Hounsfield unit

Hounsfield unit (HU) is a measurement of radiodensity in computed tomography (CT).
It is calculated with linear transformation with air being arbitrary defined as -1,000 HU and water being 0 HU. ^{(DenOtter 2019)}

Values

Medium	Min HU	Max HU	Note
Air	-1000	-1000	—
Water	0	0	—
Fat	-120	-90	—
Soft tissue with contrast	100	300	—
Muscle	35	55	—
Bone (cancellous)	300	400	—
Bone (cortical)	1800	1900	—
Blood (unclotted)	13	50	—
Blood (clotted)	50	75	—
Subdural hematoma (within hours)	75	100	—
Subdural hematoma (3–9 days)	65	85	—
Subdural hematoma (> 10 days)	35	40	—
Brain (white matter)	20	30	—
Brain (gray matter)	37	45	—
Lung	-700	-600	—
Kidney	20	45	—
Liver	54	66	—
Lymph node	10	20	—
Thymus (child)	20	40	—
Thymus (adolescent)	20	120	—
Pleural effusion (transudate)	2	15	—
Pleural effusion (exudate)	4	33	—
Chyle	-30	-30	—
Urine	-5	15	—
Cerebrospinal fluid	15	15	—
Abscess	0	45	—
Mucus	0	70	—
Earwax	0	0	—
Bile	-5	15	—
Gallstone (cholesterol)	30	100	—
Gallstone (bilirubin)	90	120	—
Glass (windowpane)	500	500	—
Glass (bottle, car window)	2100	2300	—
Aluminum	2100	2300	—
Rock	2100	2300	—
Tarmac	2100	2300	—
Limestone	2800	2800	—
Copper	14000	14000	—
Silver	17000	17000	—
Steel	20000	30000	—
Brass	30000	30000	—
Gold	30000	30000	—

DenOtter TD, Schubert J. Hounsfield Unit (open-access, PDF). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Last updated 2019-10-06 and retrieved on 2020-05-26. PMID: 31613501
WP Hounsfield scale: Wikipedia. Hounsfield scale (webpage). Last updated 2019-10-24 and retrieved on 2020-06-26.