The Hounsfield Units (HU) make up the grayscale in medical CT imaging.
4096 values levels of gray (12 bit) and
ranges from
-1024 HU to 3071 HU
-1024 HU is black as in air
0 HU represents water (
3071 HU is white
represents the densest tissue in a human body,
tooth enamel. All other tissues are somewhere within this scale; fat is around -100 HU, muscle around 100 HU and bone spans from 200 HU (trabecular/spongeous bone) to about 2000 HU (cortical bone).
For practical purposes in the body
approximate Hounsfield units from black to white
density of air -1000HU As Black as Black can Be
density of lung- -700 to -800
fat -5 to -100
density of fluid +5 to +15
density of soft tissue +50
density of calcium +50 to +500
iodinated contrast + 100 to +500
“Contrast Resolution”
“Contrast Resolution”
The reason we see things is because of their difference in density the greater the difference the easier to see
Delta of soft tissue of myocardium vs soft tissue blood = 0
When densities are distinctly different ie delta HU is great – they are easily visualized air -1000HU and bile about -10 so delta is -990 HU
Delta for air pocket in relation to the soft tissue = 1050HU
Delta of calcium in annulus vs soft tissue of heart = 450HU
Delta of fat of breast and soft tissues of glandular tissue 150HU
Why are these densities relevant to CTA of the coronaries?