuring the accurate representation of body tissues in scans.
Step-by-step explanation:
The daily quality assurance check for the computed tomography (CT) simulator typically includes checking the CT number accuracy for water. Water is used as a reference material because it has stable and well-known X-ray attenuation properties.
CT numbers, or Hounsfield units, are used in CT imaging to measure the relative density of tissues compared to water. By calibrating the CT scanner to water, technicians ensure that the images produced accurately represent the different tissues and structures within the body.