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Examples of how much contrast is needed for particular exams are:
*Liver: In males at 30 years of age, there is an estimated 0.027 HU of liver parenchymal enhancement per kilogram of body weight and per gram of iodine, when injected at 4 ml per second.<ref name="Bae2010">{{cite journal|last1=Bae|first1=Kyongtae T.|title=Intravenous Contrast Medium Administration and Scan Timing at CT: Considerations and Approaches|journal=Radiology|volume=256|issue=1|year=2010|pages=32–61|issn=0033-8419|doi=10.1148/radiol.10090908}}</ref> For example, a body weight of 70 kg and 125 ml of iodine at a concentration of 350 mg/ml confers an expected enhancement of 83 HU.
*Thorax:
:*For [[CT of pulmonary embolism]] in patients with risk factors, dual energy CTA (such as 90/150SnkVp) is feasible even at iodine doses of 6g (such as 15 ml of 370 mg/ml of iodine).<ref name="LeroyerMeier2016">{{cite journal|last1=Leroyer|first1=Christophe|last2=Meier|first2=Andreas|last3=Higashigaito|first3=Kai|last4=Martini|first4=Katharina|last5=Wurnig|first5=Moritz|last6=Seifert|first6=Burkhardt|last7=Keller|first7=Dagmar|last8=Frauenfelder|first8=Thomas|last9=Alkadhi|first9=Hatem|title=Dual Energy CT Pulmonary Angiography with 6g Iodine—A Propensity Score-Matched Study|journal=PLOS ONE|volume=11|issue=12|year=2016|pages=e0167214|issn=1932-6203|doi=10.1371/journal.pone.0167214}}</ref>
:*Other diseases of the thorax, such as parenchymal changes, can often be evaluated adequately without the use of intravenous contrast.
→How much contrast is needed: Tabled
====How much contrast is needed====
{|class="wikitable"
|+ Preferable volume, generally
!colspan=2| Exam !! 350 mg/ml !! 370 mg/ml !! Comments
|-
|colspan=2| Brain || 50 ml<ref name=NUvolume>{{NU Hospital Group}}</ref> || 45-50 ml<ref name=NUvolume/> ||
|-
|rowspan=2| Thorax || Overall || 90 - 100 ml<ref name=NUvolume/> || 85 - 95 ml<ref name=NUvolume/> || Parenchymal changes can often be evaluated adequately without the use of intravenous contrast.
|-
| [[CT of pulmonary embolism]] || 17 ml<ref name="LeroyerMeier2016" group="notes">Using dual energy CTA (such as 90/150SnkVp), according to:
*{{cite journal|last1=Leroyer|first1=Christophe|last2=Meier|first2=Andreas|last3=Higashigaito|first3=Kai|last4=Martini|first4=Katharina|last5=Wurnig|first5=Moritz|last6=Seifert|first6=Burkhardt|last7=Keller|first7=Dagmar|last8=Frauenfelder|first8=Thomas|last9=Alkadhi|first9=Hatem|title=Dual Energy CT Pulmonary Angiography with 6g Iodine—A Propensity Score-Matched Study|journal=PLOS ONE|volume=11|issue=12|year=2016|pages=e0167214|issn=1932-6203|doi=10.1371/journal.pone.0167214}}</ref> || 15 ml<ref name="LeroyerMeier2016" group="notes"/> || Minimal amount when using specific low-contrast protocol.<ref name="LeroyerMeier2016" group="notes"/>
|-
|rowspan=2| Abdomen || Overall || 120 ml<ref name=NUvolume/> || 115 ml<ref name=NUvolume/> ||
|-
| Liver || 45 ml<ref name=Liver group="notes">The liver generally needs an enhancement of at least 30 HU for proper evaluation according to:
*{{cite book|title=Multislice CT|edition=3|year=2010|publisher=Springer-Verlag Berlin and Heidelberg GmbH & Co. KG|isbn=9783642069680}}
In males at 30 years of age, there is an estimated 0.027 HU of liver parenchymal enhancement per kilogram of body weight and per gram of iodine, when injected at 4 ml per second, according to:
*{{cite journal|last1=Bae|first1=Kyongtae T.|title=Intravenous Contrast Medium Administration and Scan Timing at CT: Considerations and Approaches|journal=Radiology|volume=256|issue=1|year=2010|pages=32–61|issn=0033-8419|doi=10.1148/radiol.10090908}}
This example takes the example of a man with a typical weight of 70 kg.</ref> || 40-45 ml<ref name=Liver group="notes"/> || Minimal required amount.<ref name=Liver group="notes"/>
|}
Departments often have formulas that give the amount of contrast needed for various investigations, using patient sex and weight as main parameters. These may include creatitine levels as well, and in such cases it can help to get a value of of much contrast would hypothetically have been given if the creatinine level was normal, such as for example 80 μmol/L or 0.9 mg/dL. This value can be compared to how much can actually be given in order to determine if it is worth doing the exam with contrast.
===Treating risk factors===
