Contrast CT

Image:Volume rendered.jpg

Bolus tracking is a technique to optimize timing of the imaging. A small bolus of radio-opaque contrast media is injected into a patient via a peripheral intravenous cannula. Depending on the vessel being imaged, the volume of contrast is tracked using a region of interest (abbreviated "R.O.I.") at a certain level and then followed by the CT scanner once it reaches this level. Images are acquired at a rate as fast as the contrast moving through the blood vessels.{{cn|date=July 2024}}

This method of imaging is used primarily to produce images of arteries, such as the aorta, pulmonary artery, cerebral, carotid and hepatic arteries.{{cn|date=July 2024}}

"Washout" is where tissue loads radiocontrast during arterial phase, but then returns to a rather hypodense state in venous or later phases. This is a property of for example hepatocellular carcinoma as compared to the rest of the liver parenchyma.{{cite journal|last1=Choi|first1=Jin-Young|last2=Lee|first2=Jeong-Min|last3=Sirlin|first3=Claude B.|title=CT and MR Imaging Diagnosis and Staging of Hepatocellular Carcinoma: Part II. Extracellular Agents, Hepatobiliary Agents, and Ancillary Imaging Features|journal=Radiology|volume=273|issue=1|year=2014|pages=30–50|issn=0033-8419|doi=10.1148/radiol.14132362|pmc=4263770|pmid=25247563}}

Depending on the purpose of the investigation, there are standardized protocols for time intervals between intravenous radiocontrast administration and image acquisition, in order to visualize the dynamics of contrast enhancements in different organs and tissues.{{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|pmid=20574084|doi-access=free}} The main phases thereof are as follows:{{cite web|url=http://www.radiologyassistant.nl/en/p52c04470dbd5c/ct-contrast-injection-and-protocols.html|title=CT contrast injection and protocols|author=Robin Smithuis|website=Radiology Assistant|access-date=2017-12-13}}

{{main|CT angiography}}

CT angiography is a contrast CT taken at the location and corresponding phase of the blood vessels of interest, in order to detect vascular diseases. For example, an abdominal aortic angiography is taken in the arterial phase in the abdominal level, and is useful to detect for example aortic dissection.[https://books.google.com/books?id=E3tYBAAAQBAJ&pg=PA424 Page 424] in: {{cite book|title=Problem Solving in Emergency Radiology E-Book|author=Stuart E. Mirvis, Jorge A. Soto, Kathirkamanathan Shanmuganathan, Joseph Yu, Wayne S. Kubal|publisher=Elsevier Health Sciences|year=2014|isbn=9781455758395}}

File:CT scan of hepatocellular carcinoma, without and with IV contrast.jpg, without (top) and with (bottom) IV contrast.]]

The following table shows the preferable volume in normal weight adults. However, dosages may need to be adjusted or even withheld in patients with risks of iodinated contrast, such as hypersensitivity reactions, contrast-induced nephropathy, effects on thyroid function or adverse drug interactions.{{cn|date=July 2024}}

The dose should be adjusted in those not having normal body weight, and in such cases the adjustment should be proportional to the lean body mass of the person. In obese patients, the Boer formula is the method of choice (at least in those with body mass index (BMI) between 35 and 40):{{cite journal|last1=Caruso|first1=Damiano|last2=De Santis|first2=Domenico|last3=Rivosecchi|first3=Flaminia|last4=Zerunian|first4=Marta|last5=Panvini|first5=Nicola|last6=Montesano|first6=Marta|last7=Biondi|first7=Tommaso|last8=Bellini|first8=Davide|last9=Rengo|first9=Marco|last10=Laghi|first10=Andrea|title=Lean Body Weight-Tailored Iodinated Contrast Injection in Obese Patient: Boer versus James Formula|journal=BioMed Research International|volume=2018|year=2018|pages=1–6|issn=2314-6133|doi=10.1155/2018/8521893|pmid=30186869|pmc=6110034|doi-access=free}}

For men: Lean body mass = (0.407 × W) + (0.267 × H) − 19.2

For women: Lean body mass = (0.252 × W) + (0.473 × H) − 48.3

Standard doses in children:{{cite journal|last1=Nievelstein|first1=Rutger A. J.|last2=van Dam|first2=Ingrid M.|last3=van der Molen|first3=Aart J.|title=Multidetector CT in children: current concepts and dose reduction strategies|journal=Pediatric Radiology|volume=40|issue=8|year=2010|pages=1324–1344|issn=0301-0449|doi=10.1007/s00247-010-1714-7|pmc=2895901|pmid=20535463}}

{{Further|Iodinated contrast#Adverse effects|CT scan#Cancer}}

Iodinated contrast agents may cause allergic reactions, contrast-induced nephropathy, hyperthyroidism and possibly metformin accumulation. However, there are no absolute contraindications to iodinated contrast, so the benefits needs to be weighted against the risks.{{cite web|title=Iodine-containing contrast medium|author=Stacy Goergen|website=InsideRadiology - The Royal Australian and New Zealand College of Radiologists|url=https://www.insideradiology.com.au/iodine-containing-contrast-medium-hp/|access-date=2019-02-22}} Page last modified on 26/7/2017

As with CT scans in general, the radiation dose can potentially increase the risk of radiation-induced cancer.

The injection of iodinated contrast agents may sometimes lead to its extravasation.{{cite journal |vauthors=Hrycyk J, Heverhagen JT, Böhm I |title=What you should know about prophylaxis and treatment of radiographic and magnetic resonance contrast medium extravasation |journal=Acta Radiol |volume=60 |issue=4 |pages=496–500 |year=2019 |pmid=29896979 |doi=10.1177/0284185118782000|s2cid=48360725 }}

• Computed tomography of the abdomen and pelvis#Contrast administration

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• {{cite web|url=https://radlines.org/CT_with_IV_contrast_in_low_renal_function|title=CT with IV contrast in low renal function|website=Radlines.org}}

Category:X-ray computed tomography