What is the HU of bone?

For board exams and as a rule of thumb we say bone is 1000 HU; however that is not the complete truth. While a compact bone is typically high in HU, making a measurement of cancellous bone is much more difficult. It inherently incorporates other types of low HU tissue that is averaged into the measurement and reduces the average HU value. This measurement can be as low as 200 HU depending on the placement and size of the ROI (see image below)

As an analogy think about how your dish sponge might be yellow in color, but it is inherently filled with colorless air and so any measurement of its “yellowness” will be brought down by the colorless air inside of it.

Mean is 314HU and even max is only 560HU due to partial volume average within the pixel.
Placing the ROI only in compact bone gives us a mean value of 1441 HU which is in line with values published in text books

Leave a Reply

Your email address will not be published. Required fields are marked *