<prompt> Zero HU units is of-WaterFatSoft tissueBone  <response>: Hounsfield unit: CT scan is based on linear attenuation of X-ray Linear attenuation is measured in Hounsfield units Hypodense -0 or less than zero Hyperdense- More than zero NOTE: The reference value for Hounsfield unit is 0 seen with CSF or Water HU of -50 - -100 is seen with fat HU of -1000 is seen with air HU of 60 - 70 Acute bleed HU of 130 Contrast HU of 200 to 250 Calcifications HU of 400 to 1000 Coical bone 