Final answer:
CT numbers, based on the Hounsfield scale, quantify the density of tissues in a CT scan. Air has a CT number of -1000 HU, lung tissue ranges from -500 to -700 HU, fat is around -50 to -100 HU, water is the reference at 0 HU, blood ranges from +30 to +70 HU, and bone can be from +400 up to +3000 HU.
Step-by-step explanation:
The numbers used in CT scans are based on the Hounsfield scale (HU), where the CT number for water is defined as 0 HU by standard, and air is defined as -1000 HU. The CT numbers for different substances or tissues within the body vary depending on their density relative to water. Typically, the CT numbers for human tissues would be in the following approximate ranges:
- Air: -1000 HU
- Lung: -500 to -700 HU
- Fat: -50 to -100 HU
- Water: 0 HU (reference point)
- Blood: +30 to +70 HU
- Bone: +400 to +3000 HU, depending on bone density
Values such as these allow radiologists to distinguish between various tissues in the body on a CT scan and to identify abnormalities such as tumors or atrophy.