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{{Short description|Quantitative scale of radiodensity}}
The '''Hounsfield scale''' {{IPAc-en|ˈ|h|aʊ|n|z|ˌ|f|iː|l|d}}, named after Sir [[Godfrey Hounsfield]], is a quantitative scale for describing [[radiodensity]]. It is frequently used in [[CT scan]]s, where its value is also termed '''CT number'''.
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 scan]]s, where its value is also termed '''CT number'''.


==Definition==
==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]] ([[Standard conditions for temperature and pressure|STP]]) is defined as zero Hounsfield units (HU), while the radiodensity of [[air]] at STP is defined as -1000 HU. In a [[voxel]] with average [[linear attenuation coefficient]] <math>\mu</math>, the corresponding HU value is therefore given by:
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]] ([[Standard temperature and pressure|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 <math>\mu</math>, the corresponding HU value is therefore given by:<ref>{{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}}</ref><ref>{{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}}</ref>


<math>HU = 1000\times\frac{\mu - \mu_{\textrm{water}}}{\mu_{\textrm{water}} - \mu_{\textrm{air}}}</math>
<math display=block>HU = 1000\times\frac{\mu - \mu_{\textrm{water}}}{\mu_{\textrm{water}} - \mu_{\textrm{air}}}</math>


where <math>\mu_{\textrm{water}}</math> and <math>\mu_{\textrm{air}}</math> are respectively the linear attenuation coefficients of water and air.
where <math>\mu_{\textrm{water}}</math> and <math>\mu_{\textrm{air}}</math> 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.
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.<ref name="IAEADiagRadPhys">{{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}}</ref>{{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]] [[Radiation treatment planning|treatment planning]], where HU is converted to [[electron density]].<ref>{{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}}</ref> 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.<ref name="IAEADiagRadPhys" />{{rp|283}}<ref>{{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 }}</ref>
It is the definition for CT scanners that are calibrated with reference to water.


===Rationale===
===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.'' [[human]]s.
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.'' [[human]]s.{{cn|date=July 2024}}


==Values for different body tissues and material ==
==Value in parts of the body ==
[[File:CT Scan Thorax Lung -700 HU Window Level.jpg|thumb|CT scan of the thorax with window level set to -700 HU (lung)]]
⚫
The Hounsfield scale applies to [[X-ray computed tomography|medical-grade CT scan]]s but not to [[Cone beam computed tomography|cone beam computed tomography (CBCT)]] scans.<ref name="DEVOS">{{cite journal|last1=De Vos|first1=W.|last2=Casselman|first2=J.|last3=Swennen|first3=G.R.J.|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|date=June 2009|volume=38|issue=6|pages=609–625|doi=10.1016/j.ijom.2009.02.028|pmid=19464146}}</ref>
[[File:CT Scan Thorax Air -1000 HU Window Level.jpg|thumb|CT scan of the thorax with window level set to -1,000 HU (air)]]
[[File:CT Scan Thorax Water 0 HU Window Level.jpg|thumb|CT scan of the thorax with window level set to 0 HU (water)]]
[[File:CT Scan Thorax Liver 60 HU Window Level.jpg|thumb|CT scan of the thorax with window level set to 60 HU (liver)]]
⚫
HU-based differentiation of material applies to [[medical-grade]] [[X-ray computed tomography|dual-energy CT scan]]s but not to [[cone beam computed tomography]] (CBCT) scans, as CBCT scans provide [[Cone_beam_computed_tomography#Bone_density_and_the_Hounsfield_scale|unreliable HU readings]].<ref name="DEVOS">{{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}}</ref>

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 agent]]s modifies HU as well in some body parts (mainly blood).


{| class="wikitable"
{| class="wikitable"
|-
|-
!colspan=2| Substance !! HU
! colspan="2" | Substance !! HU
|-
|-
|colspan=2| [[Air]]
| colspan="2" | [[Air]]
| −1000
| −1000
|-
|-
|colspan=2| [[Fat]]
| colspan="2" | [[Fat]]
| −120 to −90<ref name=Lepor2000/>
| −120 to −90<ref name="Lepor2000" />
|-
|-
| colspan=2| Soft tissue on [[contrast CT]]
| colspan="2" | Soft tissue on [[contrast CT]]
| +100 to +300
| +100 to +300
|-
|-
|rowspan=2| [[Bone]] || Cancellous || +300 to +400<ref name="BirurPatrick2017">{{cite journal|last1=Birur|first1=NPraveen|last2=Patrick|first2=Sanjana|last3=Gurushanth|first3=Keerthi|last4=Raghavan|first4=AShubhasini|last5=Gurudath|first5=Shubha|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}}</ref>
| rowspan="2" | [[Bone]] || Cancellous || +300 to +400<ref name="BirurPatrick2017">{{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}}</ref>
|-
|-
| Cortical || +500 to +1900<ref>{{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}}</ref><ref name="BirurPatrick2017" /><ref>{{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}}</ref>
| Cortical || +1800 to +1900<ref name="BirurPatrick2017"/>
|-
|-
|rowspan=3| [[Subdural hematoma]] || First hours || +75 to +100<ref name="Rao2016">Fig 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=2249782X|doi=10.7860/JCDR/2016/17207.7644|pmid=27190831|pmc=4866129}}</ref>
| rowspan="3" | [[Subdural hematoma]] || First hours || +75 to +100<ref name="Rao2016">Fig 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}}</ref>
|-
|-
| After 3 days || +65 to +85<ref name="Rao2016"/>
| After 3 days || +65 to +85<ref name="Rao2016" />
|-
|-
| After 10-14 days || +35 to +40<ref>{{cite web|url=https://radiopaedia.org/articles/subdural-haemorrhage|author=Dr Rohit Sharma and A.Prof Frank Gaillard|accessdate=2018-08-14|website=[[Radiopaedia]]|title=Subdural haemorrhage}}</ref>
| After 10–14 days || +35 to +40<ref>{{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}}</ref>
|-
|-
|rowspan=2| Other [[blood]] || Unclotted || +13<ref name=fosbinder2011>[https://books.google.com/books?id=jRVg5ilM1UEC&pg=PA263 Page 263] in: {{cite book|title=Essentials of Radiologic Science|author=Robert Fosbinder, Denise Orth|publisher=Lippincott Williams & Wilkins|year=2011|isbn=9780781775540}}</ref> to +50<ref>[https://books.google.com/books?id=Bif0zpmEWtAC&pg=SA20-PA17 page 20.17] in: {{cite book|title=Radiology of the Chest and Related Conditions|author=F W Wright|publisher=CRC Press|year=2001|isbn=9780415281416}}</ref>
| rowspan="2" | Other [[blood]] || Unclotted || +13<ref name="fosbinder2011">{{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}}</ref> to +50<ref>{{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}}</ref>
|-
|-
| [[Coagulation|Clotted]] || +50<ref name=fast2006>[https://books.google.com/books?id=4HaPJYaXXSAC&pg=PA17 page 17] in: {{cite book|title=Navigating the Adult Spine: Bridging Clinical Practice and Neuroradiology|author=Dr. Avital Fast, Dorith Goldsher|publisher=Demos Medical Publishing|year=2006|isbn=9781934559741}}</ref> to +75<ref name=fosbinder2011/><ref name=fast2006/>
| [[Coagulation|Clotted]] || +50<ref name="fast2006">{{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}}</ref> to +75<ref name="fosbinder2011" /><ref name="fast2006" />
|-
|-
|rowspan=2| [[Pleural effusion]] || [[Transudate]] || +2 to +15 <ref name="CulluKalemci2013">{{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|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=13053825|doi=10.5152/dir.2013.13066|pmid=24100060|pmc=4463296}}</ref>
| rowspan="2" | [[Pleural effusion]] || [[Transudate]] || +2 to +15 <ref name="CulluKalemci2013">{{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}}</ref>
|-
|-
| [[Exudate]] || +4 to +33<ref name="CulluKalemci2013"/>
| [[Exudate]] || +4 to +33<ref name="CulluKalemci2013" />
|-
|-
|rowspan=7| Other fluids || [[Chyle]]
| rowspan="7" | Other fluids || [[Chyle]]
| −30<ref>[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, Jasjit S. Suri|publisher=CRC Press|year=2013|isbn=9781439893845}}</ref>
| −30<ref>[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}}</ref>
|-
|-
|[[Water]]
|[[Water]]
Line 56: Line 65:
|-
|-
| [[Urine]]
| [[Urine]]
| -5 to +15<ref name=Lepor2000>Page 83 in: {{cite book|title=Prostatic Diseases|author=Herbert Lepor|publisher=W.B. Saunders Company|year=2000|isbn=9780721674162}}</ref>
| −5 to +15<ref name="Lepor2000">Page 83 in: {{cite book|title=Prostatic Diseases|author=Herbert Lepor|publisher=W.B. Saunders Company|year=2000|isbn=9780721674162}}</ref>
|-
|-
| [[Bile]]
| [[Bile]]
| -5 to +15<ref name=Lepor2000/>
| −5 to +15<ref name="Lepor2000" />
|-
|-
|[[Cerebrospinal fluid|CSF]]
|[[Cerebrospinal fluid|CSF]]
Line 65: Line 74:
|-
|-
| [[Abscess]] / [[Pus]]
| [[Abscess]] / [[Pus]]
| 0<ref name=ecr>{{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|author=P. Sanchez de Medina Alba, C. Santos Montón, N. Calvo, K. El Karzazi, T. González de la Huebra Labrador, R. Corrales, N. Alegre Borge; Salamanca/ES|doi=10.1594/ecr2014/C-1927|website=ECR 2014|year=2014}}</ref> or +20<ref name="SasakiMiyata2014">{{cite journal|last1=Sasaki|first1=Toru|last2=Miyata|first2=Rie|last3=Hatai|first3=Yoshiho|last4=Makita|first4=Kohzoh|last5=Tsunoda|first5=Koichi|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}}</ref>, to +40<ref name="SasakiMiyata2014"/> or +45<ref name=ecr/>
| 0<ref name="ecr">{{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}}</ref> or +20,<ref name="SasakiMiyata2014">{{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}}</ref> to +40<ref name="SasakiMiyata2014" /> or +45<ref name="ecr" />
|-
|-
| [[Mucus]]
| [[Mucus]]
| 0<ref>{{Cite journal|url=http://medind.nic.in/ibn/t06/i2/ibnt06i2p191.pdf|title=Mucocoele Of The Appendix|author=K SAGGAR, A AHLUWALIA, P SANDHU, V KALIA|journal=Ind J Radiol Imag|year=2006|volume=16|issue=2}}</ref> - 130<ref name="GaetaVinci2001">{{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|journal=European Radiology|volume=12|issue=1|year=2001|pages=181–189|issn=0938-7994|doi=10.1007/s003300100934|pmid=11868096}}</ref> ("high attenuating" at over 70 HU)<ref>{{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|author=Subash S Phuyal, Mandeep Kumar MK Garg, Ritesh R Agarwal, Pankaj P Gupta, Arunaloke A Chakrabarti, Manavjit Singh MS Sandhu, Niranjan N Khandelwal|date=2015-09-02|journal=Current Problems in Diagnostic Radiology}}</ref><ref name="AgarwalSehgal2016">{{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=00123692|doi=10.1016/j.chest.2015.12.043|pmid=27055707}}</ref>
| 0<ref>{{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 }}</ref> - 130<ref name="GaetaVinci2001">{{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}}</ref> ("high attenuating" at over 70 HU)<ref>{{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}}</ref><ref name="AgarwalSehgal2016">{{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}}</ref>
|-
|-
|rowspan=8| [[Parenchyma]] || [[Lung]]
| rowspan="8" | [[Parenchyma]] || [[Lung]]
| -700 to −600<ref>[https://books.google.com/books?id=IJwZHPrDQYUC&pg=PA379 Page 379] in: {{cite book|title=Cardiopulmonary Imaging|volume=4|author=Ella A. Kazerooni, Barry H. Gross|publisher=Lippincott Williams & Wilkins|year=2004|isbn=9780781736558}}</ref>
| −700 to −600<ref>{{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}}</ref>
|-
|-
| [[Kidney]]
| [[Kidney]]
| +20 to +45<ref name=Lepor2000/>
| +20 to +45<ref name="Lepor2000" />
|-
|-
| [[Liver]]
| [[Liver]]
| 60 ± 6<ref>[https://books.google.com/books?id=62jMOh67D8UC&pg=PA210 page 210] in: {{cite book|title=Hepatology, Principles and Practice: History, Morphology, Biochemistry, Diagnostics, Clinic, Therapy|author=Erwin Kuntz, Hans-Dieter Kuntz|publisher=Springer Science & Business Media|year=2006|isbn=9783540289777}}</ref>
| 60 ± 6<ref>{{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}}</ref>
|-
|-
| [[Lymph node]]s
| [[Lymph node]]s
| +10 to +20<ref>[https://books.google.com/books?id=mfYkBAAAQBAJ&pg=PA58 Page 58] in: {{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|author=G. Maatman|publisher=Springer Science & Business Media|year=2012|isbn=9789400942776}}</ref>
| +10 to +20<ref>{{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}}</ref>
|-
|-
|[[Muscle]]
|[[Muscle]]
| +35 to +55<ref name=Lepor2000/>
| +35 to +55<ref name="Lepor2000" />
|-
|-
| [[Thymus]]
| [[Thymus]]
|
|
*+20 to +40 in children<ref name=givel2012>[https://books.google.se/books?id=AsTcBQAAQBAJ&pg=PT488 Page 488] in: {{cite book|title=Surgery of the Thymus: Pathology, Associated Disorders and Surgical Technique|author=Jean-Claude Givel, Marco Merlini, David B. Clarke, Michael Dusmet|publisher=Springer Science & Business Media|year=2012|isbn=9783642710766}}</ref>
*+20 to +40 in children<ref name="givel2012">{{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}}</ref>
*+20 to +120 in adolescents<ref name=givel2012/>
*+20 to +120 in adolescents<ref name="givel2012" />
|-
|-
|[[White matter]]
|[[White matter]]
Line 96: Line 105:
| +37 to +45
| +37 to +45
|-
|-
|rowspan=2| [[Gallstone]] || Cholesterol stone || +30 to +100<ref name="pmid2121509">{{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| pmc= }} </ref>
| rowspan="2" | [[Gallstone]] || Cholesterol stone || +30 to +100<ref name="pmid2121509">{{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 }}</ref>
|-
|-
| Bilirubin stone || +90 to +120<ref name="pmid2121509"/>
| Bilirubin stone || +90 to +120<ref name="pmid2121509" />
|-
|-
|rowspan=7| [[Foreign body]]<ref name="BolligerOesterhelweg2009">{{cite journal|last1=Bolliger|first1=Stephan A.|last2=Oesterhelweg|first2=Lars|last3=Spendlove|first3=Danny|last4=Ross|first4=Steffen|last5=Thali|first5=Michael J.|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=00221198|doi=10.1111/j.1556-4029.2009.01100.x|pmid=19627414}}</ref>
| rowspan="7" | [[Foreign body]]<ref name="BolligerOesterhelweg2009">{{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}}</ref>
|| Windowpane glass || +500
|| Windowpane glass || +500
|-
|-
Line 115: Line 124:
| Gold, steel, and brass || +30,000 (upper measurable limit)
| Gold, steel, and brass || +30,000 (upper measurable limit)
|-
|-
|colspan=2| [[Earwax]] || <0
| 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]].<ref>[http://emedicine.medscape.com/article/376240 medscape >Adrenal Adenoma Imaging]. Author: Perry J Horwich. Chief Editor: Eugene C Lin. Updated: Apr 21, 2011</ref>
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]].<ref>{{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}}</ref>


==See also==
==See also==
* [[Cone beam computed tomography#Bone density and the Hounsfield scale]]
* [[Cone beam computed tomography#Bone density and the Hounsfield scale|Cone beam computed tomography: Bone density and the Hounsfield scale]].


==References==
==References==
⚫
{{reflist}}
*{{cite book
*{{cite book
|last=Feeman
|last=Feeman
Line 133: Line 143:
|isbn=978-0387927114
|isbn=978-0387927114
}}
}}

==Notes==
⚫
{{reflist}}


==External links==
==External links==
*{{cite web|url=http://www.medcyclopaedia.com/library/topics/volume_i/h/hounsfield_unit.aspx|title=Hounsfield unit|publisher=[[General Electric|GE]]|website=Medcyclopaedia}}{{dead link|date=September 2016|bot=medic}}{{cbignore|bot=medic}}
*{{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=[[General Electric|GE]]|website=Medcyclopaedia}}
*[http://www.fpnotebook.com/Rad/CT/HnsfldUnt.htm Hounsfield Unit] - fpnotebook.com
*[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|archiveurl=https://web.archive.org/web/20070926231241/http://www.intl.elsevierhealth.com/e-books/pdf/940.pdf|archivedate=2007-09-26}}
*{{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]
* [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]


{{Medical imaging}}
[[Category:Radiology]]
[[Category:Radiology]]
__FORCETOC__

Latest revision as of 14:30, 8 November 2024

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

[edit]

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 , the corresponding HU value is therefore given by:[1][2]

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.[3]: 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.[4] 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.[3]: 283 [5]

Rationale

[edit]

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.[citation needed]

Values for different body tissues and material

[edit]
CT scan of the thorax with window level set to -700 HU (lung)
CT scan of the thorax with window level set to -1,000 HU (air)
CT scan of the thorax with window level set to 0 HU (water)
CT scan of the thorax with window level set to 60 HU (liver)

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.[6]

Values reported here are approximations. Different dynamics are reported from one study to another.[citation needed]

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[7]
Soft tissue on contrast CT +100 to +300
Bone Cancellous +300 to +400[8]
Cortical +500 to +1900[9][8][10]
Subdural hematoma First hours +75 to +100[11]
After 3 days +65 to +85[11]
After 10–14 days +35 to +40[12]
Other blood Unclotted +13[13] to +50[14]
Clotted +50[15] to +75[13][15]
Pleural effusion Transudate +2 to +15 [16]
Exudate +4 to +33[16]
Other fluids Chyle −30[17]
Water 0
Urine −5 to +15[7]
Bile −5 to +15[7]
CSF +15
Abscess / Pus 0[18] or +20,[19] to +40[19] or +45[18]
Mucus 0[20] - 130[21] ("high attenuating" at over 70 HU)[22][23]
Parenchyma Lung −700 to −600[24]
Kidney +20 to +45[7]
Liver 60 ± 6[25]
Lymph nodes +10 to +20[26]
Muscle +35 to +55[7]
Thymus
  • +20 to +40 in children[27]
  • +20 to +120 in adolescents[27]
White matter +20 to +30
Grey matter +37 to +45
Gallstone Cholesterol stone +30 to +100[28]
Bilirubin stone +90 to +120[28]
Foreign body[29] 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 adrenal tumor with a radiodensity of less than 10 HU is rather fatty in composition and almost certainly a benign adrenal adenoma.[30]

See also

[edit]

References

[edit]
  1. ^ Levine, Zachary H.; Peskin, Adele P.; Holmgren, Andrew D.; Garboczi, Edward J. (2018-12-20). "Preliminary X-ray CT investigation to link Hounsfield unit measurements with the International System of Units (SI)". PLOS ONE. 13 (12): e0208820. doi:10.1371/journal.pone.0208820. ISSN 1932-6203. PMC 6301669. PMID 30571779.
  2. ^ Hurrell, Michael Anthony; Butler, Anthony Philip Howard; Cook, Nicholas James; Butler, Philip Howard; Ronaldson, J. Paul; Zainon, Rafidah (2012-05-01). "Spectral Hounsfield units: a new radiological concept". European Radiology. 22 (5): 1008–1013. doi:10.1007/s00330-011-2348-3. ISSN 1432-1084. PMID 22134894.
  3. ^ a b Diagnostic radiology physics: a handbook for teachers and students. Vienna: International Atomic Energy Agency. 2014. pp. 1–682. ISBN 978-92-0-131010-1.
  4. ^ Radiation oncology physics: a handbook for teachers and students. Vienna: International Atomic Energy Agency. 2005. p. 230. ISBN 92-0-107304-6.
  5. ^ Samei, Ehsan; Bakalyar, Donovan; Boedeker, Kirsten; Brady, Samuel; Fan, Jiahua; Leng, Shuai; Myers, Kyle; Popescu, Lucretiu; Ramirez-Giraldo, Juan Carlos; Ranallo, Frank; Solomon, Justin; Vaishnav, Jay; Wang, Jia (2019). AAPM Report No. 233: Performance Evaluation of Computed Tomography Systems - The Report of AAPM Task Group 233. Alexandria, VA: American Association of Physicists in Medicine. doi:10.37206/186. ISBN 978-1-936366-69-9. S2CID 214010953.
  6. ^ De Vos, W.; Casselman, J.; Swennen, G.R.J. (June 2009). "Cone-beam computerized tomography (CBCT) imaging of the oral and maxillofacial region: A systematic review of the literature". International Journal of Oral and Maxillofacial Surgery. 38 (6): 609–625. doi:10.1016/j.ijom.2009.02.028. PMID 19464146.
  7. ^ a b c d e Page 83 in: Herbert Lepor (2000). Prostatic Diseases. W.B. Saunders Company. ISBN 9780721674162.
  8. ^ a b Birur, N. Praveen; Patrick, Sanjana; Gurushanth, Keerthi; et al. (2017). "Comparison of gray values of cone-beam computed tomography with hounsfield units of multislice computed tomography: An in vitro study". Indian Journal of Dental Research. 28 (1): 66–70. doi:10.4103/ijdr.IJDR_415_16. ISSN 0970-9290. PMID 28393820.
  9. ^ Lim Fat, Daren; Kennedy, Jim; Galvin, Rose; et al. (2012-05-01). "The Hounsfield value for cortical bone geometry in the proximal humerus—an in vitro study". Skeletal Radiology. 41 (5): 557–568. doi:10.1007/s00256-011-1255-7. ISSN 1432-2161. PMID 21932054. S2CID 23463451.
  10. ^ Aamodt, A.; Kvistad, K. A.; Andersen, E.; et al. (January 1999). "Determination of Hounsfield value for CT-based design of custom femoral stems". The Journal of Bone and Joint Surgery. British Volume. 81 (1): 143–147. doi:10.1302/0301-620X.81B1.0810143. ISSN 0301-620X. PMID 10068022.
  11. ^ a b Fig 3 in: Rao, Murali Gundu (2016). "Dating of Early Subdural Haematoma: A Correlative Clinico-Radiological Study". Journal of Clinical and Diagnostic Research. 10 (4): HC01–5. doi:10.7860/JCDR/2016/17207.7644. ISSN 2249-782X. PMC 4866129. PMID 27190831.
  12. ^ Sharma, Rohit; Gaillard, Frank. "Subdural haemorrhage". Radiopaedia. Retrieved 2018-08-14.
  13. ^ a b Fosbinder, Robert; Orth, Denise (2011). Essentials of Radiologic Science. Lippincott Williams & Wilkins. p. 263. ISBN 9780781775540.
  14. ^ Wright, F. W. (2001). Radiology of the Chest and Related Conditions. CRC Press. p. 20.17. ISBN 9780415281416.
  15. ^ a b Fast, Avital; Goldsher, Dorith (2006). Navigating the Adult Spine: Bridging Clinical Practice and Neuroradiology. Demos Medical Publishing. p. 17. ISBN 9781934559741.
  16. ^ a b Cullu, Nesat; Kalemci, Serdar; Karakas, Omer; et al. (2013). "Efficacy of CT in diagnosis of transudates and exudates in patients with pleural effusion". Diagnostic and Interventional Radiology. 20 (2): 116–20. doi:10.5152/dir.2013.13066. ISSN 1305-3825. PMC 4463296. PMID 24100060.
  17. ^ Page 342 in: Luca Saba; Jasjit S. Suri (2013). Multi-Detector CT Imaging: Principles, Head, Neck, and Vascular Systems, Volume 1. CRC Press. ISBN 9781439893845.
  18. ^ a b Sanchez de Medina Alba, P.; Santos Montón, C.; Calvo, N.; et al. (2014). "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". ECR 2014. Salamanca. doi:10.1594/ecr2014/C-1927. Archived from the original on 2019-01-12. Retrieved 2019-01-12.
  19. ^ a b Sasaki, Toru; Miyata, Rie; Hatai, Yoshiho; et al. (2014). "Hounsfield unit values of retropharyngeal abscess-like lesions seen in Kawasaki disease". Acta Oto-Laryngologica. 134 (4): 437–440. doi:10.3109/00016489.2013.878475. ISSN 0001-6489. PMID 24512428. S2CID 6248808.
  20. ^ Saggar, K; Ahluwalia, A; Sandhu, P; Kalia, V (2006). "Mucocoele of the Appendix" (PDF). Ind J Radiol Imag. 16 (2).[permanent dead link‍]
  21. ^ Gaeta, Michele; Vinci, Sergio; Minutoli, Fabio; et al. (2001). "CT and MRI findings of mucin-containing tumors and pseudotumors of the thorax: pictorial review". European Radiology. 12 (1): 181–189. doi:10.1007/s003300100934. ISSN 0938-7994. PMID 11868096. S2CID 28755973.
  22. ^ 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.
  23. ^ Agarwal, Ritesh; Sehgal, Inderpaul Singh; Dhooria, Sahajal; Aggarwal, Ashutosh (2016). "Radiologic Criteria for the Diagnosis of High-Attenuation Mucus in Allergic Bronchopulmonary Aspergillosis". Chest. 149 (4): 1109–1110. doi:10.1016/j.chest.2015.12.043. ISSN 0012-3692. PMID 27055707.
  24. ^ Kazerooni, Ella A.; Gross, Barry H. (2004). Cardiopulmonary Imaging. Vol. 4. Lippincott Williams & Wilkins. p. 379. ISBN 9780781736558.
  25. ^ Kuntz, Erwin; Kuntz, Hans-Dieter (2006). Hepatology, Principles and Practice: History, Morphology, Biochemistry, Diagnostics, Clinic, Therapy. Springer Science & Business Media. p. 210. ISBN 9783540289777.
  26. ^ Maatman, G. (2012). 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. Springer Science & Business Media. p. 58. ISBN 9789400942776.
  27. ^ a b Givel, Jean-Claude; Merlini, Marco; Clarke, David B.; Dusmet, Michael (2012). Surgery of the Thymus: Pathology, Associated Disorders and Surgical Technique. Springer Science & Business Media. p. 488. ISBN 9783642710766.
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