Hounsfield scale

The Hounsfield scale ({{IPAc-en|ˈ|h|aʊ|n|z|f|iː|l|d}} {{respell|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 linear attenuation coefficient measurement into one in which the radiodensity of distilled water at standard pressure and temperature (STP) is defined as 0 Hounsfield units (HU), while the radiodensity of air at STP is defined as −1000 HU. In a voxel with average linear attenuation coefficient $\mu$ , the corresponding HU value is therefore given by:{{Cite journal |last1=Levine |first1=Zachary H. |last2=Peskin |first2=Adele P. |last3=Holmgren |first3=Andrew D. |last4=Garboczi |first4=Edward J. |date=2018-12-20 |title=Preliminary X-ray CT investigation to link Hounsfield unit measurements with the International System of Units (SI) |journal=PLOS ONE |language=en |volume=13 |issue=12 |pages=e0208820 |doi=10.1371/journal.pone.0208820 |doi-access=free |issn=1932-6203 |pmc=6301669 |pmid=30571779}}{{Cite journal |last1=Hurrell |first1=Michael Anthony |last2=Butler |first2=Anthony Philip Howard |last3=Cook |first3=Nicholas James |last4=Butler |first4=Philip Howard |last5=Ronaldson |first5=J. Paul |last6=Zainon |first6=Rafidah |date=2012-05-01 |title=Spectral Hounsfield units: a new radiological concept |url=https://link.springer.com/article/10.1007/s00330-011-2348-3 |journal=European Radiology |language=en |volume=22 |issue=5 |pages=1008–1013 |doi=10.1007/s00330-011-2348-3 |pmid=22134894 |issn=1432-1084|url-access=subscription }}

$HU = 1000\times\frac{\mu - \mu_{\textrm{water}}}{\mu_{\textrm{water}} - \mu_{\textrm{air}}}$

where $\mu_{\textrm{water}}$ and $\mu_{\textrm{air}}$ 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.{{cite book |title=Diagnostic radiology physics: a handbook for teachers and students |date=2014 |pages=1–682 |publisher=International Atomic Energy Agency |location=Vienna |isbn=978-92-0-131010-1 |url=https://www.iaea.org/publications/8841/diagnostic-radiology-physics}}{{rp|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 radiotherapy treatment planning, where HU is converted to electron density.{{cite book |title=Radiation oncology physics: a handbook for teachers and students. |date=2005 |publisher=International Atomic Energy Agency |location=Vienna |isbn=92-0-107304-6 |page=230 |url=https://www.iaea.org/publications/7086/radiation-oncology-physics}} Variation in the measured values of reference materials with known composition, and variation between and within slices may be used as part of test procedures.{{rp|283}}{{cite book |title=AAPM Report No. 233: Performance Evaluation of Computed Tomography Systems - The Report of AAPM Task Group 233 |date=2019 |publisher=American Association of Physicists in Medicine |location=Alexandria, VA |isbn=978-1-936366-69-9 |url=https://www.aapm.org/pubs/reports/detail.asp?docid=186|doi=10.37206/186|last1=Samei |first1=Ehsan |last2=Bakalyar |first2=Donovan |last3=Boedeker |first3=Kirsten |last4=Brady |first4=Samuel |last5=Fan |first5=Jiahua |last6=Leng |first6=Shuai |last7=Myers |first7=Kyle |last8=Popescu |first8=Lucretiu |last9=Ramirez-Giraldo |first9=Juan Carlos |last10=Ranallo |first10=Frank |last11=Solomon |first11=Justin |last12=Vaishnav |first12=Jay |last13=Wang |first13=Jia |s2cid=214010953 }}

=Rationale=

The above standards were chosen originally to encode the radiodensity of organic tissues relative to water for 12-bit processing on clinical CT scanners.{{Cite journal |last=Jayamani |first=Jayapramila |last2=Osman |first2=Noor Diyana |last3=Tajuddin |first3=Abdul Aziz |last4=Salehi |first4=Zaker |last5=Ali |first5=Mohd Hanafi |last6=Abdul Aziz |first6=Mohd Zahri |date=2019-02-19 |title=Determination of computed tomography number of high-density materials in 12-bit, 12-bit extended and 16-bit depth for dosimetric calculation in treatment planning system |url=https://doi.org/10.1017/s1460396919000013 |journal=Journal of Radiotherapy in Practice |volume=18 |issue=03 |pages=285–294 |doi=10.1017/s1460396919000013 |issn=1460-3969|url-access=subscription }} A 12-bit encoding corresponds to 4096 ( $2^{12}$ ) values, where the range (–1024 to 3071) encompasses HU values for air, soft tissue and bone.

Values for different body tissues and material

File:CT Scan Thorax Lung -700 HU Window Level.jpg

File:CT Scan Thorax Air -1000 HU Window Level.jpg

File:CT Scan Thorax Water 0 HU Window Level.jpg

File:CT Scan Thorax Liver 60 HU Window Level.jpg

HU-based differentiation of material applies to medical-grade dual-energy CT scans but not to cone beam computed tomography (CBCT) scans, as CBCT scans provide unreliable HU readings.{{cite journal |last1=De Vos| first1= W. |last2=Casselman|first2=J.|last3=Swennen|first3=G.R.J.|date=June 2009|title=Cone-beam computerized tomography (CBCT) imaging of the oral and maxillofacial region: A systematic review of the literature|journal=International Journal of Oral and Maxillofacial Surgery|volume=38|issue=6|pages=609–625| doi= 10.1016/j.ijom.2009.02.028|pmid=19464146}}

Values reported here are approximations. Different dynamics are reported from one study to another.{{cn|date=July 2024}}

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).

colspan="2" \| Substance	HU
class="wikitable"
colspan="2" \| Air \| −1000
colspan="2" \| Fat \| −120 to −90
colspan="2" \| Soft tissue on contrast CT \| +100 to +300
rowspan="2" \| Bone	Cancellous	+300 to +400{{cite journal\|last1=Birur\|first1=N. Praveen \|last2= Patrick \|first2= Sanjana \|last3= Gurushanth \|first3= Keerthi\|last4=Raghavan\|first4=AShubhasini\|last5=Gurudath\|first5=Shubha\|display-authors= 3 \|title=Comparison of gray values of cone-beam computed tomography with hounsfield units of multislice computed tomography: An in vitro study\|journal=Indian Journal of Dental Research \|volume= 28 \|issue=1\|year=2017\|pages=66–70\|issn=0970-9290\|doi=10.4103/ijdr.IJDR_415_16\|pmid=28393820\|doi-access=free}}
Cortical	+500 to +1900{{Cite journal\|last1=Lim Fat\|first1=Daren\|last2=Kennedy\|first2=Jim\|last3=Galvin\|first3=Rose\|last4=O’Brien\|first4=Fergal\|last5=Mc Grath \|first5= Frank\|last6=Mullett\|first6=Hannan\|display-authors= 3 \|date=2012-05-01\|title=The Hounsfield value for cortical bone geometry in the proximal humerus—an in vitro study\| url= https://doi.org/10.1007/s00256-011-1255-7\|journal=Skeletal Radiology\|language=en\|volume=41\|issue=5\|pages=557–568\|doi=10.1007/s00256-011-1255-7\| pmid= 21932054 \|s2cid= 23463451\|issn=1432-2161\|url-access=subscription}}{{Cite journal\|last1=Aamodt\|first1=A.\|last2=Kvistad\|first2=K. A.\| last3= Andersen \|first3=E.\|last4=Lund-Larsen \|first4=J.\|last5=Eine\|first5=J.\|last6=Benum\|first6=P.\|last7=Husby\|first7=O. S.\|display-authors= 3 \|date=January 1999\| title=Determination of Hounsfield value for CT-based design of custom femoral stems\|journal=The Journal of Bone and Joint Surgery. British Volume \|volume=81\|issue=1\|pages=143–147\|doi=10.1302/0301-620X.81B1.0810143\|issn=0301-620X\|pmid=10068022\|doi-access=free}}
rowspan="3" \| Subdural hematoma	First hours	+75 to +100Fig 3 in: {{cite journal\|last1=Rao\|first1=Murali Gundu\|title=Dating of Early Subdural Haematoma: A Correlative Clinico-Radiological Study\|journal=Journal of Clinical and Diagnostic Research\|volume=10\|issue=4\|pages=HC01–5\|year=2016\|issn=2249-782X \|doi= 10.7860/JCDR/2016/17207.7644\| pmid=27190831\|pmc=4866129}}
After 3 days	+65 to +85
After 10–14 days	+35 to +40{{cite web\|url=https://radiopaedia.org/articles/subdural-haemorrhage\|first1= Rohit \|last1= Sharma\| first2= Frank \|last2= Gaillard \|access-date=2018-08-14\|website=Radiopaedia\|title=Subdural haemorrhage}}
rowspan="2" \| Other blood	Unclotted	+13{{cite book \|title=Essentials of Radiologic Science\| first1= Robert \|last1= Fosbinder\| first2= Denise \|last2= Orth\| page= [https://books.google.com/books?id=jRVg5ilM1UEC&pg=PA263 263]\|publisher=Lippincott Williams & Wilkins\|year=2011\|isbn=9780781775540}} to +50{{cite book\|title=Radiology of the Chest and Related Conditions\| first= F. W. \|last= Wright\| page= [https://books.google.com/books?id=Bif0zpmEWtAC&pg=SA20-PA17 20.17] \|publisher=CRC Press\|year=2001\|isbn=9780415281416}}
Clotted	+50{{cite book\|title=Navigating the Adult Spine: Bridging Clinical Practice and Neuroradiology\| first1= Avital \|last1= Fast\| first2= Dorith \|last2= Goldsher\| page= [https://books.google.com/books?id=4HaPJYaXXSAC&pg=PA17 17] \|publisher=Demos Medical Publishing\|year=2006\|isbn=9781934559741}} to +75
rowspan="2" \| Pleural effusion	Transudate	+2 to +15 {{cite journal \|last1= Cullu \|first1= Nesat \|last2= Kalemci \|first2= Serdar \|last3= Karakas \|first3=Omer\|last4=Eser\|first4=Irfan\|last5=Yalcin\|first5=Funda\|last6=Boyaci\|first6=Fatma Nurefsan\|last7=Karakas\|first7=Ekrem \| display-authors= 3 \|title= Efficacy of CT in diagnosis of transudates and exudates in patients with pleural effusion\|journal=Diagnostic and Interventional Radiology\|volume=20\|issue=2\|pages=116–20\|year=2013\|issn=1305-3825\|doi=10.5152/dir.2013.13066\|pmid=24100060\|pmc=4463296}}
Exudate	+4 to +33
rowspan="7" \| Other fluids	Chyle \| −30[https://books.google.com/books?id=QmLNBQAAQBAJ&pg=PA342 Page 342] in: {{cite book\|title=Multi-Detector CT Imaging: Principles, Head, Neck, and Vascular Systems, Volume 1\|author=Luca Saba\|author2=Jasjit S. Suri\|publisher=CRC Press\|year=2013\|isbn=9781439893845}}
Water \| 0
Urine \| −5 to +15Page 83 in: {{cite book\|title=Prostatic Diseases\|author=Herbert Lepor\|publisher=W.B. Saunders Company\|year=2000\|isbn=9780721674162}}
Bile \| −5 to +15
CSF \| +15
Abscess / Pus \| 0{{cite journal\| url= http://pdf.posterng.netkey.at/download/index.php?module=get_pdf_by_id&poster_id=119826\| title= Liver abscesses: where do they come from? A review of the main types of liver abscesses and the correlation between their causes and the radiologic findings\| first1= P.\| last1= Sanchez de Medina Alba\| first2= C.\| last2= Santos Montón\| first3= N.\| last3= Calvo\| first4= K.\| last4= El Karzazi\| first5= T.\| last5= González de la Huebra Labrador\| first6= R.\| last6= Corrales\| first7= N.\| last7= Alegre Borge\| place= Salamanca\| display-authors= 3\| doi= 10.1594/ecr2014/C-1927\| website= ECR 2014\| year= 2014\| access-date= 2019-01-12\| archive-date= 2019-01-12\| archive-url= https://web.archive.org/web/20190112195058/http://pdf.posterng.netkey.at/download/index.php?module=get_pdf_by_id&poster_id=119826\| url-status= dead}} or +20,{{cite journal\| last1= Sasaki\| first1= Toru\| last2= Miyata \|first2=Rie \|last3=Hatai\| first3=Yoshiho \|last4=Makita\|first4=Kohzoh\|last5=Tsunoda\|first5=Koichi \|display-authors= 3\| title= Hounsfield unit values of retropharyngeal abscess-like lesions seen in Kawasaki disease\|journal=Acta Oto-Laryngologica\|volume=134\|issue=4\|year=2014\|pages=437–440\|issn=0001-6489\| doi= 10.3109/00016489.2013.878475\| pmid= 24512428\| s2cid=6248808}} to +40 or +45
Mucus \| 0{{Cite journal\|url=http://medind.nic.in/ibn/t06/i2/ibnt06i2p191.pdf\|title=Mucocoele of the Appendix\|first1=K\|last1=Saggar\|first2=A\|last2=Ahluwalia\|first3=P\|last3=Sandhu\|first4=V\|last4=Kalia\|journal=Ind J Radiol Imag\|year=2006\|volume=16\|issue=2}}{{Dead link\|date=August 2024 \|bot=InternetArchiveBot \|fix-attempted=yes }} - 130{{cite journal \|last1= Gaeta \|first1= Michele \|last2= Vinci \|first2= Sergio \|last3= Minutoli \|first3= Fabio \|last4= Mazziotti \|first4= Silvio \|last5= Ascenti\| first5= Giorgio \|last6= Salamone \|first6= Ignazio \|last7= Lamberto \|first7=Salvatore\|last8=Blandino\|first8=Alfredo\|title=CT and MRI findings of mucin-containing tumors and pseudotumors of the thorax: pictorial review\| display-authors= 3\| journal=European Radiology\|volume=12\|issue=1\|year=2001\|pages=181–189\|issn=0938-7994\|doi=10.1007/s003300100934\|pmid=11868096\|s2cid=28755973}} ("high attenuating" at over 70 HU){{cite journal\|title=High-Attenuation Mucus Impaction in Patients With Allergic Bronchopulmonary Aspergillosis: Objective Criteria on High-Resolution Computed Tomography and Correlation With Serologic Parameters\| first1=Subash S. \|last1= Phuyal\| first2= Mandeep Kumar MK \|last2= Garg\| first3=Ritesh R \|last3= Agarwal\| first4=Pankaj P \|last4= Gupta\| first5= Arunaloke A \|last5= Chakrabarti\| first6= Manavjit Singh MS \|last6=Sandhu\| first7= Niranjan N \|last7= Khandelwal\| display-authors= 3\| date=2015-09-02\| journal= Current Problems in Diagnostic Radiology}}{{cite journal \|last1=Agarwal \|first1=Ritesh\| last2=Sehgal\| first2=Inderpaul Singh\| last3= Dhooria\| first3=Sahajal\|last4=Aggarwal\|first4=Ashutosh\|title=Radiologic Criteria for the Diagnosis of High-Attenuation Mucus in Allergic Bronchopulmonary Aspergillosis \|journal=Chest\|volume=149\|issue=4\|year=2016\|pages=1109–1110\|issn=0012-3692\|doi=10.1016/j.chest.2015.12.043\|pmid=27055707\|doi-access=free}}
rowspan="8" \| Parenchyma	Lung \| −700 to −600{{cite book\|title=Cardiopulmonary Imaging\|volume=4\|first1= Ella A. \|last1= Kazerooni \|first2= Barry H.\|last2= Gross\|publisher=Lippincott Williams & Wilkins \| page= [https://books.google.com/books?id=IJwZHPrDQYUC&pg=PA379 379] \|year=2004\|isbn=9780781736558}}
Kidney \| +20 to +45
Liver \| 60 ± 6{{cite book\|title=Hepatology, Principles and Practice: History, Morphology, Biochemistry, Diagnostics, Clinic, Therapy\|first1= Erwin \|last1= Kuntz\| first2= Hans-Dieter \|last2= Kuntz\|page= [https://books.google.com/books?id=62jMOh67D8UC&pg=PA210 210] \|publisher=Springer Science & Business Media\|year=2006\|isbn=9783540289777}}
Lymph nodes \| +10 to +20{{cite book\|title=High-Resolution Computed Tomography of the Paranasal Sinuses and Pharynx and Related Regions: Impact of CT identification on diagnosis and patient management. Volume 12 of Series in Radiology\| first= G.\| last= Maatman\| page= [https://books.google.com/books?id=mfYkBAAAQBAJ&pg=PA58 58] \|publisher=Springer Science & Business Media\|year=2012\|isbn=9789400942776}}
Muscle \| +35 to +55
Thymus \| +20 to +40 in children{{cite book\|title=Surgery of the Thymus: Pathology, Associated Disorders and Surgical Technique\| first1= Jean-Claude \|last1= Givel\| first2=Marco \|last2= Merlini\| first3=David B. \|last3= Clarke\| first4= Michael \|last4= Dusmet \|page= [https://books.google.com/books?id=AsTcBQAAQBAJ&pg=PT488 488] \|publisher= Springer Science & Business Media\|year=2012\|isbn=9783642710766}} +20 to +120 in adolescents
White matter \| +20 to +30
Grey matter \| +37 to +45
rowspan="2" \| Gallstone	Cholesterol stone	+30 to +100{{cite journal\|vauthors=Rambow A, Staritz M, Wosiewitz U, Mildenburger P, Thelen M, Meyer zum Büschenfelde KH\| title=Analysis of radiolucent gallstones by computed tomography for in vivo estimation of stone components \| journal=Eur J Clin Invest \| year= 1990 \| volume= 20 \| issue= 4 \| pages= 475–8 \| pmid=2121509 \| doi= 10.1111/j.1365-2362.1990.tb01887.x\| s2cid=39138974 }}
Bilirubin stone	+90 to +120
rowspan="7" \| Foreign body{{cite journal\|last1=Bolliger\|first1=Stephan A. \|last2= Oesterhelweg\| first2= Lars \|last3= Spendlove \|first3= Danny \|last4=Ross\|first4=Steffen\|last5=Thali\|first5=Michael J.\|display-authors= 3 \|title=Is Differentiation of Frequently Encountered Foreign Bodies in Corpses Possible by Hounsfield Density Measurement?\|journal=Journal of Forensic Sciences\|volume=54\|issue=5\|year=2009\|pages=1119–1122\|issn=0022-1198\|doi=10.1111/j.1556-4029.2009.01100.x \|pmid= 19627414\| s2cid=40300162}}	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)
colspan="2" \| Earwax	<0

A practical application of this is in evaluation of tumors, where, for example, an adrenal tumor with a radiodensity of less than 10 HU is rather fatty in composition and almost certainly a benign adrenal adenoma.{{cite web| url= http://emedicine.medscape.com/article/376240 |title= Adrenal Adenoma Imaging| first= Perry J.| last= Horwich| editor= Eugene C Lin| date= December 20, 2018| website= Medscape | access-date= July 28, 2023}}

References

{{cite book

|last=Feeman

|first=Timothy G.

|title=The Mathematics of Medical Imaging: A Beginner's Guide

|series=Springer Undergraduate Texts in Mathematics and Technology

|publisher=Springer

|year=2010

|isbn=978-0387927114

}}

External links

{{cite web|url=http://www.medcyclopaedia.com/library/topics/volume_i/h/hounsfield_unit.aspx|archive-url=https://archive.today/20120404030558/http://www.medcyclopaedia.com/library/topics/volume_i/h/hounsfield_unit.aspx|url-status=dead|archive-date=2012-04-04|title=Hounsfield unit|publisher=GE|website=Medcyclopaedia}}
[http://www.fpnotebook.com/Rad/CT/HnsfldUnt.htm Hounsfield Unit] - fpnotebook.com
{{cite web|url=http://www.intl.elsevierhealth.com/e-books/pdf/940.pdf|title=Introduction to CT physics|publisher=elsevierhealth.com|archive-url=https://web.archive.org/web/20070926231241/http://www.intl.elsevierhealth.com/e-books/pdf/940.pdf|archive-date=2007-09-26}}
[https://www.researchgate.net/publication/24234798_Imaging_of_deep_brain_stimulation_leads_using_extended_Hounsfield_unit_CT Imaging of deep brain stimulation leads using extended Hounsfield unit CT. Stereotact Funct Neurosurg. 2009;87(3):155-60. doi: 10.1159/000209296]

Category:Radiology

colspan="2" \| Substance	HU
class="wikitable"
colspan="2" \| Air \| −1000
colspan="2" \| Fat \| −120 to −90
colspan="2" \| Soft tissue on contrast CT \| +100 to +300
rowspan="2" \| Bone	Cancellous	+300 to +400{{cite journal\|last1=Birur\|first1=N. Praveen \|last2= Patrick \|first2= Sanjana \|last3= Gurushanth \|first3= Keerthi\|last4=Raghavan\|first4=AShubhasini\|last5=Gurudath\|first5=Shubha\|display-authors= 3 \|title=Comparison of gray values of cone-beam computed tomography with hounsfield units of multislice computed tomography: An in vitro study\|journal=Indian Journal of Dental Research \|volume= 28 \|issue=1\|year=2017\|pages=66–70\|issn=0970-9290\|doi=10.4103/ijdr.IJDR_415_16\|pmid=28393820\|doi-access=free}}
Cortical	+500 to +1900{{Cite journal\|last1=Lim Fat\|first1=Daren\|last2=Kennedy\|first2=Jim\|last3=Galvin\|first3=Rose\|last4=O’Brien\|first4=Fergal\|last5=Mc Grath \|first5= Frank\|last6=Mullett\|first6=Hannan\|display-authors= 3 \|date=2012-05-01\|title=The Hounsfield value for cortical bone geometry in the proximal humerus—an in vitro study\| url= https://doi.org/10.1007/s00256-011-1255-7\|journal=Skeletal Radiology\|language=en\|volume=41\|issue=5\|pages=557–568\|doi=10.1007/s00256-011-1255-7\| pmid= 21932054 \|s2cid= 23463451\|issn=1432-2161\|url-access=subscription}}{{Cite journal\|last1=Aamodt\|first1=A.\|last2=Kvistad\|first2=K. A.\| last3= Andersen \|first3=E.\|last4=Lund-Larsen \|first4=J.\|last5=Eine\|first5=J.\|last6=Benum\|first6=P.\|last7=Husby\|first7=O. S.\|display-authors= 3 \|date=January 1999\| title=Determination of Hounsfield value for CT-based design of custom femoral stems\|journal=The Journal of Bone and Joint Surgery. British Volume \|volume=81\|issue=1\|pages=143–147\|doi=10.1302/0301-620X.81B1.0810143\|issn=0301-620X\|pmid=10068022\|doi-access=free}}
rowspan="3" \| Subdural hematoma	First hours	+75 to +100Fig 3 in: {{cite journal\|last1=Rao\|first1=Murali Gundu\|title=Dating of Early Subdural Haematoma: A Correlative Clinico-Radiological Study\|journal=Journal of Clinical and Diagnostic Research\|volume=10\|issue=4\|pages=HC01–5\|year=2016\|issn=2249-782X \|doi= 10.7860/JCDR/2016/17207.7644\| pmid=27190831\|pmc=4866129}}
After 3 days	+65 to +85
After 10–14 days	+35 to +40{{cite web\|url=https://radiopaedia.org/articles/subdural-haemorrhage\|first1= Rohit \|last1= Sharma\| first2= Frank \|last2= Gaillard \|access-date=2018-08-14\|website=Radiopaedia\|title=Subdural haemorrhage}}
rowspan="2" \| Other blood	Unclotted	+13{{cite book \|title=Essentials of Radiologic Science\| first1= Robert \|last1= Fosbinder\| first2= Denise \|last2= Orth\| page= [https://books.google.com/books?id=jRVg5ilM1UEC&pg=PA263 263]\|publisher=Lippincott Williams & Wilkins\|year=2011\|isbn=9780781775540}} to +50{{cite book\|title=Radiology of the Chest and Related Conditions\| first= F. W. \|last= Wright\| page= [https://books.google.com/books?id=Bif0zpmEWtAC&pg=SA20-PA17 20.17] \|publisher=CRC Press\|year=2001\|isbn=9780415281416}}
Clotted	+50{{cite book\|title=Navigating the Adult Spine: Bridging Clinical Practice and Neuroradiology\| first1= Avital \|last1= Fast\| first2= Dorith \|last2= Goldsher\| page= [https://books.google.com/books?id=4HaPJYaXXSAC&pg=PA17 17] \|publisher=Demos Medical Publishing\|year=2006\|isbn=9781934559741}} to +75
rowspan="2" \| Pleural effusion	Transudate	+2 to +15 {{cite journal \|last1= Cullu \|first1= Nesat \|last2= Kalemci \|first2= Serdar \|last3= Karakas \|first3=Omer\|last4=Eser\|first4=Irfan\|last5=Yalcin\|first5=Funda\|last6=Boyaci\|first6=Fatma Nurefsan\|last7=Karakas\|first7=Ekrem \| display-authors= 3 \|title= Efficacy of CT in diagnosis of transudates and exudates in patients with pleural effusion\|journal=Diagnostic and Interventional Radiology\|volume=20\|issue=2\|pages=116–20\|year=2013\|issn=1305-3825\|doi=10.5152/dir.2013.13066\|pmid=24100060\|pmc=4463296}}
Exudate	+4 to +33
rowspan="7" \| Other fluids	Chyle \| −30[https://books.google.com/books?id=QmLNBQAAQBAJ&pg=PA342 Page 342] in: {{cite book\|title=Multi-Detector CT Imaging: Principles, Head, Neck, and Vascular Systems, Volume 1\|author=Luca Saba\|author2=Jasjit S. Suri\|publisher=CRC Press\|year=2013\|isbn=9781439893845}}
Water \| 0
Urine \| −5 to +15Page 83 in: {{cite book\|title=Prostatic Diseases\|author=Herbert Lepor\|publisher=W.B. Saunders Company\|year=2000\|isbn=9780721674162}}
Bile \| −5 to +15
CSF \| +15
Abscess / Pus \| 0{{cite journal\| url= http://pdf.posterng.netkey.at/download/index.php?module=get_pdf_by_id&poster_id=119826\| title= Liver abscesses: where do they come from? A review of the main types of liver abscesses and the correlation between their causes and the radiologic findings\| first1= P.\| last1= Sanchez de Medina Alba\| first2= C.\| last2= Santos Montón\| first3= N.\| last3= Calvo\| first4= K.\| last4= El Karzazi\| first5= T.\| last5= González de la Huebra Labrador\| first6= R.\| last6= Corrales\| first7= N.\| last7= Alegre Borge\| place= Salamanca\| display-authors= 3\| doi= 10.1594/ecr2014/C-1927\| website= ECR 2014\| year= 2014\| access-date= 2019-01-12\| archive-date= 2019-01-12\| archive-url= https://web.archive.org/web/20190112195058/http://pdf.posterng.netkey.at/download/index.php?module=get_pdf_by_id&poster_id=119826\| url-status= dead}} or +20,{{cite journal\| last1= Sasaki\| first1= Toru\| last2= Miyata \|first2=Rie \|last3=Hatai\| first3=Yoshiho \|last4=Makita\|first4=Kohzoh\|last5=Tsunoda\|first5=Koichi \|display-authors= 3\| title= Hounsfield unit values of retropharyngeal abscess-like lesions seen in Kawasaki disease\|journal=Acta Oto-Laryngologica\|volume=134\|issue=4\|year=2014\|pages=437–440\|issn=0001-6489\| doi= 10.3109/00016489.2013.878475\| pmid= 24512428\| s2cid=6248808}} to +40 or +45
Mucus \| 0{{Cite journal\|url=http://medind.nic.in/ibn/t06/i2/ibnt06i2p191.pdf\|title=Mucocoele of the Appendix\|first1=K\|last1=Saggar\|first2=A\|last2=Ahluwalia\|first3=P\|last3=Sandhu\|first4=V\|last4=Kalia\|journal=Ind J Radiol Imag\|year=2006\|volume=16\|issue=2}}{{Dead link\|date=August 2024 \|bot=InternetArchiveBot \|fix-attempted=yes }} - 130{{cite journal \|last1= Gaeta \|first1= Michele \|last2= Vinci \|first2= Sergio \|last3= Minutoli \|first3= Fabio \|last4= Mazziotti \|first4= Silvio \|last5= Ascenti\| first5= Giorgio \|last6= Salamone \|first6= Ignazio \|last7= Lamberto \|first7=Salvatore\|last8=Blandino\|first8=Alfredo\|title=CT and MRI findings of mucin-containing tumors and pseudotumors of the thorax: pictorial review\| display-authors= 3\| journal=European Radiology\|volume=12\|issue=1\|year=2001\|pages=181–189\|issn=0938-7994\|doi=10.1007/s003300100934\|pmid=11868096\|s2cid=28755973}} ("high attenuating" at over 70 HU){{cite journal\|title=High-Attenuation Mucus Impaction in Patients With Allergic Bronchopulmonary Aspergillosis: Objective Criteria on High-Resolution Computed Tomography and Correlation With Serologic Parameters\| first1=Subash S. \|last1= Phuyal\| first2= Mandeep Kumar MK \|last2= Garg\| first3=Ritesh R \|last3= Agarwal\| first4=Pankaj P \|last4= Gupta\| first5= Arunaloke A \|last5= Chakrabarti\| first6= Manavjit Singh MS \|last6=Sandhu\| first7= Niranjan N \|last7= Khandelwal\| display-authors= 3\| date=2015-09-02\| journal= Current Problems in Diagnostic Radiology}}{{cite journal \|last1=Agarwal \|first1=Ritesh\| last2=Sehgal\| first2=Inderpaul Singh\| last3= Dhooria\| first3=Sahajal\|last4=Aggarwal\|first4=Ashutosh\|title=Radiologic Criteria for the Diagnosis of High-Attenuation Mucus in Allergic Bronchopulmonary Aspergillosis \|journal=Chest\|volume=149\|issue=4\|year=2016\|pages=1109–1110\|issn=0012-3692\|doi=10.1016/j.chest.2015.12.043\|pmid=27055707\|doi-access=free}}
rowspan="8" \| Parenchyma	Lung \| −700 to −600{{cite book\|title=Cardiopulmonary Imaging\|volume=4\|first1= Ella A. \|last1= Kazerooni \|first2= Barry H.\|last2= Gross\|publisher=Lippincott Williams & Wilkins \| page= [https://books.google.com/books?id=IJwZHPrDQYUC&pg=PA379 379] \|year=2004\|isbn=9780781736558}}
Kidney \| +20 to +45
Liver \| 60 ± 6{{cite book\|title=Hepatology, Principles and Practice: History, Morphology, Biochemistry, Diagnostics, Clinic, Therapy\|first1= Erwin \|last1= Kuntz\| first2= Hans-Dieter \|last2= Kuntz\|page= [https://books.google.com/books?id=62jMOh67D8UC&pg=PA210 210] \|publisher=Springer Science & Business Media\|year=2006\|isbn=9783540289777}}
Lymph nodes \| +10 to +20{{cite book\|title=High-Resolution Computed Tomography of the Paranasal Sinuses and Pharynx and Related Regions: Impact of CT identification on diagnosis and patient management. Volume 12 of Series in Radiology\| first= G.\| last= Maatman\| page= [https://books.google.com/books?id=mfYkBAAAQBAJ&pg=PA58 58] \|publisher=Springer Science & Business Media\|year=2012\|isbn=9789400942776}}
Muscle \| +35 to +55
Thymus \| +20 to +40 in children{{cite book\|title=Surgery of the Thymus: Pathology, Associated Disorders and Surgical Technique\| first1= Jean-Claude \|last1= Givel\| first2=Marco \|last2= Merlini\| first3=David B. \|last3= Clarke\| first4= Michael \|last4= Dusmet \|page= [https://books.google.com/books?id=AsTcBQAAQBAJ&pg=PT488 488] \|publisher= Springer Science & Business Media\|year=2012\|isbn=9783642710766}} +20 to +120 in adolescents
White matter \| +20 to +30
Grey matter \| +37 to +45
rowspan="2" \| Gallstone	Cholesterol stone	+30 to +100{{cite journal\|vauthors=Rambow A, Staritz M, Wosiewitz U, Mildenburger P, Thelen M, Meyer zum Büschenfelde KH\| title=Analysis of radiolucent gallstones by computed tomography for in vivo estimation of stone components \| journal=Eur J Clin Invest \| year= 1990 \| volume= 20 \| issue= 4 \| pages= 475–8 \| pmid=2121509 \| doi= 10.1111/j.1365-2362.1990.tb01887.x\| s2cid=39138974 }}
Bilirubin stone	+90 to +120
rowspan="7" \| Foreign body{{cite journal\|last1=Bolliger\|first1=Stephan A. \|last2= Oesterhelweg\| first2= Lars \|last3= Spendlove \|first3= Danny \|last4=Ross\|first4=Steffen\|last5=Thali\|first5=Michael J.\|display-authors= 3 \|title=Is Differentiation of Frequently Encountered Foreign Bodies in Corpses Possible by Hounsfield Density Measurement?\|journal=Journal of Forensic Sciences\|volume=54\|issue=5\|year=2009\|pages=1119–1122\|issn=0022-1198\|doi=10.1111/j.1556-4029.2009.01100.x \|pmid= 19627414\| s2cid=40300162}}	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)
colspan="2" \| Earwax	<0