Hounsfield units (HU) are a dimensionless unit universally used in Computed Tomography (CT) scanning to express CT numbers in a standardized and convenient form. These units are named after Sir Godfrey N Hounsfield (1919-2004), a Nobel Prize winner who pioneered the CT scanner and made great contributions to radiology and medicine.
Generally, CT Images store values ranging from -1024 HU to 3071 HU; with -1024 HU representing air (in the lungs), 0 HU representing water and 3071 HU representing the most dense human tissue (Tooth Enamel). Metal medical implants generally have very high densities, and are attributed the highest value in the HU Scale, 3071.
The table below summarizes the predetermined tissue values provided in Visual Anatomy.
From a visual perspective, in Visual Anatomy, -1024 HU is black and 3071 HU is white. Different tissue HU values fall under this grayscale producing the CT Images as above (right). This explains how your choice of HU values in the application, directly correspond to the tissue visualized in the final 3D model.