Hounsfield scale
The Hounsfield scale (/ˈhaʊnzfiːld/ HOWNZ-feeld), named after Sir Godfrey Hounsfield, is a quantitative scale for describing radiodensity. It is frequently used in CT scans, where its value is also termed CT number.
Definition
The Hounsfield unit (HU) scale is a linear transformation of the original
where and are respectively the linear attenuation coefficients of water and air.
Thus, a change of one Hounsfield unit (HU) represents a change of 0.1% of the attenuation coefficient of water since the attenuation coefficient of air is nearly zero.[1]: 259
Calibration tests of HU with reference to water and other materials may be done to ensure standardised response. This is particularly important for CT scans used in
Rationale
The above standards were chosen as they are universally available references and suited to the key application for which computed axial tomography was developed: imaging the internal anatomy of living creatures based on organized water structures and mostly living in air, e.g. humans.
Values for different body tissues and material
HU-based differentiation of material applies to
Values reported here are approximations. Different dynamics are reported from one study to another.
Exact HU dynamics can vary from one CT acquisition to another due to CT acquisition and reconstruction parameters (kV, filters, reconstruction algorithms, etc.). The use of contrast agents modifies HU as well in some body parts (mainly blood).
Substance | HU | |
---|---|---|
Air
|
−1000 | |
Fat | −120 to −90[5] | |
Soft tissue on contrast CT | +100 to +300 | |
Bone | Cancellous | +300 to +400[6] |
Cortical | +500 to +1900[7][6][8] | |
Subdural hematoma | First hours | +75 to +100[9] |
After 3 days | +65 to +85[9] | |
After 10–14 days | +35 to +40[10] | |
Other blood | Unclotted | +13[11] to +50[12] |
Clotted | +50[13] to +75[11][13] | |
Pleural effusion | Transudate | +2 to +15 [14] |
Exudate | +4 to +33[14] | |
Other fluids | Chyle | −30[15] |
Water | 0 | |
Urine | −5 to +15[5] | |
Bile | −5 to +15[5] | |
CSF | +15 | |
Abscess / Pus | 0[16] or +20,[17] to +40[17] or +45[16] | |
Mucus | 0[18] - 130[19] ("high attenuating" at over 70 HU)[20][21] | |
Parenchyma | Lung | −700 to −600[22] |
Kidney | +20 to +45[5] | |
Liver | 60 ± 6[23] | |
Lymph nodes | +10 to +20[24] | |
Muscle | +35 to +55[5] | |
Thymus | ||
White matter | +20 to +30 | |
Grey matter | +37 to +45 | |
Gallstone | Cholesterol stone | +30 to +100[26] |
Bilirubin stone | +90 to +120[26] | |
Foreign body[27] | Windowpane glass | +500 |
Aluminum, tarmac, car window glass, bottle glass, and other rocks | +2,100 to +2,300 | |
Limestone | +2,800 | |
Copper | +14,000 | |
Silver | +17,000 | |
Steel | +20,000 | |
Gold, steel, and brass | +30,000 (upper measurable limit) | |
Earwax | <0 |
A practical application of this is in evaluation of tumors, where, for example, an
See also
References
- ^ ISBN 978-92-0-131010-1.
- ISBN 92-0-107304-6.
- S2CID 214010953.
- PMID 19464146.
- ^ ISBN 9780721674162.
- ^ PMID 28393820.
- S2CID 23463451.
- PMID 10068022.
- ^ PMID 27190831.
- ^ Sharma, Rohit; Gaillard, Frank. "Subdural haemorrhage". Radiopaedia. Retrieved 2018-08-14.
- ^ ISBN 9780781775540.
- ISBN 9780415281416.
- ^ ISBN 9781934559741.
- ^ PMID 24100060.
- ISBN 9781439893845.
- ^ .
- ^ S2CID 6248808.
- ^ Saggar, K; Ahluwalia, A; Sandhu, P; Kalia, V (2006). "Mucocoele of the Appendix" (PDF). Ind J Radiol Imag. 16 (2).
- S2CID 28755973.
- ^ Phuyal, Subash S.; Garg, Mandeep Kumar MK; Agarwal, Ritesh R; et al. (2015-09-02). "High-Attenuation Mucus Impaction in Patients With Allergic Bronchopulmonary Aspergillosis: Objective Criteria on High-Resolution Computed Tomography and Correlation With Serologic Parameters". Current Problems in Diagnostic Radiology.
- PMID 27055707.
- ISBN 9780781736558.
- ISBN 9783540289777.
- ISBN 9789400942776.
- ^ ISBN 9783642710766.
- ^ S2CID 39138974.
- S2CID 40300162.
- ^ Horwich, Perry J. (December 20, 2018). Eugene C Lin (ed.). "Adrenal Adenoma Imaging". Medscape. Retrieved July 28, 2023.
- Feeman, Timothy G. (2010). The Mathematics of Medical Imaging: A Beginner's Guide. Springer ISBN 978-0387927114.
External links
- "Hounsfield unit". Medcyclopaedia. GE. Archived from the original on 2012-04-04.
- Hounsfield Unit - fpnotebook.com
- "Introduction to CT physics" (PDF). elsevierhealth.com. Archived from the original (PDF) on 2007-09-26.
- Imaging of deep brain stimulation leads using extended Hounsfield unit CT. Stereotact Funct Neurosurg. 2009;87(3):155-60. doi: 10.1159/000209296